Abstract
Powder mixture of Al-40mol% Ni was mechanically alloyed for various milling times. After 72 ks of milling, AINi (β') phase has formed. The crystalline size of AM (β') phase decreases with milling time, and it becomes about 30 nm after 180 ks of milling. When the mechanically alloyed Al-Ni alloy powder was heat-treated at 823 K, the AlNi (β') phase transforms to equilibrium AlNi phase with about 40 nm in crystalline size. The 180 ks milled powders was consolidated by the hot pressing (HP) under various conditions, and structural change of the compacts during the HP was investigated. The microstructure of the compacts consists of equilibrium AlNi phase with about 40 nm of crystalline size. Density of the compacts is increased with the increasing of hot pressing pressure and holding time. Compression tests of the compacts have been carried out to investigate mechanical properties at high temperatures. The intermetallic AINi sample made from the MA powder deforms to high strain under low stress, when compressed at 1073K-1123K for 10-1s-1 of initial strain rate. The strain rate sensitivity exponent of yield stress (m-value) reaches to 0.32-0.36 under this compressing condition. Therefore, the ultra fine grained intermetallic AlNi alloy made by the MA and HP process can be formed to near net shapes by superplastic deformation at high strain rate suitable for industrial working.
