Mild Wear Regime Research Articles

Comparative Study of the Tribocorrosion Performance of NiTiNOL60 in Acidic, Alkaline, and Saline Environments

AbstractIn order to enhance the durability of tribological interfaces, an investigation into the synergistic effects of sliding wear, corrosion, and their interactions is crucial. This study focuses on understanding the deformation mechanisms of NiTiNOL60, a nickel-rich nickel-titanium alloy, during sliding against Al2O3 in different corrosive environments, including acidic, alkaline, and saline mediums. The pH of the environments is found to play a significant role in the tribocorrosion process, leading to electromechanically induced transformations and various wear patterns. Plastic deformations are observed on the wear track surfaces, particularly in the severe and mild wear regimes. In an alkaline environment, depassivation of the oxide layer triggers oxidational wear, with the depassivation rate dependent on factors like contact pressure, sliding velocity, and passive film properties. The wear volume is highest in saline environments, with contributions from mechanical wear, corrosion, and third-body abrasion. Grain deformations occur in the alkaline environment due to shear forces, while in the acidic medium, corrosion accelerates mild wear involving abrasion and delamination. The findings provide insights into wear mechanisms and localized corrosion, highlighting the influence of H+ and OH− groups (pH values) on corrosive wear and crack propagation.

Investigation of the wear resistance of in-situ Al-Ti composites fabricated by mechanical alloying and hot extrusion

ABSTRACT In this research, the wear behaviour of Al-20%Ti composites, fabricated by mechanical alloying and hot extrusion at different conditions, was investigated using the pin-on-disc method. A high-energy vibratory mill was applied to produce the nanocomposite (Al-20Ti-4hrV) and nanocrystalline (NC) Al samples, while a low-energy planetary mill was used to produce the other composites (Al-20Ti-20hrP and Al-20Ti-60hrP). To examine the microstructure and worn surface of specimens, optical microscopy and scanning electron microscopy were performed. To estimate the mechanical properties of the samples, their density and Brinell hardness were measured. The use of a high-energy vibratory mill caused the formation of an ultrafine aluminium matrix with in-situ nanometric intermetallic particles in the Al-20Ti-4hrV sample. As a result, the highest relative density and hardness and the best wear resistance were obtained in the Al-20Ti-4hrV sample. The application of the low-energy planetary mill led to the formation of flaky particles; accordingly, low relative density, poor mechanical properties and wear resistance in Al-20Ti-20hrP and Al-20Ti-60hrP samples were observed. The dominant wear mechanisms for Al-20Ti-4hrV and NC Al samples were identified as microploughing, adhesion and oxidation in the mild wear regime, whereas those of the Al-20Ti-20hrP and Al-20Ti-60hrP samples were mainly adhesion wear mechanism and inconsiderable delamination in the mild wear regime. The highest hardness and wear resistance were obtained for the nanocomposite sample owing to nanometric Al3Ti reinforcement, nanocrystalline Al matrix and good adhesion between particles and the matrix. This study confirmed that the nanocomposite production method presented in this research is suitable for wear-resistance applications.

Dry Sliding Wear Behavior and Mild–Severe Wear Transition of the AA2195-T6 Alloy under Different Loads

The mild–severe wear transition of aluminum alloys is considered evidence that the wear changes from a stable state to an unstable state, which is of great importance in engineering applications. The purpose of this study is to evaluate the mild–severe wear transition of the 2195 Al–Li alloy for different loads and to elucidate the causes behind it. To this end, dry sliding tribometric tests were carried out by varying the normal load from 2 to 40 N at room temperature. The results show that the change in wear rate can be divided into three distinct stages, including weak growth at low load (2–4 N), rapidly increased growth at medium load (8–16 N), and gradually increased growth at high load (32–40 N). The transition from mild to severe wear is observed at loads ranging from 4 to 8 N. Characterization of the worn surface of the Al–Li alloy via scanning electron microscopy shows that abrasion and oxidation are the dominant wear phenomena in the mild wear regime. On the other hand, delamination, adhesion, and severe plastic deformation become dominant in the severe wear regime. The reason for the occurrence of the transition is the tribo-induced plastic deformation of the substrate.

