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

摘要

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 γ_2 phase is precipitated in the cast-rod betatized at 650°C and the volume fraction of it is decreased by increasing the betatizing temperature above 700°C. However, a small amount of γ_2 phase is left behind despite betatizing at 800°C. No martensitic transformation takes place in the cast-rod betatized at 650°C, because the precipitation of γ_2 phase leads to stabilization of β_1 parent phase. However, β_1→β_1' martensitic transformation occurs in the cast-rod betatized at 700°C and both β_1→β_1' and β_1→γ_1' martensitic transformations concurrently undergoes in the cast-rod betatized above 750°C because of the slope of Al concentration nearby γ_2 phase. The load-displacement loop of the as-cast rod betatized at 750°C is linear, but those of the as-cast rods betatized at 800°C and 850°C are non-linear showing the typical pseudoelastic loop and the deformation is completely recovered upon unloading.