Activated sintering of tungsten with nickel additions

Summary

• 1. A study was made of the influence of sintering temperature, nickel content, and the method of introduction of nickel into the compact on various properties of tungsten bars. It was demonstrated that: a) The density, strength, and microhardness of tungsten bars increase within the temperature range 1000–2000°C with rise in sintering temperature and nickel content of compacts (up to 0.5 wt.%); b) the decrease in the strength and other characteristics of tungsten at sintering temperatures of 1600–1800°C is due to an intensive “sweating out” of the nickel addition, which exceeds the rate of sintering in the presence of nickel; c) the rate of growth of tungsten grains increases with rising temperature and nickel content. At temperatures below the melting point of nickel, the size of tungsten grains in specimens with nickel powder additions is smaller than in specimens with nickel introduced in the form of an aqueous solution; d) the properties of tungsten bars are practically independent of the method of introduction of nickel; e) the optimum size of the activating nickel addition is 0.5 wt.%.

• 2. A hypothesis is advanced according to which the activating action of nickel consists in the yielding by nickel of some unlocalized electrons to the tungsten atoms, which results in a decrease in the energy reserve of the whole system. This enables sintering to be performed at relatively low temperatures, without the generation of energetically stable configurations formed by the localized valence electrons of tungsten.