In this work, Al alloys with 6.6%, 10.4%, and 14.6% Si were deposited as thick coatings by Friction Surfacing (FS), resulting in grain refinement and spheroidization of needle-shaped eutectic Si phase. Lubricated sliding wear tests were performed on a pin-on-disc tribometer using Al-Si alloys in as-cast and FS processed states as pins and 42CrMo4 steel discs. The chemical composition of the worn surfaces was analyzed by X-ray photoelectron spectroscopy (XPS). The wear mechanisms were studied by scanning electron microscopy (SEM) and focused ion beam (FIB), and the wear was evaluated by measuring the weight loss of the samples. For the hypoeutectic alloys, spheroidization of the Si phase particles in particular leads to a significant improvement in wear resistance. The needle-shaped Si phase in as-cast state fractures during the wear test and small fragments easily detach from the surface. The spherical Si phase particles in the FS state also break away from the surface, but to a smaller extent. No reduction in wear due to FS was observed for the hypereutectic alloy. Here, large bulky primary Si phase particles are already present in the as-cast state and do not change significantly during FS, providing high wear resistance in both material states. This study highlights the mechanisms and limitations of improved wear resistance of Si-rich Al alloys deposited as thick coatings by Friction Surfacing. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

multiaxial stress states frequently occur in technical components and, due to the multitude of possible load situations and variations in behaviour of different materials, are to date not fully predictable. This is particularly the case when loads lie in the plastic range, when strain accumulation, hardening and softening play a decisive role for the material reaction. This study therefore aims at adding to the understanding of material behaviour under complex load conditions. Fatigue tests conducted under cyclic torsional angles (5°, 7.5°, 10° and 15°), with superimposed axial static compression loads (250 MPa and 350 MPa), were carried out using smooth specimens at room temperature. A high nitrogen alloyed austenitic stainless steel (nickel free), was employed to determine not only the number of cycles to failure but particularly to aid in the understanding of the mechanical material reaction to the multiaxial stresses as well as modes of crack formation and growth. Experimental test results indicate that strain hardening occurs under the compressive strain, while at the same time cyclic softening is observable in the torsional shear stresses. Furthermore, the cracks’ nature is unusual with multiple branching and presence of cracks perpendicular in direction to the surface cracks, indicative of the varying multiaxial stress states across the samples’ cross section as cross slip is activated in different directions. In addition, it is believed that the static compressive stress facilitated the Stage I (mode II) crack to change direction from the axial direction to a plane perpendicular to the specimen’s axis. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.

Incubation time and erosion rate of C15 steel (SAE 1016) are measured in a cavitation test-rig utilizing an ultrasonic horn. The gap width (separation distance) between horn tip and stationary sample is varied and effects on material damage are studied. Cavitation erosion shows a local maximum for a gap width of 0.5 mm at the stationary specimen, while it continuously rises on the horn tip with rising gap width. A characteristic erosion pattern develops at horn tip and stationary specimen. By a-posteriori surface erosion topography measurements, radial erosion depth profiles are evaluated. Together with scanning electron microscopy investigations, they provide information on the spatial distribution of the flow aggressiveness and on wear mechanisms. By means of computational fluid dynamics (CFD) results, the local surface erosion topography is associated to harmonic and subharmonic collapse events within the gap. Pressure measurements have been performed by piezoelectric polyvinylidene fluoride (PVDF) sensors, mounted in central as well as eccentric position on the specimen surface. A local mean of the erosion depth profile is evaluated on the surface portion that corresponds to the PVDF sensor locations. By temporally high-resolved pressure data, a cumulative force load is evaluated. For larger gap width, a good correlation of cumulative force load with the inverse incubation time, erosion rate, as well as mean erosion depth is obtained, while for the smallest gap width of 0.3 mm, the correlation deteriorates. © 2021 Elsevier B.V.

Cavitation is the formation and collapse of bubbles due to pressure changes in fluids. In the vicinity of a solid surface, shock waves, an impinging water jet, and other effects of collapsing bubbles may cause severe damage. Cavitation erosion is extensively studied using techniques generating clouds of bubbles, e.g. flow channels or ultrasonic oscillations. Single bubbles can be generated in a highly controlled manner by evaporating fluid by a short laser pulse. This technique is typically used to study bubble dynamics and the damage from one single bubble on very soft materials. In the present study, two austenitic steels and a NiAl-bronze are exposed to standard acoustic cavitation and repeated laser-induced single bubbles. The evolution of surface damage and the underlying mechanisms are investigated. Surface changes are not observed before 200 single bubbles. After 50,000 bubbles the three alloys are still within the incubation phase. Comparable damage mechanisms act on the materials under both testing techniques. Since the surface area affected by repeated single bubbles is relatively small (≈500 μm diameter), the weight loss could not be measured and correlations are based on surface roughening and the mechanisms of damage specific for each material. © 2021 Elsevier B.V.

