Pin Surface Research Articles

Study on the Damage Mechanism of an H62-Cu/7075-Al Tribo-Pair Under the Influences of Current Direction and Density

In the present study, we used 7075 Al-H62 Cu and H62 Cu-7075 Al pairs to study the effects of current density and direction on their tribological properties and on the damage caused by the current-carrying friction and wear. We found that, when the current density increased from 0 A/mm2 to 79.61 A/mm2, the coefficients of friction for both pairs decreased. Results obtained after wear indicate that the current direction influences the electromigration between the two tracks, leading to different kinds of damage on the worn surface. In the case of the 7075 Al-H62 Cu pair, damage mainly involved mechanical wear at low current densities. As the current density increased, electro-erosion damage gradually became more dominant. Under the action of a large electric arc, the material surface was severely eroded, and a dense oxide film formed on the material contact surface, ultimately leading to the failure of electrical conduction between the materials. In the case of the H62 Cu-7075 Al pair, damage mainly involved mechanical wear. A layer of copper film was found on the surface of the worn aluminum pin, which caused its mass to be greater than it was before wear.

Enhanced Thermodynamic Stability of Delithiated Nano-LiCoO2 by Lanthanum Doping.

The dynamic environment within lithium-ion batteries induces significant changes in local thermodynamic functions, hampering the accurate prediction of the stability of the cathodes during cycling. While delithiation primarily affects the surface properties of the cathode structure, there is a lack of fundamental understanding concerning the evolution of interfacial energies with varying stoichiometry. Here, we used microcalorimetry to quantify the thermodynamic changes between the stoichiometric and partially delithiated nano-LiCoO2 states for the first time. A mild delithiation from LiCoO2 to Li0.71CoO2 caused a surface energy reduction, negatively affecting the adhesion between adjacent grains by ∼0.4J/m2. The introduction of lanthanum at 1.0 atom % reduced the surface energy of the stoichiometric LiCoO2 while forcing a constant surface energy state during delithiation down to Li0.57CoO2. This reduced the thermodynamic stress between grains during lithium cycling, mitigating degradation mechanisms. The lanthanum-induced surface stabilization also inhibited the coarsening and dissolution of the cathode particles. We used electron microscopy to propose an atomistic mechanism by which the lanthanum doping pins surface dissolution for improved cathode stability.

Development workflow based on in situ synchrotron investigations to optimize laser processing of copper pins

To design future laser manufacturing processes for welding of copper materials, more and more high-end analysis methods are required. A fundamental process understanding by analyzing cause-and-effect relations of process dynamics using inline in situ diagnostics allows for an improved description of laser material interaction. Strategies for a reliable and robust welding process are derived from the findings. In this study, a four-step advanced methodical approach is presented and discussed. In the first step, a fundamental process description of the geometry of the vapor capillary and the formation of weld defects is developed. Therefore, welds on electrolytic tough pitch copper (Cu-ETP) and CuSn6 are carried out to analyze the temporal and spatial vapor capillary dynamics depending on laser power, welding speed, and focal diameter. This fundamental process understanding is transferred to the welding of copper pins in the form of I-pins. For this purpose, impurities and imperfections were applied to the pin surface to investigate the effects on the process result. As a third step, strategies by means of laser intensity distributions were adapted to compensate for imperfections in the welding process. Finally, a sensor vision system is adapted for ideal welding results. Investigations are based on in situ synchrotron analysis at Petra III, DESY in Hamburg. For the experiments, a TRUMPF TruDisk laser (100/400 μm fiber diameter), a TRUMPF TruFiber 6000P (50/100 μm fiber diameter), and a single-mode fiber laser (14 μm fiber diameter) were used. The focal diameter was adjusted with the optical system depending on the investigation.

