Abstract:Through tensile test, tensile-unload test and SEM observation, the effects of loading rate on fracture mechanism of TiAl-based alloys with fully lamellar and duplex microstructures were investigated. The result reveals that when the rate is lower, microcrack density is larger and microcracks have sufficient time to initiate along many grain boundaries or lamellar interface, and propagate basically along interlamellar within the grain. There are no river patterns on the fracture surface. A majority of the fracture surface belongs to interlamellar fracture, and grain structure is not obvious on fracture surface, such case effects on the mechanical properties are dominant. While the microcracks have no time to initiate and propagate in the case of high loading rate, many river patterns come into being in the course of fracture, and we can also find the grain structure no longer obvious on the fracture surface. Because many microcracks initiate ahead, the size of fracture facet is smaller, so the effects are much less obvious, in this case.