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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.

Iron powder metallurgy is a well-established field in the powder metal (PM) industry due to its ease of processing and appreciable mechanical properties. One area that can contribute significantly to increased production and warrants more study is green machining. Additionally, our current global environmental state calls for more energy efficient processing methods. Cold sintering process (CSP) of metals may provide a means for decreasing required sintering temperature for metal via liquid phase sintering. Our application of CSP utilizes surface modification of iron particles to form an ultrathin hydrated phosphate layer (~10 nm). The hydrated layer promotes driving force for rearrangement and densification under warm compaction to yield compacts with significantly increased green strength up to 70 MPa. This method is currently under investigation for the impact of alloyed iron as well. Implementation of CSP for iron may result in increased mechanical properties, decreased sintering temperature requirements, and decreased energy consumption.

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