Effect of Stress Level on the High Temperature Deformation and Fracture Mechanisms of Ti-45Al-2Nb-2Mn-0.8 vol. pct TiB2: An In Situ Experimental Study

摘要

The effect of the applied stress on the deformation and crack nucleation and propagationudmechanisms of a c-TiAl intermetallic alloy (Ti-45Al-2Nb-2Mn (at. pct)-0.8 vol. pct TiB2) wasudexamined by means of in situ tensile (constant strain rate) and tensile-creep (constant load)udexperiments performed at 973 K (700 �C) using a scanning electron microscope. Colonyudboundary cracking developed during the secondary stage in creep tests at 300 and 400 MPa andudduring the tertiary stage of the creep tests performed at higher stresses. Colony boundaryudcracking was also observed in the constant strain rate tensile test. Interlamellar ledges were onlyudfound during the tensile-creep tests at high stresses (r>400 MPa) and during the constantudstrain rate tensile test. Quantitative measurements of the nature of the crack propagation pathudalong secondary cracks and along the primary crack indicated that colony boundaries wereudpreferential sites for crack propagation under all the conditions investigated. The frequency ofudinterlamellar cracking increased with stress, but this fracture mechanism was always of secondaryudimportance. Translamellar cracking was only observed along the primary crack.