SPS densification behavior of W-5.6Ni-1.4Fe heavy alloy powders

Abstract

Spark plasma sintering (SPS) method was used to sinter two different types of 93W-5.6Ni-1.4Fe (wt pct) heavy alloy powders which were respectively prepared by simple mixing and high-energy ball milling (HEBM) for 40 h. In SPS processing, the powder compacts were heated at 100 °C/min to the desired sintering temperature with 5 min holding. The SPS densification behavior of the two types of powders was investigated. For the simple mixed powders, the compacts start to shrink around 850 °C, and the densification is enhanced by diffusion and plastic deformation with the increase of temperature. Consequently the compacts shrink effectively and obtain nearly full density around 1230 °C. While for the as-milled powders, recovery and recrystallization occur between 700 -850 °C due to the crystal lattice distortion and defects resulted from HEBM, causing the soften of particles and a slight shrink of compacts. When increasing temperature, nanosintering of W crystallines in the matrix occurs in the inside of the composite powders, and the densification rate accelerates and maximizes at about 1050 °C. Owing to the improved activity of powders from HEBM, the tungsten grains coarsen rapidly in the sintering, simultaneously, the harmful intermetallic phases Ni 2 W 4 C and Fe 6 W 6 C are generated.

Carbon uptake during Spark Plasma Sintering: investigation through the analysis of the carbide “footprint” in a Ni–W alloy

“…We can assume that during sintering, the carbon concentration gradient is established such that the concentration of carbon in the interior is still sufficient for the Ni 2 W 4 C phase to form. This phase was observed by Fabičovicová et al 22 during the preparation of Ni-W-activated carbon catalysts and by Hu et al, 23 who Spark Plasma Sintered W-Ni-Fe alloys from mechanically milled powders. In ref.…”

“…In ref. 23, the milling was carried out using tungsten carbide balls, so the powders already contained a certain ) is likely to be due to crystallite growth retardation by carbon dissolved in nickel, 24 which is present in the subsurface layer in the form of interstitial solute atoms in higher concentrations than in the interior.…”

Recent Progress in Processing of Tungsten Heavy Alloys

“…For the SPS alloyed specimen, oxide film elimination of powders may improve the binding strength of the interface [108]. According to the literature [109], by optimizing the sintering times of pulsed-and constant-currents on the milled W-4Ni-2Co-1Fe powders, the density, hardness, and transverse rupture strength of the sintered alloy reach 16.78 g/cm 3 , HRA 84.3, and 968 MPa, respectively. Meanwhile, W grain growth in sintering is effectively inhibited, and full density is obtained at approximately 1230 ∘ C with 5 min holding time [110,111].…”

Effect of High Energy Ball Milling Time on the Density and Mechanical Properties of W-7%Ni-3%Fe Alloy

“…feature of SPS technology, which allows reducing the grain growth rate [23,27]. The fine-grained HTAs obtained by SPS have simultaneously high strength and hardness [28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] (Table A1, see Appendix A).…”

“…The formation of the supersaturated solid solution of tungsten atoms in the -phase leads to manifestation of some unexpected effects. The effect of non-monotonous dependence of the density on the sintering temperature [28,29,35,[43][44][45] as well as the effect of reduction of the activation energy of sintering of the nanopowders [45] deserve high attention. One should note separately the effect of decreasing of the density of the tungsten alloys sintered from mechanically activated nanopowders [33,39,45], the nature of which remains unclear now.…”