Wear resistance of HVOF- and HVAF-sprayed (Ti,Mo)(C,N)–Ni coatings from an agglomerated and sintered powder

(Ti,Mo)(C,N)-25 wt% Ni coatings obtained by spraying an agglomerated and sintered feedstock powder using different high velocity air-fuel (HVAF) and high velocity oxygen-fuel (HVOF) deposition processes are comparatively analysed for their sliding, abrasion and impact resistance.All HVOF-sprayed coatings are particularly dense, with ≈800 HV hardness (tested at 100 gf, 300 gf and 500 gf). In-flight oxidation resulted in some embrittlement, as revealed by scratch tests. In ball-on-disk sliding against an Al2O3 counterpart, they maintained a mild wear regime (wear rates ≤10−6 mm3/(N⋅m)) from room temperature up to 600 °C, with better performance in comparison to Cr3C2–NiCr reference coatings. At room temperature, the Ti(C,N) hard phase limited the abrasive cutting by counterbody asperities. At 400 °C and 600 °C, the coatings developed a thin, protective oxide tribofilm. They also exhibited no interface delamination in cyclic impact tests. However, they suffered higher wear (≈3–5 × 10−3 mm3/(N⋅m)) in high-stress particle abrasion testing, particularly when compared to HVAF-sprayed Cr3C2–NiCr. Gaining improved control over in-flight oxidation of (Ti,Mo)(C,N)–Ni during spraying is probably the key to overcome this limitation.The HVAF-sprayed (Ti,Mo)(C,N)–Ni coating exhibited severe interlamellar decohesion under all test conditions, as the limited melting degree of the feedstock did not compensate for the intrinsic microstructural inhomogeneity of the powder particles.

Superlubricity and running-in wear maps of water-lubricated dissimilar ceramics

Water-lubricated ceramic sliding tribosystems, when operating under superlubricity conditions, reduce frictional energy losses in many applications. Aqueous superlubricity of 5 dissimilar ceramic tribopairs (Si3N4–Al2O3, Si3N4-ZTA, Si3N4–SiC, Al2O3–SiC, ZrO2–SiC) was thus studied in a series of ball-on-disk tests, with the identification of wear mechanisms and lubrication regimes, while introducing a running-in wear map approach to elucidate transient tribological phenomena. All pairs presented superlubricity for certain combinations of normal load and sliding speed, after a running-in period where mechanical and thermal severities of contact remained mostly below their respective threshold values, promoting mild wear regimes. Load-carrying capacity of ZrO2–SiC was the highest due to high homogeneity and low roughness of the tribofilm on SiC disk’s wear track.

Effect of precipitation hardening on wear behavior of premix Al7075 hybrid matrix composites

Al 7075 alloy is high strength alloy with excellent physical and mechanical properties. Though the alloy has capacity to work as structural material, many a times poor tribological properties limit its applications. Tribological properties can be improved by addition of hard ceramic reinforcement or by adding soft solid lubricants. But this solitary addition shows improvement at the cost of certain mechanical properties.In this study, premix alloy of Al 7075 was fabricated by blending elemental powders followed by Hot Press Sintering (HPS). The optimum operating window for HPS at 550 °C, 40 MPa for 6 min was used to obtain maximum densification. Al 7075–10 wt% B4C (ABC 10) was used as starting material for development of Hybrid Matrix Composites namely (HMC-G) and HMC-M containing solid lubricants viz. Graphite and MoS2 (1 to 5 % by wt.) respectively. Post sintering heat treatment consisting of solutionising at 480 °C followed by artificially ageing at 120 °C for 24 h was employed. The wear tests were carried out in Pin on Disc (POD) machine at various combination of sliding speeds (1, 1.5, 2, 2.5 m/s) and applied loads (10, 20, 30, 40 N) with constant sliding distance of 3000 m. These composites were then characterized for hardness and density measurement, microstructures, SEM-EDS and worn-out feature analysis. Surface response analysis was done to locate mild wear and severe regimes. Hybrid matrix composites containing 3 % wt. of MoS2/Graphite in ABC 10 shows improved wear resistance due to synergistic effect of dispersion and precipitation strengthening.

