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In this paper, thermal residual stresses in multi-layered and compositionally graded NiCrAlY/yttria-stabilized zirconia coatings are analyzed by finite element method. These coatings are fabricated by detonation gun spraying using mechanically alloyed, plasma-spheroidized composite powders. The residual stresses of the as-sprayed coatings with different graded layers and different thickness, as well as the variations of residual stresses during thermal cycling are simulated by finite element analysis. The problems in design of compositionally graded materials are outlined and their modeling approaches are reviewed. Results showed that graded coating was more stable on the mechanical properties than normal duplex composites. And, the maximum compressive radial stress is found to be at or near the surface of the specimen where surface cracking may be generated.

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The purpose of this study is to find out the AE characteristics and fracture mechanisms through AE signal analysis for the weldment, PWHT specimen and basemetal of the pressure vessel steel. Charpy sized specimens were taken from the multi-passed weld block. Specimens were given to four point bend and AE tests. Lots of AE signals were emitted from the weldment compared with the basemetal and PWHT specimen. Besides, amplitude for the weldment was the largest, followed by PWHT specimen and basemetal and more AE counts for the weldment were emitted in the process of deformation. Lots of microcracks around the notch for the weldment were formed so that more AE signals were produced. In addition, second phase particle such as MgO for the basemetal acts as AE source. However, in case of weldment, debonding mechanisms between matrix and hard oxides which are formed during welding in air attributed to the emission of AE signals and softened particles for the PWHT specimen cause to produce the low level AE signals.

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