Cu-5 at%Ni-2.5 at%Al合金の析出硬化

Abstract

The deformation behavior was studied on the age hardened Cu-5 at%Ni-2.5 at%Al alloy single crystals, initially quenched from 1173 K and aged at 623∼773 K up to 3600 ks. The results obtained are as follows.(1) The critical resolved shear stresses (CRSS) had maximum by ageing at 773 K for 2160 ks. By ageing at lower temperatures, CRSS continued to increase, though much lower than the values at 773 K.(2) By ageing at 773 K, spherical precipitates grew, distributed uniformly and were coherent with the matrix. The electron diffraction pattern showed that precipitates were Ni3Al with L12 type ordered structure.(3) Single crystals exhibited three stage hardening. In stage I Lüders type deformation occurred. Slip bands became more and more localized and concentrated as the ageing proceeded.(4) Piled-up arrays of dislocations were typical structure in the aged crystals. In both the polycrystalline specimens and single crystals, however, dislocation pairs on the same slip plane, that is, superlattice dislocations, were observed sometimes.(5) The above-mentioned results suggest that the interaction of dislocations with the strain field of precipitates and the cutting of ordered precipitates by superlattice dislocations are the main mechanisms that govern the strength of the age-hardened Cu-5 at%Ni-2.5 at%Al alloys.