Finished Si3N4 components can present fine surface cracks from manufacturing process origins. These cracks can be made visible with special visual inspection methods but their exact origin and therefore morphology (depth) and associated level criticality (low/high) are difficult to distinguish. A conservative approach can lead to unnecessary rejects of components that were energy intensive to process. This contributes to undesirable cost and waste.
A surface crack healing treatment is therefore an approach to mitigate these features and considerations. Si3N4 materials for bearing applications are ruled by tight specifications (finished products and materials). Even though few papers deal with crack healing in Si3N4 and offer mechanisms, results are very variable and dependent on the exact material composition (sintering additive package and intergranular phase resulting from sintering process). Therefore, research is still needed on exact heat treatment conditions for effective crack healing and mechanisms as well as the resulting effect of such heat treatment on mechanical properties and detailed microstructure and surface attributes that could have changed by the treatment.
Such treatment, if successful and although being an added step in manufacturing, can contribute to improving production yield and product performance while reducing waste levels and risks of failure in applications. Needed efforts in quality inspection could also be reduced.