Dry sliding wear behavior of as-cast ZE41A magnesium alloy

In present work, an attempt has been made to investigate the wear behavior of as-cast ZE41A magnesium alloy during dry sliding. The experiments were performed using pin-on-disc type wear apparatus against a EN32 steel counterface in a load range of 30–150 N, sliding velocity range of 0.5–2.5 m/s and at a constant sliding distance of 1500 m. Microstructural investigations on the worn surfaces were undertaken using a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) for determination of type of damage and nature of distortion at the surface. Wear mechanisms such as abrasion, oxidation, delamination, plastic deformation and melting were identified. Wear maps were drawn for the test result data. Mild wear, severe wear and ultra severe wear regimes were identified using wear transition map through microstructural observations.     

Influence of graphite filler on two-body abrasive wear behaviour of carbon fabric reinforced epoxy composites

The influence of graphite filler additions on two-body abrasive wear behaviour of compression moulded carbon–epoxy (C–E) composites have been evaluated using reciprocating wear unit and pin-on-disc wear unit under single pass and multi-pass conditions respectively. The carbon fabric used in the present study is a plain one; each warp fiber pass alternately under and over each weft fiber. The fabric is symmetrical, with good stability and reasonable porosity. Abrasive wear studies were carried out under different loads/abrading distance using different grades of SiC abrasive paper (150 and 320 grit size). Graphite filler in C–E reduced the specific wear rate. Further, the wear volume loss drops significantly with increase in graphite content. Comparative wear performance of all the composites showed higher specific wear rate in two-body wear (single-pass conditions) compared to multi-pass conditions. Further, the tribo-performance of C–E indicated that the graphite filler inclusion resulted in enhancement of wear behaviour significantly. Wear mechanisms were suggested and strongly supported by worn surface morphology using scanning electron microscopy.     

Dry sliding wear behavior of cast SiC-reinforced Al MMCs

Dry sliding block-on-ring wear tests were performed on a squeeze cast A390 Al alloy, a high pressure die cast 20%SiC–Al MMC, and a newly developed as-cast 50%SiC–Al MMC. The testing conditions spanned the transition that control the mild to severe wear for all materials. The results show that the sliding wear resistance increases as SiC particle volume fraction increases. The critical transition temperature, at which wear rates transit from mild to severe, also increases with increasing SiC content. Examination of the wear surfaces, the subsurface characteristics, and the wear debris indicate that a hard ‘mechanically alloyed’ layer, high in SiC content, forms on the sliding surface of the 50%SiC composite. This layer prevents the surface adhesion wear mechanisms active in the A390 alloy, and it inhibits delamination wear mechanisms that control the mild wear of the 20%SiC composite. As a result, mild wear of the 50%SiC composite occurs by an oxidation process. In the 20%SiC material, severe wear occurs as a consequence of material removal by a flow-related extrusion-like process. In contrast, the high SiC content prevents plasticity in the 50%SiC composite, which eventually is susceptible to severe wear at very high temperatures (≈450 °C) due to a near-brittle cracking processes.     

Effects of volume ratio on the microstructure and mechanical properties of particle reinforced magnesium matrix composite

In the present study, the AZ91 alloy reinforced by (submicron + micron) SiCp with four kind volume ratio was fabricated by the semisolid stirring casting technology. The influence of volume ratio between submicron and micron SiCp on the microstructure and mechanical properties of Mg matrix was investigated. Results show that the submicron SiCp is more conducive to grain refinement as compared with micron SiCp. With the increase of volume ratio, the submicron particle dense regions increase and the average grain size decreases. The yield strength of bimodal size SiCp/AZ91 composite is higher than monolithic micron SiCp/AZ91composite. Both Δσ_Hall–Petch and Δσ_CTE increase as the volume ratio changes from 0:10, 0.5:9.5, 1:9 to 1.5:8.5. Among the composite with different volume ratio, the S-1.5 + 10-8.5 composite has the best mechanical properties. The interface debonding is found at the interface of micron SiCp-Mg. As the increase of volume ratio, the phenomenon of interface debonding weakens and the amount of dimples increases.     

Dry sliding wear behaviour of fly ash particles reinforced AA 2024 composites

AA 2024 alloy has been melted and cast in a permanent cast iron mould in the form of 18 mm ?? fingers. The synthesis of AA2024 alloy ? 5wt.% fly ash composite was made by stir cast technique. A uniform distribution of fly ash particles in the matrix phase was obtained. Good bonding between the matrix and reinforcement was also achieved. Dry sliding wear behavior of the alloy and the composite has been investigated using a pin-on-disc wear tester. The investigation was carried out at a fixed sliding velocity of 2.0 m/s, track diameter of 60 mm and load ranging from 0.5 kgf to 1.5 kgf (4.9?C14.7 N). SEM studies were carried out to assess the wear behavior of the alloy and the composite. The composite showed better wear resistance than the base alloy for the lower loads. However, for the higher loads and longer sliding distances, the wear in the composite was extensive due to the existence of fractured and dislodged fly ash particles in the alloy matrix.     

