agent shall be agreed between the purchar and manufacturer
of the coating and shall meet the following requirements.3
5.1.1The bonding agent shall be capable of bonding the
coating to the loading fixture with a tensile strength that is at
least as great as the minimum required adhesion and cohesion
strength of the coating.
5.1.2The bonding agent shall be sufficiently viscous not to
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
satisfactory.If any other bonding agent is to be ud,it shall
first be compared with a proven bonding agent using this test
method with the desired thermal spray coating.
N OTE 2—Thermal spray coatings may have an inherent porosity.
Excessive penetration of the adhesive bonding agent into this porosity
may affect the results determined by this test method.Unless proved satisfactory by comparison testing,any agent requiring elevated tempera-ture for curing should be avoided becau viscosity may decrea at high temperature,allowing penetration.N OTE 3—When liquid epoxy bonding agents are ud,there should be a procedure in place to ensure relatively consistent thickness on every sample.5.1.3The adhesion strength of the bonding agent shall be determined each time this test method is performed.This shall be done by using the bonding agent to attach a loading fixture to a cond loading fixture,in accordance with 6.5,except that the coated substrate fixture of 6.5is replaced with the cond loading fixture.N OTE 4—One reason for testing the bonding agent each ti
me is to detect improper preparation of the agent if it is a two-part mix.Another reason is that adhesion strength generally decreas with age of the unud agent.If strength is lower than required,more adhesive bonding agent shall be
prepared and tested,or the agent shall be discarded and replaced.
6.Test Specimens 6.1Substrate and Loading Fixtures —Each test specimen is an asmbly comprising a substrate fixture,to which the
3A list of satisfactory bonding agents is provided in the annex which follows this
standard.Metric Equivalents
in.
3⁄161⁄
43⁄
41
11⁄8
17⁄16
11⁄2
21⁄2
(mm )(4.8)(6.4)(19)(25.4)(29)(37)(38)(64)
FIG.1Self-Aligning
Device
coating is applied,and a loadingfixture.The substrate and loadingfixtures shall each be circular,solid cylinders of no less than1.5in.in length,or as agreed upon by the manufacturer and customer.A suggested detail for eitherfixture is shown in Fig.2.One end of eachfixture shall be adapted for attachment to the lf-aligning loading devices of the tension testing machine.Both ends of eachfixture shall have faces parallel to each other and normal to the loading axis.The facing diameters shall be not less than0.9in.(23mm),nor more than1.0in.(25 mm).The diameters of the twofixtures shall be the same and shall be measured so that the error is no greater than0.5%. N OTE5—In Appendix X1,an alternative substrate andfixture arrange-ment is provided that has proved cost effective and simple.
6.1.1Material for Substrate Fixture—The substratefixture shall be constructed of metal,preferably metal intended for u as the substrate for the coating.If no such substrate material is specified,the substratefixture shall be SAE1018or1020steel. N OTE6—If desired becau of cost or ea of fabric
ation,it may be suitable to attach or bond a layer of the specified substrate material to a fixture formed of any convenient metal.Such a layer of substrate material need not be metal.The layer must be substantially thicker than the possible depth of effects on the substrate,such as recrystallization or diffusion zones,that may result from applying the coating.A layer greater than0.1in.(2.5mm)thick should be sufficient.
6.1.2Material for Loading Fixture—The loadingfixture shall be constructed of metal,but material is otherwi op-tional.It is usually convenient to make the loadingfixture of the same material as the substratefixture;thus,thefixtures may be interchangeable until a coating is applied to one.
6.2Coating Application—The front facing of the substrate fixture shall be prepared in the manner required by the specification for the coating.(Roughening by grit blasting or surface grinding may be typical preparations.)The coating shall be thermal sprayed onto this prepared surface.
6.3Coating Thickness—The coating thickness shall be measured with a micrometer by measuring the total length of the coatingfixture before and after the coating is applied.(Care must be taken to avoid contaminating the prepared surface before coating.)Thefinal coating thickness shall be more than 0.015in.(0.38mm).If the coating is to be ground or machined, the as-sprayed coating shall be ap
proximately0.005in.(0.13 mm)thicker to allow for removal of material.The coating thickness shall not vary across the surface by more than0.001 in.(0.025mm).(This thickness variation,as measured from
the U.S.0.003in.1⁄64in.31⁄64in.1⁄2in.5⁄8in.
Metric(0.08mm)(0.39mm)(12.3mm)(12.7mm)(15.9mm)
U.S.3⁄4in.0.990in.1in. 1.000in.1ft.24in.
