ASTM B875-96(2008)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:B875 −96(Reapproved2008)
Standard Specification for
Aluminum Diffusion Coating Applied by Pack Cementation
Process
This standard is issued under the fixed designation B875; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D3951Practice for Commercial Packaging
1.1 Thisspecificationcoverstherequirementsforaluminum
3. Terminology
diffusion of metals by the pack cementation method. Pack
3.1 Definitions used in this specification are in accordance
diffusion employs the chemical vapor deposition of a metal
with Terminology B374.
whichissubsequentlydiffusedintothesurfaceofasubstrateat
high temperature. The material to be coated (substrate) is
3.2 Definitions of Terms Specific to This Standard:
immersed or suspended in a powder containing aluminum
3.2.1 diffusion coating—a diffusion coating is one produced
(source), a halide salt (activator), and an inert diluent such as
bycausinganelementtoreactwithordiffuseinto,orboth,the
alumina (filler). When the mixture is heated, the activator
surface of a metallic substrate, thus, chemically altering the
reacts to produce an atmosphere of aluminum halides which
surface of the substrate.
transfers aluminum to the substrate for subsequent diffusion.
3.2.2 retorts—containers in which powder and parts are
The aluminum-rich surface enhances corrosion, thermal
packed for processing. They can be constructed of carbon,
stability, and wear-resistant properties.
stainless, or high alloys and fabricated in all shapes and sizes
1.2 This standard does not purport to address all of the
to accommodate parts being processed.
safety concerns, if any, associated with its use. It is the
3.2.3 significant surface—areas that are essential to the
responsibility of the user of this standard to establish appro-
serviceabilityorfunctionofthearticle.Thesesurfacesmustbe
priate safety and health practices and determine the applica-
identifiedonadrawingormarked-upsampleofproduct.Areas
bility of regulatory limitations prior to use.
can fall into one of three categories as follows:
3.2.4 coating required—these surfaces must be in accor-
2. Referenced Documents
dance with all quality requirements of this specification.
2.1 ASTM Standards:
3.2.5 no coating required—these surfaces are areas where
B374Terminology Relating to Electroplating
no coating is allowed due to a number of reasons including
B487Test Method for Measurement of Metal and Oxide
dimensional, fabrication, and welding, as well as others.
Coating Thickness by Microscopical Examination of
Materials used for masking are commercially available.
Cross Section
3.2.6 optional—these surfaces do not require coating, but at
B602Test Method for Attribute Sampling of Metallic and
the same time do not require masking.
Inorganic Coatings
B697Guide for Selection of Sampling Plans for Inspection
4. Classification
of Electrodeposited Metallic and Inorganic Coatings
4.1 Therearethreeclassesofaluminumdiffusiondefinedby
B762Test Method of Variables Sampling of Metallic and
Inorganic Coatings base (basis) metal category.
4.1.1 Class I—Carbon steel and low alloy.
C664Test Methods for Thickness of Diffusion Coating
4.1.2 Class II—Stainless steels.
4.1.3 Class III—Nickel-based alloys.
This specification is under the jurisdiction of ASTM Committee B08 on
5. Ordering Information
Metallic and Inorganic Coatingsand is the direct responsibility of Subcommittee
B08.03 on Engineering Coatings.
5.1 In order to make the application of this specification
Current edition approved Aug. 1, 2008. Published September 2008. Originally
complete,thepurchasershallsupplythefollowinginformation
approved in 1996. Last previous edition approved in 2003 as B875–96 (2003).
DOI: 10.1520/B0875-96R08.
to the vendor through a purchase order and drawings:
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
5.1.1 Title,ASTM designation number, and date of issue of
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
this specification.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 5.1.2 Deposit by classification (see Section 4).
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B875−96(2008)
5.1.3 Composition and metallurgical condition of substrate 6.5 Post-Cleaning—Retorts should be allowed to cool suf-
to be coated. ficiently before opening.When parts are removed from retorts,
residual pack mix is removed from surfaces by a supplier-
5.1.4 Location of significant surfaces (see 3.2.3).
approved method.
5.1.5 Samples for destructive metallurgical test (see 8.1).
6.6 Diffusion Heat Treatment—Parts processed in high ac-
5.1.6 Any post heat treatment required.
tivity packs are placed in the retort and under inert atmosphere
5.1.7 Acceptance inspection procedure to be used (see
ofargonorhydrogenareheatedto1900to2000°Fandheldfor
Section 9).
the amount of time needed to produce the desired level of
5.1.8 Any requirement for certification (see Section 11).
diffusion.
6. Processing Requirements 6.7 Post-Straightening—Long tubes may have distortion
due to the high temperature of process. Use rotary straightener
6.1 Substrate Preparation—The metal to be aluminized
or hydraulic press to restore straightness and ovality.
shallbefreeofflawsanddefectsthatwillbedetrimentaltothe
6.8 Visual Inspection—Inspect in accordance with 7.3.
coating. Thorough cleaning is essential to ensure satisfactory
diffusion. Materials used for cleaning should not damage the
6.9 Marking and Packaging—To be defined by the pur-
base metal. Oils, dirt, grease, and stains must be removed.
chaser in the purchase order. Parts processed for the U.S.
Whenblastingisalsorequired,usealuminumoxide(90to220
government and military, including subcontracts, shall be
mesh) at 60 to 80 psi from 4 to 6 in. standoff.
packaged in accordance with Practice D3951.
6.2 Pack Mix—Can be categorized by the following:
7. Coating Requirements
6.2.1 Types of Activity:
7.1 Diffusion Thickness—The following are minimums for
6.2.1.1 High Activity—Deposit aluminum rapidly and per-
the different classes of materials based on standard process
form at temperatures (1000 to 1500°F). This is usually fol-
parameters. Thicker coatings require special processing and
lowed by a diffusion heat treatment at (1900 to 2000°F).
must be called out for in the purchase order if required.
6.2.1.2 Low Activity—Deposit aluminum slowly and per-
Class Minimum, in.
form at temperatures in excess of 1650°F.
Class I (carbon and low alloy) 0.005
6.2.2 Materials: Class II (stainless steels) 0.003
Class III (nickel-base alloys) 0.001
6.2.2.1 Masteralloy with 50 to 100 % Pure Aluminum
7.2 Aluminum Content—The outer 15% of coating shall
—Sold under a number of trade names in various mesh sizes.
contain a minimum of 28% (by weight) aluminum.
Percentage in mix depends on material being processed.
6.2.2.2 Activator—Most commonly used is ammonium 7.3 Appearance—The diffusion zone shall be nonporous
chloride, but many others are available. Percentage in mix andadherenttothebasemetalandshallhaveauniformsurface
depends on material and type of activity. free from objectionable imperfections. Minor variations in
color and surface appearance shall be considered acceptable,
6.2.2.3 Inert Filler—Aluminum oxide or calcined alumina
providing the require
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