Plastic deformation under compression of Cu–Zn–Al martensitic single crystals

In Cu–Zn–Al single crystals, a bcc to 18R martensitic transition can be induced either termally or under applied stresses. In the latter case, a martensite single crystal is obtained. In this work, the plastic deformation behavior of the 18R martensitic phase for two different compositions (e/a=1.43 and e/a=1.48, Ms≈263 K) is analyzed in order to find out possible differences in both the mechanical behavior and the microstructure. Optical microscopy and transmission electron microscopy were used to study surface and bulk defects. The observed primary slip system was the same for all the samples, independently of the composition and orientation: (011)[100]β, which corresponds to slip in the basal plane of the martensite. In addition, for compression axes near [100]β, a secondary slip system appeared. The corresponding surface traces were far larger than those corresponding to the primary slip system. The measured resolved shear stresses to activate the primary slip system were on average 15% lower for compositions with e/a=1.43, compared to the samples with e/a=1.48. The results obtained for the yield stress of the martensite lend support to the role of plasticity of this phase on the nucleation and growth of the surface and bulk defects generated after pseudo-elastic cycling.