Metric(19mm)(25.15mm)(25.4mm)(25.4mm)(0.3m)(610mm)
FIG.2Substrate and Loading
Fixture
rear face,does not refer to the ordinary surface texture or
roughness typical of thermal spray coatings.)If,upon comple-
tion of the thermal spraying,the coating thickness varies in
excess of this limit,this shall be corrected by removing the
coating and respraying or by grinding or machining the coating
surface.
6.4Grinding or Machining the Coating Surface —The sur-
face of the coating may be finished by grinding or machining
when the thickness variation is excessive.If the thickness
variation is not excessive,it shall be optional to finish the
surface of the coating as a uful and convenient aid in holding
the fixtures together parallel and aligned as required for the
next step.No specific grinding or machining procedure can be
recommended,as this depends on the type of coating material.
Usually manufacturers of the coatings have recommendations
published or available.Only a rough grinding or machining
step is needed,to provide a final coating thickness that does not
vary by more than 0.001in.(0.025mm).Removal rate shall be
insufficient to damage the coating or bond.A recommended
method is to u a surface grinder with a magnetic chuck,
positioning the rear face of the coated fixture on this magnetic
chuck.No other treatment,such as grit blasting,shall be done
to the surface of the coating.
6.5Attachment of Fixtures —The facing of the loading
fixture shall be free of oil,grea,or grinding or cutting fluids.
The facing shall be mechanically cleaned by such means as
machining,grinding,light grit blasting,or rubbing with emory
cloth.This facing shall be attached to the surface of the
coating,using the adhesive bonding agent according to its
manufacturer’s instructions.Excessive adhesive shall be wiped
from the asmbly with soft paper or cloth.The two fixtures
shall be held together parallel and aligned until the bonding
agent is cured or hardened.A suitable holding device such as a
“V-block”shall be ud for the purpo,except such a device
is not necessary if the surface of the coating has been ground
or machined smooth.
6.6Number of Test Specimens —The number of test speci-
mens chon depends upon the purpo of the particular tests
under consideration.However,if specimens are to be ud for
acceptance tests,not less than five specimens of a type shall be
tested.
7.Procedure
7.1Prepare the chon number of substrate fixtures,and apply a thermal spray coating to each.Finish the coating surface if required.7.2Prepare the adhesive bonding agent.Attach cleaned loading fixtures to all the coated substrate fixtures at esntially the same time.In addition,prepare one t of uncoated fixtures for measurement of the adhesion strength of the bonding agent.7.3Apply a tensile load to each test specimen at a constant rate of cross-head travel between 0.030in./min (0.013mm/s)and 0.050in./min (0.021mm/s)until rupture occurs.Record the maximum load applied.N
OTE 7—Loading fixtures may be gravity or pressure devices.The design of the loading fixtures should enable the correct alignment of the specimen.8.Calculation 8.1Calculate the degree of adhesion or cohesion strength as follows:Adhesion or cohesion strength 5maximum load/cross 2ctional area (1)9.Interpretation of Results 9.1Any interpretation of results depends on the purpo of using this test method and on the description of failure.The adhesion or cohesion strength value measured reprents the weakest part of the system,whether in the coating or at an interface.A low-power microscope with a magnification range up to 1003is suggested for determining location of failure (also termed as the “locus”of failure).9.2The adhesion strength of the coating is given if failure is entirely at the coating-substrate interface.9.3The cohesion strength of the coating is given if rupture is only within the coating.Failure in the bonding agent may be a satisfactory result for a quality control assurance test or for a qualification test,if the strength of the bonding agent is greater than the minimum required adhesion or cohesion strength of the coating.9.4If failure occurs in a combination of the locations in one specimen,generally no interpretation of the initial cau can be provided.Fig.3diagrams the possible modes of failure.9.5For a multicomponent system;for example,a bond coat with a ceramic overlay,then failure at the interface between two coatings is described as “internal
adhesive.”
FIG.3Nomenclature of Specimen Components and Classification of Failure
Locii
10.Report
10.1The report shall include the following:
10.1.1Coating material or manufacturer’s designation tech-nique ud to apply the coating,including type of thermal spray equipment,and spray parameters.
10.1.2Final coating thickness and statement of whether surface isfinished or as-sprayed.
10.1.3Substrate material.
10.1.4Description of surface preparation of substrate. 10.1.5Name or description of bonding agent and details of bonding procedure if different from manufacturer’s instruc-tions.
10.1.6Number of thermal spray specimens and number of specimens tested.
10.1.7The adhesion or cohesion strength of each specimen tested.
