Materials Science Forum, Vol.357-3, 315-320, 2001
Influence of reversible hydrogen alloying on formation of SMC structure and superplasticity of titanium alloys
A method of production of a submicrocrystalline (SMC) structure (d<1m) in large workpieces of the commercial pure titanium and the two-phase titanium alloys based on initiation of dynamic recrystallization (DRX) during hot working and reversible hydrogen alloying has been developed. The method involves continuous grain refinement due to DRX at decreasing temperature. Hydrogen alloying decreases deformation stresses and increases ductility at lower temperatures than in hydrogen-free alloy and promotes the formation of the finest grain structure. The grain sizes of 0.1-0.2 mum and 0.04 mum have been produced in the hydrogenated commercial pure Ti and Ti-11.4Al-1.7Mo-0.88Zr (at.%) based alloys, respectively. An oxidized layer retards the hydrogen removal in these alloys at temperatures lower than 500 degreesC. Therefore the SMC structure during degassing can be retained only in complex alloyed two-phase titanium alloys. After degassing the grain size as low as 0.04 mum has been obtained. The hydrogen alloying of commercial pure Ti prevents observing of low temperature superplasticity (SP), but sharply increases superplastic properties at higher temperatures. The low temperature SP at 550 degreesC occurs in the two-phase titanium alloy with the grain size 0.04 pm that has been obtained by using reversible hydrogen alloying.
Keywords:dynamic recrystallization;hydrogen alloying;submicrocrystalline structure;superplasticity;titanium alloy