Occurrence and Morphology of Martensite in β-Cu-Zn Alloys with Minor Al Additions

Abstract

The limits of occurrence and the morphology of martensite in Cu-Zn-Al alloys with 30 to 50 wt pct Zn and ≤ 1.5 wt pct Al have been investigated. In samples with concentration gradients, various conditions for the competition between martensitic and massive transformation have been observed. Microstructural details of martensite were obtained by combining vibration polishing, chemical or plasma etching and polarized light, backscattered electron channeling contrast or electron backscatter diffraction analysis. Depending on the cooling rate, martensite undergoes a morphological change from self-accommodating thin plates to lenticular shaped plates, which is documented for the first time in Cu-based alloys. The number of martensite twins in the investigated compositional range was found to be significantly smaller than that in commercial Cu-Zn-Al alloys that are used as shape memory alloys.