ASTM C664-87(1999)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:C664–87(Reapproved1999)
Standard Test Methods for
Thickness of Diffusion Coating
This standard is issued under the fixed designation C 664; 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 1.7 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 These test methods cover two procedures for measuring
responsibility of the user of this standard to establish appro-
the thickness of diffusion coatings.
priate safety and health practices and determine the applica-
1.2 Test Method A is the determination of the dimensional-
bility of regulatory limitations prior to use.
change thickness, defined as the difference in the thickness of
the part before and after coating. (The terms micrometer
2. Referenced Documents
thickness and part growth are considered synonymous with
2.1 ASTM Standards:
dimensional change thickness.)
D 374 Test Methods for Thickness of Solid Electrical Insu-
1.3 Test Method B is the determination of total coating
lation
thickness, defined as the distance between the observably
E 3 Methods of Preparation of Metallographic Specimens
unaffected substrate and the exterior surface of the coating.
This includes the total of all included phases, zones and layers.
3. Significance and Use
(Thetermcasedepthisconsideredtobesynonymouswithtotal
3.1 A diffusion coating is one produced by causing an
coatingthickness.)Thetotalcoatingthicknessisdeterminedby
element or elements to react with or diffuse into, or both, the
cross-sectioning the coating, preparing a metallurgical mount
surface of a metallic substrate, thus chemically altering the
and microscopically measuring the coating thickness.
substrate adjacent to the surface. To appreciate the significance
1.4 The total coating thickness as determined microscopi-
of coating thickness measurements one must understand the
cally from a cross-section will usually be greater than, or equal
contributions to a particular coating of solid-solution zones in
to, the dimensional change thickness determined by part
the substrate and reaction products such as intermetallic
growth. When the coating is produced primarily by reaction
compounds.
withthesubstrate,thesubstrate-coatinginterfacerecedesasthe
substrate is consumed in the reaction. In such cases the
4. Test Method A
difference between the total coating thickness and the dimen-
4.1 Apparatus—The instrument shall be a machinist’s type
sional change thickness is the thickness of the substrate
micrometer without a locking device. If calibrated in inches, it
consumed.
shall be constructed with a vernier reading to 0.0001 in. (0.1
1.5 Diffusion coatings are usually formed at elevated tem-
mil). If calibrated in metric units, it shall be capable of reading
peratures for service at elevated temperatures. This means that
to 0.01 mm. It shall have a ratchet or similar mechanism, such
diffusion coatings are dynamic systems which are continually
as a friction thimble, for controlling measuring pressure and
undergoing changes while in an elevated-temperature environ-
shall have anvil and spindle surfaces 6.006 0.03 mm (0.250 6
ment. It is necessary to know that certain phases are growing at
0.001 in.) in diameter. It shall meet all other requirements and
the expense of others and to know the previous history of a
calibration procedure for Method A of Test Method D 374.
coating to understand the significance of coating thickness
4.2 Procedure:
data.
4.2.1 Clean the area selected for coating-thickness measure-
1.6 Values in SI units are to be regarded as the standard.
ment of dust or other powdery materials prior to coating.
Inch-pound units are provided for information only.
Record the precise area to be measured, so that the same area
can be remeasured after coating.
These test methods are under the jurisdiction of ASTM Committee B-8 on
Metallic and Inorganic Coatingsand are the direct responsibility of Subcommittee
B08.12on Materials for Porcelain Enamel and Ceramic-Metal Systems.
Current edition approved Aug. 28, 1987. Published October 1987. Originally Annual Book of ASTM Standards, Vol 10.02.
published as C 664 – 70. Last previous edition C 664 – 70 (1981). Annual Book of ASTM Standards, Vol 03.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C664
4.2.2 Take a minimum of two readings, using the machin- the coating a minimum of 2503 diameters, although 5003 is
ist’s micrometer, in each area selected. Use the same procedure preferable. When measuring from ground glass, measure the
for using the micrometer as that stipulated in Test Methods image of the coating to the closest 1.27 mm (0.05 in.). The
D 374. exterior bounds of the coating is the average of the peaks and
4.2.3 Aftertheparthasbeencoatedandthesurfacehasbeen
...