Strengthening of a Near β-Ti Alloy through β Grain Refinement and Stress-Induced α Precipitation

Near beta-Ti alloys with high strength and good ductility are desirable for application in aviation and aerospace industries. Nevertheless, strength and ductility are usually mutually exclusive in structural materials. Here we report a new thermo-mechanical process, that is, the alloy was cross-rolled in beta field then aged at 600 degrees C for 1 h. By such a process, a high strength (ultimate tensile strength: 1480 MPa) and acceptable ductility (elongation: 10%) can be simultaneously achieved in the near beta-Ti alloy, based on the microscale beta matrix and nanoscale alpha phase. The microstructure evolution, mechanical properties and strengthening mechanisms have been clarified by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the grain size of the beta phase progressively decreased with the increasing of rolling reduction. Moreover, dense dislocation structures and martensite phases distributed in the cross-rolled beta matrix can effectively promote the precipitation of nanoscale alpha particles. TEM analyses confirmed that a heat-treatment twin was generated in the newly formed alpha lath during aging. These findings provide insights towards developing Ti alloys with optimized mechanical properties.