The application of grain strengthening to improve low temperature embrittlement of titanium alloys

The production of titanium and its alloys requires strict control of oxygen content, mainly because interstitial oxygen will cause low temperature embrittlement of titanium material. A grain refinement strategy was proposed by Kyoto University in Japan, which apply high-pressure torsion and electric discharge machining on titanium ingots to obtain ultrafine-grained Ti-0.3wt.%O alloys with an average grain size of 2.0 μm. It combines high strength and ductility at 77 K (-196.15°C). Compared with the coarse-grained Ti- O alloy sample, the strength of the Ti-0.3O alloy is 1250 MPa, and the elongation rate is about 14%. The strength-ductility synergistic effect of Ti-0.3O alloy has a triple mechanism. First, the grain boundary area per unit volume in the ultrafine grain structure is increased by 34 times, and the harmful oxygen grain boundary segregation is diluted to limit the intergranular cracking tendency, thereby Improve the grain boundary binding energy in the ultrafine grain structure. Second, the high stress level inherent in the deformation of the ultrafine-grained microstructure activates the <c + a> dislocations, which greatly relieve the regional plastic deformation inside the grains. Finally, the proportion of intergranular and transgranular microcracks/cavities in the ultrafine-grained structure is about the same, leading to delayed fracture. This research has realized the harmless treatment of oxygen elements that are usually considered harmful in titanium alloys, which not only promotes the low-temperature application of titanium alloys, but also applicable to other types of alloy.