Spark-Plasma Sintering of W-5.6Ni-1.4Fe Heavy Alloys: Densification and Grain Growth
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W-NI-FE heavy alloys are typical two-phase composites used in the applications requiring high density, such as kinetic energy penetrators, counter weights, and radiation shields.[1–3] Generally, the alloys are liquid sintered from blended elemental powders of tungsten, nickel, and iron at a temperature above 1733 K (1460 C).[4] After sintering, the microstructure consists of coarsened spherical body-centered cubic tungsten grains dispersed in a face-centered cubic (fcc) Ni-Fe-W solid-solution matrix.[5] In the past decades, many investigators have presented that the fine-grain microstructure can improve the mechanical properties of tungsten heavy alloys.[6–10] In order to refine microstructure, lots of research papers focused on adding inhibitors to prevent the grain growth. Recent literature has reported that adding a trace amount of rare earth elements or their oxides can refine the grain size and enhance the penetration performance of tungsten heavy alloys.[11–14] Some researchers adopted high-energy ball milling (HEBM) combining with novel sintering technologies, such as two-stage sintering, microwave sintering, and electric current activated sintering, to prepare ultrafine grained heavy alloys or tungsten.[2,15–18] Spark-plasma sintering (SPS), often referred to as fieldassisted sintering technique (FAST) or pulsed electric current sintering (PECS), is a newly arisen sintering technique that employs a pulsed direct current (DC) to powders subject to a modest applied pressure (
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