Development of a trimodal microstructure with superior combined strength, ductility and creep-rupture properties in a near alpha titanium alloy

In the present study a new microstructure was introduced for a Ti-6242S alloy that has an appropriate combination of mechanical properties such as strength, ductility and creep-rupture. This trimodal microstructure was developed through thermomechanical processing consisted of a near beta rolling followed by solution annealing in alpha/beta region. In the following, the mechanical properties of this microstructure was investigated and compared to the conventional microstructures i.e., widmanstatten and bimodal microstructures to demonstrate its superiority. The results indicated that the yield strength, ductility and toughness in trimodal microstructure lies between those of the two other microstructures. However, the ductility and toughness of trimodal microstructure is significantly higher than that of the widmanstatten microstructure and almost close to the bimodal microstructure. The steady state creep rate in trimodal microstructure at 540 degrees C and under an applied stress of 540 MPa approached closely to that of widmanstatten microstructure and was considerably lower than the value in bimodal microstructure. Furthermore, time to rupture for trimodal microstructure is 1.3 and 3.5 times higher than the widmanstatten and bimodal microstructures, respectively. These results clearly confirm a more optimized combination of mechanical properties in the trimodal microstructure compared to the widmanstatten and bimodal microstructures.