Study and characterization of the ductile-brittle transition zone in sintered zirconia

Ceramics, being brittle in nature are highly prone to surface damage during machining. However, at depths of cut lower than a critical depth of cut, brittle materials undergo microscopic plastic shearing resulting in a crack-free surface. The transition from ductile to brittle takes place over a finite time and depth variation. The identification and characterization of the transition zone is important to attain damages free surface grinding. This work focuses on the identification of the ductile-brittle transition (DBT) zone in yttria stabilized sintered zirconia via the analyses of the force signatures. An algorithm has been developed for the prediction of the onset and end of the transition zone based on the gradients and fluctuations in the cutting force signals. The visual inspection of the ground surface validates the proposed methodology based on force signal processing. The transition zone characteristics were found to be affected by the process parameters and the tool geometry. The increase in the scratch speed reduced the transition onset depth but had negligible effect on the transition end depth. Smaller tool tip radius resulted in increased surface damage whereas larger tip radius gave a relatively smoother surface finish. This methodology of accurate prediction of DBT zone using cutting/thrust force behavior allows the manufacturers to achieve crack-free surfaces in brittle materials without keeping track of cutting depth during machining. Thus, the prediction of the ductile regime by the analysis of force signals opens new horizons in deciding threshold force and depth values in real time, which should be maintained to achieve a damage free surface during grinding.