Reinforcement Particle Size Research Articles

Microstructures and mechanical properties of pure Al matrix composites reinforced by Al[sbnd];Cu[sbnd];Fe alloy particles

A new type of composite material was produced from elemental Al matrix powders and 30 vol.% Al;Cu;Fe quasicrystal particles by a powder metallurgy technique. SEM examination shows that reinforcement particle cracking perpendicular to the loading axis is the dominant failure mechanism for the composites. Because of the fine (diameter<10 μm) matrix and reinforcement particle sizes that match closely and a homogenous spatial distribution, the ultimate tensile strength (UTS) and yield strength (Y.S.) of this model composite material were improved over the matrix properties by 111 and 220%, respectively, for the commercial purity composite sample. Remarkably, the UTS and Y.S. of the composite were improved over the matrix properties by 201 and 328%, respectively, for a high purity version of the composite material. The elastic modulus of the composite, in both versions, is very close to the theoretical upper bound value from the rule of mixtures estimation. This highly effective composite strengthening is also consistent with the good interface bonding between the spherical reinforcement particles and Al matrix that was revealed by fracture surface examination. Diffusion layer measurements at the Al/reinforcement interface by an Auger method verified the good bonding condition, as well.

Production of nanometre bismuth oxide powders : Z. Sheng et al. (Guangzhou Research Inst. for Non-Ferrous Metals, Guangzhou, China.)

Abrasive wear behaviour of materials can be assessed using a wide variety of testing methods, and the relative performance of materials will tend to depend upon the testing procedure employed. In this work, two cermet type coatings have been examined, namely (i) a conventional tungsten carbide-cobalt thermally sprayed coating with a carbide size of between ∼0.3–5 μm and (ii) a tungsten carbide-nickel alloy weld overlay with large spherical carbides of the order of ∼50–140 μm in diameter (DuraStell). The wear behaviour of these two materials has been examined by the use of two abrasion tests, namely the micro-scale abrasion test using both silica and alumina abrasives (typically 2-10 μm in size), and the dry sand-rubber wheel test (ASTM G65), again with both silica and alumina abrasives (typically 180–300 μm in size). It was found that when the abrasive particles were of the same scale or larger than the mean free path between the hard phase particles, then the matrix phase was well protected by the hard phases. Testing (in both test types) with alumina abrasives resulted in wear of both the hard carbide phases and the matrix phases in both the thermally sprayed coating and the weld overlay, with the thermally sprayed coating exhibiting lower wear rates. The wear behaviour of the materials with the more industrially relevant silica abrasive was more complex; the thermally sprayed coating exhibited a lower wear rate than the weld overlay with the fine abrasive in the micro-scale abrasion test due to effective shielding of the matrix from abrasive action due to the fine reinforcement particle size. In contrast, with the coarser silica abrasive in the dry sand-rubber wheel test, the weld overlay with the large carbides was able to provide matrix protection with low rates of wear, whereas the thermally sprayed coating wore by fracture of the more brittle microstructure. These findings demonstrate the importance of selection of appropriate laboratory test procedures and abrasives to simulate behaviour of materials in service environments.

Effect of overaging and particle size on tensile deformation and fracture of particle-reinforced aluminum matrix composites

The effect of reinforcement particle size and overaging treatment on the tensile behavior and fracture morphology of a 2080/SiC/20p composite was investigated. Tensile behavior was profoundly influenced by particle size and matrix strength. The composite strength increased with a decrease in particle size, while overaging greatly reduced the strength of the composite, independent of particle size. Almost all particles on the fracture plane were fractured, and the amount of particle fracture in the composites was insensitive to overaging and particle size, due to the excellent bonding between SiC particles and the Al matrix. Fractography showed that void nucleation in the matrix of peak-aged composites took place primarily at very fine SiC particles, which were much smaller than the average SiC particle size. Subsequent failure took place by the tearing topography surface (TTS) mechanism. In the overaged composite, composites failed by a more conventional void nucleation and growth process, where void nucleation took place at coarsened S precipitate particles, resulting in smaller and more elongated voids.

