Effects of Aging Treatment on the Microstructures and Mechanical Properties of a TC18 Alloy

In the present work, the effects of aging treatment on the microstructures of a TC18 alloy are studied. The influence of aging treatment on the tensile properties and failure mechanisms is systematically analyzed. It is found that the size and morphology of the primary alpha (alpha p) phases are insensitive to aging temperature and time. Furthermore, the aging temperature and time dramatically influence the precipitation of the secondary alpha (alpha s) phases. Massive alpha s phases precipitate and gradually coarsen, and finally weave together by increasing the aging temperature or extending the aging time. The variations in alpha p and alpha s phases induced by aging parameters also affect the mechanical properties. Both yield strength (YS) and ultimate tensile strength (UTS) first increase and then decrease by increasing the aging temperature and time, while ductility first decreases and then increases. There is an excellent balance between the strengths and ductility. When the aging temperature is changed from 450 to 550 degrees C, YS varies from 1238.6 to 1381.6 MPa, UTS varies from 1363.2 to 1516.8 MPa, and the moderate elongation ranges from 9.0% to 10.3%. These results reveal that the thickness of alpha s phases is responsible for material strengths, while the content of alpha phases can enhance material ductility. The ductile characteristics of the alloy with coarser alpha s phases are more obvious than those with thinner alpha s phases. Therefore, the aging treatment is helpful for the precipitation and homogeneous distribution of alpha s phases, which are essential for balancing the strengths and ductility of the studied Ti alloy.