Martensitic transformation and grain size in a Cu-Al-Be alloy

S. MONTECINOS; A. CUNIBERTI

Procedia Materials Science

Elsevier

Año: 2012 vol. 1 p. 149 - 155

2211-8128

In copper-based shape memory alloys, within an appropriate range of compositions and temperatures, the beta phase (a long range ordered bcc phase) transforms martensitically to an 18R structure by cooling, spontaneous transformation, or by application of stress. The martensitic transformation is responsible for the shape memory properties exhibited by these alloys. The influence of the grain size on Ms and sigmas in a beta Cu-11.41Al-0.50Be (wt.%) with a DO3 to 18R transformation was studied. It was determined that Ms decreases and sigmas increases as the grain size decreases. To analyze the functional relation of sigmas with d, the Hall-Petch type mechanical model and modifications by three-dimensional grain constraint were analyzed. It was found that sigmas can not be described by any of these relations in the studied alloy. From the Claussius-Clapeyron relationship and introducing an additional component of stress associated to the grain constraint effect, the decomposition of sigmas in two components is proposed: one of them a function of T and Ms, and the other one a function of T and d.