Sintered Metal Matrix Composites Research Articles

Spark Plasma Sintering of Copper Matrix Composites Reinforced with TiB2 Particles.

The aim of this study is to fabricate a Cu-0.5wt%TiB2 composite by mechanical alloying (MA) and spark plasma sintering (SPS). Increasing the milling time, the powders are subjected firstly to a severe flattening process and then to intense welding, which promotes the refinement of TiB2 particles, their uniform dispersion in the metal matrix, and the adhesion between the two constituents. Sintered metal matrix composites (MMC) exhibit density values between 99 and 96%, which are generally decreased by increasing milling time in view of the stronger strain hardening. On the other side, the hardness increases with milling time due to the refinement of TiB2 particles and their improved distribution. The hardness of MMC is three times higher (225 HV0.05) than the starting hardness of atomized copper (90 HV0.05). Tensile tests show a loss of ductility, but ultimate tensile strength has been increased from 276 MPa of atomized copper to 489 MPa of MMC milled for 240 min. The thermal conductivity of MMC is comparable to that of atomized copper (300 W/mK), i.e., much higher than that of the commercial Cu-Be alloy (Uddeholm Moldmax HH, 106 W/mK) typically used for tooling applications.

Influence of size and volume share of WC particles on the properties of sintered metal matrix composites

Steel matrix composites are being increasingly investigated because of their wear and corrosion properties, allowing their wide application in various industrial sectors. The interaction of tungsten carbide (WC) with the steel matrix, including an analysis of its volume share and particle size, is crucial in determining the resistance to wear and corrosion of the metal matrix composite (MMC). However, there is little information in the literature about sintered MMCs based on low-alloy steels. This paper presents the results of an analysis of the influence of the volume share of WC (5 vol.% and 20 vol.%) and carbide particle size (0.7 µm and 5.0 µm) on the resistance to abrasion of a friction pair: sintered composite and bearing steel, analysed using two rotational speeds (0.02 m/s and 0.2 m/s). Moreover, the resistance to corrosion in 3.5% NaCl solution is also characterized. It is shown that both the volume share and the size of the WC particles used as reinforcement of the steel matrix have a significant impact on the densification behaviour as well as the resistance to abrasive wear and corrosion of sintered MMCs based on low-alloy steel.

Understanding the negative thermal expansion in planar graphite–metal composites

The addition of graphitic fibers and flakes as fillers is commonly used to control the thermal expansion of metals. Sintered metal matrix composites with a planar distribution of graphite flakes show a low or negative thermal expansion coefficient perpendicular to the orientation plane of the graphite (z-CTE). Since the metal matrix has a positive isotropic expansion and graphite has a high z-CTE, this effect cannot be explained by a simple model of stapled metal–graphite layers. Instead, a mechanical interaction between graphite and matrix must be considered. With neutron scattering measurements, we show that there is little or no strain of the graphite flakes caused by the matrix, which can be explained by the high modulus of graphite. Instead, we suggest that a macroscopic crumpling of the flakes is responsible for the low z-CTE of the composite. The crumpled flakes are thicker at low temperature and get stretched and flattened by the expanding matrix at high temperature, explaining the reduction in the thermal expansion across the orientation plane.

Development of reinforced TiN-SS316 metal matrix composite (MMC) using direct Metal laser sintering (DMLS) and its characterization

In the present work, formation of reinforced TiN -SS316 metal matrix composites using fiber laser sintering through DMLS process were studied. Different laser input parameters, for example, laser power (50-65W), scanning speed 4000 mm/min, spot diameter 0.4 mm, layer thickness (0.4mm), and hatching distance (0.2 mm) were taken to conduct experiments under nitrogen atmosphere. The sintered materials were investigated in term of microstructure, density, porosity, micro-hardness and wear behavior. The sintered metal matrix composites (MMCs) were subjected to Field Emission Scanning Electron Microscope (FE-SEM) and X-ray diffraction (XRD) test for microstructural and phase analysis respectively. The experimental results showed that the density of the sintered MMCs increases with increase in laser power, but decreases with increasing the reinforcement (TiN) content. It has also been observed that the developed MMCs showed that the wear resistance and hardness increased with TiN. It was found that the TiN and SS316 particles establish good metallurgical bond during the sintering process showing compatibility of matrix and reinforcement under nitrogen atmosphere. The experimental results demonstrate suitability of TiN-SS316 based MMCs for some engineering applications.