Wear and Morphological Analysis on Basalt/Sisal Hybrid Fiber Reinforced Poly lactic acid Composites

The investigation was undertaken to evaluate the wear behavior of basalt fiber and sisal fiber reinforced polylactic acid PLA composites. Basalt saline-treated chopped fiber and treated sisal chopped fiber were alloyed with polylactic acid and the samples were obtained using an injection mold in a twin-screw extruder. Three weight fraction samples were prepared, namely PBSi-1 (90% by weight polylactic acid, 5% by weight basalt and 5% by weight sisal), PBSi-2 (85% by weight polylactic acid, 7.5% by weight basalt and 7.5% by weight sisal) and PBSi-3 (80% by weight polylactic acid, 10% by weight basalt and 10% by weight sisal). The wear behavior of the prepared specimen were determined using a Pin-on-disc. The wear loss was measured at four different loads (10 N, 20 N, 30 N and 40 N) and four different sliding speeds (100 rpm, 150 rpm, 200 rpm and 250). The wear mechanism map was generated based on the wear regime nature using the Fuzzy Cluster C-means algorithm. The PBSi-3 composite showed a more mild wear regime than the severe and ultra-severe wear, due to the increase in the basalt and sisal fiber content within the composite that results in an increase of hardness and wear resistance. The predominant mechanism observed in the SEM image of PBSi-3 composite is ironing, which indicates the lesser wear occurrence in the composite.

The impact of microstructural refinement on the tribological behavior of niobium processed by Indirect Extrusion Angular Pressing

This research, for the first time, conducted a comprehensive study into the effect of a modern Severe Plastic Deformation technique, “Indirect Extrusion Angular Pressing (IEAP)”, on the microstructural refinement of niobium and the subsequent impact on the tribological properties. The samples were processed for 4, 9, and 12 passes of IEAP and then exposed to Pin-on-disk wear test in dry sliding conditions. The results showed that the grain refinement occurred in niobium from an average grain size of 13 μm to 0.5 μm, along with an increase in hardness from the initial value of 79 HV to 180 HV after 12 passes. Results of wear tests revealed that IEAP processing reduced the wear width, volume loss, and specific wear rate by 14%, 38%, and 38%, respectively, and thereby enhancing the wear resistance of the material. Evaluation of the morphology of wear tracks demonstrated less spalling and less fatigue propagated cracks as well as finer detachment of wear debris on the surface of the processed samples, which led to producing a mild wear regime. The outcomes suggested that IEAP processing resulted in higher resistance in niobium against abrasion and against the development of fatigue propagated cracks which were respectively associated with higher hardness and larger fractions of high-angle grain boundaries (HAGBs).

The high temperature wear mechanisms of iron-nickel steel (NCF 3015) and nickel based superalloy (inconel 751) engine valves

High temperature sliding wear tests were performed on samples taken from NCF 3015 austenitic steel (Fe-32% Ni–14% Cr based 0.8% C alloy with Al, Ti, Nb, Mo) and Inconel 751 superalloy (Ni–16%Cr alloy with Al, Ti, Nb) engine valves using the counterfaces made of PL12 chromium alloyed cast iron seat insert. The contact surfaces were characterized by SEM-EDS, Optical Profilometer, Raman, XRD. The wear mechanisms of the valve systems were explored using the results of these analyses that determined compositions of the tribolayers that formed on the contact surfaces. The Calphad based thermodynamic analyses that revealed stability of the precipitates in the alloys at the test temperatures. An increase of wear occurred between 25 °C and 350 °C, but for T > 350 °C, a continuous reduction in volumetric wear losses were observed with increasing temperature for both alloys. At all temperatures Inconel 751 showed higher wear performance than NCF 3015. It was found that the formation of (Fe1-x-yCrxNiy)3O4 mixed spinel oxides controlled the high temperature wear behavior of these alloys and these structures support the formation of tribolayer under local pressure and high temperature during sliding. Besides the direct effect of oxide compositions within tribolayer, the formation of high amount of (Ti,Nb)C carbides, Ni3(Ti,Nb,Al) and Ni3Nb precipitates play important role in transition from severe to mild wear regime above 350 °C.

