ASTM B875-96(2003)
(Specification)Standard Specification for Aluminum Diffusion Coating Applied by Pack Cementation Process
Standard Specification for Aluminum Diffusion Coating Applied by Pack Cementation Process
SCOPE
1.1 This specification covers the requirements for aluminum diffusion of metals by the pack cementation method. Pack diffusion employs the chemical vapor deposition of a metal which is subsequently diffused into the surface of a substrate at high temperature. The material to be coated (substrate) is immersed or suspended in a powder containing aluminum (source), a halide salt (activator), and an inert diluent such as alumina (filler). When the mixture is heated, the activator reacts to produce an atmosphere of aluminum halides which transfers aluminum to the substrate for subsequent diffusion. The aluminum-rich surface enhances corrosion, thermal stability, and wear-resistant properties.
1.2 This standard does not purport to address all of 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.
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Designation: B 875 – 96 (Reapproved 2003)
Standard Specification for
Aluminum Diffusion Coating Applied by Pack Cementation
Process
This standard is issued under the fixed designation B 875; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope C 664 Test Methods for Thickness of Diffusion Coating
D 3951 Practice for Commercial Packaging
1.1 Thisspecificationcoverstherequirementsforaluminum
E 3 Practice for Preparation of Metallographic Specimens
diffusion of metals by the pack cementation method. Pack
F 1330 Guide for Metallic Abrasive Blasting to Descale
diffusion employs the chemical vapor deposition of a metal
Surfaces of Pipe
which is subsequently diffused into the surface of a substrate at
high temperature. The material to be coated (substrate) is
3. Terminology
immersed or suspended in a powder containing aluminum
3.1 Definitions used in this specification are in accordance
(source), a halide salt (activator), and an inert diluent such as
with Terminology B 374.
alumina (filler). When the mixture is heated, the activator
3.2 Definitions of Terms Specific to This Standard:
reacts to produce an atmosphere of aluminum halides which
3.2.1 diffusion coating—a diffusion coating is one produced
transfers aluminum to the substrate for subsequent diffusion.
by causing an element to react with or diffuse into, or both, the
The aluminum-rich surface enhances corrosion, thermal stabil-
surface of a metallic substrate, thus, chemically altering the
ity, and wear-resistant properties.
surface of the substrate.
1.2 This standard does not purport to address all of the
3.2.2 retorts—containers in which powder and parts are
safety concerns, if any, associated with its use. It is the
packed for processing. They can be constructed of carbon,
responsibility of the user of this standard to establish appro-
stainless, or high alloys and fabricated in all shapes and sizes
priate safety and health practices and determine the applica-
to accommodate parts being processed.
bility of regulatory limitations prior to use.
3.2.3 significant surface—areas that are essential to the
2. Referenced Documents serviceability or function of the article.These surfaces must be
identified on a drawing or marked-up sample of product.Areas
2.1 ASTM Standards:
can fall into one of three categories as follows:
B 374 Terminology Relating to Electroplating
3.2.4 coating required—these surfaces must be in accor-
B 487 Test Method for Measurement of Metal and Oxide
dance with all quality requirements of this specification.
CoatingThicknessbyMicroscopicalExaminationofCross
3.2.5 no coating required—these surfaces are areas where
Section
no coating is allowed due to a number of reasons including
B 567 Test Method for Measurement of Coating Thickness
dimensional, fabrication, and welding, as well as others.
by Beta Backscatter Method
Materials used for masking are commercially available.
B 602 Test Method for Attribute Sampling of Metallic and
3.2.6 optional—these surfaces do not require coating, but at
Inorganic Coatings
the same time do not require masking.
B 697 Guide for Selection of Sampling Plans for Inspection
of Electrodeposited Metallic and Inorganic Coatings
4. Classification
B 762 Test Method of Variables Sampling of Metallic and
4.1 Therearethreeclassesofaluminumdiffusiondefinedby
Inorganic Coatings
base (basis) metal category.
