A study on the improvement of the sintered density of W-Ni-Mn heavy alloy

Abstract

Liquid phase sintering behavior of 90W-6Ni-4Mn heavy alloy has been studied. The present work takes into account the thermodynamic oxidation/reduction reactions of the constituent elements W, Ni, and Mn. The sintering cycle consists of heating under high purity nitrogen gas, holding at reduction temperatures after the atmosphere is changed to dry hydrogen, and sintering at 1260 ЊC for 1 hour. As the reduction temperature increases from 1050 ЊC to 1200 ЊC, the relative sintered density increases from 92 pct, reaching 100 pct at temperatures above 1150 ЊC. The relative density increases with increasing holding time at the reduction temperature and remains unchanged with heating rate. The sintered microstructure has been analyzed by a scanning electron microscope and energy dispersive X-ray spectroscopy. The relative density was compared with those obtained from other investigators. It is found that the formation of manganese oxide due to reducing reactions of W and Ni powders should be avoided in order to obtain a W-Ni-Mn heavy alloy without pores.

Effect of Uniform Distribution of Fine Cementite on Hydrogen Embrittlement of Low Carbon Martensitic Steel Plates

“…As described above, cementite is a low-energy hydrogen trap state, [17][18][19][20] while the results by K. Takai et al 39) suggest that hydrogen trap state at cementite can be high-energy with plastic deformation.…”

“…and cementite. [17][18][19][20] Some alloy carbides and inclusions such as NbC 31) and MnS 32) should also play some role as hydrogen trap sites in these steels; however, their role would be negligible compared to that of other trap sites due to their small volumes.…”

“…Figure 6 shows that the peak 1 hydrogen in the studied steels is reversible hydrogen, which diffuses in a material at room temperature, since a large part of the peak 1 hydrogen egressed within 48 h. Trap sites responsible for the peak 1 should include cementite due to its low-energy hydrogen trap state. [17][18][19][20] Figure 12 shows hydrogen desorption profiles of TDA of hydrogen-charged slowly-heated and rapidly-heated Steel-B shown in Fig. 10.…”

“…Cementite acts as a brittle fracture origin 16) and a hydrogen trap site [17][18][19][20] and would accordingly affect toughness and hydrogen embrittlement resistance. Accordingly, the cementite morphology and distribution were observed with TEM.…”

The effect of managanese addition on the microstructure of W-Ni-Fe heavy alloy

“…RECENTLY, the addition of Mn into conventional heavy alloy, which consists of W, Ni, and Fe, has received attention to give rise to increased self-sharpening ability that stems from the localized adiabatic shear band of the penetrator, [1,2,3] because it is considered that the increased self-sharpening ability leads to superior penetration performance in kinetic energy ammunition. [4] The enhancement of the adiabatic shear band in the Mn containing alloy is based on the lowered thermal conduction, which promotes thermal softening rather than work hardening, through the material due the extremely low thermal conductivity of Mn compared to those of the other constituents such as W, Ni, and Fe, as shown in Table 1.…”