Abrasive Wear Testing of Cold-Sprayed Copper Components

Abrasive wear testing of cold-sprayed copper components evaluates the resistance of solid-state copper deposits and coatings against abrasion by hard particles, sand, and slurry environments. This testing is essential for validating the durability of cold spray copper coatings used in electrical, thermal, marine, and repair applications. Accredited third-party laboratories perform these tests according to recognized standards such as ASTM G65 and ASTM G75 to deliver quantifiable wear rate data for design and quality assurance.

Technical Overview

Cold spray, also known as cold gas dynamic spraying (CGDS), is a solid-state coating and manufacturing process in which fine copper powder is accelerated to supersonic velocities by a heated high-pressure gas stream and deposited onto a substrate without melting. Because the particles remain well below their melting point, cold-sprayed copper deposits exhibit very low oxidation, minimal thermal distortion of the substrate, and compressive residual stresses that can be beneficial for fatigue and surface integrity.

Copper is intrinsically a soft, ductile metal, so when cold-sprayed copper coatings or free-standing parts are deployed in environments containing hard mineral particles, sand, or abrasive slurries, their wear performance becomes a critical design parameter. Abrasive wear testing quantifies how the material responds to three-body and two-body abrasion, generating data on mass loss, volume loss, and wear rate that can be directly compared against alternative materials, process parameters, or post-treatment conditions.

Key factors that influence the abrasive wear behavior of cold-sprayed copper include:

• Porosity level and interparticle bonding quality of the deposit
• As-sprayed microhardness and residual stress state
• Carrier gas type (nitrogen or helium) and process temperature/pressure
• Powder feedstock morphology, purity, and particle size distribution
• Post-deposition treatments such as heat treatment, shot peening, or friction stir processing
• Surface finishing condition (as-sprayed versus machined or ground)

A systematic abrasive wear test program allows manufacturers and end users to qualify cold spray copper coatings for service, optimize spray parameters, and demonstrate compliance with procurement specifications.

Testing Samples

Cold-Sprayed Copper Coatings on Metallic Substrates

Flat rectangular coupons, typically 25 mm × 50 mm to 75 mm × 100 mm, consisting of a cold-sprayed pure copper or copper alloy layer (commonly 0.5 mm to 3 mm thick) on steel, aluminum, or copper alloy substrates. Both as-sprayed and machined surface conditions can be evaluated to reflect actual service configurations.

Free-Standing Cold-Sprayed Copper Parts

Additively manufactured or repaired copper components produced entirely by cold spray, sectioned into test pieces. These samples characterize the bulk wear behavior of the deposited material independent of substrate effects.

Post-Processed and Comparative Samples

Samples subjected to annealing, hot isostatic pressing, laser remelting, or surface rolling, tested alongside baseline as-sprayed specimens. Comparative sets may also include reference materials such as wrought copper, bronze, or thermal-spray copper coatings for benchmarking.

Sample Preparation Requirements

• Surfaces cleaned with solvent and dried to remove oils, moisture, and loose debris before testing
• Specimens weighed on an analytical balance with 0.1 mg resolution to establish initial mass
• Coating thickness and adhesion verified prior to abrasion testing to exclude spallation artifacts
• Minimum coating thickness sufficient to ensure wear occurs within the deposit, not the substrate

Testing Items

A comprehensive abrasive wear evaluation of cold-sprayed copper typically includes the following measured and derived parameters:

• Mass loss after a defined number of abrasion cycles or test duration
• Wear volume loss, calculated from mass loss and deposit density
• Specific wear rate (volume loss per unit sliding distance and applied load)
• Wear depth and wear scar profile measured by stylus or optical profilometry
• Wear track surface morphology examined by optical microscopy and SEM
• Microhardness of the deposit before and after testing (e.g., HV0.1 to HV0.5)
• Porosity and microstructure assessment of cross-sections in the worn region
• Changes in surface roughness induced by abrasion
• Coefficient of friction, where the selected test method provides friction measurement

Testing Methods

ASTM G65 – Dry Sand Rubber Wheel Abrasion Test

The most widely applied method for ranking the abrasion resistance of cold-sprayed copper coatings. A rectangular specimen is pressed against a rotating rubber-rimmed wheel under a defined load while standard Ottawa silica sand is fed into the contact zone, producing three-body abrasive wear. Test parameters typically include a 228.6 mm diameter wheel, wheel speeds of approximately 200 rpm, and procedure variants (A through F) covering different loads and cycle counts suited to soft materials such as copper. Results are reported as volume loss in cubic millimeters, with lower values indicating better abrasion resistance.

