1、Designation: B 875 96 (Reapproved 2003)Standard Specification forAluminum Diffusion Coating Applied by Pack CementationProcess1This standard is issued under the fixed designation B 875; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, the 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.1. Scope1.1 This specification covers the requirements for aluminumdiffusion of metals by the pack cementation met
3、hod. Packdiffusion employs the chemical vapor deposition of a metalwhich is subsequently diffused into the surface of a substrate athigh temperature. The material to be coated (substrate) isimmersed or suspended in a powder containing aluminum(source), a halide salt (activator), and an inert diluent
4、 such asalumina (filler). When the mixture is heated, the activatorreacts to produce an atmosphere of aluminum halides whichtransfers aluminum to the substrate for subsequent diffusion.The aluminum-rich surface enhances corrosion, thermal stabil-ity, and wear-resistant properties.1.2 This standard d
5、oes not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM St
6、andards:2B 374 Terminology Relating to ElectroplatingB 487 Test Method for Measurement of Metal and OxideCoating Thickness by Microscopical Examination of CrossSectionB 567 Test Method for Measurement of Coating Thicknessby Beta Backscatter MethodB 602 Test Method for Attribute Sampling of Metallic
7、andInorganic CoatingsB 697 Guide for Selection of Sampling Plans for Inspectionof Electrodeposited Metallic and Inorganic CoatingsB 762 Test Method of Variables Sampling of Metallic andInorganic CoatingsC 664 Test Methods for Thickness of Diffusion CoatingD 3951 Practice for Commercial PackagingE 3
8、Practice for Preparation of Metallographic SpecimensF 1330 Guide for Metallic Abrasive Blasting to DescaleSurfaces of Pipe3. Terminology3.1 Definitions used in this specification are in accordancewith Terminology B 374.3.2 Definitions of Terms Specific to This Standard:3.2.1 diffusion coatinga diffu
9、sion coating is one producedby causing an element to react with or diffuse into, or both, thesurface of a metallic substrate, thus, chemically altering thesurface of the substrate.3.2.2 retortscontainers in which powder and parts arepacked for processing. They can be constructed of carbon,stainless,
10、 or high alloys and fabricated in all shapes and sizesto accommodate parts being processed.3.2.3 significant surfaceareas that are essential to theserviceability or function of the article. These surfaces must beidentified on a drawing or marked-up sample of product. Areascan fall into one of three
11、categories as follows:3.2.4 coating requiredthese surfaces must be in accor-dance with all quality requirements of this specification.3.2.5 no coating requiredthese surfaces are areas whereno coating is allowed due to a number of reasons includingdimensional, fabrication, and welding, as well as oth
12、ers.Materials used for masking are commercially available.3.2.6 optionalthese surfaces do not require coating, but atthe same time do not require masking.4. Classification4.1 There are three classes of aluminum diffusion defined bybase (basis) metal category.4.1.1 Class ICarbon steel and low alloy.4
13、.1.2 Class IIStainless steels.4.1.3 Class IIINickel-based alloys.5. Ordering Information5.1 In order to make the application of this specificationcomplete, the purchaser shall supply the following informationto the vendor through a purchase order and drawings:1This specification is under the jurisdi
14、ction of ASTM Committee B08 onMetallic and Inorganic Coatings and is the direct responsibility of SubcommitteeB08.08.01 on Engineering Coatings.Current edition approved Sept. 10, 2003. Published Sept. 2003. Originallyapproved in 1996. Last previous edition approved in 1996 as B 875 96.2For reference
15、d ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Con
16、shohocken, PA 19428-2959, United States.5.1.1 Title, ASTM designation number, and date of issue ofthis specification.5.1.2 Deposit by classification (see Section 4).5.1.3 Composition and metallurgical condition of substrateto be coated.5.1.4 Location of significant surfaces (see 3.2.3).5.1.5 Samples
17、 for destructive metallurgical test (see 8.1).5.1.6 Any post heat treatment required.5.1.7 Acceptance inspection procedure to be used (seeSection 9).5.1.8 Any requirement for certification (see Section 11).6. Processing Requirements6.1 Substrate PreparationThe metal to be aluminizedshall be free of
