ASTM B875-96(2018)

Standard Specification for Aluminum Diffusion Coating Applied by Pack Cementation Process

ABSTRACT
This specification covers the requirements for aluminum diffusion of metals applied by pack cementation process. The three classes of aluminum diffusion coating, defined by the type of base metal, are as follows: Class I (carbon and low alloy steels); Class II (stainless steels); and Class III (nickel-based alloys). Specimens shall adhere to processing requirements such as substrate preparation, high and low activity pack mix, materials (masteralloys, activators, and inert fillers), loading, furnace cycle, post cleaning, diffusion heat treatment, post straightening, visual inspection, and marking and packaging. Specimens shall also adhere to coating requirements such as diffusion thickness, aluminum content, appearance, and mechanical properties (tensile strength, and macro- and micro-hardness).
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-May-2018
• ICS: 25.220.40 - Metallic coatings
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.03 - Engineering Coatings

Relations

• Replaces: ASTM B875-96(2013) - Standard Specification for Aluminum Diffusion Coating Applied by Pack Cementation Process
• Effective Date: 01-Jun-2018
• Refers: ASTM D3951-18(2023) - Standard Practice for Commercial Packaging
• Effective Date: 01-Oct-2023
• Refers: ASTM D3951-18 - Standard Practice for Commercial Packaging
• Effective Date: 01-May-2018
• Refers: ASTM D3951-15 - Standard Practice for Commercial Packaging
• Effective Date: 01-Dec-2015
• Refers: ASTM B374-06(2011) - Standard Terminology Relating to Electroplating
• Effective Date: 01-Apr-2011
• Refers: ASTM D3951-10 - Standard Practice for Commercial Packaging
• Effective Date: 15-Aug-2010
• Refers: ASTM C664-10 - Standard Test Methods for Thickness of Diffusion Coating
• Effective Date: 01-Apr-2010
• Refers: ASTM B602-88(2010) - Standard Test Method for Attribute Sampling of Metallic and Inorganic Coatings
• Effective Date: 01-Apr-2010
• Refers: ASTM B697-88(2010) - Standard Guide for Selection of Sampling Plans for Inspection of Electrodeposited Metallic and Inorganic Coatings
• Effective Date: 01-Apr-2010
• Refers: ASTM B762-90(2010) - Standard Test Method of Variables Sampling of Metallic and Inorganic Coatings
• Effective Date: 01-Apr-2010
• Refers: ASTM B487-85(2007) - Standard Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of a Cross Section
• Effective Date: 01-Mar-2007
• Refers: ASTM B374-06 - Standard Terminology Relating to Electroplating
• Effective Date: 15-May-2006
• Refers: ASTM C664-87(2005) - Standard Test Methods for Thickness of Diffusion Coating
• Effective Date: 15-Sep-2005
• Refers: ASTM B697-88(2005) - Standard Guide for Selection of Sampling Plans for Inspection of Electrodeposited Metallic and Inorganic Coatings
• Effective Date: 15-May-2005
• Refers: ASTM B602-88(2005) - Standard Test Method for Attribute Sampling of Metallic and Inorganic Coatings
• Effective Date: 15-May-2005

Overview

ASTM B875-96(2018): Standard Specification for Aluminum Diffusion Coating Applied by Pack Cementation Process defines requirements for applying aluminum diffusion coatings to metals using the pack cementation method. This process involves chemical vapor deposition followed by diffusion of aluminum into the surface of various metallic substrates at elevated temperatures. The treated surface significantly enhances corrosion resistance, thermal stability, and wear resistance, making this standard vital for industries where component longevity and protection in harsh environments are essential.

The specification covers three main classes based on substrate type:

• Class I: Carbon and low alloy steels
• Class II: Stainless steels
• Class III: Nickel-based alloys

Key Topics

Key elements and topics addressed in ASTM B875-96(2018) include:

• Process Requirements

  • Substrate preparation to remove flaws, dirt, grease, and stains
  • Formulation and categorization of the pack mix (aluminum source, halide salt activator, inert filler)
  • Processing steps: mixing, loading into retorts, furnace cycle, and post-cleaning
  • Diffusion heat treatment and post-straightening