Effect of TiO2-SiC and heat treatment on tribological characteristics of bimodal hybrid aluminium composites under dry sliding condition

Abstract The dry sliding wear behavior of bimodal TiO2np/SiCp/Al6082 composites was studied using a pin-on-disk tribometer. The investigation included both as-cast alloy and T6 heat-treated composites, with variations in applied load (40 N, 60 N, and 80 N) and sliding distance (600, 900, 1200, 1500, 1800, and 2100 m) at a constant sliding speed of 2 m/s. The microstructure of the composites and the worn surface were examined using a scanning electron microscope. A linear increase in wear rate was observed with sliding distance up to the transition limit. It was found that at 40 N, a shield began to develop between the disc and pin surface, reducing the coefficient of friction (COF), and friction and oxide were the primary processes of wear mechanisms. A larger load caused the protective layer to be destroyed; increasing COF, and adhesion and delamination were the two types of wear that were noticed. The wear resistance of alloys and bimodal composites were increased by heat treatment because it strengthened the matrix.

Friction mechanisms of Ni-based and Zr-based bulk metallic glasses under different contact pressures

Pin-on-plane dry friction tests of Ni-based and Zr-based bulk metallic glasses were performed at ambient temperature under reciprocating sliding condition at 4 mm/s, under 160 MPa and 290 MPa. Domed 100Cr6 steel pins were used as counterface material. The friction performance of Ni-based glass is worse than the Zr-based glass but the former has a relatively more stable feature. For all metallic glasses, lower friction and more stable process can be observed upon higher contact pressure. Transfer of material from metallic glass samples onto steel pin surfaces is analyzed in details at the micrometer scale, showing that tribological properties of metallic glasses at high pressure could be related to the volume hardness of materials, together with the glass transition temperature.Keyworks:Metallic glasses, Third body flow, Wear, Friction performance

Triggered Release of Ampicillin from Metallic Implant Coatings for Combating Periprosthetic Infections.

Periprosthetic infections caused by Staphylococcus aureus (S. aureus) pose unique challenges in orthopedic surgeries, in part due to the bacterium's capacity to invade surrounding bone tissues besides forming recalcitrant biofilms on implant surfaces. We previously developed prophylactic implant coatings for the on-demand release of vancomycin, triggered by the cleavage of an oligonucleotide (Oligo) linker by micrococcal nuclease (MN) secreted by the Gram-positive bacterium, to eradicate S. aureus surrounding the implant in vitro and in vivo. Building upon this coating platform, here we explore the feasibility of extending the on-demand release to ampicillin, a broad-spectrum aminopenicillin β-lactam antibiotic that is more effective than vancomycin in killing Gram-negative bacteria that may accompany S. aureus infections. The amino group of ampicillin was successfully conjugated to the carboxyl end of an MN-sensitive Oligo covalently integrated in a polymethacrylate hydrogel coating applied to titanium alloy pins. The resultant Oligo-Ampicillin hydrogel coating released the β-lactam in the presence of S. aureus and successfully cleared nearby S. aureus in vitro. When the Oligo-Ampicillin-coated pin was delivered to a rat femoral canal inoculated with 1000 cfu S. aureus, it prevented periprosthetic infection with timely on-demand drug release. The clearance of the bacteria from the pin surface as well as surrounding tissue persisted over 3 months, with no local or systemic toxicity observed with the coating. The negatively charged Oligo fragment attached to ampicillin upon cleavage from the coating did diminish the antibiotic's potency against S. aureus and Escherichia coli (E. coli) to varying degrees, likely due to electrostatic repulsion by the anionic surfaces of the bacteria. Although the on-demand release of the β-lactam led to adequate killing of S. aureus but not E. coli in the presence of a mixture of the bacteria, strong inhibition of the colonization of the remaining E. coli on hydrogel coating was observed. These findings will inspire considerations of alternative broad-spectrum antibiotics, optimized drug conjugation, and Oligo linker engineering for more effective protection against polymicrobial periprosthetic infections.

