Rapidly quenched ZrSiO4 melts produced by CO2 and pulsed YAG lasers have been analysed using infrared (IR) and Raman spectroscopy. The quenched melts exhibit decomposition into binary oxides (ZrO2 and SiO2), while other phases or complex SiO4 tetrahedron networks are also observed. The local structures and the phases of the quenched melts depend strongly on the quenching rate and melting conditions. Monoclinic ZrO2 are found to be the main ZrO2 phase in the samples treated by CO2 laser, although tetragonal ZrO2 was found near boundaries between the untreated and melted regions. High concentrations of tetragonal ZrO2 were detected in the samples treated by pulsed YAG lasers. Our observations indicate that the formation of tetragonal ZrO2 is related to relatively high quench rates. Micro-IR and Raman data from areas near the boundaries between the quenched melts and untreated zircon show systematic variations of local structures and compositions. We observe a small region with relatively low density between the untreated and melted boundaries, which consists of tetragonal ZrO2 or glassy ZrO2, and SiO2. Broad vibrational bands occur in the wavenumber region where the characteristic frequencies of zircon are located. This observation could indicate the possible existence of small amounts of glassy ZrSiO4 in the melt state of zircon, although zircon tends to decompose above the melting point. These observations are in sharp contrast with the behaviour of radiation-damaged zircon, the so-called metamict zircon, where no phase separation occurs in samples which have not been subsequently annealed.

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690 MPa grade HSLA steel has wide application in engineering, such as mechanical equipment and oceanographic platform. Qualified joint is crucial for structure safety. Many factors, such as preheating temperature and interpass temperature, welding heat input and plate thickness, may influence the welding thermal cycle so that microstructure and mechanical properties of weld metal are changed. In this paper, the effect of interpass temperature on microstructure and mechanical properties of weld metal of 690 MPa grade steel are studied. Gas metal arc welding method was used to weld the joint. Four interpass temperatures, 80°C, 120°C, 160°C and 200°C are adopted during welding. Optical microscope, scanning electron microscope, transmission electron microscope and electron back-scattered diffraction (EBSD) were used to analyze the microstructure of weld metal. Tensile test and impact test were used to measure its mechanical properties. Research results show that the weld metal are composed of lath bainite and granular bainite. M-A constituents are found on grain boundary and inside grains. The shape and size of bainite structure and M-A constituent are detailed. The distribution and quantity of residual austenite are also detected. The relationship between microstructure and mechanical properties is discussed. Experiment results show that when interpass temperature is 80°C the yield strength and impact toughness are higher than the other three cases.

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Stellite 12/TiC/CaF2 composite coating has been successfully fabricated on copper substrate by a pulsed Nd:YAG laser system with preplacment powder bed to improve the absorbance of copper substrate to laser energy. Microstructures, phases and wear properties were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), dry sliding wear tester. The results showed that the existence phases of Co-based solid solution, Cr4Ni15W, TiC, Cr23C6, CaF2 and Ti8C5. The morphology of titanium carbide is mainly spherical and exists in two forms, one is TiC and the other is Ti8C5. The microhardness of the layers reveals a gradient variation along the cross section of the LSA layers. The friction coefficient of the coating is oscillating around approximately 0.17 because CaF2 is a solid lubricant because of the lamellar structure and softness and Titanium carbide is hard. The dry sliding wear testing shows the wear resistance of as-receive copper is significantly improved by laser cladding Stellite 12/TiC/CaF2 composite coating.