What inspection methods are commonly used after heat treatment?

Mechanical Property Verification

Following heat treatment, the primary goal of inspection is to verify that the component has achieved the required mechanical properties. This is most directly measured through material testing and analysis, which includes hardness testing as a quick and common quality control check. For critical components, tensile and impact tests are performed on witness coupons processed alongside the production parts to confirm yield strength, ductility, and toughness meet the stringent specifications necessary for industries like aerospace and aviation.

Microstructural and Metallurgical Examination

Confirming the correct metallurgical structure is crucial. Samples are sectioned, mounted, polished, and etched for microscopic analysis. This examination verifies critical factors such as grain size, phase distribution, and the absence of detrimental microstructural features like excessive carbide precipitation or incipient melting. This level of analysis is essential for advanced materials processed via single crystal casting or powder metallurgy, where the microstructure dictates high-temperature performance.

Non-Destructive Testing (NDT) for Integrity

Non-destructive evaluation methods are universally applied to check for surface and subsurface defects without damaging the part. Dye Penetrant Inspection (DPI) is used to reveal surface-breaking cracks, while Magnetic Particle Inspection (MPI) is employed on ferromagnetic materials. Ultrasonic Testing (UT) and Radiographic Testing (RT) are critical for detecting internal flaws like voids or porosity that could initiate failure under load. These processes are integral to the final validation of a component's structural integrity after the thermal cycles of heat treatment.

Dimensional and Surface Inspection

Heat treatment can introduce dimensional changes or distortion due to stress relief and phase transformations. Post-treatment inspection, therefore, always includes precise dimensional checks using Coordinate Measuring Machines (CMM), optical comparators, and laser scanners to ensure compliance with drawing tolerances. This is particularly important for components that will undergo final CNC machining, as it confirms sufficient stock material remains for the finishing operations.