Polymer composite coatings subjected to sliding wear under simulated lunar temperature and dust conditions

Due to the detrimental effect of lunar dust on tribological components, it is imperative to develop bearing materials and surfaces which can survive and mitigate dust at the interface while operating under lunar environmental conditions. This issue is poised to become more significant in the near future, with lunar exploration evolving beyond the short probing missions of the Apollo era. Therefore, this study aims to investigate the combined effect of temperature and lunar dust on the tribological performance of aromatic thermosetting copolyester (ATSP) and polyether ether ketone (PEEK) -based polymer composite coatings from −150 to 110 °C. The experiments were conducted using a flat pin-on-disk configuration under dry sliding conditions, sliding speed of 0.25 m/s, 17.5 MPa contact pressure, and nitrogen gas environment. It was found that metal-on-polymer coating sliding results in dust embedment and accumulation on the softer material, which yields high friction and two-body abrasive wear. The chemical analysis of transfer film on the metal pin surface indicated a mixture of dust and polymer phases, which increased with increasing temperature, and thus resulted in deteriorated tribological performance. Self-mating polymer coatings yielded lower friction coefficient and wear due to a better dust mitigation resulting in three-body wear at the interface. The ATSP-based coatings showed higher wear resistance at all temperatures, particularly under self-mating sliding condition.

Effect of onion-like carbon on the resistance and adhesion of pogo pins with titanium adhesive layer of varying thicknesses

A test probe is a component used to attach microchips to a semiconductor testing device. Pogo pins are one of the several types of probes available on the market. However, probes exhibit some drawbacks, such as high manufacturing costs, low test lifespan, and susceptibility to sticking. In this study, a dual-layer structure that can enhance the wear resistance and anti-sticking properties of gold (Au)-plated pogo pins, as well as overcome surface adhesion issues, is proposed. Oxygen plasma cleaning is first performed for 30 min. Subsequently, a direct current plasma of 250 W is applied to deposit a titanium (Ti) layer to enhance the adhesion of onion-like carbon (OLC) on the surface. The four thicknesses of the deposited Ti metal are 20, 30, 50, and 70 nm. Finally, extremely hard and conductive OLC with a thickness of 110 nm is deposited on the Ti/Au-plated pogo pin surface by physical vapor deposition. Results reveal that most of the area of OLC with the Ti adhesion layer remains on the substrates even after cycle testing at 200 K. Nanoindenter measurements reveal that with an increase in the Ti thickness, the probe hardness increases; in particular, at a thickness of 70 nm, the hardness is 121 % greater than that of the as-grown probe. Furthermore, under the 200 K wear test, the probe with 70 nm Ti exhibits ∼9 % reduction in surface wear in comparison with that of the as-grown probe. Finally, while the resistance of the dual-layer coated probe is greater than that of the as-grown probe at 0 K, its resistance becomes markedly less than that of the as-grown probe after undergoing a 200 K cycle test. On the basis of these results, a mechanism of adhesion, hardness, and wear resistance improvement by the OLC/Ti dual-layer structure is proposed.

Influence of Friction Stir Additive Manufacturing Parameters on Dry Friction and Wear Properties of Al-Mg-Si Alloy's Built Surfaces Fabricated by Sheet Lamination

Abstract In this article, friction-stir additive manufacturing, a solid-state process for rapid fabrication of large components, is employed to investigate laminated Al-Mg-Si alloy blocks. The study delves into microstructural changes, hardness distribution, and wear behavior on two distinct surfaces using various parameters such as rotational speed (800 and 1200 rpm), traverse speed (41 and 82 mm/min), and a 50% pin overlap for block fabrication. Macrographs demonstrate the influence of adjacent toolpath overlap on layer integrity through interfacial mixing and consolidation of plastically deformed material. Within the overall stirred zone, re-stirring effects lead to refined grain formation and the dissolution of Mg2Si precipitates, resulting in an uneven micro-hardness distribution due to varying thermal cycles. Notably, specimens with a traverse speed of 41 mm/min exhibit reduced wear loss, attributed to microstructural changes that enhance resistance to plastic deformation during sliding, thereby improving tribolayer stability. This enhancement is attributed to increased hardness arising from refined grains and the strain hardening effect. Interestingly, the study finds that the horizontal surface of the fabricated blocks displays superior wear resistance compared to the vertical surface, due to the more homogeneous microstructure in individual layers. Further analysis using FESEM and EDS unveils the presence of glaze layers, oxide films, galling surfaces, grooving, trimming impacts, ploughing marks, and the accumulation of wear debris within wide pits and on worn-out pin surfaces. Scar morphology reveals that both abrasive and adhesive wear mechanisms contribute to volumetric losses in the specimens.