• Coating Requirements

  • Minimum diffusion thickness varies by material class (e.g., 0.005" for carbon/low alloy, 0.003" for stainless, 0.001" for nickel-based alloys)
  • Aluminum content: the outer 15% of the coating must contain at least 28% aluminum by weight
  • Uniform appearance, adhesion, and absence of objectionable imperfections
  • Testing of mechanical properties if specified (tensile, hardness)

• Inspection and Acceptance

  • Sampling and inspection procedures, including destructive and nondestructive test methodologies
  • Certification, reporting, and record retention requirements for suppliers and purchasers

• Classification

  • Clear definition of significant surfaces, coating and masking requirements, and marking and packaging instructions

Applications

ASTM B875-96(2018) is essential in various industry sectors requiring durable, corrosion-resistant metal components:

• Power generation: Steam and gas turbine components (rotors, blades, casings)
• Petrochemical: Reactor tubes, heat exchangers, and piping exposed to aggressive atmospheres
• Aerospace: Protective coatings for aircraft engine parts and high-temperature structural components
• Automotive and Transport: Critical parts subjected to high heat and oxidation conditions
• Military and Defense: High-performance equipment requiring long-term durability in harsh environments

The pack cementation diffusion coating process governed by this ASTM standard ensures reliable protection for components subjected to extended service in corrosive and high-temperature settings.

Related Standards

For organizations aiming for full compliance and optimal process control, familiarity with referenced and related ASTM standards is critical. Key documents include:

• ASTM B697: Guide for Selection of Sampling Plans for Inspection of Electrodeposited Metallic and Inorganic Coatings
• ASTM B602 / B762: Test methods for attribute and variables sampling of metallic and inorganic coatings
• ASTM B487: Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of Cross Section
• ASTM C664: Test Methods for Thickness of Diffusion Coating
• ASTM D3951: Practice for Commercial Packaging
• ASTM B374: Terminology Relating to Electroplating

