Papers by Author: Yan Chun Zhou

Abstract: A relative method, defined as indirect approach to evaluate the material properties via the relationship between unknown properties and a known property, is proposed to estimate some properties that could not be measured by the traditional methods for ceramics. Experiments and theoretic analysis based on the relative method were carried out in this study to estimate the properties in following aspects: determining the temperature dependence of elastic modulus of some machineable ceramics by comparing the deflections; obtaining the modulus and strength of ceramic coatings supported by substrates, from the variation in properties of the rectangular beam samples before and after coating; estimating the residual stresses in tempered glass by comparing the change in the surface strength after strengthening.

Abstract: Creep and stress relaxation of Ti3AlC2 were investigated using three-point bending tests at 800-1200°C under various load levels. The results show that the creep rate significantly increases with increasing temperature in the rang of 1000-1200°C. Subcritical crack growth during the creep process was found to be the main failure mechanism, i.e., the stress intensity factor increases with the creep-induced crack growth and results in the ultimate fracture. The lower limit of stress relaxation was considered as the threshold value of zero-creep stresses, and the ratio of the threshold stress to the applied stress was defined to be a parameter of creep resistance for estimating deformation behavior at high temperature. SEM examination confirmed that the creep failure in Ti3AlC2 was governed by such a damage evolution: cavitation ® crack initiation ® crack extension ® fracture.

Abstract: Thermal barrier coatings (TBCs) with the ceramic coats of hollow spherical ZrO2-8%Y2O3 powder (HSP-YSZ) were obtained on Ni-base superalloy by detonation gun (D-gun) spraying. Thermal shock cyclic tests were performed by holding samples at 1100°C for 10 min and then water quenching to room temperature repeatedly. The D-gun sprayed TBCs didn’t fail up to 300 cycles and exhibited excellent resistance to thermal shock. Failure mechanism of D-gun sprayed TBCs subjected to thermal shock cycling was discussed.