Effect of two-time spark plasma sintering on microstructure and mechanical properties of W–6Ni–4Mn alloy

Tungsten heavy alloys (WHAs) are extensively applied in kinetic energy penetrators, but they exhibit poor self-sharpening properties—connected with high thermal conductivity, large grain size, and low hardness—which limit their application. In this study, we fabricated W–6Ni–4Mn alloys with low ther...

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Published in:Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2019-02, Vol.745, p.300-306
Main Authors: Fan, Z.S., Xiang, D.P., Pan, Y.L., Jiang, H.
Format: Article
Language:English
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Summary:Tungsten heavy alloys (WHAs) are extensively applied in kinetic energy penetrators, but they exhibit poor self-sharpening properties—connected with high thermal conductivity, large grain size, and low hardness—which limit their application. In this study, we fabricated W–6Ni–4Mn alloys with low thermal conductivity by using the two-time spark plasma sintering (TTSPS) technology. To be specific, raw powders underwent SPS for the first time at 1000 °C followed by the second run at 1000–1200 °C. In our studies, long-time solid-phase sintering at low temperature is used to increase the density of the alloy, while short-time liquid-phase sintering at high temperature inhibits the dissolution and re-precipitation process to suppress the W grain growth. As a result, W–6Ni–4Mn alloy with W grains as small as 3.35 µm, hardness as high as 76.6 HRA, and the bending strength of 785.30 MPa were successfully prepared at 1100 °C. The marked improvement in the hardness of W–6Ni–4Mn alloys in comparison with the previous studies may be mainly ascribed to the fine-grain strengthening effect. When the sintering temperature was increased, the matrix volume fraction improved initially and then decreased and reached a peak value at 1100 °C. However, the W–W contiguity had the opposite change trend. The gray Ni-rich binder phase existed in the microstructure of the TTSPS alloys at temperatures less than 1100 °C, but it gradually transformed into a black Mn-rich binder phase at temperatures above 1100 °C.
ISSN:0921-5093
1873-4936
DOI:10.1016/j.msea.2018.12.109