Interruptions of the passive layer of stainless steels by cavitation erosion expose the bare metal surface to the environment and can lead to cavitation-erosion-corrosion damage and synergistic effects. However, the probability for pitting corrosion is decreased during cavitation exposure of stainless steels in chloride solutions because mechanical passive film removal shifts corrosion potentials to lower cathodic values. In this study, the impact of 3.5 wt% NaCl in water on mass loss and damage features of two austenitic stainless N-containing steels is investigated to amend the understanding of cavitation erosion of passivating steels. Ultrasonic cavitation tests were carried out on steels 316LVM and CNMo0.95 in distilled water and 3.5% NaCl solution. Exposed surfaces were characterized qualitatively by light- and electron-microscopy and quantitatively by confocal microscopy. Damage mechanisms vary between the two steels but not with NaCl content in the solution. 316LVM also displayed the same mass loss in both solutions. CNMo0.95 possesses twice the strength as 316LVM, resulting in lower intensities of ductile damage mechanisms and slower damage progression. Mass loss of CNMo0.95 was lower in 3.5% NaCl solution compared to distilled water, which was primarily assigned to the effect of the salt content in the water on cavitation bubble formation. © 2020 Elsevier B.V.

Friction Surfacing (FS) coatings are deposited by severe plastic deformation at elevated temperatures (≈0.8*Tliquidus), requiring different process parameters for alloys of even small composition variations. For Al alloys it is known that with increasing Mg content the thermal softening rate decreases, i.e. the material retains higher flow strength under thermomechanical processing. Further, the stacking fault energy (SFE) decreases with increasing Mg content, which influences gliding characteristics of dislocations, and also deformation and recrystallization behavior. To elucidate the influence of such known properties on FS process parameters and resulting coatings, three Al alloys differing only in Mg content (0.27, 2 and 3.5 wt.%) were processed by FS in this study. Pronounced shear flow localization was observed for increasing Mg content, yielding thin and narrow coatings and requiring a reduction of process speeds. Further, the decrease in SFE with increasing Mg content resulted in lower recrystallized grain size and higher grain orientation differences, due to a lower tendency for dislocation annihilation by recovery. © 2021 Elsevier B.V.

Wear mechanisms have been intensively studied and described in literature. The tribological load spectrum, the surrounding conditions, the properties of materials and surfaces determine which mechanisms act. The complexity of tribological systems in practice makes it difficult to predict and sometimes even to identify wear mechanisms correctly. In this study, a basic investigation of three different steels is conducted under the same test conditions. Differences in the observed wear behavior are presented and discussed in the context of the respective materials’ microstructure and hardness. The goal of this case study is to provide a clear and well documented example of the interdependence of material properties and resulting wear behavior. A case hardened martensitic steel 18CrNiMo7-6, one corrosion resistant martensitic steel X30CrMoN15-1 (Cronidur 30) and one austenitic steel X13CrMnMoN18-14-3 (P2000) are tested against bearing balls from 100Cr6. Reciprocating sliding wear tests with silicone oil as lubricant are conducted under a normal load of 30 N and an average sliding speed of 0.06 ms−1 for 5,000 cycles. The evolution of the friction coefficients, wear volumes and wear appearances are studied. All materials display predominantly signs of abrasion, but the relation of different submechanisms and combination with other wear mechanisms vary. The case hardened steel (765 ± 13 HV10) shows appearances of micro-ploughing and plastic shear deformation is limited to a thin layer of material, resulting in low wear. The corrosion resistant martensitic steel (554 ± 10 HV10) shows similar appearances but of less pronounced ductility, resulting in increased wear by micro-fatigue delaminations. Ductile austenitic steel (311 ± 39 HV10) displays the highest wear volume caused by a mixture of micro-cutting and severe micro-ploughing. © 2021 Elsevier B.V.

Friction surfacing (FS) is a coating technique applied mainly in corrosion protection and repair of components. The study addresses the effects of deposition and rotational speeds on the rods characteristics and process efficiency for the deposition of Ti-6Al-4V on self-mating substrates by FS. The consumption rate was 1.8 mm/s, deposition speeds of 8, 16 and 24 mm/s and rotational speeds of 2000, 3000 and 4000 rpm. It was shown that the flash forms primarily at the rod, ascending around the tip and leaving the coating without flash. The higher deposition speeds led to a decrease in rod thickness and diameter. For higher rotational speeds, an increase in diameter and decrease in thickness is observed for the flash on the rod. Experiments have shown that the rotational and deposition speeds have a decisive influence on the flash formation. Its microstructure changes due to the welding process and a change in hardness can be observed. © 2019 Universidade Federal de Sao Carlos. All rights reserved.

