Densification and Strengthening of Ferrous‐Based Powder Compacts Through Cold Sintering Aided Warm Compaction

Abstract

Cold sintering of surface‐modified iron compacts results in a co‐continuous phosphate interphase between iron particles that provide both enhanced green strength and green density similar to the process that has been successfully introduced in low‐temperature densification of ceramic materials. Relative density as high as 95% along with transverse rupture strength of ≈ 75 MPa, which is almost six times that of conventional powdered metal iron compact and 2.5 times that of warm compacted controls, is achieved. Dilatometry study at different pressures shows a small but significant improvement in densification process during cold sintering relative to the larger densification of warm compacted control. Strength model based on microstructural analysis as well as in situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments reveals the nature of the interphase that imparts the large cohesive strength under the cold sintered assisted warm compaction. The process is conducive to produce iron compacts for green machining. Furthermore, the samples when subjected to high‐temperature sintering yield a fully sintered iron compact with density > 7.2 g cm−3 and transverse rupture strength as high as 780 MPa. All in all, there are major new opportunities with the cold sintered assisted warm compaction of powdered metals that will also be discussed.