Resulting morphologies on quenching of titanium aluminide alloys

The effect of alloying elements (aluminium, silicon, niobium, and zirconium) on the mechanism and morphology of the allotropic transformation Ti-beta(bcc) --> Ti-alpha(hcp), occurring during the quenching of binary, ternary, and quaternary, titanium aluminide alloys, has been studied The alloys investigated were (at.-%) Ti-16Al, Ti-16Al-1Si, Ti-16Al-3.5Si, Ti-14Al-1Si-1Nb, Ti-14Al-1Si-1Zr, Ti-22Al, Ti-22Al-1Si, Ti-22Al-3.5Si, Ti-20Al-1Si-1Nb, and Ti-20Al-1Si-1Zr. The allotropic transformation in these alloys presented a very narrow temperature range for the formation of all possible alpha morphologies resulting from quenching. The different morphologies of alpha phase observed have been correlated with the competing mechanisms of beta decomposition. The morphological observations indicated thar small variations in thermodynamic and kinetic condition's in the beta phase might account for changes in the mechanisms of formation and growth of the alpha phase. Additionally, the effect of the alloying elements on the ordering reaction alpha-->alpha(2) occurring during quenching has been investigated. Silicon addition promoted the formation of columnar alpha(2) domains during quenching. MST/3959