Effect of Humidity on Head Smear Generation in Head-Assisted Magnetic Recording

The causes of head smears deposited on the magnetic head surface due to laser heating in heat-assisted magnetic recording should be investigated to achieve high recording densities of hard disk drives. These factors, such as outgassing from components and humidity, also affect smear formation in hard disk drives. In this study, we focused on the effect of relative humidity on smears generated via laser heating. Three types of lubricant film (dipped, ultraviolet-treated, and rinsed) were prepared, and the amount of smear generated on a glass pin surface was evaluated using a pin-on-disk tester with a laser heating system. It was confirmed that the amount of smear increased as the humidity increased, and lubricant films with higher chemical bonding fractions showed less smear generation and lower dependence on humidity. In addition, time-of-flight secondary ion mass spectroscopy confirmed that the migration of cobalt from the magnetic layer was accelerated by laser heating and humidity.

Effect of the scanning strategy and tribological conditions on the wear resistance of IN718 obtained by Laser Metal Deposition

Since the advent of additive manufacturing processes, new ways of repairing damaged parts emerged. Among those, Laser Metal Deposition offers the possibility of restoration or functionalization of surface properties. In this work, we study the wear properties of an IN718 coating deposited by LMD. IN718 is deposited according to several scanning strategies. Samples are subjected to dry flat-on-flat reciprocating wear tests using the flat surface of a cylindrical pin as a counter body. Then, we investigate the impact of the scanning strategy, the normal load, and the number of cycles on wear. Finally, we compare the wear resistance of the LMD samples with the one of wrought IN718 to evaluate the competitiveness of the wear properties of the material obtained by LMD. Results show that the scanning strategy turns out to not change the wear resistance of the deposited sample despite the highly heterogeneous surface microstructure. As the chosen contact is a flat-on-flat contact, the large area covered by the pin does not perceive the local microstructural heterogeneities. It has been observed as well that the wear volume of the coating increases linearly as the normal load increases, with an evolution of the wear mechanisms. Although oxidized transfer layer is observed at lower load, the main wear mechanisms observed are abrasion and adhesion. Then, by studying the wear evolution with increasing testing time, it has been observed that after a certain amount of cycles, a protective oxide layer appears and prevents IN718 from wear. In similar tribological conditions, wrought IN718 has slightly better wear resistance than its LMD's homolog. This difference in wear between the materials obtained by two processes could certainly be explained by the high initial amount of dislocations in the LMD samples and the presence of detrimental phases in its microstructure, such as Laves phases. Nonetheless, this study highlights the good wear resistance of the IN718 samples obtained by LMD despite their non-optimized as-built properties.

