The fracture resistance and crack tip micromechanics of in-situ intermetallic composites

The Cr2Nb intermetallic compound is attractive as a high-temperature material because of its high melting point, low creep rate, and good oxidation resistance. However, this material is also extremely brittle at ambient temperature. Consequently, substantial efforts have been made to develop Cr2Nb-based in-situ composites containing a ductile phase with the aim of imparting fracture resistance while maintaining most of the high-temperature properties. This article presents an overview of the effects of matrix composition on the fracture resistance and crack-tip micromechanics for Cr2Nb-containing in-situ composites based on the Nb-Cr-Ti system. Crack-tip stain measurements are presented to illustrate the important effects of titanium addition on the ductility of the solid-solution phase and the fracture process in the in-situ composites.