A new approach for modelling mild and severe wear in wheel-rail contacts

This paper presents a new approach for modelling the wear in wheel-rail contacts for a wide range of test and contact conditions (material pairing, load, creep, lubrication etc.) in the mild and severe wear regimes with one set of model coefficients. The approach is based on a detailed analysis of 56 Twin-Disc experiments in combination with existing knowledge from the literature. The model considers the thickness of the damaged layer caused by severe plastic shear deformations in the near-surface layer of wheel or rail and the maximum shear stress in the contact as the main influencing factors responsible for the observed wear behaviour. In this way, a much better prediction quality can be reached for varying test and contact conditions compared to the state of the art energy dissipation or sliding based approaches. The model includes a low number of model coefficients which are independent of test and contact conditions.

Influence of graphene nanoplatelets on mechanical properties and adhesive wear performance of epoxy-based composites

Epoxy resin is one of the most widely used thermoset polymers in high-performance composite materials for lightweight applications. However, epoxy has a high coefficient of friction, which limits its tribological applications. In this study, the effect was investigated of different weight fractions of solid lubricant graphene nanoplatelets (GNPs), ranging from 0 to 4.5 wt%, on mechanical and adhesive wear performance of epoxy. Adhesive wear tests covered mild and severe wear regimes. The correlation of tribological and mechanical properties was studied as well. Scanning electron microscopy (SEM) was used to observe the failure mechanisms for both tribological and mechanical samples after each test. The results revealed that the addition of GNPs to the epoxy improved its stiffness and hardness but reduced its fracture strength and toughness. Adhesive wear performance exhibited high efficiency with GNP additions and showed reductions in the specific wear rate, the coefficient of friction, and the induced interface temperature by 76%, 37%, and 22%, respectively. A fatigue wear mechanism was predominant as the applied load increased. Most importantly, severe wear signs occurred when the interface temperature reached the heat distortion temperature of the epoxy. The tribological, and mechanical properties showed only a weak correlation to each other. The addition of GNPs to epoxy by less than 4.5 wt% was highly efficient to improve the wear performance while maintaining the fracture strength and toughness. Fourier transform infrared spectroscopy (FTIR) analysis shows no chemical interaction between the epoxy matrix with GNPs, which implies its physical interaction.

Картирование режимов трения композиционных материалов с интерметаллидным упрочнением на основе антифрикционного сплава системы Al-Sn-Cu

Tribological properties of a composite material with intermetallic reinforcing based on an antifriction alloy of Al-Sn-Cu system are studied. The samples were obtained by the method of reaction casting mixing micron-sized titanium particles into the melt of the matrix alloy. The formation of intermetallic phases led to an increase in the hardness and a decrease in the wear rate of the sample of composite material. Dry sliding wear tests were carried out using a fixed sleeve (counterbody made of steel 45) against a rotating disk (composite material) at sliding velocities of 0.25, 0.5, 0.75 m / s and loads 0.5, 1, 1.5, 2, 2.5, 3 MPa. Wear rate of the samples and friction coefficient for the entire set of tribo-loading parameters were determined. A general increase in the wear intensity with increasing test load was shown. There was no general tendency of the change in the wear rate with the increasing test velocity. The change in the friction coefficient during the test made it possible to determine the wear modes. The temperature change in the friction process was an additional parameter for describing the wear modes. An increase in load and velocity led to an increase in the friction temperature, in addition, the rate of temperature change was significantly influenced by the test time for equal friction paths. Maps of the wear rate which determine the wear modes during testing are constructed. The bounds and conditions of changes between the four modes of wear, soft, mild, severe and critical, are shown. Optimal loading parameters of the friction process corresponding to the sliding velocity 0.5 m / s and load 1.5 MPa are determined. The constructed wear maps made it possible to determine the friction regimes under which the exploitation of the composite material studied will be carried out in the region between soft and mild wear regimes.

