Study on compression deformation, damage and fracture behavior of TiAl alloys: Part II. Fracture behavior

Compression deformation, damage and fracture behaviors of TiAl alloys are studied systematically. The deformation and damage processes in compression tests of TiAl specimens are detailed in Part I and the fracture behaviors are described and discussed here the Part II of this work. Results indicate that: the compression properties are superior to the tensile properties and specially show a much higher fracture strength and plasticity. The macroscopic features of the fracture surfaces indicate that the fracture mechanisms are different between the full lamellar (FL) alloy and the duplex (DP) alloy. In FL alloy, the shear cracking dominates the fracture, and the shear crack extends throughout the whole specimen. At both ends of the specimen, the shear cracks initiate and propagate in directions inclined to the compression axis with an angle near 45°. In the middle of the specimen, the shear cracks propagate parallel to the compression axis. While in the DP alloy after two short shear cracks initiate and extend at both ends, the longitudinal normal cracking is triggered and propagates parallel to the compression axis and dominates the fracture. In the microscopic features the regions of shear cracking show the smooth interlamellar shear fracture facets with some translamellar shear fracture steps. The longitudinal normal cracking in DP specimens shows mixed interlamellar and translamellar cleavage fracture facets. Effect of loading rate manifests itself in increasing the shear yield strength of FL and the fracture strength of DP alloys.