1979 Volume 43 Issue 11 Pages 1013-1019
Phase analysis, the crystal structure of the matrix and the orientation relationships between the matrix and MnSi precipitates were examined by metallographic observation, EPMA, X-ray powder diffraction and the Weissenberg method for Mn-Si alloys with 62.5 to 63.8 at%Si.
Plate-like MnSi precipitates were observed in all the crystal grains of Mn-63.1 at%Si alloy, but free-Si and free-MnSi were not. These precipitated plates were parallel to the c-plane of the matrix. In contrast to Mn-63.1 at%Si alloy, Si-deficient and Si-rich alloys produced free-MnSi and free-Si in addition to the plate-like MnSi precipitates, respectively. Mn-Si alloys containing 62.5 to 63.8 at%Si thus consisted of two or three phases, i.e. the matrix, MnSi and/or Si. Threfore, it can be said that there is not a single phase in these alloys. The matrix of these alloys was Mn15Si26(MnSi1.733). The structures of Mn11Si19(MnSi1.727), Mn26Si45(MnSi1.730), Mn27Si47(MnSi1.741), and Mn4Si7(MnSi1.750), which have been reported to be formed by a small difference in Si content near MnSi1.73, were not confirmed in this Mn-Si alloy system.
The distribution of the plate-like MnSi precipitates resembles that of the eutectic lamellar structure, but there were no specific orientation relationships between the matrix and the plate-like MnSi precipitates.