Fabrication and evaluation of mechanical and tribological properties of boron carbide reinforced aluminum matrix nanocomposites

In this study, fabrication and characterization of bulk Al–B₄C nanocomposites were investigated. B₄C nanoparticles were mixed with pure Al powder by ball milling to produce Al–B₄C powder. Al–B₄C powders containing different amounts of B₄C (5, 10 and 15 wt.%) were subsequently hot pressed to produce bulk nanocomposite samples. Consolidated samples were characterized by hardness, compression and wear tests. Results showed that the sample with 15 wt.% B₄C had the optimum properties. This sample had a value of 164 HV which is significantly higher than 33 HV for pure Al. Also, ultimate compressive strength of the sample was measured to be 485 MPa which is much higher than that for pure Al (130 MPa). The wear resistance of the nanocomposites increased significantly by increasing the B₄C content. Dominant wear mechanisms for Al–B₄C nanocomposites were determined to be formation of mechanical mixed layer on the surface of samples.     

Improving the wear resistance of AZ91D magnesium alloys by laser cladding with Al-Si powders

To improve the wear resistance of AZ91D magnesium alloy, laser surface cladding with Al and Si powders was investigated using a Nd:YAG pulsed laser. With appropriate processing parameters and the suitable weight ratio of Al to Si in powders, a modified surface layer free of cracks and pores was formed by reaction synthesis of Mg with Al and Si. X-ray diffractometry (XRD) confirmed the main phases in the layer to be Mg₂Si and Mg₁₇Al₁₂. The surface hardness increased from 35 HV for as-received magnesium alloy to more than 170 HV for laser treated sample. Accompanying the increase in hardness, the wear resistance of the clad layer increased more than 4 times that of the substrate.     

Interface structure between magnesium matrix and SiCp

The microstructure of magnesium matrix composite (MMC) was investigated by transmission electron microscopy, and fracture behaviour of composite by step-by-step tensile in the strain range of 0.8–2.0% has been determined using the dislocation and microcrack analysis. The results indicated that the interface between matrix and double-sized SiC particle (SiCp) showed a good combination. With increasing the strain from 0 to 2.0%, the dislocation density was gradually increased, especially in the interface of SiCp/matrix. Some microcracks can be found in the interface between micrometre-SiCp and matrix while no microcracks were observed around nano-SiCp.     

Reciprocal sliding wear behaviour of B4C particulate reinforced aluminum alloy composites

Aluminum based composites reinforced with B₄C particles were prepared by cryomilling and subsequent hot pressing steps. The cryomilled powders dispersed with 5 wt.% or 10 wt.% B₄C particles were hot pressed under a pressure of 600 MPa at 350 °C. Microstructural studies conducted on the composites indicated that homogeneous distribution of the B₄C particles in the Al matrix and a good interface between them had been achieved. According to the results of reciprocating wear tests carried out by utilizing alumina and steel balls, wear resistance increased with increasing B₄C particle content.     

Effect of multidirectional forging on microstructures and tensile properties of a particulate reinforced magnesium matrix composite

A particulate reinforced magnesium matrix composite prepared with stir casting was subjected to multidirectional forging (MDF). The results showed that after 1 MDF pass the grain size of matrix in the composites decreased compared with as-cast composite, and increased with increasing the MDF temperature from 370 °C to 450 °C. With increasing the MDF passes at 370 °C, the particle distribution of the composite was improved until 3 MDF passes while the grain size of matrix in the composite reached a minimum after 4 MDF passes. Both the yield strength and the ultimate tensile strength of the composite were enhanced with increasing the MDF passes.     

Enhanced thermal conductivity of Cu matrix composites reinforced with Ag-coated β-Si3N4 whiskers

Cu matrix composites reinforced with 10 vol.% Ag-coated β-Si₃N₄ whiskers (ASCMMCs) were prepared by powder metallurgy method. With the aim of improving the thermal conductivity of the composites, a quite thin Ag layer was deposited on the surface of β-Si₃N₄ whiskers. The results indicated that thermal conductivity of ASCMMCs with 0.30 vol.% Ag (0.30ASCMMCs) reached up to 273 W m⁻¹ K⁻¹ at 25 °C, which was 98 W m⁻¹ K⁻¹ higher than that of Cu matrix composites reinforced with uncoated β-Si₃N₄ whiskers (USCMMCs). The Ag coating could promote the densification of composites, reduce the aggregation of β-Si₃N₄ whiskers and enhance the Cu/Si₃N₄ interfacial bonding, therefore it could efficiently enhance the thermal conductivity of Cu matrix composites reinforced with β-Si₃N₄ whiskers (SCMMCs).     