ASTM G75 – Slurry Abrasivity Test (Miller Number)

Used when cold-sprayed copper components face wet abrasive environments, such as slurry transport or marine service. A specimen block reciprocates against a neoprene lap while immersed in a sand-and-water slurry. Mass loss after a set number of strokes yields a slurry abrasion response, allowing comparison of deposit conditions under chemically active, wet conditions.

ASTM G132 – Pin Abrasion Test

A cylindrical pin of the cold-sprayed copper material is dragged across a fixed abrasive surface (such as garnet or alumina cloth) under a controlled load. This two-body abrasion test is useful for screening the influence of spray parameters and post-treatment on wear rate.

Complementary Sliding Wear Methods

Where service involves combined abrasion and sliding contact, ASTM G99 pin-on-disc or ASTM G77 block-on-ring tests may be run to determine the coefficient of friction and sliding wear rate, providing a fuller tribological profile of the copper deposit.

Test Procedure and Data Evaluation

• Condition specimens at controlled temperature and humidity, then record initial mass and dimensions
• Perform the selected abrasion test at specified load, speed, abrasive type, and cycle count
• Clean, dry, and reweigh specimens; calculate mass loss and convert to volume loss using measured deposit density
• Characterize wear scars by profilometry and microscopy to identify wear mechanisms such as plowing, cutting, and delamination
• Report wear rate, wear coefficient, and comparative ranking against reference materials
• Issue a test report documenting standards followed, equipment calibration status, test conditions, and representative wear scar images

Applications

Abrasive wear test data for cold-sprayed copper components directly support engineering decisions across multiple industries:

• Electrical infrastructure: copper coatings on busbars, connectors, and grounding components exposed to dust-laden or desert environments
• Thermal management: cold spray copper layers on heat sinks and power electronics housings subject to erosive and abrasive handling damage
• Component repair and refurbishment: dimensional restoration of worn bronze and copper alloy bearings, sleeves, and valve seats, where restored wear life must be demonstrated
• Marine and offshore engineering: copper and copper-nickel deposits on seawater-handling hardware subject to sediment-laden flow
• Mining and mineral processing: copper-clad sliding and sealing elements exposed to ore particles and slurry
• Railway systems: conductive copper deposits on current-carrying components subjected to abrasive pantograph or environmental contact
• Additive manufacturing: qualification of cold spray built copper parts prior to production release

FAQ

Q: What is the most common standard for abrasive wear testing of cold-sprayed copper?

A: ASTM G65 (dry sand rubber wheel abrasion) is the most frequently specified method because it provides a reproducible three-body abrasion condition well suited to ranking soft metallic coatings. For wet or slurry exposure, ASTM G75 is preferred.

Q: How is wear volume calculated if the coating density is not exactly known?

A: Laboratories typically determine the actual density of the cold-sprayed deposit from cross-sectional porosity analysis or Archimedes density measurement, then divide the measured mass loss by this effective density to obtain wear volume. Using bulk copper density should be avoided because residual porosity causes overestimation of wear volume.

Q: Why does porosity matter in abrasive wear results?

A: Residual porosity and incomplete interparticle bonding in cold-sprayed copper reduce load-bearing capacity and can accelerate material removal by plowing and pull-out. Wear testing is therefore a sensitive indicator of deposit quality and spray parameter optimization.

Q: Can post-processing improve the abrasion resistance of cold-sprayed copper?

A: Yes. Heat treatment, friction stir processing, and surface rolling can enhance interparticle bonding and hardness, and comparative wear testing before and after treatment quantifies the improvement for qualification purposes.

Q: What sample dimensions are required for ASTM G65 testing?

A: Standard rectangular coupons approximately 25 mm to 100 mm wide with a flat test surface are acceptable, provided the coating is thick enough that the wear scar remains entirely within the deposited copper layer throughout the test duration.

Q: Do the tests damage the samples beyond reuse?

A: Abrasive wear testing is destructive to the tested surface. Specimens are consumed during the test, so clients should submit dedicated coupons or spare components rather than production hardware.