This study evaluates the application of a new solid state joining process referred to as hybrid friction diffusion bonding. Based on heat processing and pressure, accelerated diffusion joins the materials. In the present study, two aluminum alloys were welded and characterized using leak tightness tests, tensile pull out tests, and metallographic analysis. Response surface methodology was used to optimize the tensile strength of single-hole tube-sheet samples. A Box-Behnken design was selected to evaluate the relations between the important process parameters and the ultimate tensile strength response to obtain optimal welding parameters. The data were analyzed with analysis of variance and were fitted to a second-order polynomial equation. The three-dimensional response surfaces derived from the mathematical models were applied to determine several optimum input parameters conditions. Under these conditions, the experimental ultimate tensile strength value was 202 MPa, which represents 95% of the base material strength. The experimental results obtained under optimum operating conditions were in agreement with the predicted values. Axial force was found to be the most significant factor affecting the joint strength followed by rotational speed. This can be attributed to their influence on the amount of mechanical energy introduced during the process, which is the parameter that primarily determines the joint strength. © 2019 Brazilian Metallurgical, Materials and Mining Association. Published by Elsevier Editora Ltd. Published by Elsevier Editora Ltd.

Friction surfacing is a coating process for extending the service life of components by repairing surface damaged, reducing wear, and improving anticorrosion properties. Ti-6Al-4V and titanium grade 1 have been deposited onto Ti-6Al-4V substrate to investigate the differences in material and processing behavior and analyze the coatings’ geometry and hardness. The deposition speed and consumption rate were kept constant at 16 mm/s and 1.8 mm/s, respectively, while the rotational speed was varied to 2000 rpm, 3000 rpm, or 4000 rpm. The force increased with the rotational speed, being about 10 times higher for Ti-6Al-4V compared with titanium grade 1. The peak temperatures were higher for titanium grade 1, and the β-transus temperature was exceeded in all experiments. The hardness of the coatings was about 16% higher compared with that of the Ti-6Al-4V substrate, due to formation of martensitic structure. The hardness did not vary significantly across the width of the coatings. © 2019, The Minerals, Metals & Materials Society.

An alloy that is exposed to cavitation may experience mechanical cavitation damages as well as accelerated corrosion. In the present paper, the evolution of corrosion erosion behavior of brass samples (CuZn38Pb3) during continuous exposure to ultrasonic cavitation in a salt solution (NaCl) was investigated. Various samples were sonicated for times between 0 min and 5 h. The average surface roughness and the effective surface area of the samples were measured by confocal microscopy, and the surfaces were inspected by scanning electron microscopy. Different erosion behavior of the phases present on the surface is discussed. Complementary to the surface inspection, the corrosion behavior of the samples before, during and after sonication was investigated through open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The results show that at the initial times of sonication preferably the lead islets were removed from the brass surface, resulting in a change in the open circuit potential. α and β′ phases showed ductile and brittle behavior under sonication, respectively. The corrosion rate of the alloy under cavitation increased as the sonication time increased, mainly related to the increase in effective surface area and the rise of plastic deformation of the surface material. © 2019 Elsevier B.V.

Friction surfacing (FS) coating layers are generated through severe plastic deformation (SPD) at elevated temperatures (≈0.8 Tmelt). Alloying elements in metals affect heat generation and dynamic recrystallization kinetics during SPD, and therefore require significant adjustments of FS processing conditions. In this study, custom made Aluminum alloys (AA 6060 with additions of 2 and 3.5 wt% Mg, and 6.6, 10.4 and 14.6 wt% Si) were processed by FS. It was found that for the high-Mg Aluminum alloys especially the rotational speeds require a downward adaption to achieve a steady state process. A higher content of Mg results in a reduced rate of thermal softening and more efficient heat generation. With regard to the plasticization behavior during FS, the high amount of hard phases in the high-Si alloys was expected to cause additional friction and increase heat generation. However, as the Si content increases, the process temperatures decrease. Influences of Mg and Si content on material efficiency and coating dimensions were evaluated and discussed. © 2019, The Minerals, Metals & Materials Society.

Friction Surfacing Layer Deposition (FSLD) is a friction-based process capable of depositing similar or dissimilar materials on a substrate surface. The process is based on the plastic deformation of a rotating metallic consumable rod, which is pressed against the substrate material under an applied axial load. Frictional heat is then generated at the interface between the rod and the substrate due to their relative motion, resulting in a layer of plasticized material that forms a continuous deposit by the translation of the stud along the substrate. On top of this deposit more layers can be realized to build up a multi-layered wall in a solid-state fashion. In this study, the Al alloy 5083 was deposited on an AA2024 substrate. The resulting microstructure including the layer interfaces were investigated by metallographic methods as well as SEM-based techniques including EBSD. Hardness mapping was used for examining local mechanical properties. According to the process monitoring, the quality of the layers is very reproducible. EBSD maps show a sound bonding around the interface between the first layer and the substrate with its upper part showing recrystallized grains where the lower part consists of partially recrystallized grains due to the thermal and mechanical impact, while the heat-affected changes little. All layers exhibit fine, equiaxed recrystallized grains with a typical grain size of 4-5 microns. The variation in size and shape over the height of the structure are limited. Consequently, the multilayered deposit exhibits very homogenous local mechanical properties, i.e., microhardness. In summary, FSLD has shown the feasibility and required flexibility for multilayer depositing. The process may be an effective alternative to melting-based additive manufacturing methods for specific applications. © 2019 Author(s).

