Martensitic Transformation in Au-Cu-Al Alloy System

Three heat treatment processes were carried out to study the ordering of the parent phases in Au-Cu-Al alloys. The influence of its A2-B2-L21 ordering transformation on martensitic transformation were analyzed, which contains the starting martensitic transformation temperatures(Ms), the structure of martensite and parent phases and the reason why no martensitic transformation was produced after 400°C annealing followed by cooling with furnace. The results indicate that the sample that aged at 100°C for more than 1h and then quenched into ice water (Heat treatment process II), can transform to martensite and show surface relief, as well as the sample directly quenched into liquid nitrogen from 650°C (Heat treatment process I). Both of their structures are body-centered tetragonal (bct). During the aging process, the parent phase gets more ordered, and consequently the Ms is greatly lifted. Therefore, the parent phase transforms to martensite more completely. In addition, as the sample aged at 400°C for 2 h and then cooled with furnace (Heat treatment process III). A more ordered parent phase can be obtained, which probably transforms to a new phase with bct structure through the nucleation and growth mechanism