Oxidation Resistant High Temperature Protective Coatings for Tungsten

摘要

A controlled process has been estabilished for application of (silicon-tungsten) and titanium + zirconium + (silicon-tungsten) coatings to tungsten sheet. Protective capabilities of these coatings on arc cast and powder product tungsten sheet have been determined at one atmosphere (air) from 1600 to 3600F under cyclic conditions. Exposure at static pressures below 15 mm Hg (air) at 3400-3500F resulted in varying degrees of deterioration of the (silicon-tungsten) and titanium + zirconium + (silicon-tungsten) coatings. Under dynamic low pressure conditions (2000-2800 ft/sec simulated air flow) at 16-20 mm Hg both coatings were protective to tungsten and resisted erosion in the temperature range of 2900-3400F (180 to 325 BTU/sq ft/sec heat flux range). Various refractory compound mixtures plasma sprayed on tungsten sheet were not protective at elevated temperatures in air. A silicon-tungsten + titanium nitride-boron nitride coating combination protected tungsten for short periods of time at 3700F. Tensile properties were determined for silicontungsten and titanium + zirconium + (silicon-tungsten) coated arc cast tungsten sheet at various temperatures to 3300F. In stress oxidation tests the same systems loaded at 20 percent of the yield strength showed essentially no creep after 1 hour at 3350F in air. The coatings were completely protective at this stress level. (Author)