The direct-current simulation burning method was used to investigate the burn-resistant behavior of Ti14 titanium alloy. The results show that Ti14 alloy exhibits a better burn resistance than TC4 alloy (Ti-6Al-4V). Cu is observed to preferentially migrate to the surface of Ti14 alloy during the burning reaction, and the burned product contains Cu, Cu 2 O, and TiO 2 . An oxide layer mainly comprising loose TiO 2 is observed beneath the burned product. Meanwhile, Ti 2 Cu precipitates at grain boundaries near the interface of the oxide layer, preventing the contact between O 2 and Ti and forming a rapid diffusion layer near the matrix interface. Consequently, a multiple-layer structure with a Cu-enriched layer (burned product)/Cu-lean layer (oxide layer)/Cu-enriched layer (rapid diffusion layer) configuration is formed in the burn heat-affected zone of Ti14 alloy; this multiple-layer structure is beneficial for preventing O 2 diffusion. Furthermore, although Al can migrate to form Al 2 O 3 on the surface of TC4 alloy, the burn-resistant ability of TC4 is unimproved because the Al 2 O 3 is discontinuous and not present in sufficient quantity.

Semi-solid processing (SSP) is a popular near-net-shape forming technology for metals, while its application is still limited in titanium alloy mainly due to its low formability. Recent works showed that SSP could effectively enhance the formability and mechanical properties of titanium alloys. The processing parameters such as temperature and forging rate/ratio, are directly correlated with the microstructure, which endow the alloy with different chemical and physical properties. Specifically, as a key structural material for the advanced aero-engine, the burn resistant performance is a crucial requirement for the burn resistant titanium alloy. Thus, this work aims to assess the burning behavior of Ti14, a kind of burn resistant alloy, as forged at different semi-solid forging temperatures. The burning characteristics of the alloy are analyzed by a series of burning tests with different burning durations, velocities, and microstructures of burned sample. The results showed that the burning process is highly dependent on the forging temperature, due to the fact that higher temperatures would result in more Ti2Cu precipitate within grain and along grain boundaries. Such a microstructure hinders the transport of oxygen in the stable burning stage through the formation of a kind of oxygen isolation Cu-enriched layer under the burn product zone. This work suggests that the burning resistance of the alloy can be effectively tuned by controlling the temperature during the semi-solid forging process.

The present work is focused on the development of microstructure of Ti-7Cu alloy as a function of forging temperature and forging ratio in semi-solid state and the influence of resulting microstructure on the mechanical properties. The experimental results showed that the dynamic recrystallization occurred during semi-solid forging and the grain refinement was attained which is considered to be favorable for improving the semi-solid formability. The grain size increased with forging temperature and decreased with forging ratio. Forging temperature has a significant effect on the precipitation behavior in grain boundary regions during the semi-solid processing. More acicular-Ti2Cu tended to precipitate in grain boundary regions with higher forging temperature and finally formed precipitates zones adjacent to grain boundaries after forged at 1,100°C. High ultimate tensile strengths and low elongation have been achieved after semi-solid forging. The strength and hardness decreased with increase of forging temperature, while the ductility increased with increase of forging ratio. The relative contributions of tensile properties were attributed to the varieties of grain size and the distribution of Ti2Cu precipitates obtained by semi-solid forging.

Nanostructured catalytic powders (NCP) were used to produce the laser melting deposition (LMD) amorphous-nanocrystalline composite coatings on titanium alloy. With amorphous alloy addition, amorphous surrounded nanoscale polycrystals (ASNP) and amorphous surrounded one-dimensional nanocrystals (ASON) were produced. A composite coating was fabricated by LMD of the Stellite 6-TiB2 mixed powders on a TA15 alloy. Scanning Electron Microscope (SEM) test results indicated that with Y2O3-SiC-Mo addition, an LMD amorphous-nanocrystalline composite coating was obtained. The addition of the Ce-Al-Ni amorphous alloy led a micro-nano structure LMD coating to be produced. This research provided essential theoretical and experimental basis to promote the application of LMD technique in the modern aviation industry.K e y w o r d s : catalytic powders, amorphous materials, nanomaterials, polycrystals, lasers

No abstract