ASTM C633 Adhesion or Cohesion Strength of Thermal Spray Coatings
ASTM C633 is a standardized test method crucial for measuring the adhesion or cohesion strength of thermal spray coatings, ensuring reliability in coating applications across various industries.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Overview
ASTM C633 defines the standardized method for determining the adhesion or cohesion strength of thermal-spray coatings applied to metallic or nonmetallic substrates. The test evaluates the tensile bond strength between the coating and substrate—or within the coating itself—by using a controlled tensile load until failure occurs.
This method is used to assess the performance of coatings deposited using various thermal-spray processes, such as plasma spray, HVOF, flame spray, and arc spray. ASTM C633 provides a reliable framework for comparing coating quality, verifying process parameters, and ensuring the coating’s suitability for demanding applications involving wear, corrosion, and thermal exposure.
Scope, Applications, and Benefits
ASTM C633 outlines procedures for measuring the tensile bond strength of thermal spray coatings under controlled test conditions. It evaluates:
- Adhesion strength at the coating–substrate interface
- Cohesion strength within the coating
- Strength variations due to coating thickness and spray parameters
- Influence of substrate preparation and post-treatments
The method simulates mechanical loading conditions to determine the coating’s ability to withstand service-level stresses.
- Evaluating the performance of thermal spray coatings for industrial components
- Qualification of coatings used in aerospace, automotive, power generation, and heavy-equipment sectors
- Comparing adhesion strength across different thermal spray techniques
- Verifying surface preparation effectiveness and coating process optimization
- R&D for improving coating formulations, parameters, and durability
- Provides quantitative tensile bond strength (MPa or psi)
- Differentiates between adhesion failure and cohesion failure
- Supports process validation and quality assurance programs
- Helps optimize thermal spray parameters and coating thickness
- Ensures coating reliability in high-stress environments (wear, corrosion, thermal cycling)
Test Process
Specimen Preparation
Clean, surface-prepare, coat, and machine substrates to standardized dimensions.
1Mounting and Assembly
Bond the coated specimen to loading fixtures using a high-strength adhesive to form the pull-test assembly.
2Tensile Loading and Failure
Apply a controlled tensile load until coating failure occurs and note the failure mode.
3Strength Calculation and Recording
Calculate tensile bond strength from the maximum load divided by the cross-sectional area and record results.
4Technical Specifications
| Parameter | Details |
|---|---|
| Test Principle | Tensile pull-off test to determine adhesion/cohesion strength of thermal spray coatings |
| Sample Types | Coated metallic or non-metallic substrates—flat or cylindrical |
| Typical Dimensions | Diameter: 25–30 mm; Length: 75–100 mm (varies by fixture) |
| Surface Preparation | Grit blasting or equivalent pre-treatment before coating |
| Bonding Material | High-strength adhesive suitable for test temperature |
| Measured Output | Tensile adhesion or cohesion strength in MPa or psi |
| Failure Analysis | Identification of adhesive vs. cohesive failure modes |
| Typical Duration | Test completed once peak tensile load and failure mode are recorded |
Instrumentation Used for Testing
- Tensile testing machine with pull-off fixture
- Precision alignment fixtures for specimen mounting
- High-strength adhesive curing system (oven/room-temperature cure)
- Surface preparation tools (grit blasters, machining tools)
- Measurement and data acquisition software
- Optical tools for post-test failure mode examination
Results and Deliverables
- Tensile bond strength (MPa or psi) of thermal spray coatings
- Identification of failure mode:
- Adhesive failure (coating detaches from substrate)
- Cohesive failure (crack within the coating)
- Comparison across different coatings, spray parameters, and substrates
- Evaluation of surface preparation and process consistency
- Assessment of coating performance for wear, corrosion, and thermal applications
- Validation support for industrial specifications and quality standards
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Read Case StudyFrequently Asked Questions
The test ensures coatings can withstand mechanical stress, wear, and thermal cycling. It helps in quality control, process optimization, and material selection for applications in aerospace, automotive, power generation, and industrial equipment.
Samples include coated metallic or non-metallic substrates, typically cylindrical or flat, prepared via thermal spray methods such as plasma, HVOF, flame, or arc spray.
Bond strength depends on substrate surface preparation, coating material, thickness, thermal spray parameters, and post-treatment processes.
A good value depends on the application and coating type. High tensile strength at failure indicates strong adhesion or cohesion, ensuring coating durability and performance under mechanical or thermal stress.
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