ASTM B482-85(2008)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: B482 − 85(Reapproved 2008)
Standard Practice for
Preparation of Tungsten and Tungsten Alloys for
Electroplating
This standard is issued under the fixed designation B482; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
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 little 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 µm/m · °C; the coefficient
of chromium is 6.1 µm/m · °C, therefore, chromium-coated tungsten offers a reasonable match based
on crystal structure and coefficient 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.
1. Scope 2.2 Precleaning:
2.2.1 The need for descaling, solvent cleaning, and alkaline-
1.1 This practice makes recommendations of several re-
soak cleaning of tungsten is dictated by the degree of cleanli-
ported practices for electroplating on tungsten and its alloys
ness of the surface to be coated. Remove gross scale and
alongwithcommentsasaguideintheselectionofaprocessing
surface imperfections by mechanical means. Remove grease
method for a given application. Because data on methods and
and oil by organic solvents. Remove saponifiable and dispers-
results of evaluation with electroplated coatings on tungsten
ible surface dirt by soak cleaning in a hot alkaline cleaner.
are limited, a recommendation of one method over another
2.2.2 Anodic treatment of tungsten surfaces ina5to25
cannot be made.
mass % sodium hydroxide solution at 71 6 6°C and 16 to 25
1.2 This standard does not purport to address the safety 2
A/dm can be used to remove undesired surface metal.Anodic
concerns, if any, associated with its use. It is the responsibility
etching in a 10 mass % hydrofluoric acid electrolyte at
of the user of this standard to establish appropriate safety and 2
24 6 3°C and 5.4A/dm can be used to remove light scale and
health practices and determine the applicability of regulatory
undesired surface metal before activation and electroplating of
limitations prior to use.
tungsten.
2. Processes
2.3 Activation and Electroplating —Two alternative meth-
ods are presented below. The selection of one process over the
2.1 The several processes reported for electroplating on
other should be based on preliminary experimentation. Both
tungsten can be classified as either (1) providing as-deposited
procedures produce as-deposited adhesion of electroplated
adhesion of the coatings or (2) depending on diffusion alloy
metals on tungsten.
bonding to provide such adhesion. Appraisal of the relative
2.3.1 Methods 1 —Treat the precleaned tungsten in a hy-
merits of these processes depends on the application for the
drofluoric acid electrolyte (30 6 10 mass % HF) at 24 6 3°C,
coating.
using2to5V,60-Hzac,and2to5A/dm for1to2min.Either
divide the work between two work rods or make one electrode
This prac
...