Microstructure and properties of sintered metal matrix composites reinforced with SIC particles

Microstructure and properties of sintered metal matrix composites reinforced with SIC particles

Effect of ceramic reinforcements on microwave sintered metal matrix composites

ABSTRACTMetal matrix composites (MMCs) using Aluminum Alloy 2900 and 2024 as matrix material with silicon carbide and alumina as reinforcement have been fabricated through powder metallurgy route for investigation. The average particle size of matrix metal and reinforcement material considered in this research is 10 µm. AA-SiC and AA-Al2O3 composites with 3, 6, and 9 weight percentage (wt%) of SiC and Al2O3 are fabricated. The Rockwell hardness and Compressive strength of AA-SiC and AA-Al2O3 composites were found to increase with an increase in the wt% of reinforcement when the samples were microwave sintered. AA 2024 with 6 wt% Al2O3 reinforced MMCs samples were exhibiting improved hardness results, strength behavior, and stress-strain behavior when the samples are microwave sintered. AA 2900 with 6 wt% Al2O3 exhibited good ductility and formability properties. Good Microstructural bonding was observed in the MMCs, which is attributed to finer Al2O3 particulate used as reinforcement and the microwave sintering.

Investigations on the sintering response of steel-ceramic composites

Purpose of this article is the evaluation of the influence of sintering parameters on the microstructure evolution and mechanical properties of pressureless sintered metal matrix composites consisting of metastable 16Cr7Mn7Ni-steel with 0 or 5 vol.% magnesia partially stabilized zirconia (Mg-PSZ) particles. The materials were prepared from powder raw materials via extrusion at ambient temperature. Three different temperatures between 1280 °C and 1380 °C and two varying dwell times of 40 min and 120 min at maximum temperature were applied. Both, tensile and compression tests are conducted at quasi-static strain rates for comparison of strength level, deformability and energy absorption capability. The results are discussed with regard to the porosity of the specimens, the interface between steel and ceramic, the TRansformation Induced Plasticity (TRIP)-effect occurrence and the failure behavior.

Effect of grain size on thermal residual stresses and damage in sintered chromium–alumina composites: Measurement and modeling

In this paper we present the results of experimental measurements and numerical modeling of the effect of particle size on the residual thermal stresses arising in sintered metal–matrix composites after cooling down from the fabrication temperature. On example of novel Cr(Re)/Al2O3 composites processed by (i) spark plasma sintering and (ii) hot pressing the residual thermal stresses are measured by neutron diffraction technique and determined by a FEM model based on micro-CT scans of the material microstructure. Then numerical model of microcracking induced by residual stresses is applied to predict the effective Young modulus of the damaged composite. Comparison of the numerical results with the measured data of the residual stresses and Young’s modulus is presented and fairly good agreement is noted.

Fretting wear and cracking in sintered metal matrix composites

A methodology, involving fretting tests, to develop wear and crack resistant materials for tribological applications for automotive valve train parts (e.g. cams, tappets) has been recently reported for high speed steels. Modifications to one of these sintered steels, M3 Class 2, were effected by additions, singly and in combination, of 5 wt.% of wear resistant titanium carbide and of solid lubricant manganese sulphide. In our fretting tests alternate displacements were imposed between the test material (plane) and a chromium steel or alumina ball. Running conditions fretting and material response fretting maps were constructed for the four materials. Two types of fretting damage were detected and analysed: cracking or particle detachment and wear through the tribologicaly transformed structure (TTS). Crack initiation, associated with porosity and interfaces, was detected when the maximum tensile stress in the contact reached 1.2 GPa. Cracking analyses were also carried out using static and fatigue mechanical tests and replica scanning electron microscopy. Crack growth and propagation were influenced by details of the microstructure, e.g. TiC was observed to arrest crack growth, whereas MnS made it easier. Wear analysis included the determination after each test of the wear volume, which could be related to the coefficient of friction and the cumulative dissipation energy during the fretting test.

Fracture Toughness of Sintered Metal Matrix Composites Based Upon High Speed Steels Enriched with Hard Ceramic Carbides

The fracture toughness was measured of a sintered high speed steel which contained copper phosphorus to aid sintering and to which had been added either titanium carbide or vanadium carbide particles as a means of improving its wear resistance. Relatively low fracture toughness values were obtained and these were attributed to embrittlement caused by the presence of phosphorus, but the fracture toughness was relatively independent of the presence of any porosity or carbide enrichment. Reductions in bend strength brought about by heat treatment and by the carbide enrichment process were explained by the effects that the carbide additives had on crack initiation and by the changes caused to the fracture toughness of the steel matrix. In spite of the reductions in strength which occurred as a result of introducing ceramic carbide particles into the steel matrix, useful and promising properties were still obtained. PM/0601