ASTM C633-79(1999)
(Test Method)Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings
Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings
SCOPE
1.1 This test method covers the determination of the degree of adhesion (bonding strength) of a coating to a substrate or the cohesion strength of the coating in a tension normal to the surface. The test consists of coating one face of a substrate fixture, bonding this coating to the face of a loading fixture, and subjecting this assembly of coating and fixtures to a tensile load normal to the plane of the coating. It is adapted particularly for testing coatings applied by thermal spray, which is defined to include the combustion flame, plasma arc, two-wire arc, high-velocity oxygen fuel, and detonation processes for spraying feedstock, which may be in the form of, wire, rod, or powder.
Note 1--Thermal spray coating materials include ceramics, such as metal oxides or carbides, and metals. In some cases, a coating is formed of different spray materials, such as an oxide layer sprayed onto a sprayed metal-bonding layer. The substrate generally is a metal, but may be a ceramic, such as an oxide or graphite.
1.2 Usually this test method is performed at ambient temperature. Higher temperature testing is restricted by the need for a suitable adhesive bonding agent. For certain fundamental investigations, it is suggested that very low (cryogenic) temperature be used.
1.3 This test method is limited to testing thermal spray coatings that can be applied in thickness greater than 0.015 in. (0.38 mm). The limitation is imposed because an adhesive bonding agent is used in the test. Those bonding agents established so far for this method tend to penetrate thermal spray coatings and may invalidate results unless the coatings are thick enough to prevent penetration through the coating. Further development may establish that thin layers of certain types of especially dense coatings may be tested satisfactorily. Alternatively, new adhesive bonding agents that would allow reduction of the minimum thickness limitation may become available.
1.4 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 limitations prior to use.
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Designation: C 633 – 79 (Reapproved 1999)
Standard Test Method for
Adhesion or Cohesive Strength of Flame-Sprayed Coatings
This standard is issued under the fixed designation C 633; 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 2. Referenced Documents
1.1 This test method covers the determination of the degree 2.1 ASTM Standards:
of adhesion (bonding strength) of a coating to a substrate, or E 4 Practices for Force Verification of Testing Machines
the cohesive strength of the coating in a tension normal to the
3. Significance and Use
surface. The test consists of coating one face of a substrate
fixture, bonding this coating to the face of a loading fixture, and 3.1 This test method is recommended for quality-control,
acceptance testing; or it may help to develop or qualify a
subjecting this assembly of coating and fixtures to a tensile
flame-spray operator’s equipment and procedure or to aid in
load normal to the plane of the coating. It is particularly
adapted for testing coatings applied by flame spraying, which developing flame-sprayed coatings with improved adhesion
and integrity.
is defined to include the combustion flame, plasma flame, arc
gun, and detonation processes for spraying wire, rod, or 3.2 This test method is useful for comparing adhesion or
cohesive strengths of coatings of similar types of flame-
powder.
sprayed materials. The test should not be considered to provide
NOTE 1—Flame-sprayed coating materials include ceramics, such as
an intrinsic value for direct use in making calculations such as
metal oxides or carbides, and metals. In some cases a coating is formed of
to determine if a coating will withstand specific environmental
several layers of different flame-sprayed materials, such as an oxide layer
stresses. Because of residual stresses in flame-sprayed coat-
sprayed onto a sprayed metal-bonding layer. The substrate is generally a
metal, but may be a ceramic such as an oxide or graphite.
ings, actual strength is dependent upon the shape of the
particular coated part. Also, in actual use a coating is stressed
1.2 Usually this test method is performed at ambient tem-
in a much more complicated manner than is practical for a
perature. Higher temperature testing is restricted by the need
standardized test.
for a suitable adhesive bonding agent. For certain fundamental
investigation it is suggested that very low (cryogenic) tempera-
4. Apparatus
ture be used.
4.1 A tension testing machine shall conform to the require-
1.3 This test method is limited to testing flame-sprayed
ments of Practices E 4. The loads used in determining the
coatings that can be applied in thickness greater than 0.015 in.
adherence or tensile strength shall be within the loading range
(0.38 mm). The limitation is imposed because an adhesive
of the testing machine, as defined in Practices E 4. Permissible
bonding agent is used in the test. Those bonding agents
variation shall be less than 1.0 %. It shall be possible to apply
established so far for this method tend to penetrate flame-
increasing tensile load at a constant rate of cross-head travel
sprayed coatings and may invalidate results unless the coatings
between 0.030 in./min (0.013 mm/s) and 0.050 in./min (0.021
are thick enough to prevent penetration through the coating.
mm/s). The machine shall include a load-indicating device that
Further development may establish that thin layers of certain
registers the maximum load applied before rupture occurs.
types of especially dense coatings may be tested satisfactorily.