In order to capture the stress-strain response of metallic materials under cyclic loading, it is necessary to consider the cyclic hardening behaviour in the constitutive model. Among different cyclic hardening approaches available in the literature, the Chaboche model proves to be very efficient and convenient to model the kinematic hardening and ratcheting behaviour of materials observed during cyclic loading. The purpose of this study is to determine the material parameters of the Chaboche kinematic hardening material model by using isotropic J2 plasticity and micromechanical crystal plasticity (CP) models as constitutive rules in finite element modelling. As model material, we chose a martensitic steel with a very fine microstructure. Thus, it is possible to compare the quality of description between the simpler J2 plasticity and more complex micromechanical material models. The quality of the results is rated based on the quantitative comparison between experimental and numerical stress-strain hysteresis curves for a rather wide range of loading amplitudes. It is seen that the ratcheting effect is captured well by both approaches. Furthermore, the results show that concerning macroscopic properties, J2 plasticity and CP are equally suited to describe cyclic plasticity. However, J2 plasticity is computationally less expensive whereas CP finite element analysis provides insight into local stresses and plastic strains on the microstructural length scale. With this study, we show that a consistent material description on the microstructural and the macroscopic scale is possible, which will enable future scale-bridging applications, by combining both constitutive rules within one single finite element model. © 2019 by the authors.

The solid-state deposition process Friction Surfacing (FS) was applied to Ti-6Al-4V alloy on portable welding equipment at a high-energy synchrotron beamline. The heat input and coating thickness were altered by varying the deposition speed. X-ray diffraction was carried out in-situ during the deposition process and the cooling of the coated samples. Phase transformations were evaluated and correlated with thermal cycles determined by thermocouples and an infrared camera. SEM investigation of the coating microstructure was conducted to examine the morphology of the α phase. During FS the coating material is severely deformed and dynamically recrystallized in the β phase state at temperatures > 1300 °C. Small changes in the β grain size were observed within the first 2 s after deposition only. Depending on the cooling rate it transforms into different types of α phase during cooling. Phase transformation rates were found to correlate well with the differences in α morphology. The two faster translational speeds showed transformation rates > 45 vol%/s and a partially martensitic microstructure. When a thick coating is deposited at low translational speed, α → β transformation continues for several seconds after deposition, followed by a slow cooling rate resulting in martensite free coatings containing α m from massive transformation. The potential gain and the deficiencies of this complex in-situ study of a technical process, instead of simplified model experiments, for the understanding of fundamental mechanisms involved in FS are discussed. © 2017

For a better understanding and modeling of cavitation, investigations of isolated single-bubble events are useful. They allow for describing and quantifying the physics of the bubble collapse and its interaction with surrounding material. The generation of such single bubbles in a liquid using an electric spark or focused laser beam is well described in the literature, and sophisticated analyses of bubble dynamics near surfaces exist. However, only a few studies addressed the material damage induced by single-bubble collapse. This article presents experiments in water, generating single bubbles with 3-mm diameters at various defined distances to the polished surface of a commercially pure aluminum specimen. The collapse of each laser-induced bubble was captured by high-speed imaging. A detailed quantitative analysis of the surface damage was performed using 3-D profilometry. A single bubble created a shallow pit with a typical depth of 1 to 2 μm. The overall statistics of the damage parameters, such as pit depth and volume, are consistent with previous investigations. Outliers with unusually small or multiple pits can be explained by the high-speed images of the corresponding bubble collapse. The image sequences also help identify effects of the edge of the specimen surface. In addition, a complementary numerical investigation of single bubbles based on the Navier-Stokes equations was used to obtain flow characteristics near the surface, such as microjet impact and pressure. For the commercially pure aluminum used in this study, simulation and measured surface damage correlate well. The methods developed here provide a basis for studies on more complex engineering materials. Copyright © 2018 by ASTM International

In friction surfacing (FS), material is deposited onto a substrate in the plasticized state, using frictional heat and shear stresses. The coating material remains in the solid state and undergoes severe plastic deformation (SPD) at high process temperatures (≈0.8 Tmelt), followed by high cooling rates in the range of 30 K/s. Dynamic recrystallization and the thermal cycle determine the resulting microstructure. In this study, Ni-based alloy 625 was deposited onto 42CrMo4 substrate, suitable, for instance, for repair welding of corrosion protection layers. Alloy 625 is known to undergo discontinuous dynamic recrystallization under SPD, and the resulting grain size depends on the strain rate. The coating microstructure was studied by microscopy and electron backscatter diffraction (EBSD). The coatings exhibit a fully recrystallized microstructure with equiaxed grains (0.5–12 µm) and a low degree of grain average misorientation. Flow lines caused by a localized decrease in grain size and linear alignment of grain boundaries are visible. Grain nucleation and growth were found to be strongly affected by localized shear and nonuniform material flow, resulting in varying amounts of residual strain, twins and low-angle grain boundaries in different regions within a single coating layer’s cross section. FS can be used to study dynamic recrystallization at high temperatures, strains and strain rates, while at the same time materials with a recrystallization grain size sensitive to the strain rate can be used to study the material flow during the process. © 2017 Taylor & Francis.

