EFFECT OF HETEROGENEOUS DEFORMATION ON THE CREEP-BEHAVIOR OF A NEAR-FULLY LAMELLAR TIAL-BASE ALLOY AT 750-DEGREES-C

The tensile creep behaviour of a near-fully lamellar Ti46A12W0.5Si all oy was studied at 750 degrees C in the stress range of 240-330 MPa. A long tertiary creep regime and a high stress exponent n = 7 were obser ved. On the basis of microstructural studies, the high stress exponent n was attributed to heterogeneous plastic deformation. The scatter of stress exponents reported in literature on TiAl-base alloys can be es sentially interpreted by a proposed model considering the inhomogeneou s deformation in terms of friction stress. The observed extensive neck ing and the successive localized microstructural degradation, resultin g from the heterogeneous deformation, were considered to be the major causes of long tertiary creep stage.