Studies on the development of TZM alloy by aluminothermic coreduction process and formation of protective coating over the alloy by plasma spray technique

TZM alloy is a potential candidate for high temperature structural applications. However, in the preparation of this alloy by conventional melt-casting route, difficulties are encountered in achieving homogenized alloy composition in view of high melting temperature of the alloy and presence of minor alloying components. Therefore, an alternative technique of aluminothermic co-reduction was adopted to prepare TZM alloy of composition, Mo-0.5Ti-0.1Zr-0.02 °C, wt.% by simultaneous reduction of uniformly premixed oxides of MoO₂, TiO₂ and ZrO2 by aluminium in presence of requisite amount of carbon. The as-reduced alloy was further arc melted for consolidation. Since, TZM alloy is by nature highly susceptible to oxidation at elevated temperature in air or oxygen, therefore feasibility of development of silicide type of coating over the synthesized alloy by plasma coating technique was also examined. Silicon powder coated on TZM alloy surface by plasma spray technique was finally converted into MoSi₂ coating by sintering at 1350 ^°C for 2-4 h duration under argon. A double layer coating structure was formed with two distinct phases. The inner thin layer was consisted of Mo₂Si₅ phase (~ 10 μm) followed by thick outer layer of MoSi₂ (~ 150 μm). The coating showed good adhesion strength and stable oxidation with negligible mass gain (10 g/m²) at 1000 ^°C in air.