W.J. Yao

Competition growth of α and β phases in Ti-50 at.%Al peritectic alloy during the rapid solidification by laser melting technique

Rapid solidification of Ti-50 at.%Al peritectic alloy is realized by laser melting technique at different conditions of laser power and scanning speed. The temperature field and the cooling rate under the corresponding conditions are derived from the finite element simulation. Comparing the measured pool size with the simulated result, the laser absorptivity of Ti-50 at.%Al peritectic alloy at different conditions can be deduced to establish the relationships between the laser absorptivity, the laser power and the scanning speed. The morphology evolution and the phase selection of Ti-50 at.%Al peritectic alloy are described by the temperature gradient and the cooling rate. With the increase of temperature gradient and cooling rate, β phase replaces α phase to become the leading growth phase. And the growth of α phase experiences the transition from facet to non-facet manner, while β phase is refined. To understand the underlying mechanism of the competition growth can bring benefit to the industrial application of Ti-Al alloy.

Growth Characteristics of TiCxNy Ceramics under Laser Melting Conditions

By laser melting technique, TiCxNy ceramics are prepared under the laser powers of 300, 400, 500, 600, and 700 W, respectively. The size of molten pool decreases with the increase of scanning speed from 1 to 4 mm/s at a certain power. TiCxNy microstructure continuously changes from the top to bottom of molten pool. Based on the XRD spectrum, the composition of ceramic can be confirmed as Ti(O0.19C0.53N0.32), C0.7N0.3Ti, C2MoTi, and Ti8C5. Based on the analysis of the growth process, the growth conditions can be confirmed. The maximum depth of molten pool obtained at the laser energy density of 500 W/cm2. The more deviation from this value, the more shallow the pool. The corrosion experiment result shows that TiCxNy ceramic has good corrosion resistance to various corrosive agents except HNO3.