Influences Of ω-assisted Nucleation On Microstructures And Properties Of Titanium Alloys

Titanium alloys have been widely applied to the fields of aerospace, marine and civilianfacilities because of many excellent features such as high specific strength, high corrosionresistance, heat resistance, good low temperature performance, low modulus of elasticity andso on. Therefore, the studies on the optimization in microstructures and properties of titaniumalloys by the using of ω-assisted nucleation have important theoretical significance andeconomic values. In this paper, taken Ti-23V, Ti-7Fe, Ti-14V alloys as the studied systems,the influence of ω-assisted nucleation on the microstructures and properties in titanium alloysare investigated through two-step aging treatments combined with conventional preparationmeans and XRD diffraction, scanning electron microscopy, optical microscopy, hardnesstester, universal tensile machine and other equipments. The studied results are as follows.(1) The influences of the first-step aging temperatures on the microstructures andproperties of the two-step aged Ti-23V alloy are studied. The first-step aging temperature istoo low or too high, the desired effect of assisted nucleation is not obtained. While thefirst-step aging temperature is appropriately selected (e.g,350C), the two-step aged alloyexhibits a large number of the dispersed ultra-fine intragranular in the absence of GBandPFZs, resulting in the excellent ductility and tensile strength. Moreover, the dimplesdemonstrate the fracture morphology is ductile.(2) The influences of the first-step aging times of400C on the microstructures andproperties of the two-step aged Ti-23V alloy are studied. When the first-step aging time isshorter, the higher strength as well as the lower elongation appears in the alloy; while thefirst-step aging time is enough, the strength of alloy decreases and the ductility enhancessignificantly. However, both the strength and elongation are decreased when the first-stepaging time is overlong.(3) The influences of the first-step aging temperatures on the microstructure andproperties of the two-step aged Ti-7Fe alloy are investigated. For the alloys withhomogenization or without homogenization, the strength of the alloy can be improved byω-assisted nucleation on the condition that the elongation is decreased. The specimenwithout homogenization exhibits brittle fracture, while the mixed model consisting of brittleand toughness fractures appears in the specimen with homogenization.(4) The influences of the first-step aging times of400C on the microstructure andproperties of the two-step aged Ti-7Fe alloy are investigated. When the first-step aging time ischanged, the improvement in the strength of alloy can be accomplished, but the elongationdecreases with the increase in strength. The fracture morphology exhibits the brittle fracture.(5) The influences of ω-assisted nucleation on the microstructures and properties ofTi-14V alloy are studied. During aging of400C, the tensile strength of Ti-14V alloy first increases then and increases again along the aging time is prolonged; while the variation trendin elongation is opposite to the one of the tensile strength.