The Metallurgy of Tungsten Heavy Alloys

       The name "tungsten" is derived from the Swedish term meaning "heavy stone".  Tungsten has been assigned the chemical symbol W after its German name wolfram.  While sometimes regarded as a scarce or exotic metal, its abundance in nature is actually about the same as that of copper.  The largest known tungsten reserves are in mainland China, though plentiful reserves also exist in North America.



  Tungsten has the highest melting point (3410C or 6170F) of all metals.  The extremely high melting point of pure tungsten makes all the common manufacturing techniques used for metals such as iron impractical.  Specialized methods make possible the processing of pure tungsten into rod, sheet, and wire for a wide variety of high temperature applications including incandescent lamp wire, TIG welding electrodes, and high temperature heat shielding.



  Another important industrial property of tungsten is its high density of 19.3 g/cc (0.70 lbs/in3).  In addition to high gravimetric density, its high radiographic density makes it an ideal material for shielding or collimating energetic x- and -radiation.  For such applications, tungsten is commonly alloyed in order to circumvent the extremely high processing temperatures that would otherwise be required to melt and cast the pure metal.  



  Tungsten heavy alloys (WHAs) are ideally suited to a wide range of density applications, offering a density approaching that of pure tungsten but without the very costly processing and inherent size and shape limitations of the former.  WHAs are produced by a powder metallurgy (P/M) technique known as liquid phase sintering (LPS), in which completely dense, fully alloyed parts are formed from pressed metal powders at a temperature less than half the melting point of pure tungsten.   While sintered steel and copper alloy parts commonly contain significant residual porosity that may require polymeric infiltrants to seal, sintered WHAs have a nonporous surface.