Effect of the Particle Size on the Mechanical Properties of 60 Vol.% SiCpReinforced Al Matrix Composites

Abstract The effect of the reinforcing particle size on the mechanical properties of 60 vol.% SiC reinforced aluminium matrix composites produced by the pressure infiltration technique was examined by compression, impact and wear tests. The compression strength and the impact resistance decreased with increasing reinforcing particle size. The composites exhibited different abrasion behaviour depending on the size of abrasive Al2O3 grains. On fine abrasive Al2O3 grains (85 μm), the abrasion resistance increased with increasing reinforcing SiC particle size. The contrary result was obtained on coarse abrasive Al2O3 grains (250 μm). The wear tests conducted on M2 quality tool steel revealed that reinforcing of aluminium with coarse SiC particles has a very beneficial effect on the wear resistance with respect to fine reinforcing SiC particles.

Magnetic properties of injection-moulded iron-nickel alloys

Abrasive wear behaviour of materials can be assessed using a wide variety of testing methods, and the relative performance of materials will tend to depend upon the testing procedure employed. In this work, two cermet type coatings have been examined, namely (i) a conventional tungsten carbide-cobalt thermally sprayed coating with a carbide size of between ∼0.3–5 μm and (ii) a tungsten carbide-nickel alloy weld overlay with large spherical carbides of the order of ∼50–140 μm in diameter (DuraStell). The wear behaviour of these two materials has been examined by the use of two abrasion tests, namely the micro-scale abrasion test using both silica and alumina abrasives (typically 2-10 μm in size), and the dry sand-rubber wheel test (ASTM G65), again with both silica and alumina abrasives (typically 180–300 μm in size). It was found that when the abrasive particles were of the same scale or larger than the mean free path between the hard phase particles, then the matrix phase was well protected by the hard phases. Testing (in both test types) with alumina abrasives resulted in wear of both the hard carbide phases and the matrix phases in both the thermally sprayed coating and the weld overlay, with the thermally sprayed coating exhibiting lower wear rates. The wear behaviour of the materials with the more industrially relevant silica abrasive was more complex; the thermally sprayed coating exhibited a lower wear rate than the weld overlay with the fine abrasive in the micro-scale abrasion test due to effective shielding of the matrix from abrasive action due to the fine reinforcement particle size. In contrast, with the coarser silica abrasive in the dry sand-rubber wheel test, the weld overlay with the large carbides was able to provide matrix protection with low rates of wear, whereas the thermally sprayed coating wore by fracture of the more brittle microstructure. These findings demonstrate the importance of selection of appropriate laboratory test procedures and abrasives to simulate behaviour of materials in service environments.

Effect of reinforcement volume fraction on the evolution of reinforcement size during the extrusion of Al-SiC composites

The effect of reinforcement volume fraction on the evolution of the reinforcement particle size during extrusion was investigated for the Al-SiC model composite system. Composites with 6.4, 10.0, and 16.8 volume percent of SiC particles were extruded at a temperature of 350 °C using an extrusion ratio of 12:1. Image analysis showed that the SiC particles were refined by the extrusion process and that the extent of the refinement increased with an increase in reinforcement volume fraction. A mechanistic rationale for the experimentally observed trends is formulated with reference to the corresponding change in the stress fields in the composite microstructure with the change in the reinforcement volume fraction. Possible implications of extrusion-induced particle fracture for the processing of fine particle-reinforced metal matrix composites are also explored in this paper.

Toughening of a brittle thermosetting polymer: Effects of reinforcement particle size and volume fraction

Micron- and nanometer-sized aluminum particles were used as reinforcements to enhance the fracture toughness of a highly-crosslinked, nominally brittle, thermosetting unsaturated polyester resin. Both particle size and particle volume fraction were systematically varied to investigate their effects on the fracture behavior and the fracture toughness. It was observed that, in general, the overall fracture toughness increased monotonically with the volume fraction of aluminum particles, for a given particle size, provided particle dispersion and deagglomeration was maintained. The fracture toughness of the composite was also strongly influenced by the size of the reinforcement particles. Smaller particles led to a greater increase in fracture toughness for a given particle volume fraction. Scanning electron microscopy of the fracture surfaces was employed to establish crack front trapping as the primary extrinsic toughening mechanism. Finally, the effects of particle volume fraction and size on the tensile properties of the polyester-aluminum composite were also investigated. The measured elastic modulus was in accordance with the rule-of-mixtures. Meanwhile, the tensile strength was slightly reduced upon the inclusion of aluminum particles in the polyester matrix.

