CRYSTALLINE STRUCTURE AND TWIN OF Cr_7 C_3 IN SUPERALLOYS

Experimental confirmation by analysis of single crystal electron diffraction spots is presented, showing that the Cr_7C_3 in superalloys is of the orthorhombic crystalline structure. In the Cr_7C_3, the {013} growth twin was discovered by the electron diffraction patterns and the secondary twin might be possibly found. The {013} twin is observed in Cr_7C_3 film. The interrelation of higher twin in Cr_7C_3 has also been discussed.