The threshold galling stress denotes the applied contact pressure at which visible adhesive damage will start to occur. The higher the galling threshold, the more resistance there will be to galling. Microscopic evaluation of the surfaces you tested can confirm the level of adhesion and material transfer. Additionally, results may differ based on lubrication, surface roughness, and both surface and bulk hardness of the tested materials. Comparing materials can help select a combination of alloys and coatings to minimize galling in engineering systems.
ASTM G133 is the method used for the linearly reciprocating ball-on-flat sliding wear test. Also, ASTM G73 provides the procedures for measuring fretting wear, which are complementary tests from a galling methodology perspective, as fretting wear considers wear from small-amplitude motion. The combination of these standards provides engineers with a comprehensive and multifaceted approach for assessing tribological behavior.
ASTM G98 Applications in Industry
ASTM G98 is used widely in many industries where components exhibit metal-to-metal contact. In aerospace and automotive industries, it can help engineers select alloys to be used for fasteners, couplings, valve seats, etc. In the medical device industry, it will give engineers insight into galling performance for surgical instruments and implant-grade materials. The test may also be beneficial for suppliers of stainless-steel fitting components and threaded connectors, who may want to ensure that their products can reliably perform after repetitive assembly and disassembly.
ASTM G98 Materials Commonly Tested
This method can be implemented for loads of metals and alloys, in particular, those that can be susceptible to adhesive wear. Testing substances encompasses austenitic and martensitic stainless steels, titanium alloys, nickel-based first-rate alloys, and cobalt-chromium alloys. It is not unusual for hardened tool steels, aluminum alloys, and surface-treated components to be tested so that galling performance can be compared. In addition, testing specimens with and without lubrication contributes to the knowledge of real-world performance in the service environment.
ASTM G98 Common Challenges and Troubleshooting
During testing, issues and failures can often occur due to irregular surface preparation or contamination, which can lead to variability in the end results. All specimens must be properly aligned so that adding appropriate specimen mass is avoided, which produces unequal contact stresses, distorting the galling prediction. Overheating occurs in ASTM G 98 testing due to prolonged current application, which may indirectly lead to altered surface hardness or modification of oxide layers.
ASTM G98 Safety and Best Practices
The specimens must be firmly mounted to avoid ejection due to the initiation of galling. Post-testing, surfaces that are sharp or damaged should be handled carefully to prevent injury. Furthermore, periodic preventative maintenance of equipment and cleaning of the test surfaces improve the repeatability and accuracy of galling resistance evaluation.
Importance of ASTM G98 Test Method
This method facilitates a deeper understanding and prevention of galling, a significant contributor to component failure in metal assemblies. Galling resistance can be measured, and engineers can design or specify materials and surface finishes to maximize service life, reduce maintenance cost, and improve reliability of composite systems. This test method, therefore, assists in the development of materials, assures materials, and optimizes designs across multiple sectors of engineering with metallurgical interfaces, or prevents galling failure, which provides more reliable engineered systems.
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