Hirofumi Miyahara

Sliding wear behaviour of Al-Si-Cu composites reinforced with SiC particles

Abstract The sliding wear behaviours of an unreinforced monolithic Al-Si-Cu alloy and SiC particles reinforced composites containing 5, 13, 38 and 50 vol.-% with diameters of 5.5, 11.5 and 57μm were investigated. The results showed that the wear resistance of the composites is much higher than the monolithic alloy, and the larger and the more SiC particles, the higher the enhancement of the wear resistance. Metallographic examinations revealed that the subsurface of worn composites was composed of both fragmented particles and deformed matrix alloy. The depth of the particle fracture zone in the subsurface varied in the range of 20-35 μm at a sliding distance of 1.8 km, while the plastic deformation zone of the worn subsurface on monolithic alloy was more than 100 μm. Scanning electron microanalyses of the worn surface, subsurface microstructure and debris suggested that the depth of the particle fracture zone became smaller as the diameter of SiC particles increased. Increasing the hardness and decreasing the applied wear stress changed the debris morphology from flake to very small lumps.

The fibre distribution of Al2O3/Al–Cu alloy composites

Two methods which rely on direct microstructural measurements to assess the fibre distribution in alumina continuous fibre-reinforced Al–Cu alloy composites produced via an infiltration process, are outlined. The first is based on distance analysis, i.e. the distance distribution of nearest neighbours; and the second is based on fibre–cell structures. Specimens with two fibre volume fractions, 0.39 and 0.50, were employed in this study. It was found that the fibres in both kinds of specimen appear to have a rough thread-like distributions, and the local volume fraction of the fibres varies over a larger range in the specimen with lower fibre volume fraction than does that in the specimen with the larger one. Quantitative relationships between fibre distribution and the composite defects are deduced. Some data on the microsegregation of copper and the macrosegregation of eutectic phase are given in relation to the fibre distributions. The reasons for the uneven fibre distributions are also discussed.

Quantitative evaluation on wear resistance of aluminum alloy composites densely packed with SiC particles

Abstract Wear behaviour was investigated for high volume fraction SiC particulate reinforced aluminum alloy composites by considering the shear stress acting on the specimen and the wear debris formed during sliding wear. The SEM morphology of worn subsurfaces showed that particles are fragmented, mechanically mixed, and then aligned in the wear direction caused by normal and tangential stresses. Wear debris were initially tiny lumps but finally delaminated due to the shear stress. A theoretical wear model was proposed for plastically deformable specimens worn by a rigid non-deformable steel ring by analysing the interspacing of SiC particles and the tangential stress applied to the worn surface. Predictions of this theoretical wear model were in good agreement with experimental results.

Trends of composite casting technology and joining technology for castings in Japan

Abstract State of technologies in Japan related to composite casting was reviewed based on the three year survey of Composite Casting Process Sub-Committee in Committee on Foundry Technology (24th) of JSPS. Other than making metal matrix composite, cast-in insertion, bonding and joining of cast materials and other technologies combining different materials by casting process were included. Basic theories and the key technologies are explained, and a number of typical examples of products, on production or on experimental bases, were reported. Overseas literatures were also surveyed.

Control of graphite formation in solidification of white cast iron

Abstract Graphite formation should be strictly suppressed for the most abrasion resistant white cast irons, since austenite (γ)+graphite eutectic structure shows lower hardness and selectively wears thus deteriorates the abrasion resistance even though the austenite transform to hard phase such as martensite. On the other hand, a small amount of fine graphite is desired to distribute in rolls for hot steel mills to suppress the scoring. However, strong carbide formers such as Cr, V, Nb have been increasingly added to rolls, in order to crystallise more harder carbides. As γ+carbide eutectic grows, the residual liquid among eutectic cells becomes poor in carbide formers and rich in elements which promote graphite formation. Therefore an appropriate alloy design is essential for the hot steel milling rolls. In this study, the graphite formation mechanisms are discussed for chromium cast iron, high speed steel type cast iron and Ni hard type cast iron.