The relation between the translational stud speed and the residual stress (RS) state of Friction Surfacing (FS) coated 2 mm thick Ti-6Al-4V sheets was studied using synchrotron diffraction. The influence of the RS state on fatigue crack propagation (FCP) was studied using C(T)-100 samples. It was shown that an active zone of tensile RS is present in the coated region, inducing compressive stresses in the remaining sheet. Higher depositing stud translational speeds show a tendency towards high RS peak values. The deposited material thickness has an influence on the RS distribution. FCP tests have shown branching cracks deflecting away from the coating, possibly due to the compressive RS around it. Cracks have propagated significantly slower than in uncoated samples. RS measurements on cracked samples have revealed tensile RS peaks at the crack tips with high values of 350 MPa in the direction parallel to the intended crack propagation, which prevent the cracks from reaching the coated region. © 2018 Elsevier B.V.

Aluminium alloys 5083 and 6082 were deposited by Friction Surfacing (FS) under the same process conditions. Process characteristics including torque and forces, temperatures and the deposit microstructure were compared. The observed differences are discussed with regard to material strength, thermal softening rate and recrystallization mechanisms. AA 6082 plasticises faster, reaching ≈30 K higher temperatures, thicker and wider coatings and a higher material efficiency. The specific energy required for plastification is in the same order of magnitude as the activation energy for self-diffusion, emphasising the influence of dynamic recrystallization (DRX) mechanisms. A tendency for lower grain size and larger variations in grain boundary misorientation observed for AA 5083 points towards a shift in the steady-state DRX balance towards dislocation generation, due to the higher Mg content of this alloy. This corresponds to the lower process speeds required for AA 5083. AA 6082 may undergo more localized shear because of its high thermal softening rate and additional loss of strength through dissolution of Mg2Si with increasing temperature. This may contribute to a higher energy and material efficiency for plastification and deposition of AA 6082 by FS. © 2017 Elsevier B.V.

In Friction Stir Welding (FSW), interactions between the plasticized stirred material and the tool significantly affect resulting weld properties. When welding metals with high strength and melting point, the tribological load on the tool is severe, and poses the main limiting factor for the technology's industrial exploitation. Since tool materials are loaded to their limits, it is essential to understand the interactions of specific tool material and welded metal combinations. In the present study 3.2 mm alloy 625 sheets were joined using a pcBN tool with W-Re binder phase. Wear lead to a change in tool geometry followed by tool fracture. In SEM investigations the welds revealed typical banded structures, composed of small grains and non-metallic phases containing W from the tool material. The tool surface is extensively covered by adhering sheet metal. Further, BN grain pull-outs and appearances of diffusive wear are visible on the worn tool surface. Tool wear is mainly caused by detachment of BN grains due to thermal softening of the metallic binder phase and dissolution of BN in the hot material in the stirred zone. Using low rotational speeds resulting in lower process temperatures reduces tool wear and results in a homogeneous stirred zone. © 2017 Elsevier B.V.

Titanium Grade 1 was deposited on Ti-6Al-4V, 2 mm thickness, by Friction Surfacing. The process parameters were rotational speed, deposition speed and consumption rate. Only the rotational speed was varied in order to evaluate the influence of this parameter on the coatings generated. The applicability of the process has been described for a large number of materials, although the depositions of titanium alloys are still not widely studied. The objective is to investigate the effects of the rotational speed on the coatings' geometry and microstructural evolution. This investigation has shown that Titanium Grade 1 coatings can be deposited onto a Ti-6Al-4V by Friction Surfacing depending on the rotational speed. The coatings' surface homogeneity was influenced by the rotational speed, being inhomogeneous for the lowest speed. The coatings' thickness and width increased with enhancing this speed. The heat affected zone in the substrate corresponded to the complete thickness under the depositions. © 2017 Universidade Federal de Sao Carlos. All rights reserved.

Friction surfacing process is employed to deposit metallic coatings, whereby similar and dissimilar material combinations can be realized. The process can be applied as a local repair technology, or the coating material can locally modify the surfaces. One advantage of this process is that the coatings are deposited in solid state without reaching the melting range of materials, thereby avoiding dilution with the substrate. The involved severe plastic deformation under high temperatures alters the microstructure of the coating material, leaving it fully dynamically recrystallized. The current work focuses on deposition of Ti-6Al-4V coatings. For that material, the process parameter rotational speed plays a major role in the material’s response during processing. Two different regimes with a threshold at 2000 min−1exist, upon which the flow behavior of Ti-6Al-4V significantly differs, affecting among others the coating dimensions. Microstructural analysis reveals that the material is deformed in a high temperature β phase, and the high cooling rates (46.4 Ks−1) lead to martensitic transformation. The β grain size differs in the low and high rotational speed regimes. This study shows that metallurgical processes play an important role in friction surfacing, since they influence all relevant process characteristics, including microstructure, material efficiency and process forces. © 2017 Taylor & Francis.

