ASTM C633 is an ASTM test method used to measure the adhesion of a thermal spray coating to its substrate or the cohesion of the coating itself by applying tensile force normal to the coated surface. It is commonly used when bond strength is part of coating qualification, acceptance, or process control.
This standard is typically applied to thermal spray systems such as flame spray, plasma spray, arc spray, HVOF, and detonation spray, using coated fixtures that are bonded to a mating loading fixture before tensile loading. If you need help matching ASTM C633 to your coating system or cited edition, Contact Us.
ASTM C633-24: Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings
ASTM C633 is a focused bond-strength test for thermal spray coatings. The method uses a coated substrate fixture that is bonded to a loading fixture and then pulled in direct tension so the force acts perpendicular to the coating plane.
Because the method can reveal either adhesive failure at the coating-to-substrate interface or cohesive failure within the coating, it is valuable for comparing coating systems, qualifying spray procedures, and supporting production quality control.
Quick Definition
This is a tensile bond test method for thermal spray coatings. It helps determine whether failure occurs at the interface or within the sprayed coating layer.
| Item | Summary |
|---|---|
| Document type | ASTM test method |
| Primary measurement | Adhesion to the substrate or cohesion within the coating under tensile loading |
| Typical use | Quality control, acceptance testing, spray procedure qualification, and coating development |
| Main material focus | Thermal spray coatings including ceramic and metallic systems |
What This Standard Covers
ASTM C633 covers the determination of coating adhesion or cohesion strength in tension normal to the surface. The method is adapted particularly for coatings applied by thermal spray processes.
Common spray processes covered:
- Combustion flame spray
- Plasma arc spray
- Two-wire arc spray
- High-velocity oxygen fuel (HVOF) spray
- Detonation spray
The standard is commonly used for coatings made from ceramics, carbides, metal oxides, and metals. It also notes an important thickness limitation: the method is generally limited to thermal spray coatings thicker than 0.015 in. (0.38 mm) because the bonding agent can penetrate thinner coatings and affect the result.
Testing is usually performed at ambient temperature. Higher-temperature work is more limited because the bonded assembly depends on a suitable adhesive system.
Why This Standard Matters in Testing
ASTM C633 gives buyers, coating shops, and engineering teams a consistent way to compare bond performance across similar thermal spray systems. It is often used when a customer specification, qualification plan, or internal quality program requires measurable evidence of coating integrity.
This method is also useful when evaluating changes in spray parameters, feedstock, surface preparation, or operator setup. In practice, it supports acceptance testing and process development more than direct service-life prediction.
Important caution: ASTM C633 results are valuable for comparison and control, but they are not a direct design allowable for every coated part. Residual stress, part geometry, and real service loading can differ from the simplified tensile condition used in the test.
Common Materials, Product Types, or Applications Covered
This standard is most closely associated with thermal spray coatings used for wear resistance, corrosion protection, thermal protection, and surface restoration. The coating may be a single sprayed layer or part of a layered sprayed system.
Common material categories: ceramic coatings, carbide-based coatings, metal oxide coatings, metallic coatings, and mixed thermal spray systems that include bond layers and top coats.
Common substrate situations: metal substrates are typical, but the method can also be relevant for some ceramic substrates such as oxide materials or graphite when the coating system and bonded fixture arrangement are appropriate.
Common Test or Verification Workflow
In a typical ASTM C633 workflow, one face of a substrate fixture is coated by the selected thermal spray process. That coated face is then bonded to a loading fixture, creating an assembly that can be pulled in direct tension.
The test frame applies a tensile load perpendicular to the coating plane until failure occurs. The result is used to assess whether the critical weakness is at the interface or within the coating body itself.
Common workflows: incoming process qualification, first-article approval, production quality checks, acceptance testing to a customer requirement, and comparison of coating variants during development.
Common reporting focus: measured bond-strength result, failure location, test conditions, and the exact cited edition of the standard.
Equipment Commonly Used for This Standard
ASTM C633 normally points to a tensile test setup built around a universal testing machine and a fixture arrangement designed for this bonded cylindrical specimen style. The equipment path matters because misalignment, inadequate adhesive performance, or poor specimen preparation can change the outcome.
| Equipment family | Typical role |
|---|---|
| Universal testing machine | Applies controlled tensile load to the bonded specimen assembly |
| ASTM C633 tensile fixtures | Hold the coated substrate fixture and loading fixture for axial pull testing |
| Alignment hardware | Helps keep the tensile force normal to the coating surface |
| Bonding and curing setup | Bonds the coated fixture to the loading fixture before the tensile pull |
| Specimen preparation tools | Support coating application, surface preparation, curing, and dimensional control |
Practical quoting note: ASTM C633 projects usually require more than a basic load frame. Fixture style, alignment, specimen geometry, adhesive selection, and the expected bond-strength range should all be discussed before equipment is specified.
How to Read This Designation or Revision
ASTM C633 is the base designation for this standard. When cited as ASTM C633-24, the suffix identifies the 2024 edition. Older references may appear in reapproved form, such as ASTM C633-13(2021), which indicates an earlier edition that was later reapproved.
Revision sensitivity: When a customer drawing, specification, or purchase order cites ASTM C633, the exact edition matters. Laboratories and equipment suppliers should match the version named in the governing requirement.
Related Standards, Methods, or Frameworks
ASTM C633 is often used alongside broader coating qualification requirements rather than by itself. Depending on the program, it may be paired with requirements for coating thickness, substrate preparation, process qualification, metallographic review, or application-specific acceptance criteria.
Because those companion requirements vary by coating chemistry and end use, ASTM C633 is best read as one part of a larger thermal spray verification workflow.
Talk With Us About ASTM C633 Test Equipment
If you are planning an ASTM C633 test setup, we can help you evaluate load-frame range, fixture configuration, alignment approach, and specimen handling needs for thermal spray bond testing. For pricing or system recommendations, Request a Quote.