10.1.8Average adhesion and cohesion strength,and the maximum and minimum values,in pounds per square inch(or pascals).
10.1.9Description of failure,including statement of whether failure occurred at the coating-substrate interface,in the coating,in the bonding agent,or a combination of the.For multilayered coatings,an internal adhesion failure also must be indicated if it is prent.Fig.3diagrams the possible modes of failure.
10.1.10Adhesion strength of the bonding agent in the test specimen without a thermal spray coating.
11.Precision and Bias
11.1No justifiable statements can be made regarding the precision and bias of this test method becau it evaluates coatings that exhibit brittle fracture,an unpredictable charac-teristic.
11.2This test method is applicable to a wide variety of materials with different characteristics.
11.3Since design,ba metal composition,fabrication,and processing,as well as thermal spraying the coating,will give ri to variables in adherence,each application of this test method should have tolerances and interpretation of adherence t and agreed upon between the purchar and the manufac-turer.
12.Keywords
12.1adhesion strength;cohesion strength;fracture locus; thermal spray coatings
ANNEX
(Mandatory Information)
A1.ADHESIVE BONDING AGENTS FOR ATTACHMENT OF LOADING FIXTURE TO THERMAL SPRAY COATINGS
A1.1The following adhesive is recommended for attaching the loadingfixture to thermal spray coatings that are primarily metallic or that have a metal matrix.It is not recommended for thermal spray oxide or other porous ceramic coatings becau of the possibility of excessive penetration into the coating.This is a two-part mix that is cured at300°F(149°C)for1h.When the adhesive is new,typical adherence strength to thermal spray coatings may range up to approximately8000psi(55 MPa)depending on the coating material.
A1.1.1CONAP1222,manufactured by CONAP Inc.,184 E.Union St.,Allegheny,NY14706.
A1.2The following adhesives are recommended for attach-ing the loadingfixture to thermal spray coatings of any type, ceramic or metallic.The are two-part mixes that should be cured at room temperature when ud for this test method. When the adhesive is new,typical adherence strength to thermal spray coatings may range up to approximately4000psi (28MPa)depending on the coating material.
A1.2.1Bondmaster M666or M777,manufactured by Pitts-burgh Plate Glass Co.,Adhesive Products D
iv.,225Belleville Ave.,Bloomfield,NJ07003(M777may be easier to u as it may be more viscous than M666).
A1.2.2Epon911F,manufactured by Shell Chemical Co., Adhesives Dept.,P.O.Box831,Pittsburgh,CA94565.
A1.2.3Armstrong A-12,manufactured by Armstrong Prod-ucts Co.,Argonne Rd.,Warsaw,IN46580.
A1.2.4Hysol XA7-H368Grey,manufactured by Hysol Inc.,Olean,NY
14760.
APPENDIX
X1.ALTERNATIVE SUBSTRATE AND FIXTURE ARRANGEMENT
X1.1See Fig.X1.1for an alternative substrate and fixture arrangement that has proved cost effective and simple.
BIBLIOGRAPHY
(1)F.J.Hermanek,“Determining the Adhesive and Cohesive Strengths
of Thin Thermally Sprayed Coatings,”Welding J.,V ol 57,1978,pp.
31–35.
(2)P.Ostojic and C.C.Berndt,“Variability in Strength of Thermally
Sprayed Coatings,”J.Surf.Coat.Tech.,V ol 34,1988,pp.43–50.
(3)C.C.Berndt,“Tensile Adhesion Testing Methodology for Ther-
mally Sprayed Coatings,”ASM J.Mater.Eng.,V ol.12,No.2,1990,
pp.151–160.
(4)W.Han,E.F.Rybicki,and J.R.Shadley,“An Improved Specimen
Geometry for ASTM C 633–79to Estimate Bonds Strengths of Thermal Spray Coatings,”J.Thermal S
pray Technology ,V ol.2,No.2,1993,pp.145–150.(5)C.K.Lin and C. C.Berndt,“Measurement and Analysis of Adhesion Strength for Thermally Sprayed Coatings,”J.Thermal Spray Technology ,V ol.3,No.1,1994,pp.75–104.(6)D.J.Greving,J.R.Shadley,and E.F.Rybicki,“Effects of Coating Thickness and Residual Stress on the Bond Strength of ASTM C 633–79Thermal Spray Coating Test Specimens,”J.Thermal Spray Technology ,V ol.3,No.4,1994,pp.
371–378.FIG.X1.1Alternative Load Train Geometry for Test
Asmbly