Influence of TiC Particles on Mechanical and Tribological Characteristics of Advanced Aluminium Matrix Composites Fabricated through Ultrasonic-Assisted Stir Casting

The present investigation highlights the development of high-performance materials in the construction materials industry, with a special focus on the production of aluminium matrix composites (AMCs) containing titanium carbide (TiC) particles. The stir casting method with ultrasonic assistance was employed to enhance the mechanical and tribological properties. ASTM standards were employed to evaluate the influence of TiC particles on density, hardness (VHN), ultimate tensile strength (UTS), and wear resistance at various TiC weight fraction percentages (0.0 wt.%, 2.0 wt.%, 4.0 wt.%, 6.0 wt.%, and 8.0 wt.%). Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analysis were performed to analyse the microstructural changes and elemental phases present in the synthesised composite. Results revealed that the incorporation of 8 wt.% TiC reinforcement in the metal matrix composites demonstrated significant improvements compared to the base alloy. In particular, a substantial enhancement in hardness by 32%, a notable increase of 68% in UTS, and a significant 80% rise in yield strength were observed when contrasted with the pure aluminium alloy. The tensile fracture analysis of the specimens revealed the presence of dimples, voids, and cracks, suggesting a brittle nature. To assess the wear characteristics of the composites, dry sliding wear experiments were performed using a pin-on-disc wear tester. Incorporation of TiC particles resulted in a lower coefficient of friction than the base alloy, with the lowest friction coefficient being recorded at 0.266 for 6 wt.% TiC, according to the data. FESEM and energy-dispersive X-ray spectroscopy (EDXS) were used to examine the surfaces of the worn pin. Overall, the inclusion of TiC reinforcement particles in the matrix alloy greatly enhanced the wear resistance and friction coefficient of the Al-6TiC composites. Ploughing and adhesion under lower loads and delamination under higher loads were the wear mechanisms observed in the wear test.

Development and performance evaluation of self-lubricating cemented carbide

Nowadays, there is a trend in the industry to reduce or even eliminate the use of cutting fluid in machining operations. The high costs of purchasing, using, and disposing of fluids and problems related to environmental pollution and operator health favor the dry-cutting technique. However, in some machining processes, lubrication is required. In this cases, solid lubrication may be a solution. The present study investigated the development of self-lubricating cutting tool materials by adding graphite in WC – 10 wt% Co cemented carbide and how this graphite affects the sample's mechanical properties and wear behavior. The WC - 10 wt% Co cemented carbide was prepared by spark plasma sintering (SPS), and solid graphite lubricant was added at different concentrations. The samples were mixed in a high-energy ball mill and sintered at 1200 °C under 40 MPa. Microstructure, hardness, fracture toughness, and wear analyses were performed on the samples to understand the effect of graphite addition on sintered material properties. The chemical composition of the samples was analyzed by XRD and Raman spectroscopy. The wear measurement was performed by analyzing the volume of material lost by the samples during the pin-on-disk tests. Profilometry analyzes of the samples before and after the tests made it possible to measure the volume of lost material, allowing to verify the influence of the addition of solid lubricant on the wear rate of the samples. The results of the mechanical tests show that the highest hardness and the modulus of elasticity were 1578 HV and 870 GPa, respectively. The wear presented by the samples with 1% of graphite was up to 9 times less than the standard samples. The wear mechanisms are micro-cracking and fragmentation of WC grains; however, the presence of a solid lubricant avoids the steel counterpart material transfer for the pin surface. Also, it was observed the formation of a graphite and oxide tribolayer on the worn disc surface during the tests, thus avoiding excessive wear.

Estimation Method for Residual Sodium Amount on Unloaded Dummy Fuel Assembly

This study has researched an estimation method for the amounts of residual sodium film and sodium lumps on dummy fuel pins in the Japanese prototype fast breeder reactor Monju by fundamental experiments and demonstration experiments. The residual sodium amounts on the pin surface were measured using three types of test specimens: (a) single pin, (b) 7-pin assembly, and (c) 169-pin assembly. The single pin and 7-pin assembly experiments revealed that the withdrawal speed of the pins and improvement of the sodium wetting drastically increased the residual sodium amounts. Furthermore, the 169-pin assembly experiments measured the practical amounts of the residual sodium in the Monju dummy fuel assembly and demonstrated sodium draining behavior through small gaps between the pins. The estimation method includes four models such as a viscosity flow model, Landau-Levich-Derjaguin (LLD) model, an empirical equation related to the Bretherton model, and a capillary force model in a tube. These calculation results were comparable to the residual sodium amounts obtained by the experiments. In the tests of improving sodium wetting, the amounts of residual sodium on the test specimen were close to 1.4 times larger than those of the thin sodium film estimated by the LLD model. The increased amount of residual sodium by improving the sodium wetting was explained by the ratio of the adhesion energy ( γ S O − γ S L ).