Understanding and applying ASTM B875-96(2018) alongside these related standards supports consistent, high-quality aluminum diffusion coatings by pack cementation, ensuring industrial components meet stringent performance and reliability requirements.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B875 −96 (Reapproved 2018)
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 B697Guide for Selection of Sampling Plans for Inspection
of Electrodeposited Metallic and Inorganic Coatings
1.1 Thisspecificationcoverstherequirementsforaluminum
B762Test Method of Variables Sampling of Metallic and
diffusion of metals by the pack cementation method. Pack
Inorganic Coatings
diffusion employs the chemical vapor deposition of a metal
C664Test Methods for Thickness of Diffusion Coating
whichissubsequentlydiffusedintothesurfaceofasubstrateat
D3951Practice for Commercial Packaging
high temperature. The material to be coated (substrate) is
immersed or suspended in a powder containing aluminum
3. Terminology
(source), a halide salt (activator), and an inert diluent such as
alumina (filler). When the mixture is heated, the activator
3.1 Definitions used in this specification are in accordance
reacts to produce an atmosphere of aluminum halides which
with Terminology B374.
transfers aluminum to the substrate for subsequent diffusion.
3.2 Definitions of Terms Specific to This Standard:
The aluminum-rich surface enhances corrosion, thermal
3.2.1 diffusion coating—a diffusion coating is one produced
stability, and wear-resistant properties.
bycausinganelementtoreactwithordiffuseinto,orboth,the
1.2 This standard does not purport to address all of the
surface of a metallic substrate, thus, chemically altering the
safety concerns, if any, associated with its use. It is the
surface of the substrate.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3.2.2 retorts—containers in which powder and parts are
mine the applicability of regulatory limitations prior to use.
packed for processing. They can be constructed of carbon,
1.3 This international standard was developed in accor-
stainless, or high alloys and fabricated in all shapes and sizes
dance with internationally recognized principles on standard-
to accommodate parts being processed.
ization established in the Decision on Principles for the
3.2.3 significant surface—areas that are essential to the
Development of International Standards, Guides and Recom-
serviceabilityorfunctionofthearticle.Thesesurfacesmustbe
mendations issued by the World Trade Organization Technical
identifiedonadrawingormarked-upsampleofproduct.Areas
Barriers to Trade (TBT) Committee.
can fall into one of three categories as follows:
2. Referenced Documents
3.2.4 coating required—these surfaces must be in accor-
2.1 ASTM Standards:
dance with all quality requirements of this specification.
B374Terminology Relating to Electroplating
3.2.5 no coating required—these surfaces are areas where
B487Test Method for Measurement of Metal and Oxide
no coating is allowed due to a number of reasons including
Coating Thickness by Microscopical Examination of
dimensional, fabrication, and welding, as well as others.
Cross Section
Materials used for masking are commercially available.
B602Test Method for Attribute Sampling of Metallic and
Inorganic Coatings
3.2.6 optional—these surfaces do not require coating, but at
the same time do not require masking.
This specification is under the jurisdiction of ASTM Committee B08 on
Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee
4. Classification
B08.03 on Engineering Coatings.
Current edition approved June 1, 2018. Published June 2018. Originally
4.1 Therearethreeclassesofaluminumdiffusiondefinedby
approvedin1996.Lastpreviouseditionapprovedin2013asB875–96(2013).DOI:
base (basis) metal category.
10.1520/B0875-96R18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 4.1.1 Class I—Carbon steel and low alloy.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
4.1.2 Class II—Stainless steels.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 4.1.3 Class III—Nickel-based alloys.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B875 − 96 (2018)
5. Ordering Information 6.4.2 Low-activity packs are heated to a temperature be-
tween1650and2100°Fandheldfortheamountoftimeneeded
5.1 In order to make the application of this specification
to produce the desired depth of diffusion.
complete,thepurchasershallsupplythefollowinginformation
to the vendor through a purchase order and drawings:
NOTE3—Duetothehightemperatureoftheprocess,apositivepressure
ofaninertgas,usuallyargon,mustbemaintainedinretortsthroughoutthe
5.1.1 Title,ASTM designation number, and date of issue of
entire furnace cycle.
this specification.
6.5 Post-Cleaning—Retorts should be allowed to cool suf-
5.1.2 Deposit by classification (see Section 4).
ficiently before opening.When parts are removed from retorts,
5.1.3 Composition and metallurgical condition of substrate
residual pack mix is removed from surfaces by a supplier-
to be coated.
approved method.
5.1.4 Location of significant surfaces (see 3.2.3).
6.6 Diffusion Heat Treatment—Parts processed in high ac-
5.1.5 Samples for destructive metallurgical test (see 8.1).
tivity packs are placed in the retort and under inert atmosphere
5.1.6 Any post heat treatment required.
ofargonorhydrogenareheatedto1900to2000°Fandheldfor
5.1.7 Acceptance inspection procedure to be used (see
the amount of time needed to produce the desired level of
Section 9).
diffusion.
5.1.8 Any requirement for certification (see Section 11).
6.7 Post-Straightening—Long tubes may have distortion
6. Processing Requirements
due to the high temperature of process. Use rotary straightener
or hydraulic press to restore straightness and ovality.
6.1 Substrate Preparation—The metal to be aluminized
shallbefreeofflawsanddefectsthatwillbedetrimentaltothe 6.8 Visual Inspection—Inspect in accordance with 7.3.
coating. Thorough cleaning is essential to ensure satisfactory
6.9 Marking and Packaging—To be defined by the pur-
diffusion. Materials used for cleaning should not damage the
chaser in the purchase order. Parts processed for the U.S.
base metal. Oils, dirt, grease, and stains must be removed.
government and military, including subcontracts, shall be
Whenblastingisalsorequired,usealuminumoxide(90to220
packaged in accordance with Practice D3951.
mesh) at 60 to 80 psi from 4 to 6 in. standoff.
7. Coating Requirements
6.2 Pack Mix—Can be categorized by the following:
6.2.1 Types of Activity: 7.1 Diffusion Thickness—The following are minimums for
the different classes of materials based on standard process
6.2.1.1 High Activity—Deposit aluminum rapidly and per-
parameters. Thicker coatings require special processing and
form at temperatures (1000 to 1500°F). This is usually fol-
must be called out for in the purchase order if required.
lowed by a diffusion heat treatment at (1900 to 2000°F).
6.2.1.2 Low Activity—Deposit aluminum slowly and per- Class Minimum, in.
Class I (carbon and low alloy) 0.005
form at temperatures in excess of 1650°F.
Class II (stainless steels) 0.003
6.2.2 Materials:
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.
Percentag
...