Orientation relationship between beta-Mn and L2(1) matrix in a Cu2MnAl alloy

Abstract

In the as-quenched condition, the microstructure of the Cu2MnAl alloy was L2(1) phase containing extremely fine L-J precipitates. This result is different from that reported by other workers in the as-quenched Cu2MnAl alloy. When the as-quenched alloy was aged at 350 degrees C, gamma-brass precipitates started to appear within the L2(1) matrix. The orientation relationship between the gamma-brass and the L2(1) matrix was determined to be cubic to cubic. This result is consistent with that observed by other workers in the aged Cu-Mn-Al alloy. When the alloy was aged at 460 degrees C, the gamma-brass precipitates disappeared and platelike beta-Mn precipitates occurred within the L2(1) matrix. As the aging temperature was increased to 560 degrees C, the morphology of the beta-Mn precipitates changed from platelike to granular shape. Electron diffraction examinations indicated that in spite of the morphology change the same orientation relationship between the beta-Mn and the L2(1) matrix is maintained, and it could be best stated as follows: (210)(beta-Mn)//(100)(m), ((1) over bar 20)(beta-Mn)//(010)(m), (001)(beta-Mn)/(001)(m) This result is in disagreement with that reported by Kuzobski et al. in the aged Cu2MnAl alloy. In their study, it was concluded that both the morphology of the beta-Mn precipitates and the orientation relationship between the beta-Mn and the L2(1) matrix would vary with the aging temperature.