Dry-Sliding Tribological Properties of Cu/AlMgB14 Composites

In this paper, Cu/AlMgB₁₄ composites with by weight percent, 5, 10 and 20 % of the AlMgB₁₄ (referred to CA-5, CA-10 and CA-20) were fabricated by hot-press sintering method. The mechanical and dry-sliding tribological properties of the three composites were investigated. The results indicated that the densities of the Cu/AlMgB₁₄ composites were lower than copper, whereas the hardness higher. The friction and wear behaviors of the composites were strongly dependent on the AlMgB₁₄ content. The friction coefficient was in the range of 0.73–1.0 for CA-5, but it was always steady at about 0.2 for CA-10 and CA-20. Accordingly, the increase in the AlMgB₁₄ concentration can improve the wear resistance of the composites.     

Friction and wear behaviors of C/C-SiC composites containing Ti3SiC2

In the present paper, friction and wear behaviors of a carbon fiber reinforced carbon–silicon carbide–titanium silicon carbide (C-SiC–Ti₃SiC₂) hybrid matrix composites fabricated by slurry infiltration and liquid silicon infiltration were studied for potential application as brake materials. The properties were compared with those of C/C-SiC composites. The composites containing Ti₃SiC₂ had not only higher friction stability coefficient but also much higher wear resistance than C/C-SiC composites. At an initial braking speed of 28 m/s under 0.8 MPa pressure, the weight wear rate of the composites containing 5 vol% Ti₃SiC₂ was 5.55 mg/cycle, which was only one-third of C/C-SiC composites. Self-lubricious film-like debris was formed on the composites containing Ti₃SiC₂, leading to the improvement of friction and wear properties. The effect of braking speed and braking pressure on the tribological properties of modified composites were investigated. The average friction coefficient was significantly affected by braking speed and braking pressure, but the wear rate was less affected by braking pressure.     

Friction and Wear Properties of TiAl-Ti3SiC2-MoS2 Composites Prepared by Spark Plasma Sintering

TiAl matrix self-lubricating composites (TMC) with various weight percentages of Ti₃SiC₂ and MoS₂ lubricants were prepared by spark plasma sintering (SPS). The dry sliding tribological behaviors of TMC against an Si₃N₄ ceramic ball at room temperature were investigated through the determination of friction coefficients and wear rates and the analysis of the morphologies and compositions of wear debris, worn surfaces of TMC, and the Si₃N₄ ceramic ball. The results indicated that TMC with 10 wt% (Ti₃SiC₂-MoS₂) lubricants had good tribological properties due to the unique stratification subsurface microstructure of the worn surface. The friction coefficient was about 0.57, and the wear rate was 4.22 × 10^?4 mm³ (Nm)^?1. The main wear mechanisms of TMC with 10 wt% (Ti₃SiC₂-MoS₂) lubricants were abrasive wear, oxidation wear, and delamination of the friction layer. However, the main wear mechanisms of TMC without Ti₃SiC₂ and MoS₂ lubricants were abrasive wear and oxidation wear. The continuous friction layer was not formed on the worn surfaces. The self-lubricating friction layer on the frictional surface, different phase compositions and hardness, as well as density of TMC contributed to the change in the friction coefficient and wear rate.     

Tribological Properties of TiAl Matrix Self-Lubricating Composites Containing Multilayer Graphene and Ti3SiC2 at High Temperatures

An investigation is conducted on the unexplored synergistic effects of multilayer graphene (MLG) and Ti₃SiC₂ in self-lubricating composites for use in high-temperature friction and wear applications. The tribological properties of TiAl matrix self-lubricating composites with different solid lubricant additions (Ti₃SiC₂-MLG, MLG) are investigated from room temperature to 800°C using a rotating ball-on-disk configuration. Tribological results suggest the evolution of lubrication properties of MLG and the excellent synergistic lubricating effect of MLG and Ti₃SiC₂ as the testing temperature changes. It can be deduced that MLG has great potential applications as a promising high-temperature solid lubricant within 400°C, and a combination of MLG and Ti₃SiC₂ is an effective way to achieve and maintain desired tribological properties over a wide temperature range.     

