Phase transformation and properties of quasicrystal particles/Al matrix composites

Diffusion-controlled phase transformations and tribological properties and hardness of Al65Cu20Cr15 quasicrystal particles(QC(p))/Al matrix composites have been studied. The mixtures of the quasicrystal particles with volume fractions of 15%, 20%, 25%, 30% and pure Al powder were hot-pressed at 600, 650, 700 degrees C. During the diffusion-controlled phase transformation induced by hot-pressing, a simple cubic icosahedric quasicrystal (SIQC) phase transforms into stable Theta phase with the microstructure of monoclinic of Al13Cr2 through a transitional faced cubic icosahedric quasicrystal (FIQC), a decagonal quasicrystal (DQC) and an approximant of decagonal quasicrystal (DA) phases. And G. P. zones and Al-Cu precipitates, theta'-Al2Cu and theta-Al2Cu, are separated out from the Al matrix respectively after hot-pressing. The QC,/Al composites have double-strengthening effect after hot-pressing. One is the strengthening of the particles that win-force the matrix Al; the other is the dispersion strengthening of the precipitates in the Al matrix. The hardness of the composites increases with increasing volume fraction of quasicrystal particles. The maximum hardness reaches 1 200 MPa, being 4 times that of Al. The frictional coefficient and the wear rate of the QC,/Al are lower than those of Al. In comparison with SiCp/Al matrix composites, QC(p)/Al composites have higher hardness and lower frictional coefficient.