Oxidation of PT-7M and OT4-1 titanium alloys in air

An investigation of gas corrosion in air of Ti alloys with Al, Zr and Mn and the influence of alloying on the heat resistance at 850 deg C are discussed. Alloys studied were OT4-1 PT-7M and commercial purity VT1-0. The change in weight on heating at 850 deg C was determined and the structure of the oxide layers was analyzed. The scale formation was greater on alloys than on VT1-0, the thickness being PT-7M > OT4-1 > VT1-0. The depth of gas impregnation depends on the gas diffusion coefficient. After an anneal the depth is PT-7M < VT1.0 < OT4-1. After 10 h at 850 deg C the depth increases significantly. Alloying with Al and Zr decreases the depth of the oxygen diffusion zone and Mn increases the depth of gas impregnation. It is concluded that alloying with Al in initial stages of oxidation increases the rate of scale formation and reduces O solubility in the Ti. The layers of Al sub 2 O sub 3 increase heat resistance. Alloying Ti--2Al with 2% Zr resulted in thicker scale and decreased depth of diffusion layer. Manganese increased the rate of scale formation and the depth of gas impregnation. 9 ref.--H.B.C.