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

SANCHEZ PASCAL, N.N.; GIORDANA, M.F.; NAPOLITANO, F.; ESQUIVEL, M.R.; ZELAYA, E.

ADVANCED POWDER TECHNOLOGY

ELSEVIER SCIENCE BV

Año: 2017 vol. 28 p. 2605 - 2612

0921-8831

In this work, the thermal stability of two samples of Cu-11.8wt%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°C to room temperature and two consecutive calorimetric runs at 5°C/min. After the quenching,α2 is the major phase observed, reaching 95mass%. The remaining 5mass% consisted of martensitic phases: one sample had γ´, a hexagonal structure, and the other β1´, a rhombohedral structure. During the first calorimetric run, the sample containing the γ´ phase exhibited a calorimetric event and the sample containing the β1´ phase did not. The calorimetric event is attributed to the austenitic transformation γ´→β1. The lack of calorimetric event in the sample containing the β1´ is associated with the inhibition of the transformation β1´→β1 because of the precipitation of the γ2 phase. Finally, the absence of a calorimetric event in the second run with the first sample is associated with the retransformation to β1´ instead to γ´ 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.