Studies on nano-crystalline CoNiCrAlY consolidated by conventional and microwave sintering

• Studies on development of nanocrystalline CoNiCrAlY by powder metallurgy.
• Microwave sintering is more effective in controlling grain growth.
• Order–disorder transformation for conventional sintering of CoNiCrAlY powder.
• Reduction of coefficient of thermal expansion in nano-crystalline CoNiCrAlY.
• Decreased oxidation kinetics in nano-crystalline CoNiCrAlY.

The present study concerns mechanical milling of commercially available CoNiCrAlY powder to produce nanocrystalline CoNiCrAlY and its consolidation by conventional and microwave sintering techniques. Detailed studies were undertaken to understand the effect of processing history (conventional and microwave sintering), materials parameters (as-received and mechanically milled for different time), and process parameters (temperature and time of sintering) on the density, microstructures, composition and phase distribution, coefficient of thermal expansion and high temperature oxidation resistance property. The density of the consolidated product increases with increase in milling time; increase in temperature of sintering in both conventional sintered and microwave sintered samples, with a maximum density achieved due to microwave sintering. There is a significant reduction in coefficient of thermal expansion due to sintering with a maximum reduction occurred when sintering is conducted by microwave sintering. Isothermal oxidation study showed a significant improvement in oxidation resistance due to nano-crystallization with a maximum improvement observed for 48 h milled sample microwave sintered at 1100 °C for 48 h.

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