Hybrid friction diffusion bonding (HFDB) is a solid-state bonding process first introduced by Helmholtz-Centre Geesthacht, Germany, to join aluminium tube-to-tube sheet joints of coil-wound heat exchangers (CWHE) for liquefaction of natural gas (LNG). This study describes how HFDB was in a first step successfully transferred to create austenitic S32100 single hole tube-to-tube sheet joints. Process parameters are presented and results from subsequent non-destructive bubble leak testing and destructive tensile pull-out testing are discussed. After pull out testing the bonded areas were further investigated using optical microscopy as well as scanning electron microscopy. Leak tight joints were generated due to the formation of a metallic bond close to the planar friction area of the employed tools, and failure in pull-out tests occurred by ductile fracture. The results show that the HFDB approach developed for Alalloys may well be transferred to steel, and in the future possibly to other high-temperature alloys. It thereby offers an alternative route for joining tube to tube-sheet connections in solid state, with the corresponding advantages, such as no open flames or arc, no spatter and no need for filler material. © Copyright 2017 ASME.

In recent years, interest has been increasing in application of Nickel alloys in the oil industry. For subsea engineering, the possibility to weld high-strength materials in an effective manner is essential. Friction Stir Welding (FSW) is alternative to join several materials retaining their properties or even improving them. This fact is relevant for Corrosion-Resistant Alloys (CRA) used in deep-water exploitation of hydrocarbons. Publications up to now have focused on FSW of Inconel® series as alloy 600, 625, and 718. To provide a solid basis for development, this review discusses the crucial points for FSW. The tool materials are described, as well as the joint microstructure and properties achieved. Furthermore, the basics of the corrosion resistance and the early corrosion studies of FSW joints are presented. It is concluded that FSW is a promising process for Ni alloys, but depends on upcoming research regarding tool technology and corrosion investigations. © 2017 Institute of Materials, Minerals and Mining. Published by Taylor & Francis on behalf of the Institute.

Friction surfacing is a thermo-mechanical process employed to deposit coatings in solid state resorting to friction between a rotating consumable rod and a substrate. The current work focuses on deposition of Ti-6Al-4V composite coatings reinforced with TiC particles on Ti-6Al-4V substrate. Particles were added using holes drilled into the rod tip. Different configurations of hole placements within the rod were correlated with process behavior, coating quality, deposition efficiency and particle distribution within the deposits. Configurations varied in number of holes and their distance to the rod's cross-sectional center. Holes placed near to the rod center increased axial forces during the plastification stage, whereas particles in holes far off the rod center were mainly expelled, not yielding as much effect on the process response. An increase in number of holes amplified the effects of the hole distance. The axial force during plastification stage affected both coating appearance and process efficiency. No full intermixing of coating material and particles during deposition occurred, thereby preventing a uniform distribution of particles throughout the coatings. Particles were mostly deposited along trails, which influenced the behavior of growing grains during recrystallization. © 2017 Elsevier B.V.

Friction spot welding is a solid state welding process suitable to obtain spot like-joints in overlap configuration. The process is particularly useful to weld lightweight materials in similar and dissimilar combinations, and therefore an interesting alternative to other joining techniques (rivets, resistance welding, etc.). Optimum process parameters have been defined using the Taguchi method by maximizing the response variable (the lap shear strength). A study of the fatigue life was carried out on specimens welded with the above mentioned optimized process parameters. Fatigue tests were performed using a stress ratio of R = 0.10. Two-parameter Weibull distribution was used to analyze statistically the fatigue life for the joined overlapped sheets. Subsequently, the Weibull plots were drawn, as well as S-N curves considering different reliability levels. The results show that for a relatively low load, corresponding to 10% of the maximum supported by the joint, the number of cycles surpasses 1 × 106, hence infinite life of the service component can be attributed. Fatigue fracture surfaces were investigated for the highest and lowest loads tested using scanning electron microscope (SEM). © 2016 Elsevier Ltd. All rights reserved.

Friction surfacing is a solid state technique for depositing metallic coatings. Coating materials are thermo-mechanically processed at high temperatures during deposition. The high degree of deformation involved leads to a dynamically recrystallised fine grained microstructure. For Ti-6Al-4V, the microstructure and mechanical properties of coatings generated by friction surfacing have not been studied yet. The current work focuses on investigating effects of rotational speed on microstructure, grain size evolution and mechanical properties of the coating material. Various rotational speeds in a wide range, exceeding the range of deformation used in many other severe plastic deformation processes, were used to generate Ti-6Al-4V coatings by friction surfacing. Their influence on the thermal cycle and consequently on microstructure formation was revealed. The β grain size is related to the rotational speed and thermal cycle. Grain refinement at low rotational speed was observed, while higher rotational speeds and corresponding increase in maximum temperature led to grain coarsening. Although the peak temperature dominates the grain size evolution, dynamic recrystallisation during friction surfacing counteracts this effect, reducing the grain size by one order of magnitude. The coatings exhibit a hardness ascent about 15% due to martensite formation, high dislocation density and oxide precipitations. © 2016 Elsevier Ltd