18、flaws and defects that will be detrimental to thecoating. Thorough cleaning is essential to ensure satisfactorydiffusion. Materials used for cleaning should not damage thebase metal. Oils, dirt, grease, and stains must be removed.When blasting is also required, use aluminum oxide (90 to 220mesh) at
19、60 to 80 psi from 4 to 6 in. standoff.6.2 Pack MixCan be categorized by the following:6.2.1 Types of Activity:6.2.1.1 High ActivityDeposit aluminum rapidly and per-form at temperatures (1000 to 1500F). This is usually fol-lowed by a diffusion heat treatment at (1900 to 2000F).6.2.1.2 Low ActivityDep
20、osit aluminum slowly and per-form at temperatures in excess of 1650F.6.2.2 Materials:6.2.2.1 Masteralloy with 50 to 100 % Pure AluminumSold under a number of trade names in various mesh sizes.Percentage in mix depends on material being processed.6.2.2.2 ActivatorMost commonly used is ammoniumchlorid
21、e, but many others are available. Percentage in mixdepends on material and type of activity.6.2.2.3 Inert FillerAluminum oxide or calcined aluminais used and commercially available in numerous mesh sizes.Percentage in mix depends on material being processed andmesh size being used.NOTE 1It is import
22、ant that both proper equipment is used and timeestablished to guarantee uniform blend of pack mix.NOTE 2It is common practice to rejuvenate used mixes by addition ofcoating elements, alloys, and activators. Chemical analysis of used mixesfacilitates control of critical constituents. Disposal of used
23、 mixes must beperformed in compliance with environmental regulations.6.3 LoadingPlace pack mix and parts in retorts. Retortsize is limited by dimensions of furnace used for processing.6.4 Furnace Cycle:6.4.1 High-activity packs are heated to a temperature be-tween 1100 and 1500F and held for the amo
24、unt of time neededto produce a sufficient deposit of aluminum which after ahigh-temperature diffusion cycle meets thickness requirements.Time is also dependent on activator(s) being used.6.4.2 Low-activity packs are heated to a temperature be-tween 1650 and 2100F and held for the amount of time need
25、edto produce the desired depth of diffusion.NOTE 3Due to the high temperature of the process, a positive pressureof an inert gas, usually argon, must be maintained in retorts throughout theentire furnace cycle.6.5 Post-CleaningRetorts should be allowed to cool suf-ficiently before opening. When part
26、s are removed from retorts,residual pack mix is removed from surfaces by a supplier-approved method.6.6 Diffusion Heat TreatmentParts processed in high ac-tivity packs are placed in the retort and under inert atmosphereof argon or hydrogen are heated to 1900 to 2000F and held forthe amount of time n
27、eeded to produce the desired level ofdiffusion.6.7 Post-StraighteningLong tubes may have distortiondue to the high temperature of process. Use rotary straighteneror hydraulic press to restore straightness and ovality.6.8 Visual InspectionInspect in accordance with 7.3.6.9 Marking and PackagingTo be
28、defined by the pur-chaser in the purchase order. Parts processed for the U.S.government and military, including subcontracts, shall bepackaged in accordance with Practice D 3951.7. Coating Requirements7.1 Diffusion ThicknessThe following are minimums forthe different classes of materials based on st
29、andard processparameters. Thicker coatings require special processing andmust be called out for in the purchase order if required.Class Minimum, in.Class I (carbon and low alloy) 0.005Class II (stainless steels) 0.003Class III (nickel-base alloys) 0.0017.2 Aluminum ContentThe outer 15 % of coating s
30、hallcontain a minimum of 28 % (by weight) aluminum.7.3 AppearanceThe diffusion zone shall be nonporousand adherent to the base metal and shall have a uniform surfacefree from objectionable imperfections. Minor variations incolor and surface appearance shall be considered acceptable,providing the req
31、uirements of 7.1 and 7.2 are met (see 8.6).8. Test Methods8.1 Special Test Specimens:8.1.1 The permission or the requirements to use special testspecimens, the number to be used, the material from whichthey are to be made, and their shape and size shall be stated bythe purchaser.NOTE 4Test specimens
32、 are often used to represent coated articles in atest if these articles are of a size, shape, or material that is not suitable forthe test, or if it is preferred not to submit articles to a destructive test,because, for example, the articles are expensive or few in number. Thespecimen should duplica
33、te the characteristics of the article that influencethe property being tested.8.1.2 Special test specimens used to represent articles in anadhesion, weldability, corrosion resistance, or appearance testshall be made of the same material, shall be in the samemetallurgical condition, and shall have th
