M23C6 carbide dissolution mechanisms during heat treatment of ASTM F-75 implant alloys

The dissolution of M₂₃C₆ carbides in an ASTM F-75 alloy was experimentally followed, during a liquid-phase homogenization treatment, in as-cast and pretreated for partial carbide dissolution (PTPCD) specimens. The results revealed that before the fusion of the carbides, solid-state diffusion of the elements forming the carbides occurred. After the fusion of the carbides, a serrated interface developed. Treatment periods longer than 1000 seconds led to a liquid-carbide zone morphology showing the presence of dendrites within the liquid phase. Energy dispersion spectrometry (EDS) analysis revealed that the composition of such dendrites was very close to that of the α-phase matrix. The observed microstructure features are explained in terms of a solutal diffusion-driven mechanism leading to the growth of the matrix by consuming the liquid phase formed by the carbide fusion.