ASTM C633
Thermal Spray Coating Adhesion Test Fixture
ASTM C633 Tensile Fixture – Universal Grip Data Sheet (PDF)
ASTM C633 measures the adhesion or cohesion strength of thermal spray coatings in tension normal to the surface. A coated cylindrical substrate is bonded face to face with an uncoated loading cylinder and pulled apart. Universal Grip supplies a self-aligning fixture with universal joints so the pull stays perpendicular to the coating and the result reflects true bond strength.
What ASTM C633 Measures
The test reports bond strength, the peak force divided by the cross-sectional area of the cylinder, and the location of failure. Failure can be adhesive (at the coating-substrate interface), cohesive (within the coating) or in the bonding agent. If the bonding agent fails, the coating is at least as strong as the result. The test is a standard check for plasma, HVOF and other thermal spray processes.
How the ASTM C633 Test Works
Grit blast and coat the face of the substrate cylinder.
Bond it to the uncoated loading cylinder with a suitable adhesive, keeping the two in line, and cure.
Thread both cylinders into the fixture holders.
Pull in tension at a constant crosshead rate until failure.
Record peak force, calculate bond strength and record where the failure occurred.
Specimens and Setup
Coatings should be thick enough that the adhesive cannot penetrate to the substrate; the standard sets a minimum thickness.
Use an alignment V-block when bonding so the cylinders share one axis.
Remove excess adhesive from around the joint before testing.
Check the adhesive's own strength; it limits the highest bond strength you can measure.
Confirm cylinder size, coating thickness and loading rate against your copy of the current standard.
Universal Grip ASTM C633 Fixture
Self-aligning universal joints for load normal to the coating
Accepts cylindrical substrate and loading fixtures
Quick-connect threaded holders for fast changeover
Alignment V-block available for adhesive bonding
50 kN standard capacity; higher capacities on request
Heat-treated alloy steel; clevis pin or threaded adapters
Applications
Plasma and HVOF coating qualification
Thermal barrier coating bond strength
Coating process development and QC
Aerospace and turbine component coatings
Related Standards and Products
Send us your specimen dimensions, required capacity and machine connection through our contact page and we will quote an ASTM C633 bond strength fixture. Request a quote
ASTM C633 FAQ
What does C633 measure?
It measures how strongly a thermal spray coating sticks to its substrate (adhesion) or holds together within itself (cohesion), by pulling bonded cylinders apart normal to the coating.
Why are universal joints needed?
Any bending at the bonded joint peels one edge first and lowers the result. Universal joints let the load line self-align so the pull is straight through the coating.
What if the adhesive fails instead of the coating?
Then the coating bond is at least as strong as the adhesive. Report the value as a lower limit and consider a stronger bonding agent.
Can you supply extra substrate cylinders?
Yes. Tell us the diameter, thread and quantity when you request a quote and we will supply substrate and loading cylinders with the fixture.