Microstructural characterization of Stellite 6 alloy processed by electron beam melting

Abstract

Stellite 6 alloy was subjected to electron beam melting (EBM) processing in this study. The main phases in the alloy are α-Co, ε-Co, M23C6 (M = Cr, Co, W, etc.), and M7C3 (M = Cr, Co, W, etc.) carbides. The microstructure of the EBM-processed Stellite 6 alloy comprises grains of relatively uniform sizes, with an average grain size of 11.1 μm. There is a relatively minor internal strain within the alloy. The majority of grains exhibit low intragranular misorientations, approximately around 0.5°, while a minority of grains display relatively larger intragranular misorientations, around 2.8°. The dominant {100} texture was developed in the build direction because of the fast growth of the <100> direction for a cubic crystal structure during solidification. The vertically aligned columnar grains contribute to the development of the <100> texture along the build direction. The elongated direction of columnar grains was parallel to the temperature gradient direction. This competitive growth direction at the solid-liquid interface results in slight tilts in the pole figures. The eutectic carbide phases are uniformly distributed along the grain boundaries. The cube–cube orientation relationships between the matrix and M23C6 carbide phase were identified as [001]α//[111]M23C6. The low stacking fault energy of the Stellite 6 alloy resulted in the formation of a high density of stacking faults within the grains. The interactions between stacking faults of different orientations were observed. Primary M7C3 carbides were found to transform into secondary M23C6 carbides, with a phase transition process observed where secondary carbides M23C6 surrounded primary carbides M7C3.