Processing and characterization of vertical twin roll cast aluminium alloy sheets of A356, A6061 and A6005

Aluminum alloys A356, A606 and A6005 were twin roll cast in sheets 3 mm thickness using a vertical twin roll caster. Microstructure, hardness and wear characteristics of the cast sheets were investigated. VTRC processed sheets showed finer grain size depending upon the solidification range of alloy. It was observed that hardness values of VTRC alloys were significantly higher than those of corresponding ingot cast alloy products. Approximate Hall-Petch calculations show possibilities of additional strengthening mechanisms other than grain boundary for VTRC processed alloys. Extensive wear studies were performed using a pin on disc wear testing machine. The parameters like wear constant, specific wear rate and average friction coefficient were determined to understand the wear behaviour. The wear results show that all the alloy sheets exhibit wear in the mild wear regime.

Mechanical and tribological properties of spark plasma sintered Nb–Al2O3 composites

This work presents a study of the mechanical and tribological properties of niobium-alumina composites obtained by the spark plasma sintering with a uniaxial pressure of 50 MPa at 1400 °C. The microstructure and crystalline phases of sintered materials were determined by scanning electron microscopy and X-ray diffraction, respectively. Mechanical properties of the samples related to the stiffness, hardness, and fracture toughness were determined through the instrumented indentation and the Vickers indention tests. For the tribological study, alumina, alumina-15%Nb, and alumina-25%Nb materials were tested under dry reciprocating sliding conditions, at room temperature using a ball-on-disc configuration. A three-levels factorial design was used to conduct the wear tests, considering the combination of material compositions and applied load (5 N, 10 N, and 15 N of applied load) for two types of counterbody (52100 steel and Al2O3). Niobium addition improved the fracture toughness and wear resistance of the alumina matrix composites. The index of brittleness that correlates the stiffness, hardness and fracture toughness of the materials decreased with niobium content. When sliding against the steel counterbody, composites exhibited a wear resistance two orders of magnitude higher than that of the monolithic alumina and specific wear rate values characteristic of the mild wear regime (k lower than 10−6 mm3 (N m)−1). The higher wear resistance of composites was related to the tribofilm formation on worn surfaces, due to material transfer from the 52100 steel counterbody surface. Alumina showed a higher wear rate in comparison with niobium-containing composites, due to brittle fracture occurrence, mostly when sliding against the Al2O3 counterbody at higher loads. Wear-regime maps as a function of the index of brittleness and severity of contact allowed the distinction of wear mechanisms of the studied materials and visualization of the improved wear resistance of the niobium-alumina composites.

Tribological behaviour of hypereutectic Al-Si automotive cylinder liner material under dry sliding wear condition in severe wear regime

