Experiment Of Ultrasonic Assisted Laser Clad YSZ Ceramic Coating

Yttria-stabilized zirconia (YSZ) ceramic has the advantages of high melting point, low thermal conductivity, relatively high thermal expansion coefficient and excellent thermal stability, which is one of the most widely used thermal barrier coatings (TBCs) material and has a great development potential especially at the severe application environment in the fields of aerospace and marine chemistry industry. Laser cladding could deposit the metallurgical bonded coating on the complicated substrate directly. Due to the relatively simple convection form within the molten pool under the action of single heat source, the dilution effect between coating and substrate usually would lead to the nonuniform distribution of structures and composition within the coating. Besides, the thermal stress is high due to the differences of thermal and physical properties between the metal substrate and the ceramic coating, increasing the cracking sensitivity, which would impair the coating bond strength and limit the development of metal/ceramic functional gradient coating deposited by the laser cladding technology.Through studying the application achievement of ultrasonic vibration in the fields such as casting and weld, this paper conducts the feasibility analysis that adopting ultrasonic field to improve the qualities of laser clad metal/ceramic functional gradient coating, basing on the action mechanism between ultrasonic vibration and liquid medium. Thereafter, by the experimental research of ultrasonic assisted laser clad YSZ coatings, the effect of ultrasonic vibration on the coating macroscopical morphology, microstructures, dilution characteristics, phase composition, mechanical properties is investigated, obtaining the influencing mechanism of ultrasonic vibration on the macro and micro qualities of YSZ coatings. Optical microscope, scanning electron microscopy, Vickers microhardness tester, friction and wear tester are used to conduct the observation of macroscopical morphology and microstructures, the mechanical property testing. Main contents of the research are as follows:(1) The experimental platform of ultrasonic assisted laser cladding is built up, and the performances of platform are tested. The coupling interaction between the ultrasonic field and the laser beam is investigated, which provides the theoretical guidance for the application of ultrasonic vibration to the laser cladding process properly.(2) The technical experiments are proceeded by the powder feed ultrasonic assisted laser cladding based on the raw material of yttria-stabilized zirconia ceramic powder, and the effect of ultrasonic vibration on the cross-section morphology, the interface feature, and the surface quality is analyzed. Additionally, the effect law of ultrasonic output power on the change of macroscopical qualities is analyzed. On the ultrasonic vibration, the change of temperature field in the laser cladding process is also investigated.(3) By the comparation of microstructure evolution and element distribution of coatings fabricated with and without ultrasonic vibration, the differences between the ultrasonic assisted laser cladding technology and the traditional laser cladding technology are summarized. Finally, the mechanical properties of YSZ coatings fabricated with and without ultrasonic vibration are evaluated by microhardness test as well as friction and wear test, exploring the action mechanism.The novel method of ultrasonic assisted laser clad metal/ceramic functional gradient coating is proposed, the effect law of ultrasonic vibration on the macro and micro qualities as well as the mechanical properties is studied. Experiments show that the ultrasonic assisted laser cladding technology in the fabrication of metal/ceramic functional gradient coating has the technical advantages.