Reciprocating friction and wear behavior of Ti3AlC2 and Ti3AlC2/Al2O3 composites against AISI52100 bearing steel

In this work, the dry sliding friction and wear properties of Ti₃AlC₂ and Ti₃AlC₂/Al₂O₃ composites against AISI52100 steel ball were investigated using a reciprocating ball on flat configuration under different normal loads. The results indicated that the friction/wear processes of both Ti₃AlC₂ and the composites against AISI52100 steel experienced two different stages with an abrupt transition between them under all test conditions. The first stage was characterized by low coefficient of friction (μ) and neglectable wear rate. While the second stage was of much higher wear rate and μ. When the transition occurred, μ increased dramatically accompanied with formation of a mass of debris. In Ti₃AlC₂, the main wear mechanisms during the first stage involved surface materials transfer and oxidation accompanied with subsurface damages by grains kinking, delamination as well as transgranular and intergranular cracks. Accumulating of such contact damages under repeated sliding contact finally leaded to surface and subsurface microfracture of Ti₃AlC₂. Then microfracture controlled severe wear started. Incorporation of Al₂O₃ in Ti₃AlC₂ not only improved wear resistance of Ti₃AlC₂ but also extended the first mild friction/wear stage, because Al₂O₃ particles borne load and restrained large-scale deformation and microfracture of Ti₃AlC_2.     

Wear mechanisms of K2Ti4O9 whiskers reinforced Al20Si aluminum matrix composites with lubrication of water and tetradecane

The tribological properties of K₂Ti₄O₉ whisker reinforced Al20Si aluminum matrix composites were investigated in a mode of low amplitude reciprocal sliding. The ball-on-disk tests were performed at applied loads of 20–100 N and sliding velocity of 0.09 m s⁻¹. The water lubricated composites demonstrated higher wear resistance and friction coefficient than the tetradecane lubricated composites did. The main wear mechanism is microgrooving at low applied loads and tribochemical wear at high applied loads for the pairs lubricated with water, microgrooving at all test loads for the pairs lubricated with tetradecane.     

Using atom probe tomography to analyse MAX-phase materials

Ti₂AlC belongs to an interesting group of materials with both metallic and ceramic properties. This material is highly attractive as a candidate for corrosion resistant coatings. The process of fabrication of such coatings is in the investigation stage only and the detailed knowledge of the structure and chemistry of the produced coatings is important for optimisation of their properties. In this work the applicability of atom probe tomography for investigation of both Ti₂AlC bulk materials and coatings was tested. We show that for the first time, Ti₂AlC has successfully been analysed using laser pulsing mode in a local electrode atom probe and the results from analysis of both bulk Ti₂AlC and Ti₂AlC based spray deposited coatings are presented. It appears that, in this particular material system, it is difficult to obtain the accurate stoichiometry. This is due to the loss of detection because of unavoidable multiple events and due to the peak overlaps present. Methods of how to approach these problems are discussed.     

High-Temperature Tribological Behavior of Al-20Si-5Fe-2Ni/ZrB2 Composites

Abstract

In this work, Al-20Si-5Fe-2Ni/ZrB₂ composites with 0–20?wt% ZrB₂ were fabricated by spark plasma sintering. The effects of ZrB₂ content on the microstructure, mechanical properties and high-temperature tribological behavior of the composites were investigated. The results indicate that Si, Al₅FeSi, and ZrB₂ particles are uniformly distributed in the aluminum matrix. The density, hardness, and compressive strength increase with increasing ZrB₂ content. The friction coefficient and wear rate are dependent on the ZrB₂ content and test temperature. At a certain temperature, the friction coefficient increases with an increase in ZrB₂ content, whereas the wear rate shows a reverse trend. Due to the improvement in thermal stability and high-temperature softening resistance, the composite shows improved wear resistance and increased transition temperature from mild wear to severe wear.     

Wear and Friction of TiAl Matrix Self-Lubricating Composites against Si3N4 in Air at Room and Elevated Temperatures

More durable, low-friction bearing materials over a wide temperature range are needed for turbine components and other high-temperature bearing applications. The current study reported the tribological properties of TiAl matrix self-lubricating composites (TMC) containing MoS₂ (a low-temperature lubricant, below 500°C), hBN (a medium-temperature lubricant, below 600°C), and Ti₃SiC₂ (a high-temperature lubricant, above 600°C) designated as MhT against an Si₃N₄ counterface at temperatures ranging from 25 to 800°C in air. The load was 10 N and the sliding speed was 0.2 m/s for all tests. Tribological studies indicated that TMC containing MhT showed a lower friction coefficient and wear rate in comparison to TiAl-based alloy at all test temperatures, which was attributed to the excellent synergetic lubricating effect of MoS₂, hBN, and Ti₃SiC₂. TMC containing 5 wt% MhT exhibited the best tribological properties over a wide temperature range.     

