Tungsten recrystallization temperature

Tungsten has Htde effect on recrystallization temperature or the high temperature properties of molybdenum. However, the Mo—30% W alloy is recognized as a standard commercial alloy for stirrers, pipes, and other equipment that is required to be in contact with molten zinc during processing of the metal and in galvanizing and die casting operations. 

FIGURE 5.37. Transition temperature, recrystallization temperature, and recommended temperature range for bending and stamping of tungsten sheet as a function of thickness [5.89]. 

Molybdenum, niobium, and tantalum (bcc crystal structure) form a continuous series of solid solutions with tungsten, but only Nb and Ta additions lead to a strong straining effect. Higher additions of Nb and Ta raise the recrystallization temperature but also increase the DBTT and thus decrease the workability. Therefore, none of these binary or ternary tungsten base alloys developed in the past [6.2] has attained commercial importance. The only important tungsten-base solid-solution alloy today is tungsten-rhenium. 

Compared to unalloyed tungsten the recrystallization temperature of doped tungsten is shifted fix>m 1000-1200°C up to 2000 °C or even higher [6.1]. 

Pentacarbonyl(diphenyl telluroketone)tungsten(II)3 Under dry nitrogen solutions of 980 mg (2 mmol) of pentacarbonyl(diphenylmethylene)tungsten in 20 ml of dichloromethane and of 1.38 g (2 mmol) of bis[triphenylphosphine]iminium tellurocyanate in 10 ml of dichloromethane, both at — 90°, are combined and stirred for 10 min at that temperature- The mixture is then chromatographed on silica gel at — 50° with pentane/dichloromethane (10 1 v/v) as the mobile phase. The blue fractions are collected, the solvent is distilled under high vacuum, and the residue is recrystallized from pentane, yield 220 mg (18%) m.p. 35° (dec.). 

The temperature dependence for work-hardened and annealed tungsten is shown in Fig. 1.11 [1.40,1.45]. At about 1600 °C, both curves coincide, i.e., at this temperature, the tungsten completely recrystallizes as it is heated to the testing temperature. 

The main structural influences can be described as follows. Any plastic deformation decreases the transition temperature by fining the structure. The higher the degree of deformation, the lower is the DBTT. An as- rolled tungsten sheet shows a DBTT of about 100-200 °C. Fine wires or foils are even ductile at room temperature. Any aimealing increases the transition temperature, and recrystallized samples show a maximum, mainly due to the coarsening of the structure (360 °C). 

Substrates. Suitable substrates for TiC deposition are the cemented carbides, such as tungsten carbide (WC) bonded with cobalt (Co), which are widely used as cutting-tool materials (see Ch. 16). Other substrates coated by TiC are molybdenum and graphite. 1 1 In the case of molydenum, it is essential to maintain the deposition temperature below 950"C, otherwise recrystallization of the metal and reduction in mechanical strength will occur. 

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