Fracture mechanics behaviour of aluminium matrix composites reinforced with SiC

Low fracture toughness in metal matrix composites is one of the main obstacles to using these materials in widespread ways and, therefore, various aspects of fracture mode would be examined closely, pointing out the microstructure influence. In the present paper, fracture nucleation and propagation of two aluminium matrix composites having about 30 vol.% SiC as reinforcement were studied. Tensile tests and fracture toughness tests were executed and the effect of reinforcement particle size and distribution was considered. The effect of T4 treatment (solution treating at 495°C for 2 h, quenching in water at 10°C and natural ageing three weeks long) was also evaluated in terms of mechanical properties and fracture mechanism.

The effect of reinforcing particles on the erosive wear behavior of particles reinforced silicone matrix composite coating

The effects of SiC and Al2O3 particle reinforcement on the erosive wear behavior of silicone matrix composite coatings (SMCCs) were investigated using a gas blast rig. The optimal erosion resistance was reached through varying the type of reinforcing particle, reinforcing particle size and percentage in the coating. It was found that the erosive wear behaviors of the three sizes of α-Al2O3 and SiC filled SMCC are different from each other though the optimal erosion resistance points occurred at nearly the same reinforcing particle weight percent. A plastic–brittle erosion behaviors transition occurred with the influence of reinforcing particle size. The experimental results show that coating hardness has an important influence on the SMCCs wear behavior. The maximum pencil hardness corresponds with the best erosive wear resistance of SMCC. SEM pictures of the worn surface morphology indicate that the main erosive wear mechanisms of SMCC are microploughing and microcutting when impacted at 30° impingement angle, whereas the erosion mechanisms at normal impact are mainly fatigue failure, caused by plastic deformation and microcracking.

Effect of reinforcing-particle size on the formation of microbands in SiCP/6151Al metal matrix composites

Effect of reinforcing-particle size on the formation of microbands in SiCP/6151Al metal matrix composites

Correlating macrohardness and tensile behavior in discontinuously reinforced metal matrix composites

hardness tests are routinely used as a simple and effective means of quantifying the tensile strength of metallic materials. The correlation between various hardness scales and tensile t=strength has been compiled for a variety of metals and alloys. When a metal is reinforced with ceramic particles or short fibers, higher stiffness, higher strength and lower ductility for the composite can be observed. The composite, when viewed as a continuum, displays a stronger strain hardening behavior in a tensile test. The overall elastic-plastic nature of the composite, however, bears a qualitative resemblance to that of monolithic metals. This implies that traditional macrohardness may be useful in characterizing the mechanical properties of the composite, as in the case of many engineering alloys. As metal matrix composites are generating increased interest for applications where quality control may be important, the need for understanding the relationship between hardness and tensile strength becomes essential. In a recent study of a 6061 Al/SiC particulate composite with various aging treatments, a linear relationship between the Rockwell superficial-scale hardness and the ultimate tensile strength of the composite was reported. In the present study, the authors seek to explore this correlation in greater detail, in a 2080/SiC{sub p} composite,more » by taking into account different reinforcement volume fraction, particle size, and matrix microstructure. It will be shown that the hardness-strength correlation in discontinuously reinforced metal matrix composites is not as straightforward as what has been reported for conventional monolithic materials, due to the different micromechanisms of deformation and damage.« less

Microstructure and properties of titanium boride dispersed Cu alloys fabricated by spray forming

