MnCu high damping alloys undergo a phase transformation from face-centered cubic to face-centred tetragonal, with the formation of {101} twin boundaries. In the present work, a commercial M2052 (Mn–20Cu–5Ni–2Fe) high damping alloy was used in order to characterize the features of transformation twins in specimens with differing grain sizes. For this purpose, the yield strengths, phase transformation points and axial ratio of M2052 with various grain sizes were determined by tensile tests, dynamic mechanical analysis and X-ray diffraction, respectively. The results indicated that the effects of twinning structure on the yield strength of the MnCu alloy could be divided into two terms; a grain-size-independent term and a grain-size-dependent term. The grain-size-independent term influences the nominal friction stress and the grain-size-dependent term influences the Hall–Petch slope of the specimens significantly. Analysis of the experimental data showed that the formation of twins in M2052 was affected by not only aging treatment prior to phase transformation, but also the grain size of the face-centred cubic phase. Higher nominal friction stress observed in the specimens with longer time aging treatment would be due to the higher twin density, and the decrease of Hall–Petch slope would be due to the grain-size dependence of twin density and axes ratio. It indicated that even under the same aging condition, the twin densities in larger grain-sized specimens would be higher than those in smaller grain-sized specimens.

Effects of Transformation Twin on Hall–Petch Relationship in MnCu Alloy. Y.Zhong, T.Sakaguchi, F.Yin: Materials Science and Engineering A, 2008, 492[1-2], 419-27