Partition of tungsten in the matrix phase for liquid phase sintered 93%W-4.9%Ni-2.1%Fe

Interfacial reaction-controlled reprecipitation of W atoms in liquid matrix phase during the sintering of W-8 pct Mo-7 pct Ni-3 pct Fe

“…The corresponding molar concentration of tungsten was slightly lower than 8.0 mole pct for W-7 pct Ni-3 pct Fe and 7.1 mole pct for W-8 pct Mo-7 pct Ni-3 pct Fe, [9] yet it was larger than 5.8 mole pct for W-4.9 pct Ni-2.1 pct Fe. [17] Thus, the competitive dissolution of tungsten and molybdenum in the liquid matrix phase, as suggested elsewhere, [7,[10][11][12] is found not to be a significantly important process. It may also be noted that the concentration of tungsten in the matrix phase for an isothermal holding time of 5 minutes was 54 wt pct, which is much higher than the maximum solubility of tungsten in nickel (30 wt pct), [14,18,19] that in Ni-30 wt pct Fe (16 wt pct), [14] that in Ni-15 wt pct Fe at 1480 ЊC (39.3 wt pct), [20] or even higher than the concentration of tungsten in the eutectic tungsten-nickel liquid phase (45 wt pct).…”

“…Although the growth of tungsten grains is generally believed to be a diffusion-controlled process, it has been pointed out that diffusion of tungsten atoms in the liquid matrix could hardly be the rate-controlling step, [17] owing to the relatively large diffusivity of tungsten atoms in the liquid matrix (about 2 ϫ 10 Ϫ9 m 2 /s at 1500 ЊC [3] ) and the short diffusion distance (about 1 m). Figure 7 shows the concentration profiles of tungsten and molybdenum, as determined by line scanning in EPMA, showing the absence of long-range concentration gradients of tungsten and molybdenum in the liquid matrix phase.…”

Recent Progress in Processing of Tungsten Heavy Alloys

“…Solid-state sintering in the range between 1350 and 1450 ∘ C [70] produces fully densified parts with high mechanical properties and negligible distortion. The results indicate that the ultimate tensile strength exhibits the highest value at a sintering temperature of 1500 ∘ C and an isothermal holding time of 40 min [71,72]. Micropowder injection molding ( PIM) is another new and fast-developing micromanufacturing technique for the production of metal and ceramic component.…”