The Effect of Boron Addition on the Microstructure, Hardness and Characteristic Temperatures of Cu-12Al-4Ni Memory Alloy Prepared by Mechanical Alloying, Pressing and Rolling

In this study, boron containing Cu-12wt%Al-4wt%Ni shape memory alloy was prepared by mechanical alloying, pressing and rolling. In this regard, 20 and 40 hour-milled powder was compacted and changed to the bulk alloy by cold pressing, sintering, rolling, heat treatment and quenching. Phase structure, micro-structure, micro-hardness, and transformation temperatures of the prepared samples were studied. It was found that increasing the milling time from 20 to 40 hours led to the rise of the starting temperature of martensite transformation (Ms) from 254 to 264°C. Also, the results showed that adding 0.5 wt.% B decreased the Ms temperature to 211°C and enhanced the micro-hardness from 154 (for the sample without B) to 193 vickers. These alternations were attributed to the fine structure caused by Boron rich precipitations. Moreover, two martenistic transformations with different structures were formed due to the non-homogeneity of the Al concentration in the matrix, which appeared in the form of two different transformation temperatures (Ms) in the Differential Scanning Calorimetry curves.