Study on compression deformation, damage and fracture behavior of TiAl alloys: Part I. Deformation and damage behavior

The compression deformation, damage and fracture behaviors of TiAl alloys in the fully lamellar and duplex microstructures were systematically studied. The fracture behaviors in compression tests of TiAl specimens are detailed in Part II of this work. In this paper a series of compression preloading-unloading-reloading tests were carried out. Results indicated that the compression engineering stress-strain curves were unchanged and were not affected by the numbers of multiple preloading-unloading processes until the preloading stresses reached the ultimate compression stress. However the tensile strength was significantly reduced by the multiple compression preloading-unloading-reloading processes. At the microscopic scale, the development of the microcracks on the specimen surfaces increases up to ∼1000 cracks/mm2 with the compression up to the ultimate fracture stress of ∼2200 MPa. The linking of microcracks to form macrocrack damage in the bulk is examined. A preloading-unloading-reloading process with step-by-step observation of the initiation, extension and formation of microcracks on the specimen surface with increasing compression load is described in detail. From these observations, mechanisms of crack linking and propagation are identified in duplex and fully lamellar microstructures.