Microstructures and mechanical properties of ultrafine-grained Ti/AZ31 magnesium matrix composite prepared by powder metallurgy

The microstructure of ultrafine grain for magnesium alloys can result in drastic enhancement in their room temperature strength, but the issue of low strength at elevated temperature becomes more serious as well due to grain boundary slide. Here ultrafine-grained Ti/AZ31 magnesium matrix composites with high strength at both room and elevated temperature were prepared by vacuum hot pressing and subsequent hot extrusion. The microstructure of the composite samples before and after consolidation processing was characterized, and the mechanical properties of the as-consolidated bulk samples were measured at room and elevated temperatures. The results indicate that after extrusion ultrafine-grained magnesium alloys were obtained and Ti particulates with particulate size of ～310?nm disperse in Mg matrix. The magnesium grain of AZ31-15at.%Ti grows from 66?nm to 800?nm. Meanwhile, the relative densities of Ti/AZ31 composites are higher than 99%. The yield strength (YS) of extruded AZ31-15at.%Ti composite at room temperature is 341?MPa, being 2.4 times higher than original AZ31 alloy. Theoretical estimation shows that remarkably enhanced room-temperature mechanical strength attributes to grain boundary strengthening with the contribution ratio of 74%. In addition, the peak stress of extruded AZ31-15at.%Ti composite at 573?K is 82?MPa and ultrafine Ti dispersions are responsible for the enhanced strength.     

Mechanical and three-body abrasive wear behaviour of three-dimensional glass fabric reinforced vinyl ester composite

The mechanical and three-body abrasive wear behaviour of two- and three-dimensional E-glass woven fabric reinforced vinyl ester composites were studied in this article. The mechanical properties were evaluated using universal testing machine as per ASTM D-638. Three-body abrasive wear tests were conducted using rubber wheel abrasion tester (RWAT) under different abrading distances at two loads, wherein the wear volume loss were found to increase and that of specific wear rate decrease. The results indicate that the three-dimensional glass woven fabrics in vinyl ester (G_3D–V) have significant influence on wear under varied abrading distance/loads. Further, it was found that G_3D–V composite exhibited lower wear rate compared to two-dimensional glass woven fabric reinforced vinyl ester (G_2D–V) composite. The worn surface features, as examined through scanning electron microscope (SEM), show ruptured glass fiber in G_2D–V composite compared to G_3D–V composites.     

Dry wear properties of A356-SiC particle reinforced MMCs produced by two melting routes

SiC particle reinforced metal matrix composites (MMCs) were produced by a common liquid phase technique in two melting routes. In the first route, 5, 10, 15 and 20 vol% SiC reinforced A356-based MMCs were produced. In the second route, an Alcan A356 + 20 vol% SiC composite was diluted to obtain 5, 10, 15 and 20 vol% SiC MMCs. In both cases the average particle size was 12 μm. The composites that produced by two different routes were aimed to compare the dry wear resistance properties. A dry ball-on disk wear test was carried out for both groups of MMCs and their matrix materials. The tests were performed against a WC ball, 4.6 mm in diameter, at room temperature and in laboratory air conditions with a relative humidity of 40–60%. Sliding speed was chosen as 0.4 m/s and normal loads of 1, 2, 3 and 5 N were employed. The sliding distance was kept at 1000 m. The wear damage on the specimens was evaluated via measurement of wear depth and diameter. A complete wear microstructural characterization was carried out via scanning electron microscopy. The wear behaviors were recorded nearly similar for both groups of composites. Diluted samples showed lower friction coefficient values compared with the friction coefficient values of the vortex-produced composites. This was attributed poor bonding between matrix and particles in the vortex-produced composites associated with high porosities. But, in general, diluted Alcan composites showed slightly lower wear rate relationship with the particle volume percent and applied load when compared with vortex produced materials.     

Wear behaviour of an aluminium matrix composite

The wear behaviour of a composite material consisting in AS12UNG alloy reinforced with 15% short fibres of alumina has been studied. The material composition and the wear test conditions were defined in order to evaluate the potential performance of automotive pistons produced with such composite composition. As initially expected, the results indicate that an increase in the sliding velocity lead to higher wear rates in the stationary stages, and higher applied loads also induced acceleration in the wear process. Also, reciprocating sliding movement is clearly more damaging than the circular. However, results have shown that wear rates at 150 °C are lower than those recorded at room temperature representing a promising result for the use of this material in components that operate in this condition. This advantageous behaviour is lost at temperatures near to 300 °C, when a marked increase in the wear rate and a signification contribution of adhesive wear were observed.     

