Effect of Microstructure on Martensitic Transformation and Cyclic Deformation Characteristics in a Cu-Al-Ni Based Alloy with Unidirectionally Solidified Structure

Abstract

The effect of the betatizing conditions on microstructure, transformation characteristics and pseudoelastic behavior has been studied in an unidirectionally solidified Cu-Al-Ni based alloy. The coarse γ2 phase is precipitated in the cast-rod betatized at 650 and the volume fraction of it is decreased by increasing the betatizing temperature above 700 . However, a small amount of γ2 phase is left behind despite betatizing at 800 . No martensitic transformation takes place in the cast-rod betatized at 650, because the precipitation of γ2 phase leads to stabilization of β1 parent phase. However, β1→β1′ martensitic transformation occurs in the cast-rod betatized at 700 and both β1→β1′ and β1→γ1′ martensitic transformations concurrently undergoes in the cast-rod betatized above 750 because of the slope of Al concentration nearby γ2 phase. The loaddisplacement loop of the as-cast rod betatized at 750 is linear, but those of the as-cast rods betatized at 800 and 850 are non-linear showing the typical pseudoelastic loop and the deformation is completely recovered upon unloading.