Microstructure Modification of Liquid Phase Sintered Fe–Ni–B–C Alloys for Improved Mechanical Properties

Powder metallurgy (P/M) has been widely used in automobile, home appliances, and electronic devices, but its uses are very limited due to the low relative density of 85 to 95 pct. The Fe–Ni–B–C alloy system can mitigate the aforementioned issues by the liquid phase sintering, which results in a nearly full densification. However, the boron-containing alloys produced the brittle eutectic phases [Fe 3 (C, B) and Fe 2 B] along the grain boundaries, which are detrimental to the mechanical properties. The main objective of this study is to improve the ductility of boron-containing alloys through the microstructure modification. For this, the volume fraction of solidified phase was optimized by controlling the composition, and the coarsening of solidified α -Fe particles into the pearlite matrix was induced by a post annealing, which reduces the continuous network of eutectic phases and increased the grain continuity. In addition, the effect of microstructure modification on the mechanical properties of Fe–B–C and Fe–Ni–B–C alloys was comparatively investigated. As a result of microstructure modification, the post-annealed Fe–1Ni–0.4B – 0.8C alloy exhibited a high elongation to failure of 5.2 pct.