Tantalum machining

Jets for continuous filament textile yam are typically 1 cm diameter gold—platinum ahoy stmctures with 20—500 holes of 50—200 p.m diameter. Tire yam jets are also 1 cm in diameter but typicahy use 1000—2000 holes to give the required balance of filament and yam denier. Staple fiber jets can have as many as 70,000 holes and can be made from a single dome of ahoy or from clusters of the smaller textile or tire yam jets. The precious metal ahoy is one of the few materials that can resist the harsh chemical environment of a rayon machine and yet be ductile enough to be perforated with precision. Glass jets have been used for filament production, and tantalum metal is a low cost but less durable alternative to gold—platinum. 

Straight WC—Co tools are not suitable for machining steels that produce long chips because straight grades undergo crater wear from diffusion of WC into the steel chip surface. However, soHd solutions of WC—TiC, WC—TiC—TaC, etc, resist this type of chemical attack. In addition, tantalum carbide can improve thermal-shock resistance. Steel cutting compositions thus typically contain WC—TiC—(Ta,Nb)C—Co. Tantalum carbide is often added as (Ta,Nb)C because the chemical similarity between TaC and NbC makes their separation expensive. 

Machining Tantalum is readily machined using high-speed-steel tools, provided a lubricant such as trichloroethane is employed. 

The refractory metals for which CVD is commonly used to produce free-standing shapes are tungsten, niobium, rhenium, tantalum, molybdenum, and nickelb lb lb l (see Ch. 6). Shapes presently produced include rods, tubes, crucibles, manifolds, ordnance items, nozzles, and thrust chambers. They are usually deposited on a disposable mandrel of copper, molybdenum, or graphite which is subsequently machined off or removed chemically by etching. 

The NPL (Figure 11.12) is based on the trap described by Schrama et al. [32] The outer electrodes (very fine hollow tubes of tantalum of 1 mm inner diameter and 2 mm outer diameter) are grounded, but they can receive a small DC potential. The inner electrodes, also in tantalum, are ca 0.5 mm diameter and separated from the outer electrodes by 0.56 mm. The amplitude of the RF potential is 260 Vp p at a frequency of 17.8 MHz, resulting in secular frequencies for strontium ion of 1.8 MHz (radial) and 3.0 MHz (axial). The electrodes are isolated from each other with a ceramic tube and the trap is mounted on a structure of machinable macor. Two compensation... 

Cleaning and degreasing of tantalum parts must be done after metalworking and machining in order to remove adherent greases and scales. It presents no special problems, and conventional methods and materials maybe used. However, owing to hydrogen embrittlement and corrosion by alkaline solutions, hot caustics (e.g., NaOH and KOH) must be avoided. 

Table 4.82. Tantalum metal machining and forming facilities...

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