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.

In situ observation of the multistep process of cold sintering

“…The methods of producing a cold sintered sample are relatively blunt: an oxide powder is mixed with a small amount of solvent (the oxide must be at least partially soluble in the solvent), and the powder is loaded into a die and heated to moderate temperatures under a uniaxial load 4–6 . Densification using this method has successfully been demonstrated on a multitude of oxide, 7 oxide–polymer composite, 8,9 functionally graded, 10 and even metallic materials 11 . Cold sintering shows promise as a low carbon producing, energy efficient technology compared to traditional high temperature sintering 12 …”

“…[4][5][6] Densification using this method has successfully been demonstrated on a multitude of oxide, 7 oxide-polymer composite, 8,9 functionally graded, 10 and even metallic materials. 11 Cold sintering shows promise as a low carbon producing, energy efficient technology compared to traditional high temperature sintering. 12 ZnO was one of the first ceramic materials successfully cold sintered to greater than 95% theoretical density.…”

Finite Element Modeling and Optimization Analysis of Cutting Force in Powder Metallurgy Green Compacts

“…Green machining represents a transformative approach in the fabrication of PM materials, wherein the PM green compacts are machined to their desired geometries prior to the sintering process, effectively addressing the traditionally challenging machining of PM materials [19][20][21]. Drawing parallels with the low-temperature densification observed in ceramics, Paradis and colleagues discovered an innovative method through the cold sintering of surface-altered iron powders [22]. This technique facilitated the emergence of a mutually continuous phosphate phase amidst the iron powder particles, enhancing both the robustness and density of the green compacts.…”