Effect of Sliding Speed and Applied Load on Dry Sliding Tribological Performance of TiAl Matrix Self-lubricating Composites

More durable, low-friction self-lubricating materials in modern industry are greatly needed for tribological systems. The current paper presents the tribological performance of TiAl matrix self-lubricating composites (TSC) containing MoS₂, hexagonal BN and Ti₃SiC₂ designated as MhT against GCr15 steel counterface under several sliding speeds from 0.2 to 0.8 m s^?1 and applied loads from 6 to 12 N. The results suggested that MhT played an important role in decreasing friction coefficients and wear rates. The covering percentage of transfer layers on worn surfaces varied with the changing of sliding speeds and applied loads, hence resulting in the distinct friction and wear characteristics of TSC. TSC containing 10 wt% MhT exhibited the best excellent tribological performance at 10 N–0.8 m s^?1, which could be due to the formation of the best compaction and largest coverage of transfer layer on the worn surfaces.     

Effect of Ag and Ti3SiC2 on Tribological Properties of TiAl Matrix Self-lubricating Composites at Room and Increased Temperatures

Dry sliding tribological properties of TiAl matrix self-lubricating composites (TMSC) containing Ag, Ti₃SiC₂, Ag and Ti₃SiC₂ were investigated from 25 to 800 °C under ball-on-disk test conditions against Si₃N₄ counterface under the same conditions of 10 N-0.234 m/s. The results indicated that the tribological properties were strongly dependent on the lubricant additives. TMSC with the addition of Ag and Ti₃SiC₂ (TAT) exhibited the lower friction coefficients (0.32–0.43) and less wear rates (1.23–4.13 × 10^?4 mm³ N^?1m^?1) in the wide temperature range of 25–800 °C. The excellent tribological properties of TAT over the wide temperature range were attributed to the synergetic effect of Ag and Ti₃SiC₂ lubricants, silver diffusion forming a rich-silver smooth tribo-film on the frictional surface of TAT at low and moderate temperatures from 25 to 400 °C, while Ti₃SiC₂ oxidation reaction forming rich-oxide tribo-film on the worn surface of TAT at higher temperatures of 600 and 800 °C.     

Effect of SiC particles on the friction and wear behavior of Ti3Si(Al)C2-based composites

The non-lubricated, sliding friction and wear behavior of Ti₃Si(Al)C₂ and SiC-reinforced Ti₃Si(Al)C₂ composites against AISI 52100 bearing steel ball were investigated using a ball-on-flat, reciprocating tribometer at room temperature. The contact load was varied from 5 to 20 N. For monolithic Ti₃Si(Al)C₂, high friction coefficients between 0.61 and 0.90 and wear rates between 1.79 × 10⁻³ and 2.68 × 10⁻³ mm³ (N m)⁻¹ were measured. With increasing SiC content in the composites, both the friction coefficients and the wear rates were significantly decreased. The friction coefficients reduced to a value between 0.38 and 0.50, and the wear rates to between 2.64 × 10⁻⁴ and 1.93 × 10⁻⁵ mm³ (N m)⁻¹ when the SiC content ranged from 10 to 30 vol.%. The enhanced wear resistance of Ti₃Si(Al)C₂ is mainly attributed to the facts that the hard SiC particles inhibit the plastic deformation and fracture of the soft matrix, the oxide debris lubricate the counterpair, and the wear mode converts from adhesive wear to abrasive wear during dry sliding.     

Sliding friction and wear of alumina-reinforced zirconia-toughened mullite composites

The friction and wear characteristic of self-mated alumina-reinforced zirconia-toughened mullite (ZTM/A) composites has been investigated using a block-on-ring tribometer in different lubricants at varying loads. Load-dependent wear transitions were observed for these ceramics. The wear transition was usually accompanied by an abrupt change of friction coefficient and wear rate. The addition of Al₂O₃ effectively reduces the wear rate of ZTM/A composites before the wear transition in water and at middle loads in machine oil. Scanning electron microscope (SEM) micrographs show that the main pre-transition wear mechanism of ZTM/A composites is plastic deformation, ploughing and occasionally grains pulling out, while fracture is the dominant mechanism of post-transition. Al₂O₃ can restrain the t→m phase transformation of zirconia to some extent and improve the resistance of these materials to wear by fracture, ploughing and plastic deformation.     