Tribological Properties of Cu-Based Self-Lubricating Materials Composed with Cu- or Ni-Plated Graphite

Cu-based self-lubricating materials can effectively adapt to complex natural environments and ensure consistency in materials used for switch transitions. These materials were tested through interface reinforcement research, improving their mechanical and tribological properties and providing a theoretical basis for new switch slide baseplate materials. Results showed that the coefficient of friction and wear weight loss of Cu-based self-lubricating materials decreased with an increase in graphite content after Cu and Ni plating on the graphite surface, reaching a minimum value at a graphite content of 6 wt.%. The coefficient of friction and wear weight loss of the Ni-plated material were reduced 11.1% and 85.6%, respectively, whereas the coefficient of friction and wear weight loss of Cu-plated materials were reduced 7.2% and 78.4%, respectively. Compared to Cu plating, Ni plating substantially enhanced the friction and wear performance of Cu-based self-lubricating materials. Cu and Ni plating increased the adhesion of the materials on the pin surface and the adhesive materials’ composition was consistent with the lubricating film, which changed the grinding mechanism between the pin and the disk. Ni plating had a stronger effect on the tribological performance of Cu-based self-lubricating materials than Cu plating.

Effects of sintering temperatures on the microstructure and mechanical properties of S390 powder metallurgy high-speed steel

High-performance complex gear cutters and high-temperature bearings are just some of the applications where high-speed steels (HSSs) shine as a preferred material choice owing to their high hardness and outstanding wear resistance. In this work, the effects of sintering temperature on the microstructure and mechanical properties of S390 HSS prepared via spark plasma sintering (SPS) were investigated with a range of sintering temperatures from 930°C to 1,090°C, a uniaxial pressure of 50 MPa, and a holding time of 5 min. The results demonstrated that the improvements in density, hardness, red hardness, and three-point bending strength were confirmed as the sintering temperature increased from 930°C to 1,090°C. Temperature-induced microstructure evolutions were assessed for their contribution to property enhancement, such as powders with varying dimensions and carbides with diverse morphology and diameter. The specimen with the best comprehensive mechanical properties (67.1 HRC and 1,196.67 MPa) was prepared at 1,050°C via SPS. The wear coefficients decreased as the sintering temperature increased, and the observation results of worn surfaces of test pins confirmed that abrasive wear and oxidation wear dominated the wear experiments. Furthermore, the wear mechanism of dense and porous SPS HSS was illustrated and analyzed in terms of the debris and trapped carbides.

Some recent progress in reactor core thermal-hydraulics modelling

In the last more than ten years the research groups of the present authors have been working on some of the key phenomena or parameters widely used in sub-channel thermal-hydraulics (SCTH) codes, e.g. (a) transversal exchange between sub-channels, (b) circumferential non-uniform heat transfer in fuel assemblies with tight or semi-tight lattice (pitch-to-diameter ratio smaller than 1.25), (c) PDO heat transfer and rewetting and (d) CFD analysis of two-phase flow and heat transfer, incl. critical heat flux. Among others, three transversal exchange phenomena were studied, i.e. turbulent mixing coefficients, void drift and wire wrap induced sweeping flow. New models for various turbulent mixings, void drift and wire wrap induced cross flow were developed based on analytical analysis and CFD simulations. Importance of the non-uniform heat transfer behavior inside single sub-channel was identified in fuel assemblies with tight or semi-tight lattice. Correlations for predicting the non-uniform heat transfer coefficient were proposed, which were implemented into SCTH codes, to accurately determine the local hot spot on the fuel pin surface. A large experimental data base containing more than 60,000 data points of PDO heat transfer and rewetting was established. Based on the data base a new empirical correlation of PDO heat transfer was proposed. In addition, dynamic behavior of droplets (droplet size and velocity) and the thermal non-equilibrium were experimentally measured, which can be used for the validation and improvement of mechanistic models of PDO heat transfer and rewetting, also proposed by the research groups of the present authors. For the CFD prediction of CHF, a new and robust method for wall boiling heat transfer was developed to calculate the near wall void fraction and its connection to CHF.

