Microstructure, Plasticity and Ductility of a TNM+ Alloy Densified by Spark Plasma Sintering

This work presents a study of the microstructure and mechanical properties of a TNM+ alloy (Ti-43.5Al-4Nb-1Mo-0.1B-0.3C-0.3Si, in at.%) densified by Spark Plasma Sintering (SPS), in comparison to the as-SPSed TNM alloy, which contains neither carbon nor silicon. Tensile tests at room temperature and 800 degrees C, as well as creep tests at 800 degrees C and 200 MPa, were performed. The microstructures and the fracture surfaces of deformed samples were studied by scanning and transmission electron microscopies, as well as by X-ray diffraction. The deformation mechanisms were investigated by means of in situ straining experiments and post-mortem analyses of deformed samples, both performed by transmission electron microscopy. Contrary to the TNM alloy, the as-SPSed microstructure of the TNM+ alloy does not contain beta/beta(o) phase due to the incorporation of carbon. At room temperature, the TNM+ alloy exhibits a yield stress of 520 MPa but a poor ductility of less than 0.1% of plastic strain. The incorporation of carbon and silicon leads to an increase in the creep resistance of the alloy at 800 degrees C. Despite the fact that iron inclusions are responsible for the premature failure of some samples during tensile tests, the TNM+ alloy is found to be able to deform plastically at room temperature by the glide of ordinary dislocations and by twinning.