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

Abstract

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 a-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 postannealed Fe-1Ni-0.4B-0.8C alloy exhibited a high elongation to failure of 5.2 pct.

Improved Mechanical and Corrosion Properties of Powder Metallurgy Austenitic, Ferritic, and Martensitic Stainless Steels by Liquid Phase Sintering

“…Liquid phase sintering (LPS) is an economical technique to facilitate the sintering densification of PM materials by adding specific alloying elements for liquid generation without obviously increasing the cost [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. For PM steel, boron (B) is an effective alloying element for LPS due to an Fe–B eutectic reaction [ 11 , 12 , 13 , 14 , 15 , 16 ].…”

“…Several techniques, such as warm compaction, double-press double-sintering, powder forging, and spark plasma sintering can decrease the porosity, though these techniques greatly raise the production cost [ 4 , 5 , 6 , 7 , 8 ]. Liquid phase sintering (LPS) is an economical technique to facilitate the sintering densification of PM materials by adding specific alloying elements for liquid generation without obviously increasing the cost [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. For PM steel, boron (B) is an effective alloying element for LPS due to an Fe–B eutectic reaction [ 11 , 12 , 13 , 14 , 15 , 16 ].…”

“…The alloying elements of B-alloyed PM steel can modify the liquid generation temperature. In PM alloy steels, Cr and Mo raise the liquid formation temperature, but Ni decreases it [ 13 , 16 , 17 , 18 ]. However, 0.5 wt% C additive in B-alloyed PM steel not only induces the generation of a secondary liquid but also increases the equilibrium liquid volume at 1250 °C by ~5 vol% [ 17 ].…”

“…Moreover, the crystal structures of borides are also modified by the alloying elements. Several types of boride structures, such as M 2 B, M 3 (B,C), and M 23 (B,C) 6 , where M represents the metallic elements, have been experimentally identified in the literature [ 3 , 12 , 13 , 14 , 17 , 18 ]. Recently, You et al [ 14 ] determined that MoFe(C,B) boride (WCoB-type) exists in the Fe-5Mo-0.8C-0.4B PM steel by using an atomic resolution high angle annular dark field (HAADF) scanning transmission electron microscope (STEM).…”

The Microstructure of Fe-Based Laminated Metal Composite Produced by Powder Metallurgy

“…Powder metallurgy (PM) is a cost-effective process for manufacturing nearly net-shaped metallic materials, particularly Fe-based alloys, in mass production, one that has been widely investigated [ 11 , 12 , 13 , 14 , 15 ]. However, the use of PM technology to fabricate LMCs has been rare to date in industry.…”