ASTM B482-1985 (2013) pdf free.Standard Practice for Preparation of Tungsten and Tungsten Alloys for Electroplating.
1.1 This practice makes recommendations of several re- ported practices for electroplating on tungsten and its alloys along with comments as a guide in the selection of a processing method for a given application. Because data on methods and results of evaluation with electroplated coatings on tungsten are limited, a recommendation of one method over another cannot be made.
1.2 This standard does not purport to address the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2.1 The several processes reported for electroplating on tungsten can be classified as either (I) providing as- deposited adhesion of the coatings or (2) depending on diffusion alloy bonding to provide such adhesion. Appraisal of the relative merits of these processes depends on the application for the coating.
2.2 The need for descaling, solvent cleaning, and alkalinesoak cleaning of tungsten is dictated by the degree of cleanliness of the surface to be coated. Remove gross scale and surface imperfections by mechanical means. Remove grease and oil by organic solvents. Remove saponifiable and dispersible surface dirt by soak cleaning in a hot alkaline cleaner.
2.3 Activation and Electroplating Two alternative methods are presented below. The selection of one process over the other should be based on preliminary experimentation. Both procedures produce as-deposited adhesion of electroplated metals on tungsten.
Because of the high melting point of tungsten, (3410°C) this metal and its alloys are used in ultra-high-temperature applications. However, tungsten oxidizes readily and the oxides offer ltte or no protection to the metal because they melt or sublime below 2200°C. Tungsten has a body-centered- cubic structure as does chromium. Its coefficient of thermal expansion is 4.3 um/m . °C; the coefficient of chromium is 6. I μm/m . °C, therefore, chromium- coated tungsten offers a reasonable match based on crystal structure and cofficient of thermal expansion. The effect of hydrogen must be considered in the design of coating systems for tungsten. Molecular hydrogen when trapped under a coating can result in failure of the part. Although failure can occur if the adhesion of the coating to the tungsten is inadequate, failure within the basis metal as rupture at laminations of stringers has been observed with off-grade tungsten.ASTM B482 free download.