Abstract Dispersion strengthened Cu alloys have been manufactured by conventional spray forming and also by reactive spray forming, followed by hot extrusion of the spray deposited billets. In this work, we have systematically investigated the relationship between the microstructure and mechanical properties of the Cu alloys fabricated through two techniques by means of optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and tensile testing. The size of dispersed particles in the reactive spray formed alloy was much finer than that in the conventionally spray formed alloy. That was because the dominant chemical reaction between Ti and B had occurred in Cu–Ti–B alloy melt in conventional spray forming while it had occurred after deposition of droplets in reactive spray forming. The yield strength of the reactive spray formed alloy was greater than that of the conventional spray formed alloy in spite of a lower volume fraction of reinforced particles. To understand the mechanism responsible for this experimental observation, the yield strength of the two Cu alloys were analyzed using the dislocation pile-up model and Orowan mechanism, which were fairly consistent with the experimental results. Increase in yield strength of reactive spray formed alloy compared with that of conventional spray formed alloy was largely attributed to nanoscale TiB dispersoids. This indicates that refining the reinforced particle size to nanoscale is of special importance for the development of high strength Cu alloys since the yield strength predominantly depends on the size and volume fraction of the reinforcement. From this point of view, reactive spray forming can be considered as a new promising process to develop high strength Cu alloys.

The influence of reinforcement particle size distribution on the mechanical behavior of a stainless steel/tin composite

A stainless steel-based composite reinforced with TiN particles has been developed for potential applications in industry. The results show that the compatibility between the matrix and reinforcement is good and the bonding between the two phases is strong and of the diffusion type. The ductility and toughness of the composites are lower than those of the matrix. The strengthening behavior of the composites, however, is not straightforward. It is also found that reinforcements that differ only in particle-size distribution can bring about a large change in the mechanical properties of the composites. It is believed that the microstructural change of the matrix after incorporating the reinforcement, together with the load-bearing effect of the reinforcement, gives rise to the results.

Fractography, Fluidity,and Tensile Properties of Aluminum/Hematite Particulate Composites

This paper examines the effect of hematite (iron oxide) particles on the fluidity of the molten composite as well as the tensile properties and fracture behavior of the solidified as-cast aluminum composites. The percentage of hematite in the composite was varied from 1 to 7% in steps of 2% by weight. The vortex method was employed to prepare the composites. It followed from the results obtained that the ultimate tensile strength and Young’s modulus of the composite increased while the liquid fluidity and solid ductility decreased with the increase in hematite content in the composite specimens. The fluidity of the liquid was greater in a metal mold than in a sand mold, and it decreased with an increase in reinforcing particle size and increased with pouring temperature. The presence of the reinforcing particles altered the fracture behavior of the solid composites considerably. Final fracture of the composite occurred due to the propagation of cracks through the matrix between the reinforcing particles.

High-speed tribological properties of some Al/SiC p composites: I. Frictional and wear-rate characteristics

The friction and wear behaviour of four Al/SiC p composites has been investigated over a wide range of sliding conditions by the use of a specially adapted high-speed tester of the pin-on-disk configuration. Two of the composites tested were fabricated in-house by a powder metallurgy route incorporating mechanical alloying; two commercially sourced composites were also tested for comparison. Generally, wear rate increased with increasing load, but it varied in a rather complex manner with speed depending on which regime the sliding condition fell into. Three regimes of tribological behaviour, demarcated by sliding speed, were observed for these composites. In Regime I, lower rates of wear are observed while in Regime II, catastrophic failures occur when a certain critical load is exceeded, resulting in the rapid adhesion of a large amount of specimen material to the counterface: it is no longer possible to continue with the test when this happens. In Regime III, extensive melting of the composites takes place, and under such a sliding condition, the size of reinforcement particles appears to have an important influence on the rate of wear of these composites.

Modeling and Simulation of Response of Pariticulate-Reinforced Composite Materials under a Plane Strain Condition.

In order to determine the characteristic feature in the deformation behavior of particulatereinforced composite material, a constitutive equation that takes into account the characteristic length scale has been developed using the strain gradient theory. By means of the plane-strain finite element method with the proposed constitutive equation, a series of simulations of inhomogeneous deformation behavior of composite materials with different volume fractions of reinforcement, particle size and distribution pattern of reinforcement have been performed. As a result, it has been determined that the resistance of composite material to deformation is substantially increased with the refinement of the particle size under constant volume fraction of reinforcement. Furthermore, the regulaization of the distribution pattern which increases the value of the maximum strain gradient in the matrix contributes toward improving the resistance to deformation.

