Effect Of Loading Speed On Damage And Fracture Behavior Of TiAl-based Alloys

TiAl-based alloys as one of the materials for turbocharger and aviation have very much application prospect. Effect of strain rate on fracture mechanism of TiAl-based alloys is significant, and combining with actual application condition, effect of loading speed on mechanical properties do not ignore during the accelerate and stop of engine turbine. So, it is necessary to study carefully effect of loading speed on damage and fracture behavior of TiAl- based alloys.At room temperature the tensile tests and 3PB tests were used to study the effect of the loading speed on fracture and damage mechanism of TiAl-based alloys with fully lamellar (FL) and duplex (DP) microstructure. It is shown that: With loading speed lowering, the tensile strength of DP alloy and notch fracture toughness of FL alloys are decreased. For tensile tests the strength decrease with lowering loading speed, which results from the sustained accumulation of microcrack-induced damage at lower loading speed. For 3PB tests of notched FL specimens fracture toughness decreased with loading speed lowering, which offered the time necessary for propagation of the main crack through more sectors of low resistance interlamellar cracks. The fracture mechanism is different between tensile test and 3PB test. Fracture in tensile tests happens on an arbitrarily located weakest section seriously damaged by accumulation of large interlamellar microcracks. Fracture in 3PB notched specimens develops by stretching of a bifurcated crack through a high normal stress region constrained to a strip in line with the centerline. The inverse behavior of FL TiAl alloy showing inferior tensile properties but superior fracture toughness, which resulted from the different fracture mechanisms of these two types of tests. Large lamellar grains cause serious damage and low strength in tensile specimens, however form largely bifurcated crack tip and form large obstacles necessarily to be bypassed by the main crack.Effect of loading speed on damage and fracture behavior of TiAl-based alloys are carefully studied in this paper. By this work, material's properties and evolution could be appraised more accurately, and the main factors of influencing performance are clarified, which could promote development of the new material and the new microstructure finally in the near future.