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Titanium alloy has extensive applications in numerous fields, such as in aerospace, shipbuilding, petrochemical, and bio-medical. However, under the condition of high temperature (above 700 °C), it is difficult to meet the requirements of the performance of the turbine blades, piston rings, valves, etc. In this paper, the alloy powder is composed of Ni60A, TiN, Al, and Si in accordance with the proportion of 1:3:4:2 (mass ratio), and the composite coating, such as TiN, TiB, Ti5Si3, and Al3Ti were synthesized on Ti-6Al-4V alloy by Yttrium Aluminium Garnet(YAG) laser. The friction and wear experiments were carried out on Ti-6Al-4V alloy and alloyed coatings at different loads (3N, 6N, 9N), and different temperatures (25 °C, 350 °C, 700 °C). The impact of load and temperature on wear performance were analyzed by analyzing the friction traces. The results showed that the abrasion loss, wear width, and depth, wear volume, and wear ratio of the alloyed coatings were less than Ti-6Al-4V alloy, and the surface of furrow was shallow and the wear was less. However, under high temperature conditions, the alloy coating wears worse than Ti-6Al-4V alloy, and the high temperature wear resistance is not ideal.

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In this work, the effect of the sample temperature on the magnesium (Mg) and titanium (Ti) plasmas generated by a Q-switched Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) laser operating at its fundamental wavelength of 1064 nm has been investigated. We observed that increasing the sample temperature significantly enhanced the emission intensities of the plasmas. Comparing the emission peak intensities of the case of 100 °C to the case of 300 °C, we recorded a substantial enhancement of the peak intensities of the latter compared to the former. From these results it can be observed that increasing the sample temperature has a significant effect on the emission intensities of the plasmas. We also studied the plasma dynamics and found that increasing the sample temperature also decreases the air density around the Mg sample surface. The reduction in the air density resulted in a decrease in the radiation process and lowers collision probability. Furthermore, as the plasma expands, the plasma pressure also decreases. In addition, we also employed circular and square cavities to confine the titanium plasma, and investigated the effect of the sizes of the circular and square cavities on the titanium plasma. We observed a general improvement in the emission intensities with both the circular and square cavities and attributed this improvement to the plasma compression effect of the shock waves produced by the plasma within the cavities.

The local dry underwater laser welding of cp-Ti, with air as an assisting gas, and in a simulated underwater facility was researched, aiming to find a viable and economical method for repairing titanium alloy underwater vehicles in situ in the future. Macro-morphology, microstructure, and microhardness of the cp-Ti laser welds, as a function of welding parameters, were experimentally characterized. The oxidation and hardening behaviors of the welds were also studied in detail. It was found that local dry underwater laser welding with air assisted blowing is feasible for obtaining a complete and glossy weld. Compared with a weld in atmosphere, the cross-section morphology of the weld was almost unaffected by the special underwater welding environment. The weld presented a three-layer structure. High temperature and high pressure water vapor and local blowing are the direct causes of weld oxidation, and porosity defects further aggravate the oxidation behavior. The oxygen-enriched areas were mostly concentrated in the top area of the weld center and near the fusion zone, because of the higher number of grain boundaries and phase boundaries. In addition, the partial oxidation caused by local blowing and water vapor atmosphere, and also the higher strength acicular martensite caused by the rapid cooling effect of water, will lead to weld hardening. However, adjusting the welding process parameters, such as increasing the welding speed, can effectively reduce the microhardness of the weld. Our findings can provide an understanding of the influence of water environment on underwater laser welding, and verify the feasibility of a more economical method for the in situ repair of large underwater facilities.