By the process of friction surfacing, coatings are generated from metallic materials at temperatures below their melting range. The high degree of deformation while depositing leads to grain refinement in the microstructure, which has a positive effect on the mechanical properties of the layer. The applicability of the process has been described for a large number of materials. The deposition of Ti-6Al-4V has been reported in one publication but was not systematically studied. Therefore, the main aims of the present work are to define the process parameter fields for the deposition of Ti-6Al-4V leading to flash and defect free coatings and associate them with geometric features of the deposited layer.This investigation has shown that Ti-6Al-4V coatings can be effectively deposited onto a Ti-6Al-4V substrate by friction surfacing. A wide range of process parameters was established in which coatings of high quality have been obtained. The consumption rate control has been implemented as an efficient mode for the deposition of Ti-6Al-4V coatings. Temperature measurements at the coating interface have been accomplished showing that the coating material has been deformed in the β-phase. Furthermore, the homogeneity of the coating surface has been established to be a function of the rotational speed. The coatings exhibited a defect-free bond at the interface with the substrate. Two process parameter ranges with respect to the flash formation have been established. One of them enables flash-free coatings and the other generates coatings with flash formation on the retreating side, which can be controlled by the rotational and deposition speeds. Moreover, an increase in the rotational speed has been shown to lead to an increase in the coating thickness and width as well as an increase in the deposition efficiency up to 39 %. © 2015 Elsevier B.V.

Friction surfacing is a solid-state surface engineering technology. Previous studies have shown that underwater friction surfacing has some advantages in efficiency and homogeneity of the deposited material. To use these advantages a water spray cooling system was implemented to achieve a more flexible process. This concept has been investigated by depositing Al alloy AA6082 T6 on AA2024 T351 substrate. The efficiency of the process was increased from 19% to 31% without influencing the properties of the deposited material. Temperature measurements revealed that the intensity and chosen location of cooling also affect the process characteristics and allow modifying the coating geometry. © 2015 Society of Manufacturing Engineers (SME).

Coil-wound heat exchangers (CWHE) for low temperature applications such as the liquefaction of natural gas (LNG) are often made of aluminium alloys. The fabrication of these aluminium coil-wound heat exchangers holds several challenges, one of which is joining the tubes to the tube sheet. For this specific task, conventional joining technologies such as laser beam welding (LBW) or tungsten inert gas (TIG) welding cannot be easily performed in fully-mechanised mode or are not cost-effective. A joint project between the Helmholtz-Zentrum Geesthacht (HZG) and LINDE Engineering aims at the development of a new solid state joining process, Hybrid Friction Diffusion Bonding (HFDB), to fabricate tube-to-tubesheet connections for aluminium coil-wound heat exchangers. In the present study, the HFDB process has been developed to industrial maturity and the quality of the joints has been demonstrated by gas leak tightness tests and tensile pull-out tests. The joints meet the requirements for industrial application. Furthermore, the thermal field development in the weld area and the applied process forces have been monitored and correlated to process parameters. The microstructure of the joint has been investigated, and dynamic recrystallization is assumed to be the primary grain refinement mechanism in the thermomechanically affected zone. Copyright © 2015 by ASME.

Friction surfacing is a method suitable to generate a wide variety of metallic coatings by means of frictional heating and severe shear deformation. It is a solid-state joining method, and therefore may be applied to non-fusion weldable as well as non-deformable brittle materials, as Cr-based alloys are. In the present study coatings of Cr60Ni40 alloy are generated onto Nimonic 80A substrates. Microstructural investigations of the coating material are carried out and compared to the usual cast state. The wear behaviour of the coatings as well as the cast material is examined under reciprocating sliding against 52100 ball bearing steel by means of a ball-on-flat test rig, lubricated with silicone oil to prevent oxidation. In this tribological system, wear takes place by abrasion with microploughing being the predominant submechanism, surface fatigue as well as adhesion by materials transfer of Cr60Ni40 from the flats to the steel balls. White etching layers form on Cr60Ni40 underneath the worn surfaces, which show cracks and delaminations. The amount of wear of all coatings is within the same magnitude compared to the cast state but slightly smaller. This can be explained by the distinctly finer microstructure (grain boundary strengthening) and a high degree of supersaturation of the solid solutions (solid solution strengthening) within the coatings. The results of this study show that it is possible to generate coatings of brittle alloys like Cr60Ni40 by friction surfacing, which show a slightly better wear behaviour under reciprocating sliding. Thus, in combination with a ductile substrate, these coatings are likely to extend the range of applicability of such high-temperature wear and corrosion resistant alloys. © 2015 Elsevier B.V.

CrNi-alloys with high Cr-content generally are quite brittle and, therefore, only available as castings and regarded as neither weldable nor deformable. The process of friction surfacing offers a possibility to generate Cr60Ni40 coatings e.g. on steel or Ni-base substrates. Cavitation tests were carried out using an ultrasonic vibratory test rig (~ASTM G32) with cast specimens and friction surfaced coatings. The coatings show less deformation and smaller disruptions, and wear rates in steady state were found to be three times higher for the cast and heat treated samples than for the coatings, caused by a highly wear resistant Cr-rich phase. The results of this study show that it is possible to generate defect free coatings of Cr60Ni40 with a thickness of about 250. μm by friction surfacing, which under cavitation show a better wear behavior than the cast material. Thus, in combination with a ductile substrate, these coatings are likely to extend the range of applicability of such high-temperature corrosion resistant alloys. © 2012 Elsevier B.V.