Dry sliding wear behaviour of a conventional and recycled high pressure die cast magnesium alloys

The dry sliding wear behaviour of a conventional and a recycled magnesium alloy produced by high pressure die casting was assessed by ball-on-disc tests under three different loads at a constant sliding velocity. The recycled alloy showed a lower friction coefficient and a lower wear rate when compared to the conventional alloy. A higher hardness and a relatively higher volume fraction of β-phase with a denser distribution near the surface were the reasons for the improved wear behaviour.     

The investigation of the effect of particle size on wear performance of AA7075/Al2O3 composites using statistical analysis and different machine learning methods

In this study, 7075 - Al₂O₃ (5 wt%) composites with a particle size of 0.3 µm, 2 µm, and 15 µm were developed by hot pressing. The dry sliding wear performance of the specimens was evaluated under loads of 5 N, 10 N, 20 N, 30 N, and at sliding speeds of 80 mm/s, 110 mm/s, 140 mm/s by reciprocating wear tests. The wear tests showed that 7075 - 5Al₂O₃ (15 µm) exhibited the best wear performance. The volume loss of 7075 - 5Al₂O₃ (15 µm) under load of 30 N for sliding speed of 140 mm/s was 37.1% lower than the unreinforced 7075 alloy. The volume loss (mm³) of composites reinforced with the particle size of 0.3 µm, 2 µm, and 15 µm was 11.62, 9.87, and 8.07, respectively, for load of 30 N and sliding speed of 140 mm/s. An increase in the applied load and sliding speed increased the wear severity by changing the wear mechanism from abrasion to delamination. The analysis of variance (ANOVA) showed that the load was the most significant parameter on the volume loss. The linear regression (LR), support vector regression (SVR), artificial neural network (ANN), and extreme learning machine (ELM) were used for the prediction of volume loss. The determination coefficient (R²) of the LR, SVR, ANN, and ELM was 0.814, 0.976, 0.935, and 0.989, respectively. The ELM model has the highest success. Thus, the ELM model has significant potential for the prediction of wear behaviour for Al matrix composites.     

颗粒增强镁基复合材料的研究现状

综述了颗粒增强镁基复合材料常用的基体合金,常用的增强相及其镁基复合材料的制备技术、组织和性能等,并对颗粒增强镁基复合材料的发展进行了展望.     

Crack and wear behavior of SiC particulate reinforced aluminium based metal matrix composite fabricated by direct metal laser sintering process

In this investigation, crack density and wear performance of SiC particulate (SiCp) reinforced Al-based metal matrix composite (Al-MMC) fabricated by direct metal laser sintering (DMLS) process have been studied. Mainly, size and volume fraction of SiCp have been varied to analyze the crack and wear behavior of the composite. The study has suggested that crack density increases significantly after 15 volume percentage (vol.%) of SiCp. The paper has also suggested that when size (mesh) of reinforcement increases, wear resistance of the composite drops. Three hundred mesh of SiCp offers better wear resistance; above 300 mesh the specific wear rate increases significantly. Similarly, there has been no improvement of wear resistance after 20 vol.% of reinforcement. The scanning electron micrographs of the worn surfaces have revealed that during the wear test SiCp fragments into small pieces which act as abrasives to result in abrasive wear in the specimen.     

Processing,microstructure and mechanical properties of micro-SiC particles reinforced magnesium matrix composites fabricated by stir casting assisted by ultrasonic treatment processing

The novel stir casting assisted by ultrasonic treatment processing was studied. Unlike traditional stir casting, short semi-solid stir time was needed for addition and pre-dispersion of the particles in the novel processing. For ultrasonic treatment, there existed an optimal time. Both too short and too long time for the treatment resulted in nonhomogeneous particle distribution. Furthermore, the liquid stirring after ultrasonic treatment was proved to be necessary to further improve particle distribution. The mechanical properties of the composites fabricated by different parameters indicated that ultrasonic treatment evidently improved the mechanical properties compared with traditional stir casting. 5–20% SiCp/AZ91 composites were fabricated by the novel processing. The particle distribution was uniform in these composites. The grains were refined by addition of SiC particles. Grain sizes of composites decreased with the increases of particle contents. The ultimate tensile strength, yield strength and elastic modulus were enhanced as the particle contents increased.