Particle size dependent microstructure evolution of inert gas atomized nickel base superalloy powders

Abstract

Powder of an experimental Nickel base superalloy produced through Inert Gas Atomization technique is characterized for its physical properties, chemical composition, morphology, micro-segregation and orientation distribution of grains. The atomized powders exhibits near spherical morphology with average particle size of 61 µm. Micro-chemical analysis reveal, elements like Ti, Mo, Ta and Hf partition at inter-dendritic regions, irrespective of particle size.The extent of micro-segregation however is found to be intimately related to the cooling rate and particle size. The EBSD analysis reveals random texture in the particles with the number of grains per particle decrease with decreasing particle size. The nucleation event is found to be initiated on particle surfaces as evidenced from the dominant presence of the Low Angle Grain Boundaries (LAGBs) near the particle surfaces. The selective growth of favourably oriented nuclei are observed towards the core of the particle and characterized by presence of High Angle Grain Boundaries (HAGBs) in the particle interior. A mechanistic understanding correlating evolution of grain size distribution and micro-segregation with droplet solidification process, has been elucidated through the present study.