4.2 Self-aligning devices, for applying the tensile load to the
Alternatively, new adhesive bonding agents that would allow
assembly of the coating and fixtures, shall not permit eccentric
reduction of the minimum thickness limitation may be discov-
load or bending moment to the specimen. Self-alignment is
ered or developed.
often provided by the manufacturer as an integral part of the
1.4 This standard does not purport to address all of the
testing machine. An alternative, satisfactory apparatus is shown
safety concerns, if any, associated with its use. It is the
in Fig. 1, which also shows a method of connecting the
responsibility of the user of this standard to establish appro-
self-aligning apparatus to an assembled test specimen.
priate safety and health limitations prior to use.
5. Material
This test method is under the jurisdiction of ASTM Committee B-8 on Metallic
5.1 Adhesive Bonding Agent—A suitable adhesive bonding
and Inorganic Coatingsand is the direct responsibility of Subcommittee B08.12 on
Materials for Porcelain Enamel and Ceramic-Metal Systems.
Current edition approved Dec. 28, 1979. Published February 1980. Originally
published as C 633 – 69. Last previous edition C 633 – 69 (1974). Annual Book of ASTM Standards, Vol 03.01.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
C 633
Metric Equivalents
3 1 3 1 7 1 1
in. ⁄16 ⁄4 ⁄4 11 ⁄8 1 ⁄16 1 ⁄2 2 ⁄2
(mm) (4.8) (6.4) (19) (25.4) (29) (37) (38) (64)
FIG. 1 Self-Aligning Device
agent shall be agreed between the purchaser and manufacturer least as great as the minimum required adhesion and cohesive
of the coating and shall meet the following requirements. strength of the coating.
5.1.1 The bonding agent shall be capable of bonding the
5.1.2 The bonding agent shall be sufficiently viscous not to
coating to the loading fixture with a tensile strength that is at
penetrate through a 0.015-in. (0.38-mm) thickness of the
coating. Certain commercial resins that cure or harden at room
temperature by means of a curing agent have been proven
A list of satisfactory bonding agents is provided in the annex which follows this
standard. satisfactory. If any other bonding agent is to be used, it shall
C 633
first be compared with a proven bonding agent using this prior to coating.) The final coating thickness shall be more than
method with the desired flame-sprayed coating. 0.015 in. (0.38 mm). If the coating is to be ground or machined,
the as-sprayed coating shall be approximately 0.005 in. (0.13
NOTE 2—Flame-sprayed coatings generally have an inherent porosity.
mm) thicker to allow for removal of material. The coating
Excessive penetration of the adhesive bonding agent into this porosity
thickness shall not vary across the surface by more than 0.001
may affect the results determined by this test method. Unless proved
in. (0.025 mm). (This thickness variation, as measured from the
satisfactory by comparison testing, any agent requiring elevated tempera-
ture for curing should be avoided because viscosity may decrease at high
rare face, does not refer to the ordinary surface texture or
temperature, allowing penetration.
roughness typical of flame-sprayed coatings.) If, upon comple-
tion of the flame spraying, the coating thickness varies in
5.1.3 The adhesion strength of the bonding agent shall be
excess of this limit, this shall be corrected by removing the
determined each time this method is performed. This shall be
coating and respraying, or by grinding or machining the
done by using the bonding agent to attach a loading fixture to
coating surface.
a second loading fixture, in accordance with 6.5, except that the
6.4 Grinding or Machining the Coating Surface—The sur-
coated substrate fixture of 6.5 is replaced with the second
face of the coating may be finished by grinding or machining
loading fixture.
when the thickness variation is excessive as defined in 6.3. If
NOTE 3—One reason for testing the bonding agent each time is to detect
the thickness variation is not excessive, it shall be optional to
improper preparation of the agent if it is a two-part mix. Another reason
finish the surface of the coating as a useful and convenient aid
is that adhesive strength generally decreases with age of the unused agent.
in holding the fixtures together parallel and aligned as required
If strength is lower than required, more adhesive bonding agent shall be
prepared and tested, or the agent shall be discarded and replaced. for the next step, 6.5. No specific grinding or machining
procedure can be recommended, as this depends on the type of
6. Test Specimens
coating material. Usually manufacturers of the coatings have
6.1 Substrate and Loading Fixtures— Each test specimen is
recommendations published or available. Only a rough grind-
an assembly comprising a substrate fixture, to which the
ing or machining step is needed, in order to provide a final
coating is applied, and a loading fixture. The substrate and
coating thickness that does not vary by more than 0.001 in.
loading fixtures shall each be circular, solid cylinders of a
(0.025 mm). Removal rate shall be insufficient to damage the
length not substantially less than the diameter. A suggested
coating or bond. A recommended method is to use a surface
detail for either fixture is shown in Fig. 2. One end of each
grinder with a magnetic chuck, positioning the rear face of the
fixture shall be adapted for attaching to the self-aligning
coated fixture on this magnetic chuck. No other treatment such
loading devices of the tensio
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