Control of Carbides and Graphite in Ni-hard Type Cast Iron for Hot Strip Mills

The carbide and graphite formation and redistribution of alloy elements during solidification were investigated on Ni-hard type cast iron (Fe-C-Si-Ni-Cr-Mo) to develop higher quality rolls for hot steel strip mills. By the control of Ni and Si contents of iron, eutectic graphite flakes crystallize even in cast irons containing strong carbide formers such as V, Nb and Cr. The crystallization of Ni-hard type cast iron with V and Nb proceeds in the order of primary , + MC, + M3C and + graphite eutectic. Since the influence of each alloying element on graphite formation is estimated based on the solubility of C in molten iron, the change in graphite forming tendency of residual liquid is evaluated by the parameter expressing the solubility limit of C to molten iron. The amount of graphite increases with the decreasing of solubility parameter. In addition, inoculation with ferrosilicon effectively increases the graphite flakes.

Alloy design for heat and abrasion resistant high alloy cast iron

Influences of Mo, Nb, V on the microstructure, the oxidization behavior and the high-temperature compressive strength of 35–40%Cr-9%Ni cast irons were investigated. The addition of Mo raises the compressive strength at higher temperature, since Mo distributes into the matrix and enhances the high temperature strength. The crystallization of fine eutectic M7C3 and M2C type carbides should also contribute to the higher strength. The MC type carbide formers such as V and Nb can significantly improve the abrasion resistance at lower temperature. However, these elements also promote the oxidization of alloys. Especially V causes abnormally severe in both matrix and the hard phases. On the other hand, Nb preferentially distributes to NbC, the oxidation behaviors of M7C3 and matrix are little influenced by the addition of Nb. Among the trial alloys, Fe-2.2 4.5%C-35 40%Cr-9%Ni-5%Mo-0/7%Nb maintain 900Mpa of compressive strength even at 1073K, while the strength of conventional heat resistant alloys and high Cr cast irons drop below 500MPa at the temperature from 873K to 923K. The developed alloys show high oxidation resistance and superior high temperature wear resistance.

Control of Carbides and Graphite in Cast Irons Type Alloy’s Microstructures for Hot Strip Mills

The carbide and graphite formation and redistribution of alloy elements during solidification were investigated on high-speed steel (HS) and Ni-hard type cast irons with Nb and V. The crystallization of hypereutectic HSS proceeds in the order of primary MC, γ

Abrasion behavior of high Cr-V-Nb cast iron

A series of abrasion tests on high Cr-V-Nb cast irons revealed that the addition of MC type carbide formers, V and Nb, remarkably enhances the abrasion resistance of high Cr cast iron, and the abrasion resistance becomes higher with the increase in MC type carbides[1]. Therefore, hyper eutectic Fe-4.7%C-15%Cr-7%V-5%Nb-5%Mo alloy melt was poured into 30kg and 1kg sand mold castings to distribute different sizes of primary and eutectic carbides in hardenable matrix. The abrasion test specimens cut from each casting were austenitized at 1323K for 1h then cooled in air. These specimens were tempered at 773K for 1h followed by air cooling. The hardness of specimens was 1015-1018HV50. The rubber wheel abrasion test, a typical 3 body type one, was performed on these quenched and tempered specimens with 56-107, 107-150 and 297 μm dia. silica grit. The testing load was 86.3N and 172.5N, and the rubber wheel rotation speed was varied from 1s-1 to 4s-1. Though the higher testing load increases the wear loss, the wear rate expressed by the wear volume/( testing load × wear distance) changes depending on the wear condition and the microstructure. In case of 30kg cast specimen, the silica grit preferentially attack and scrape off the matrix, and the wear rate increases with the increase in the testing load. The fine carbides in 1kg cast specimens effectively protect the matrix from the attack of silica grit, and the wear rate decreases with increasing load which causes silica grit blunt and fracture. However, fine carbides tend to be fractured by silica grit and diminish the protective effect. Based on the worn surface structures, the abrasion mechanism is discussed comparing those of steel and eutectic 25%Cr cast iron.

Effect of Reentrant Twin Corners on Directional Solidification of Polycrystalline Silicon

The solidification microstructure and crystal orientation have been investigated for solar cell grade high purity polycrystalline silicon through a unidirectional solidification technique. In the solidification velocity range of 1.25-2.5times10-6 m/s, the grain size enlarges as solidification progresses. Furthermore, large columnar grains contain many twin boundaries. However, in above the critical velocity around 40times10-6 m/s, equiaxed structure appears. A model of two-dimensional nucleation on the reentrant corner was established, and the critical nucleus could be estimated to be 70 % to 80 % of the radius of the general two-dimensional nucleus. The reduction of the critical radius and undercooling on the reentrant corner could influence on the priority growth direction and the enlargement of the grain size