SURFACE CRACKING DURING CREEP OF A TI-25AL-11NB ALLOY

The surface cracking behavior of a Ti-25Al-11Nb alloy has been quantit atively evaluated at 923 K. The influence of prior exposure at 923 K f or 30-488 h on surface crack nucleation and growth has been determined at 160, 200 and 250 MPa by interrupted creep tests. A critical strain exists for surface cracking. The value of critical strain depends on the applied stress and the pre-exposure duration. The stress dependenc e of crack opening and intercrack spacing agrees with Riedel model for surface cracking. Microstructure insensitive transgranular crack grow th suggests local embrittlement and cracking at the crack tip as crack growth mechanism.