34、e same surfacecondition as the articles they represent, and they shall be placedand processed in the production lot along with the articles theyrepresent.8.2 ThicknessPerform the destructive test on samples inaccordance with Test Methods C 664. Read and record theresults in accordance with Test Meth
35、od B 487.8.3 Aluminum ContentShall be performed by beta back-scatter or X-ray fluorescence.B 875 96 (2003)28.4 Mechanical Properties (if required)Tensile testing onsamples from each process batch.8.5 Hardness Testing (if required)Macrohardness and mi-crohardness testing are both acceptable means.8.6
36、 AppearanceThe coating can be examined at up to 53magnification for conformance to appearance requirements.9. Sampling9.1 The sampling plan used for inspection of a quantity ofcoated articles shall be agreed upon by the purchaser and thesupplier.NOTE 5Usually, when a collection of coated articles, t
37、he inspectionlot (9.2), is examined for compliance with the requirements placed on thecoating, a relatively small number of the articles, the sample, is selectedat random and is inspected. The inspection lot is then classified ascomplying or not complying with the requirements based on the results o
38、fthe inspection of the sample. The size of the sample and the criteria ofcompliance are determined by the application of statistics. This procedureis known as sampling inspection. Three standards, Test Method B 602,Guide B 697, and Method B 762, contain sampling plans that are designedfor the sampli
39、ng inspection of coatings.Test Method B 602 contains four sampling plans, three for use with teststhat are nondestructive and one for tests that are destructive. The buyerand seller may agree on the plan or plans to be used. If they do not, TestMethod B 602 designates the plan to be used.Guide B 697
40、 provides a large number of plans and also gives guidancein the selection of a plan. When Guide B 697 is specified, the buyer andthe seller need to agree on the plan to be used.Method B 762 can be used only for coating requirements that have anumerical limit, such as a coating thickness. The test mu
41、st yield anumerical value, and certain statistical requirements must be met. MethodB 762 contains several plans and also gives instructions for designatingplans to meet special needs. The buyer and the seller may agree on theplan or plans to be used. If they do not, Method B 762 designates the plant
42、o be used.NOTE 6When both destructive and nondestructive tests exist for themeasurement of a characteristic, the purchaser needs to state which one isto be used so that the proper sampling plan is selected. A test may destroythe coating, but in a noncritical area; or, although it may destroy thecoat
43、ing, a tested part may be reclaimed by stripping and recoating. Thepurchaser needs to state whether the test is to be considered destructive ornondestructive.9.2 An inspection lot shall be defined as a collection ofcoated articles of the same kind that have been produced to thesame specifications, c
44、oated by a single supplier at one time orapproximately the same time under essentially identical con-ditions, and that are submitted for acceptance or rejection as agroup.9.3 If special test specimens are used to represent the coatedarticles in a test, the number used shall be that required in 8.1.1
45、.10. Rejection and Rehearing10.1 Parts that fail to conform to the requirements of thisspecification may be rejected. Rejection shall be reported to theproducer promptly in writing. In the case of dissatisfactionwith the results of a test, the producer may make a claim for arehearing. Coatings that
46、show imperfections may be rejected.11. Certification11.1 When specified in the purchase order or contract, thepurchaser shall be furnished with certifications that the samplesrepresenting each lot have been either tested or inspected asdirected by this specification and the requirements have beenmet
47、. When specified in the purchase order or contract, a reportof the test results must be furnished.12. Record Retention12.1 The seller is to maintain all job records and samples fora period of two years unless the purchaser requires a longerperiod.13. Keywords13.1 aluminizing; corrosion-resistant coa
48、tings; diffusioncoating; pack cementationASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and th
49、e riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible 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 consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your