Friction surfacing is a solid-state joining process, during which process temperatures below melting, a high cooling rate, and a high degree of deformation lead to a very fine microstructure and exceptional mechanical properties of the coating material. In the presented study, the friction surfacing process was used to apply self-mating layers onto cold work tool steels, which e.g. are used for deep-drawing dies in the automotive industry. Such dies are subject to wear during operation and the repair of the dies by arc-welding includes many process steps besides the final hard surfacing. By the use of friction surfacing, hard tool steel coatings can be generated in one process step before the final machining operation. A martensitic microstructure and high hardness up to 900 HV10 can be reached within the coatings. Boundary lubricated reciprocating sliding wear tests (ball-on-flat) were conducted on cast and hardened material as well as the coatings. The results showed that over a wide range of loading the coated samples perform as well as the original die material, showing tribochemical reactions and very small wear volumes. After more than 500,000 sliding passes, both the coatings' and the original tool material's wear is dominated by surface fatigue. © 2013.

One of the main problems during the welding of ferritic stainless steels is severe grain growth in the heat affected zone (HAZ). In the present study, microstructural characteristics of tungsten inert gas (TIG) welded AISI409 ferritic stainless steel were investigated. The effect of the welding parameters on grain size? local misorientation and low angle grain boundaries was studied. It was found that the base metal was partly in recrystallization state. Complete recrystallization followed by severe grain growth occurs after joining process due to welding heating cycle. A decrease in the number of low angle grain boundaries in HAZ was observed. Nevertheless, the welding plastic strain increases the density of local misorientation and low angle grain boundaries. This investigation shows that the final state of strain is the result of the competition between welding plastic strains and stress relieving from recrystallization but the decisive factor in determining the grain size in HAZ is heat input.

One of the main problems during the welding of ferritic stainless steels is severe grain growth within the heat-affected zone (HAZ). In the present study, the microstructural characteristics of tungsten inert gas (TIG) welded AISI409 ferritic stainless steel were investigated by electron backscattered diffraction (EBSD), and the effects of welding parameters on the grain size, local misorientation, and low-angle grain boundaries were studied. A 3-D finite element model (FEM) was developed to predict the effects of welding parameters on the holding time of the HAZ above the critical temperature of grain growth. It is found that the base metal is not fully recrystallized. During the welding, complete recrystallization is followed by severe grain growth. A decrease in the number of low-angle grain boundaries is observed within the HAZ. FEM results show that the final state of residual strains is caused by competition between welding plastic strains and their release by recrystallization. Still, the decisive factor for grain growth is heat input. © 2012 University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.

We present a computer simulation study on the influence of the impact angle of the projectile on kinetic electron emission yields for 5-keV Ag → Ag bombardment. By means of a hybrid computer simulation model incorporating (i) the particle dynamics following the primary particle impact, (ii) the kinetically induced electronic substrate excitations via electronic friction and electron promotion and (iii) the transport of excitation energy away from the spot of generation, a full three-dimensional electron temperature profile within the volume affected by the atomic collision cascade is calculated. This profile is evaluated at the very surface of the target and taken as input for a thermionic model ('hot-spot-model') for kinetic electron emission. Averaging the results for different choices of the polar angle of incidence Θ over a large set of impact points, the obtained kinetic electron emission yields can be compared with experimental data and predictions from simple geometrical calculations. The presented simulation results appear to be reasonable in comparison with experimental data as well as with simple geometrical considerations of kinetic electron emission under oblique incidence. © 2010 Elsevier B.V. All rights reserved.

Friction surfacing is a solid-state process, which allows deposition welding at temperatures below the melting range. For this investigation coating layers of NiAl-bronze were deposited by friction surfacing on self-mating substrates, followed by microstructural characterisation. Further, cavitation tests were performed in order to investigate wear resistance. Cavitation erosion mechanisms were analysed by means of optical and electron microscopy. All coatings show incubation periods about twice as long as those of the substrate material, while their average rate of material loss is about one half of that of the substrate. The differences in cavitation erosion resistance are due to more ductile behaviour of the coatings, as well as corrosion increasing the wear of the as-cast material. © 2011 Elsevier B.V.

In the present study, a thermo-elastic-plastic model was developed in order to evaluate the residual stresses in dissimilar automatic tungsten inert gas (TIG) welds between plain carbon steel CK4 and a ferritic stainless steel AISI409. The effect of welding heat input on the magnitude and the distribution of residual stresses was investigated and the results of simulation were validated by X-ray diffraction measurements. It is shown that the calculated residual stresses are in good agreement with the residual stresses determined experimentally. It was found that the magnitudes of stresses at the weld center line increases with increasing the welding speed. © 2010 Springer-Verlag London Limited.