Thermal stability analysis of Cu-11.8 wt%Al milled samples by TEM and HT-XRD

In this work, the thermal stability of two samples of Cu-11.8 wt%Al obtained by different milling processes is analyzed. Several TEM techniques were used and HT-XRD experiments performed to determine the crystal structure and the morphological microstructure of the samples obtained during different heat treatments. The heat treatments were: quenching from 850 degrees C to room temperature and two consecutive calorimetric runs at 5 degrees C/min. After the quenching, alpha 2 is the major phase observed, reaching 95 mass%. The remaining 5 mass% consisted of martensitic phases: one sample ha gamma', a hexagonal structure, and the other beta(1)', a rhombohedral structure. During the first calorimetric run, the sample containing the gamma' phase exhibited a calorimetric event and the sample containing the beta(1)' phase did not. The calorimetric event is attributed to the austenitic transformation gamma' -> beta(1). The lack of calorimetric event in the sample containing the beta(1)' is associated with the inhibition of the transformation beta(1)' -> beta(1) because of the precipitation of the gamma(2) phase. Finally, the absence of a calorimetric event in the second run with the first sample is associated with the retransformation to beta(1)' instead to gamma' phase during cooling of the first calorimetric run. These studies determined that the first sample is a better candidate than the second sample to produce a shape memory alloy after thermo-mechanical treatments of the milled powders. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.