Hypereutectic Al-Si alloys are used as material for the engine block and cylinder liners in automobiles. Wear behaviour of hypereutectic Al-Si alloy system changes significantly with applied normal load in both mild wear and severe wear regime. Significant improvement in wear resistance can be obtained by exposing silicon particles through the chemical etching process. For Al-25% Si alloys, most studies are reported in mild and ultra-mild wear regime. In the present work, the wear of exposed silicon particles with varying load and speed in severe wear regime was investigated under the unidirectional sliding condition and bi-directional sliding condition using a pin-on-disk tribometer (POD) and a linear reciprocating tribometer (LRT), respectively. Rapidly solidified and T6 heat-treated Al-25Si alloy was polished and etched using 5% NaOH solution to expose the silicon particles. Experiments were carried out with normal loads varying from 40 N to 120 N in dry sliding conditions. Sliding speeds of 0.8 m/s and 1.5 m/s were applied for each load in case of a pin on disk tribometer whereas, in an LRT, the sliding velocities were 0.2 m/s and 0.45 m/s respectively for each set of the load. The surface topography was measured by means of a 3-D optical profilometer, and surface morphology was analyzed using SEM images. It was observed that at higher loads, larger Si particles were fractured and pushed into the matrix. Fractured silicon particles, along with smaller particles, were embedded into the matrix, thereby increasing the silicon concentration in the wear region. The comparison of the experimental results of unidirectional and bi-directional sliding that reveal the change in surface morphology of silicon particles, the friction characteristics at the interface, variation of surface 3-D roughness parameters, the wear rate and wear mechanisms of Al-25% Si alloys are analyzed and reported in the study.

Correlation between test temperature, applied load and wear transition of Mg97Zn1Y2 alloy

Dry sliding wear tests were performed on Mg97Zn1Y2 alloy at various temperatures of 20, 50, 100, 150 and 200°C using a pin-on-disc wear testing machine in order to reveal mild-severe (M-S) wear transition mechanism during elevated-temperature wear testing. It was shown that at each test temperature, the wear rate increased with increasing load, and all wear rate-load curves demonstrated two distinct stages i.e. mild and severe wear stages. The predominant wear mechanisms operating in mild and severe wear stages were analyzed, and they were indicated in the mild and severe wear regimes of a wear mechanism transition map, respectively. M-S wear transition mechanism was analyzed by comparison of microstructure transformation and hardness change in subsurfaces of samples tested in mild and severe wear stages, from which M-S wear transition mechanism was confirmed as softening of surface material arising from dynamic recrystallization (DRX) microstructure transformation. The M-S wear transition load was found to have a linear relationship with test temperature, and decreased with rising test temperature. M-S wear transition obeyed a critical surface DRX temperature (SDT) criterion under given conditions, and the transition loads were estimated at various test temperatures by using the criterion.

Tribological investigations on tribofilm formation and retention under dry sliding conditions with increasing loads

This paper presents a tribological investigation of austenitic steel 21-4N exhaust valve material, dry sliding against ductile cast iron GGG-40 seat material, at a temperature of 500°C, to study the effect of increasing loads on tribofilm formation and retention at the contact interface. The effect of these tribofilms, on the friction and wear behaviour of the tribo-pair, is highlighted. High temperature reciprocating pin-on-disc tests were performed on a tribometer at loads of 20 N to 50 N with a constant stroke of 2 mm and an oscillating frequency of 20 Hz. A distinct running-in behaviour is observed at loads up to 40 N with the coefficient of friction attaining a very low and stable level with increase in sliding time. The average Coefficient of Friction ranges between 0.12 and 0.15. Optical/Scanning Electron Microscope micrographs and Energy Dispersive Spectroscopy analysis indicate the creation of compact and durable tribofilms at loads up to 40 N. At the highest load of 50 N, the Coefficient of Friction behaviour is slightly different. With a low value at the beginning, it shows an increasing trend and reaches a peak around the 10-min mark and reduces thereafter. At this load, despite indications of higher abrasive wear, the Coefficient of Friction behaviour, Optical/Scanning Electron Microscope micrographs and Energy Dispersive Spectroscopy analysis indicate evidence of early deterioration and subsequent reformation of the tribofilms with increase in sliding time. The seat material exhibited comparatively more wear than the valve material; however, the wear coefficients lie in the mild wear regime for the tribo-pair. The results of this investigation indicate the compatibility of the tribo-pair and suggest its use in the exhaust valve/seat application.

