Phase Selection and Microstructure Evolution in Laser Additive Manufactured Ni-Based Hardfacing Alloy Bush.

Nickel-based hardfacing alloy bushes are used in dynamic moving components inside fast breeder reactors. Due to the difficulties associated with their fabrication through casting or weld deposition, laser rapid manufacturing (LRM) was attempted. In this work, microstructure development and phase selection in laser additive manufactured Ni-based hardfacing alloy bushes are investigated. The as-fabricated bushes had a uniform, defect-free microstructure perpendicular to the material build direction, whereas microstructural heterogeneity could be detected parallel to the build direction due to coarsening of precipitates. Overall microstructure was dominated by γ-Ni, γ-Ni + Ni₃B anomalous and lamellar eutectic and Ni–B–Si lamellar eutectic constituents. In addition, Cr-rich borides and carbides were also found. Phase property diagrams and Scheil's non-equilibrium solidification simulated using ThermoCalc® provided supporting insights into the phase selection phenomena under rapid cooling conditions. Microstructure of LRM Ni-based hardfacing alloy bushes was quite distinct from weld deposited ones and is analyzed in terms of a non-equilibrium eutectic solidification reaction occurring in Ni–Cr–B–C–Si–Fe multicomponent alloy system due to rapid cooling. [ABSTRACT FROM AUTHOR]