金属陶瓷复合涂层的激光熔覆与无裂纹的实现

鉴于传统的激光熔覆金属陶瓷复合涂层技术主要存在2方面不足：其一,熔覆效率低,导致大面积熔覆时成本昂贵;其二,由于激光熔覆本身的特点,即快速加热与快速凝固,在激光熔覆过程中,热应力极易诱导熔覆层开裂。基于此,综述了国内外激光熔覆金属陶瓷复合涂层的研究进展,指出其存在的主要问题,并提出了激光感应复合快速熔覆的新方法,即感应预热基材的同时快速激光熔覆。该方法不仅可使熔覆效率大大提高而且获得了无裂纹的金属陶瓷复合涂层。     

Composite ceramic-metal plates tested with flexural waves and holography

A method to determine weak or defective bonding areas within the brazed adjoining contact surfaces of composite ceramic-metal plates is proposed. The plates include voids, as well as hairline cracks in the ceramic layer, caused by the high-temperature brazing process. To detect these flaws, transient flexural waves are generated and transmitted through the plate by means of an attached piezoelectric transducer. These pulses are a narrow band signal generated in the time domain. The characteristic wavelengths corresponding to the narrow frequency spectrum may be larger than the size of the flaw. Dynamic holographic interferometry using a double-pulsed twin-cavity Nd:YAG laser, comprising two independent reference beams, was used to measure the response. The experimental interferograms (phase maps) coincide rather precisely with analytic results derived from Mindlin's plate equations (including effects of shear and rotary inertia).