Effects of Cr on the abnormal grain growth of Cu-Al-Mn-Ni-Cr superelastic alloy

Composition design is one of the effective methods to promote abnormal grain growth (AGG) behavior. In this study, a series of CuAlMnNi-Cr-x (x = 0, 0.5 and 1 at%) alloys are designed to study the effects of Cr on the AGG behavior during the cyclic heat treatments (CHTs) of CuAlMnNiCr alloy. The results indicate that adding 0.5% Cr can promote the AGG behavior, in which the average grain size of the (Cu71.6Al17Mn11.4)(97.5)Ni2.0Cr0.5 (0.5Cr) is about 1.5 times of that for (Cu71.6Al17Mn11.4)(98.0)Ni-2 (0Cr) after 2 CHTs. Remarkably, the activation energy of grain boundary migration (Q) of 0.5Cr (= 90 kJ/mol) is similar to that of 0Cr (= 91 kJ/mol), while the subgrain boundary energy (Delta G(s)) of 0.5Cr (= 6.9x10(-2) J/mol) is significantly higher than that of 0Cr (= 4.7x10(-2) J/mol). The higher subgrain misorientation of 0.5Cr (= 1.25 degrees), as compared with that of 0Cr (= 0.72 degrees) is the main reason. Thus, tuning Cr content can promote the AGG behavior of the CuAlMnNiCr alloy, through controlling the subgrain misorientation. Moreover, a maximum of 13.0% superelastic strain is obtained after adding 0.5% Cr.