4.1.1 Class I—Carbon steel and low alloy.
This specification is under the jurisdiction of ASTM Committee B08 on
4.1.2 Class II—Stainless steels.
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee
4.1.3 Class III—Nickel-based alloys.
B08.08.01 on Engineering Coatings.
Current edition approved Sept. 10, 2003. Published Sept. 2003. Originally
5. Ordering Information
approved in 1996. Last previous edition approved in 1996 as B 875 – 96.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
5.1 In order to make the application of this specification
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
complete, the purchaser shall supply the following information
Standards volume information, refer to the standard’s Document Summary page on
to the vendor through a purchase order and drawings:
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B 875 – 96 (2003)
5.1.1 Title,ASTM designation number, and date of issue of 6.5 Post-Cleaning—Retorts should be allowed to cool suf-
this specification. ficiently before opening. When parts are removed from retorts,
5.1.2 Deposit by classification (see Section 4). residual pack mix is removed from surfaces by a supplier-
5.1.3 Composition and metallurgical condition of substrate approved method.
to be coated. 6.6 Diffusion Heat Treatment—Parts processed in high ac-
5.1.4 Location of significant surfaces (see 3.2.3). tivity packs are placed in the retort and under inert atmosphere
5.1.5 Samples for destructive metallurgical test (see 8.1). ofargonorhydrogenareheatedto1900to2000°Fandheldfor
5.1.6 Any post heat treatment required. the amount of time needed to produce the desired level of
5.1.7 Acceptance inspection procedure to be used (see diffusion.
Section 9). 6.7 Post-Straightening—Long tubes may have distortion
5.1.8 Any requirement for certification (see Section 11). due to the high temperature of process. Use rotary straightener
or hydraulic press to restore straightness and ovality.
6.8 Visual Inspection—Inspect in accordance with 7.3.
6. Processing Requirements
6.9 Marking and Packaging—To be defined by the pur-
6.1 Substrate Preparation—The metal to be aluminized
chaser in the purchase order. Parts processed for the U.S.
shall be free of flaws and defects that will be detrimental to the
government and military, including subcontracts, shall be
coating. Thorough cleaning is essential to ensure satisfactory
packaged in accordance with Practice D 3951.
diffusion. Materials used for cleaning should not damage the
base metal. Oils, dirt, grease, and stains must be removed.
7. Coating Requirements
When blasting is also required, use aluminum oxide (90 to 220
7.1 Diffusion Thickness—The following are minimums for
mesh) at 60 to 80 psi from 4 to 6 in. standoff.
the different classes of materials based on standard process
6.2 Pack Mix—Can be categorized by the following:
parameters. Thicker coatings require special processing and
6.2.1 Types of Activity:
must be called out for in the purchase order if required.
6.2.1.1 High Activity—Deposit aluminum rapidly and per-
Class Minimum, in.
form at temperatures (1000 to 1500°F). This is usually fol-
Class I (carbon and low alloy) 0.005
lowed by a diffusion heat treatment at (1900 to 2000°F).
Class II (stainless steels) 0.003
6.2.1.2 Low Activity—Deposit aluminum slowly and per- Class III (nickel-base alloys) 0.001
form at temperatures in excess of 1650°F.
7.2 Aluminum Content—The outer 15 % of coating shall
6.2.2 Materials:
contain a minimum of 28 % (by weight) aluminum.
6.2.2.1 Masteralloy with 50 to 100 % Pure Aluminum—
7.3 Appearance—The diffusion zone shall be nonporous
Sold under a number of trade names in various mesh sizes.
andadherenttothebasemetalandshallhaveauniformsurface
Percentage in mix depends on material being processed.
free from objectionable imperfections. Minor variations in
6.2.2.2 Activator—Most commonly used is ammonium
color and surface appearance shall be considered acceptable,
chloride, but many others are available
...
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