Numerical studies on liquid sodium flow boiling in a 7-pin hexagonal subassembly towards flow rundown scenario in SFR

The present study is intended for the development of high resolution CFD based model for the prediction of two-phase flow and heat transfer characteristics of liquid sodium in a 7-pin bundle. The sodium flow boiling from its inception to nucleate boiling and the forced convective vaporization regimes are analyzed by developing an Eulerian-Eulerian model (two-fluid model) using flow regime dependent constitutive correlations and modified non-equilibrium wall boiling model. The Algebraic Interfacial Area Density (AIAD) model is implemented for providing required closure terms as flow regime dependent based on the local flow topology within the two-fluid model. The sodium flow boiling simulations are performed in a 7-pin subassembly using the model under constant wall heat flux for different inlet mass flow rates and predicted the quasi-steady boiling. The radial and axial void fraction progress in the flow sub-channels, variation of sodium temperature, and wall boiling components along the heated pin length are numerically predicted. Also analyzed the transient sodium boiling under flow rundown scenario in the 7-pin subassembly with a continuous reduction in the inlet mass flow rate under constant wall heat flux. The prediction of wall temperature variation during this flow scenario confirmed the incidence of local dry-out at the end of the transient which causes loss of heat transfer from the pin surface. Also, the mechanistic model based evaluations for wall heat transfer coefficient and possible flow regimes are obtained based on the flow and thermal conditions predicted.

Current-carrying wear characteristics of Al-Cu alloys against stainless steel

The wear characteristics of Al-Cu alloy against stainless steel were investigated on the equipment with current applied across the sliding interface. The effects of Cu content (5% ∼ 15%) and current density on the wear surface morphology and wear rate of the alloy were discussed. The results show the wear rate of Al-Cu alloys generally increased with increasing current density and Cu content, revealing a negative relationship between hardness and current-carrying wear rate. It was found that a material transfer layer would be formed on the sliding surface of the stainless steel pin, which induced the adhesive wear of Al-Cu alloy samples and decreased the wear rate of the alloy. Al-Cu alloy with high Cu content had a slower formation of the material transfer layer.

Experimental Investigation on Friction Behavior of Selective Laser Sintering Processed Parts.

Selective laser sintering (SLS) is a powder bed fusion additive manufacturing process that uses polymer powders to produce functional parts directly from digital 3D models. SLS supports small- to medium-batch fabrication of customized products for various end-use applications. These parts can be used as tooling to support conventional manufacturing and inspection where mechanical and tribological behaviors are important. This article evaluates the friction behavior of parts fabricated by SLS polyamide (PA12) and glass bead-filled polyamide (PA-GF) materials. Pin-on-Disk tribometer was used to characterize the behavior in dry sliding conditions with part build orientation, load, and speed as factors. Taguchi's approach and analysis of variance are used to quantify the influence of these factors on the friction coefficient. Both materials show reduction in friction coefficient with the increase in load; on the other hand, an increase in speed affects adversely. However, the influence of part orientation is comparatively lesser than the other two factors considered in this study. The debris, pin, and disk wear surfaces were examined to learn wear mechanisms. It is observed that surface porosity resulting from the fabrication process plays a significant role in friction behavior. The glass beads in PA-GF material function as reinforcement against load and influences the friction behavior. Low friction and wear characteristics make both materials as a prospective contender for tooling application.