Wear behaviour of in situ Cu–Al2O3 composites produced by internal oxidation of as cast alloys

Abstract

In the present study, the wear behaviour of Cu–Al₂O₃ composites and Cu–Al alloys has been investigated. The experiment involved casting of Cu–Al alloys with 0·37, 1, 2 and 3 wt-% of aluminium under inert gas atmosphere. The composites were produced by internal oxidation of alloys at 950°C for 10 h in presence of Fe₂O₃ and Al₂O₃ powders mixture. The microstructures of composites were studied using SEM and atomic force microscopy. To identify wear behaviour of specimens, dry sliding pin-on-disk wear tests were conducted according to ASTM G99-95a standard. The normal loads of 20, 30, and 40 N were applied on specimens during wear tests. The sliding speed and distances were selected as 0·5 m s^–1 and 500, 1000 and 1500 m respectively. To specify the wear mechanisms, the worn surfaces of composites were examined by SEM equipped with EDX. According to wear test results, increasing applied load and sliding distance leads to more volume loss in all specimens. Composites represent better wear resistance in comparison to alloys. Additionally, increasing the volume fraction of alumina particles in composites enhances the wear resistance, especially under high applied load. The wear mechanisms are mainly abrasion, oxidation and delamination.     

Wear Behavior of Composites Based on ZA-27 Alloy Reinforced by Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Particles Under Dry Sliding Condition

In present study, the effect of Al₂O₃ particle reinforcement on the sliding behavior of ZA-27 alloy composites was investigated. The composites with 3, 5, and 10 wt% of Al₂O₃ particles were produced by the compocasting procedure. Tribological properties of unreinforced alloy and composite were studied, using block-on-disk tribometer under unlubricated sliding conditions at different specific loads and sliding speeds. The worn surfaces of samples were examined by the scanning electron microscopy (SEM). The test results revealed that those composite specimens exhibited significantly lower wear rate than the ZA-27 matrix alloy specimens in all combinations of applied loads and sliding speeds. The difference in the wear resistance of composite with respect to the matrix alloy, increased with the increase of the applied load/sliding speed and Al₂O₃ particle content. The highest degree of improvement of the ZA-27 alloy tribological behavior corresponded with change of the Al₂O₃ particles content from 3 to 5 wt%. At low sliding speed, moderate lower wear rate of the composites over that of the matrix alloy was noticed. This has been attributed to micro cracking tendency of the composites. Significantly reduced wear rate, experienced by the composite over that of the matrix alloy at the higher sliding speeds and loads, could be explained due to enhanced compatibility of matrix alloy with dispersoid phase and greater thermal stability of the composite in view of the presence of the dispersoid. Level of wear rate of tested ZA-27/Al₂O₃ samples pointed to the process of mild wear, which was primarily controlled by the formation and destruction of mechanical mixed layers (MMLs).     

Wear properties of Saffil/Al,Saffil/Al2O3/Al and Saffil/SiC/Al hybrid metal matrix composites

The purpose of this study is to investigate the wear properties of Saffil/Al, Saffil/Al₂O₃/Al and Saffil/SiC/Al hybrid metal matrix composites (MMCs) fabricated by squeeze casting method. Wear tests were done on a pin-on-disk friction and wear tester under both dry and lubricated conditions. The wear properties of the three composites were evaluated in many respects. The effects of Saffil fibers, Al₂O₃ particles and SiC particles on the wear behavior of the composites were elucidated. Wear mechanisms were analyzed by observing the worn surfaces of the composites. The variation of coefficient of friction (COF) during the wear process was recorded by using a computer. Under dry sliding condition, Saffil/SiC/Al showed the best wear resistance under high temperature and high load, while the wear resistances of Saffil/Al and Saffil/Al₂O₃/Al were very similar. Under dry sliding condition, the dominant wear mechanism was abrasive wear under mild load and room temperature, and the dominant wear mechanism changed to adhesive wear as load or temperature increased. Molten wear occurred at high temperature. Compared with the dry sliding condition, all three composites showed excellent wear resistance when lubricated by liquid paraffin. Under lubricated condition, Saffil/Al showed the best wear resistance among them, and its COF value was the smallest. The dominant wear mechanism of the composites under lubricated condition was microploughing, but microcracking also occurred to them to different extents.     