Effect of crystal size on the tribological properties of lithium disilicate glass-ceramics sliding against alumina and tungsten carbide spheres

PurposeLithium disilicate glass-ceramics (LS2 GC) are widely used as dental prosthetics and dental restorations. Based LS2 GC have hardness and translucency similar to that of natural teeth. This study aims to investigate the tribological features of LS2 GC with crystalline volume fraction of 64% and different crystal sizes from 8 µm to 34 µm for different counterparts.Design/methodology/approachThe tribological behavior was investigated using a pin-on-disc tribometer with alumina and tungsten carbide (WC) spheres, applied load of 5 N and sliding speed of 5 cm/s at normal conditions. The coefficient of friction was measured continuously up to 10,000 sliding cycles. The specific wear rate was calculated from tribological and profile measurements. The wear mechanism was investigated by surface morphology analysis.FindingsThe coefficient of friction during running-in varied from 0.8 to 1.0 for the alumina counterpart, because of severe wear. Afterwards, it reduced and reached a stationary regime, characterized by a mild wear regime and the formation of a tribolayer formed by the debris. For the WC counterpart, the coefficient of friction curves increased initially with sliding cycles up to a stationary regime. The samples tested against WC presented the lowest specific wear rate (k), and no variation of wear rate with crystal size was observed. For samples tested against the alumina, crystallization and crystal size increased the wear resistance.Originality/valueThis study evaluated the effect of different counterfaces on the tribological properties of the LS2 GC, an important glass-ceramic base for many dental prosthetics and dental restorations, discussing results in light of the contact mechanics. Different specific wear rates, wear regimes and dependence on the glass-ceramic microstructure were observed depending on the counterpart.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2019-0352/

Adhesive wear and interaction of tangentially loaded micro-contacts

Current engineering wear models are often based on empirical parameters rather than built upon physical considerations. Here, we look for a physical description of adhesive wear at the microscale, at which the interaction between two surfaces comes down to the contact of asperities. Recent theoretical work has shown that there is a critical micro-contact size above which it becomes energetically favorable to form a wear particle. We extend this model by taking into consideration the elastic interaction of multiple closely-spaced micro-contacts in 2D, with different sizes and separation distances. Fundamental contact mechanics solutions are used to evaluate the elastic energy stored by shearing the micro-contacts, and the stored energy is compared to the energy needed to detach a single joined debris particle or multiple debris particles under the micro-contacts. Molecular dynamics simulations are used to test the predictions of the outcome for various sets of parameters. Our model provides simple criteria to evaluate the energetic feasibility of the different wear formation scenarios. Those criteria can be used to rationalize the transition between mild and severe wear regimes and help define the notion of asperity.

ZrB2 nanoparticles transmuting tribological properties of Al3Zr/AA5052 composite

Good work hardenability, moderate to high strength of AA5052 alloy and high melting point and elastic modulus of Al3Zr with limited wear resistance have been the driving force to transmute Al3Zr/AA5052 composite by generations of ZrB2 nanoparticles. For this purpose, the varying amounts of ZrB2 particles in Al3Zr/AA5052 composite have been produced by direct melt reaction in situ technique. The phase identification, microstructural studies and wear testing have been performed for all the composites. The phase identification and microstructural studies indicate that the ZrB2 particles are formed successfully in the Al3Zr/AA5052Al composite with hexagonal and rectangular morphology within a size range of 10–190 nm. Wear testing results show that friction coefficient (COF) fluctuates with sliding distance, whereas it decreases with normal load. For the composite without ZrB2, the COF is exhibited increasing trend with sliding velocity, while for the hybrid composites initially it decreases, but beyond 2 m/s sliding velocities it starts increasing. Wear studies also show that with ZrB2 generation in Al3Zr/AA5052 composites can be used up to larger loads and higher sliding velocities while being in mild wear regime. It is observed that the mild wear regime extends and COF increases with the increase in vol% of ZrB2 particles. Texture analysis of worn surfaces is in agreement with the results. The present investigation shows that in situ (ZrB2 + Al3Zr)/AA5052 hybrid composites could be a promising material in the applications requiring high wear resistance and high COF such as braking system.