Sintering of tungsten

Sintering of tungsten is activated by addition of small amounts of Pd, Ni, Fe, or other elements. Data are for 1 h at the indicated temperatures. Reprinted with permission from Powder Metallurgy Science, 1984, Metal Powder Industries Federation, 105 College Road East, Princeton, New Jersey, USA. 

FIGURE 5.33. Modem industrial aggregate for direct sintering of tungsten. By courtesy of OSRAM GmbH, Germany. 

Gessinge GH, Fischmei HF (1972) Modified model for sintering of tungsten with nickel additions. J Less-Common Metals 27 129-141... 

German RM, Munir ZA (1976) Enhanced low-temperature sintering of tungsten. Metall Trans A-Phys Metall Mater Sci 7 1873-1877... 

Sintering of powdered metals such as aluminum, beryllium, tungsten, and zinc as well as ceramics under pressure is widely practiced as a shaping process, but that is different from the sintering process described here. 

Sometimes the addition of a very small amount of a second material greatly increases the rate of sintering. Usually this can be attributed to the formation of a phase with a much lower melting point in which the diffusion is much faster. Figure 14.9 shows that the sintering rate of tungsten is drastically increased by enough of certain elements to form a four-atom-thick layer. 

Such a desintering might also be responsible for the slow uptake of hydrogen in the case of nickel and of tungsten films. The activation energy would then be due at least partly to the work that is required to reopen the capillary space closed by the previous sintering. 

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