A METHOD TO COMPARE THE THERMAL-SHOCK RESISTANCES AND THE SEVERITY OFQUENCHING CONDITIONS OF BRITTLE SOLIDS

The thermal shock behavior and resistance of brittle materials are mos tly investigated through the determination of a critical quenching tem perature difference, Delta T-c. This technique, however, needs a large number of, almost, identical samples and is thus poorly adapted to pr oducts being in the stage of research and development. In order to ove rcome this difficulty, the indentation technique has been used in this work. The residual contact stresses, created during indentation, perm it a stage of stable extension of the indentation cracks under the act ion of further stressing. The relative increase of radial crack length as a function of Vickers indentation load, c/c(0) vs. P, is taken as a criterion, or indicator, of relative thermal shock resistance, or of the severities of quenching conditions. This is validated, first in q uenching materials whose empirical ranking is well established, and se cond in varying parameters of the Plot number. Finally, are two batche s of a functional ceramic compared. The proposed criterion reflects th e competition between the toughness of the quenched material, as an in trinsic property, and the thermal transient stresses, as a consequence of the physical properties of both the quenched sample and the quench ing medium. Possibilities for extending the developed approach towards a more accurate description of quenching phenomena and stress states such as to refine theoretical models are discussed.