Micromechanisms of Cleavage Behavior for Mo, Nb, and Mo-Nb Alloy Crystals as Probed by Synchrotron Radiation Topography

摘要

The fracture energy of Nb, Mo, and Mo-Nb alloys varies with composition when monocrystals are cleaved on the (001) plane at 77 degrees K. The subsurface microstructure in oriented (001) crystals of Nb, Mo, and equiatomic Mo-Nb was assessed using SXR fractography. The limited plastic response of Nb during cleavage crack propagation at 77 degrees K is explained as follows: mobile dislocations are driven to high velocities, undergoing a slip-to-twinning transition, and glissile dislocations are transformed into sessile products. The twins which form are those that relieve the tensile stresses. (ERA citation 10:002606)