Advanced Nano-crystalline

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A nanocrystalline (NC) material is a polycrystalline material with a crystallite size of only a few nanometers. These materials fill the gap between amorphous materials without any long range order and conventional coarse-grained materials. Definitions vary, but nanocrystalline material is commonly defined as a crystallite (grain) size below 100 nm. Grain sizes from 100–500 nm are typically considered “ultrafine” grains.

Solidification process involves the release of latent heat and, therefore, heat from the liquid metal needs to be transferred to the surroundings. The directional solidification process and single-crystal casting technique have advanced considerably in the past three decades.

The introduction of Bridgman furnace for casting columnar grain structures and the innovation in single-crystal grain selection have made a huge impact on processing high-temperature turbine components and other high value-added components. Both techniques have been widely used in industry. Solidification structures in Ni-based alloys for turbine blades have progressed from equiaxed gains, to directionally solidified columnar gains, and then to single-crystal grain structures. These developments have allowed ever higher combustion temperatures and hence improved thrust and thermal efficiency of gas turbines.

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