Effect of Microstructure on Martensitic Transformation and Cyclic Deformation Characteristics in a Cu-AI-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 72 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 72 phase is left behind despite betatizing at 800 ℃. No martensitic transformation takes place in the cast-rod betatized at 650℃, because the precipitation of 72 phase leads to stabilization of Pi parent phase. However, Pi-HV martensitic transformation occurs in the cast-rod betatized at 700 ℃ and both Pi-"pY and Pi-*yi' martensitic transformations concurrently undergoes in the cast-rod betatized above 750 ℃ because of the slope of Al concentration nearby 72 phase. The load-displacement 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.