Tarou Tokuda

DETECTION AND EVALUATION OF DELAMINATION USING ACOUSTIC EMISSION METHOD IN THERMALLY SPRAYED COATING UNDER TENSILE STRESS

AE was measured under a static tensile load for the thermally sprayed ceramic coating in order to investigate the relationship between the detected m-value and the destruction (delamination) of the sprayed coating. This was an effective method to detect and evaluate the delamination of a sprayed coating based on the m-value, because changes of the m-value were closely related in thermally sprayed coatings. Stress level of the delamination analyzed by AE method was almost the same as that predicted by the ESPI method. The generation of delamination was confirmed by cross-section observation of the coating using both stress levels. Therefore, the ESPI method seems to be an effective way to define and evaluate the delamination of sprayed coating determine.

Nondestructive Detection of Delamination of Thermally Sprayed Material Using ESPI

Detection of delamination of a thermally sprayed coating on an SUS304 substrate was carried out nondestructively using electronic speckle pattern interferometry (ESPI) method in both static and cyclic tests at T=298 K and 873 K. Results showed that the surface strain of the coating becomes smaller than that of the substrate when delamination occurs from the interface of the substrate. Two parameters of critical strain of ε c and ε f, which correspond respectively for the static test and the cyclic test, are introduced to evaluate the existence of delamination according to the ε- σ s and ε-N curve. It is considered possible to evaluate the occurrence of delamination in cyclic tests using the static critical strain of ε c, instead of ε f.

Influence of Additives and Hot-Press Sintering on Lipophilic Properties of Silicon Nitride Ceramics

Fe 3 O 4 and Mo and were added to hot-press sintered Si 3 N 4 ceramics to improve their lipophilic and mechanical properties. The bending strength, relative density, hardness and fracture toughness of Si 3 N 4 ceramics with addition of Fe 3 O 4 and Mo were improved by hot-press sintering compared with samples prepared with the pressureless process. In particular, the bending strength and relative density were improved to about 200% and 104%, respectively. Both the macro- and micro-lipophilicity of Fe 3 O 4 - and Mo-added ceramics were improved when prepared with the hot-press process, compared with those prepared with the pressureless process. This can be attributed to the addition of Fe 3 O 4 , and the formation of MoO 3 and Si 2 N 2 O during hot-press sintering. The lower friction coefficient and high wear resistance of Fe 3 O 4 - and Mo-added ceramics have been achieved by applying the hot press process. The high wear resistance is considered to be due to the improvement of hardness and fracture toughness, which decreased the loss of particles during the wear test.

Residual Stress Measurement and Evaluation on Ceramics with X-Ray and Indentation Method

In this report, the indentation method of measurement for residual stress in structural ceramics is discussed. The residual stresses in Al2O3, Si3N4 and ZrO2 ceramics were evaluated with the indentation method. The value obtained by the indentation method was examined as a function of the microstructure, using Al2O3 ceramics differing in microstructure (grain size and aspect ratio). The residual stress values in Al2O3 and Si3N4 obtained by the indentation method at 98 N agreed well with the values obtained by the X-ray method. The residual stress value in ZrO2 obtained by the indentation method was close to the value obtained by the X-ray method, when the indentation load was 294 N. For estimating the residual stress in ZrO2 with the indentation method, the influence of the phase transformation induced by the indentation is added to the original residual stress, when the indentation is small. The value obtained by indentation method differed with the aspect ratio of the grains in Al2O3. It was thought that the origin of the variation was the difference in crack propagation resistance in different materials

Measuring Residual Stress with the Indentation Method in Struc­tural Ceramics

This study deals with the indentation method of measuring residual stress in structural ceramics. First we investigate the appropriate pretreatment for measuring fracture toughness (basis value, KC) while avoiding any influence from residual stress, which is important when estimating residual stress using the indentation method. Based on the fracture toughness value, the residual stresses in Al2O3, Si3N4 and ZrO2 ceramics are estimated using the indentation method. Phase transformation is a problem when estimating residual stress using the indentation method with ZrO2 ceramics. Residual stresses in Al2O3 and Si3N4 can be largely eliminated by annealing the specimen after hand grinding. Consequently, it is thought that this treatment method is effective for determining the basis value KC. The estimated residual stress values in Al2O3 and Si3N4 obtained by the indentation method at 98 N corresponded closely to the values obtained wih X-rays. The residual stress value obtained by the indentation method for ZrO2 was close to the value obtained through the X-ray method, when the indentation load was 294 N. When estimating the residual stress in ZrO2 using the indentation method, the influence of the phase transformation caused by the indentation is added onto the original residual stress, when the indentation is small. The influence becomes smaller when the indentation load is large. If the applied indentation load is between 294 N and 490 N, the indentation method is effective for estimating the residual stresses in Al2O3, Si3N4 and ZrO2 ceramics.