Effects of filler crystal structure and shape on the tribological properties of PTFE composites

In this paper, effects of filler crystal structure and shape on the friction and wear properties of potassium titanate whisker (K₂Ti₄O₉ whisker, K₂Ti₆O₁₃ whisker), TiO₂ whisker and TiO₂ particle filled polytetrafluoroethylene (PTFE) composites under dry friction conditions were studied. Meanwhile the influence of filler content, sliding duration, test speed and load were also investigated. Experimental results show that the friction coefficients of various PTFE-based composites are weakly dependent on filler shape but they are more strongly dependent on filler crystal structure. However, for improving the anti-wear property of PTFE, filler crystal structure has less importance than filler shape in the wear-reducing action of PTFE-based composites, and whisker-like filler is better than particle-like filler.     

Microstructure and High-Temperature Frictional Wear Property of Mo-Based Composites Reinforced by Aluminum and Lanthanum Oxides

In this article, we developed Mo-based composites reinforced with aluminum and lanthanum oxides using a sol-gel method combined with a sintering process and researched the microstructure and frictional wear properties under high-temperature conditions. The microstructure of composites was characterized by α-Al₂O₃ and composite oxide (La_0.62Mo_0.38)AlO₃, which were uniformly distributed in the molybdenum matrix. The composite oxide (La_0.62Mo_0.38)AlO₃ was mainly attached to α-Al₂O₃. The interfaces of α-Al₂O₃/Mo and α-Al₂O₃/(La_0.62Mo_0.38)AlO₃ were well bonded. The α-Al₂O₃ refined the molybdenum grains, increased the relative density and hardness of Mo-based composites, and had an obvious effect on the frictional wear properties of the composites. With increasing α-Al₂O₃ content, the friction coefficient first increased and then decreased, and the wear weight loss decreased continuously. The wear failure mode varied from microcutting to fatigue with increasing α-Al₂O₃ content. The better wear resistance of Mo-based composites, compared to pure molybdenum, was mainly attributed to the characteristics of α-Al₂O₃, such as high microhardness, good morphology, well-bonded phase interface, and high hardness matrix due to the effects of α-Al₂O₃ reinforcement.     

Microstructure and tribological properties of laser clad γ/Cr7C3/TiC composite coatings on γ-TiAl intermetallic alloy

In order to improve the wear resistance of the γ-TiAl intermetallic alloy, microstructure, room- and high-temperature (600 °C) wear behaviors of laser clad γ/Cr₇C₃/TiC composite coatings with different constitution of NiCr–Cr₃C₂ precursor-mixed powders have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS), block-on-ring (room-temperature) and pin-on-disk (high-temperature) wear tests. The responding wear mechanisms are discussed in detail. Results show that microstructures of the laser clad composite coatings have non-equilibrium solidified microstructures consisting of primary hard Cr₇C₃ and TiC carbides and the inter-primary γ/Cr₇C₃ eutectic matrix, about three to five times higher average microhardness compared with the TiAl alloy substrate. Higher wear resistance than the original TiAl alloy is achieved in the clad composite coatings under dry sliding wear conditions, which is closely related to the formation of non-equilibrium solidified reinforced Cr₇C₃ and TiC carbides and the positive contribution of the relatively ductile and tough γ/Cr₇C₃ eutectics matrix and their stability under high-temperature exposure.     

Abrasive wear of WC-FeAl composites

The abrasive wear behavior of tungsten-carbide iron-aluminide composite materials was investigated using a pin-on-drum wear-testing machine. Samples were prepared by uniaxially hot pressing blended powders. The wear rates of specimens containing 40 vol.% matrix of atomic composition, Fe₆₀Al₄₀, were measured and results compared with those of conventional WC-10 vol.% Co hardmetal. They were found to be comparable to those of WC-10% Co hardmetal, when abraded by 120 μm SiC papers under identical conditions. The wear resistance of WC-Fe₆₀Al₄₀ composites increased with reduction in WC-grain size and associated with increase in composite hardness. Scanning electron microscopy revealed that the wear surfaces of WC-40% Fe₆₀Al₄₀ composites and WC-Co hardmetal were similar in appearance. The higher hardness and work hardening ability of Fe₆₀Al₄₀ binder, as compared to Co metal, are believed to be responsible for the excellent abrasive wear resistance of WC composites containing iron aluminide binder.