The effect of reinforcement on the notched and unnotched room temperature tensile properties of Al–4wt.%Cu/SiC p MMCs

The tensile and toughness related properties of SiC (3, 17 and 29 μm) particulate (SiC p) reinforced Al–4wt.%Cu metal matrix composites (MMCs) produced via a powder metallurgy route were studied. The assessment of toughness related properties was carried out by notched tensile testing. The strength of the MMCs increased with decreasing size of the reinforcement. This predominated over any effect on strength of the small variation in 3-dimensional spatial distribution of the reinforcement. Examination of fracture surfaces of failed unnotched tensile specimens indicated that the MMCs with the most inhomogeneous distributions of the reinforcement (those containing 3 μm SiC p) exhibited a number of anomalies. Strings of large ductile dimples corresponding to ductile failure of thin layers of reinforcement free material, and regions of delamination between matrix rich and reinforcement rich layers of material indicated that local differences in the spatial distribution of the reinforcing particles led to local variation of the fracture mechanism of those MMCs containing 3 μm SiC p. Those MMCs also exhibited multiple crack initiation below the final fracture which indicated that the toughness related performance of these composites might be worse than those with larger reinforcing particles. The results of notched tensile testing showed that the best indicator of toughness related properties was the ratio of notched ultimate tensile stress to unnotched proof stress. It was found that the materials became less sensitive to the presence of a notch as the size of the reinforcing particles decreased and as the matrix:reinforcement particle size ratio increased which was contrary to initial expectations. It was concluded that the MMCs containing 3 μm SiC p exhibited the least resistance to crack initiation, but showed the greatest resistance to crack propagation.

Effect of reinforcement size on the elevated-temperature tensile properties and low-cycle fatigue behavior of particulate SiC/Al composites

The cyclic stress response characteristics and low-cycle fatigue endurance of powder-metallurgy-processed commercially pure aluminum composites reinforced with SiC particles of different sizes and of the unreinforced matrix were studied under a range of cyclic plastic strains at 441 K. Tensile properties of these materials were also examined. At elevated temperature the composites and unreinforced aluminum all definitely show cyclic softening. Under the same plastic strain amplitudes, the cyclic response stresses of the composites are higher than that of their unreinforced counterpart. Reinforcing particle size has no apparent influence on the cyclic stress/strain features of the composites. The amount of cyclic softening is similar except that the cyclic response stress is slightly higher for the composite reinforced with small particles than for the large-particle-reinforced composite at a given cyclic strain amplitude. At high plastic strain ranges, the two composites display shorter fatigue lives than the unreinforced matrix material and, of the two composites, the large-particle-reinforced composite exhibits slightly superior fatigue resistance.

Influence of processing on the microstructural development and flexure strength of Al 2O 3/SiC nanocomposites

Alumina/10 wt% SiC nanocomposites were prepared by using a number of processing techniques, in order to produce different microstructures while keeping a uniform distribution of the SiC particles in the alumina matrix. Basically, this study used three techniques, i.e. mechanical mixture of powders, the use of an inorganic precursor for alumina precipitated onto SiC particles and the use of different polymeric precursors for SiC precipitated on alumina particles. Hot pressing at 1700 °C was necessary to produce fully dense nanocomposites. The alumina precursor route produced the smallest matrix grain size and the SiC precursor route produced the smallest reinforcement particle size. Despite the differences in microstructure between the nanocomposites, the flexure strength remained the same, and no distinct improvement over the monolithic alumina was observed. The fracture mode, however, changed from intergranular to transgranular with the presence of the SiC particles.

Effects of process parameters on the properties of squeeze-cast SiC p-6061 Al metal-matrix composite

The effects of process parameters on the properties of squeeze-cast high reinforcement volume-fraction SiC p-6061 Al metal matrix composite (MMC) have been examined. The process parameters included cooling rate, reinforcement particle size, addition of silica binder, and solution treatment temperature. The properties studied were flexure strength, microstructure, variation of hardness, solute content gradient, and aging behavior. It was found that water cooling improved the flexure strength and hardness of MMC significantly when compared with furnace-cooled MMC. For the same volume fraction of reinforcement, lowering the average particle size from 85 to 14 μm increased the flexure strength and hardness of the MMC greatly. A solution treatment temperature very close to the eutectic point was found to improve the strength. Mechanisms leading to the above-mentioned effects and suggestions are discussed.