1、Designation: B 482 85 (Reapproved 2003)Standard Practice forPreparation of Tungsten and Tungsten Alloys forElectroplating1This standard is issued under the fixed designation B 482; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONBecause of the high melting point of tungsten, (3410C) this metal and its alloys are used inultra-high-temp
3、erature applications. However, tungsten oxidizes readily and the oxides offer little orno protection to the metal because they melt or sublime below 2200C. Tungsten has a body-centered-cubic structure as does chromium. Its coefficient of thermal expansion is 4.3 m/m C; the coefficientof chromium is
4、6.1 m/m C, therefore, chromium-coated tungsten offers a reasonable match basedon crystal structure and coefficient of thermal expansion. The effect of hydrogen must be consideredin the design of coating systems for tungsten. Molecular hydrogen when trapped under a coating canresult in failure of the
5、 part. Although failure can occur if the adhesion of the coating to the tungstenis inadequate, failure within the basis metal as rupture at laminations of stringers has been observedwith off-grade tungsten.1. Scope1.1 This practice makes recommendations of several re-ported practices for electroplat
6、ing on tungsten and its alloysalong with comments as a guide in the selection of a processingmethod for a given application. Because data on methods andresults of evaluation with electroplated coatings on tungstenare limited, a recommendation of one method over anothercannot be made.1.2 This standar
7、d does not purport to address the safetyconcerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety andhealth practices and determine the applicability of regulatorylimitations prior to use.2. Processes2.1 The several processes repo
8、rted for electroplating ontungsten can be classified as either (1) providing as-depositedadhesion of the coatings or (2) depending on diffusion alloybonding to provide such adhesion. Appraisal of the relativemerits of these processes depends on the application for thecoating.2.2 Precleaning:2.2.1 Th
9、e need for descaling, solvent cleaning, and alkaline-soak cleaning of tungsten is dictated by the degree of cleanli-ness of the surface to be coated. Remove gross scale andsurface imperfections by mechanical means. Remove greaseand oil by organic solvents. Remove saponifiable and dispers-ible surfac
10、e dirt by soak cleaning in a hot alkaline cleaner.2.2.2 Anodic treatment of tungsten surfaces ina5to25mass % sodium hydroxide solution at 71 6 6C and 16 to 25A/dm2can be used to remove undesired surface metal. Anodicetching in a 10 mass % hydrofluoric acid electrolyte at24 6 3C and 5.4 A/dm2can be u
11、sed to remove light scale andundesired surface metal before activation and electroplating oftungsten.2.3 Activation and ElectroplatingTwo alternative meth-ods are presented below. The selection of one process over theother should be based on preliminary experimentation. Bothprocedures produce as-dep
12、osited adhesion of electroplatedmetals on tungsten.2.3.1 Methods 12Treat the precleaned tungsten in a hy-drofluoric acid electrolyte (30 6 10 mass % HF) at 24 6 3C,using 2 to 5 V, 60-Hz ac, and 2 to 5 A/dm2for 1 to 2 min. Eitherdivide the work between two work rods or make one electrodeof platinum.
13、After rinsing, the work is electroplated in acidelectrolytes.1This practice is under the jurisdiction of ASTM Committee B08 on Metallicand Inorganic Coatings and is the direct responsibility of Subcommittee B08.02 onPre Treatment.Current edition approved Feb. 10, 2003. Published May 2003. Originally
14、approved in 1968. Last previous edition approved in 1998 as B 482 85 (1998).2Cannizaro, J. J., U.S. Patent No. 2,433,651, June, 1948.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.2.3.2 Method 2Electroplate the precleaned tungsten w
15、itha chromium strike prior to subsequent electroplating with othermetals3,4using the following processing steps:2.3.2.1 Anodic EtchEtch anodically at 10 to 30 A/dm2inthe following solution for 2 to 5 min.KOH 30 mass %Temperature 48 to 60C2.3.2.2 Rinse.2.3.2.3 Acid NeutralizeImmerse for 1 min in 10 m
16、ass %sulfuric acid at 27 6 6C.2.3.2.4 Rinse.2.3.2.5 Chromium StrikeStrike at 15 to 25 A/dm2in thefollowing chromium solution for 1 to 3 min. Enter the solutionwith the parts cathodic.CrO3250 g/LH2SO42.5 g/LTemperature 60 to 72C2.3.2.6 Rinse.2.3.2.7 Acid ActivationImmerse in 20 mass % hydrochlo-ric a
17、cid at 21 to 33C for 2 to 5 s.2.3.2.8 Nickel StrikeStrike at 5 to 10 A/dm2in thefollowing nickel solution for 2 to 5 min.NiSO46H2O 240 g/LH2SO440 g/LTemperature 21 to 33C2.3.2.9 Rinse.2.3.2.10 ElectroplateElectroplate with desired metal.2.4 Alloying and Heating Effects:2.4.1 A number of other proces
18、ses, involving heat treating(927 6 56C) to diffusion-alloy bond an electrodeposited coat-ing to the basis tungsten have been proposed but offer noapparent advantage.2.4.2 Chromium-strike coated tungsten3,4subsequentlyelectroplated with nickel and heated for12 h at 980C shows nodeterioration of the e
19、lectroplated coatings. Chromium-tungstendiffusion does not form the weak brittle intermetallic alloyzones such as are evident when nickel, iron, or cobalt coatingson tungsten are similarly heat treated.ASTM International takes no position respecting the validity of any patent rights asserted in conn
20、ection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the respons
21、ible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful c
22、onsideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 10
23、0 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).3Korbelak, A., U.S. Patent No. 2,697,130, Dec. 14, 1954.4Marzano, C., “Plating on Tungsten,” Plating, Vol 51, 1964, pp. 207211.B 482 85 (2003)2
