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.

中文翻译：

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纯钛的水下激光焊接：氧化和硬化行为

以空气为辅助气体，在模拟水下设备中对cp-Ti进行局部水下水下激光焊接研究，旨在寻找一种可行且经济的方法来现场修复钛合金水下航行器。实验表征了cp-Ti激光焊缝的宏观形貌，微观结构和显微硬度，它们是焊接参数的函数。还详细研究了焊缝的氧化和硬化行为。已经发现，采用空气辅助吹气进行局部水下水下激光焊接对于获得完整而有光泽的焊缝是可行的。与大气中的焊缝相比，特殊的水下焊接环境几乎不影响焊缝的截面形态。焊缝呈三层结构。高温高压水蒸气和局部吹气是焊缝氧化的直接原因，而气孔缺陷进一步加剧了氧化行为。富氧区域主要集中在焊接中心的顶部区域和熔合区附近，这是因为晶界和相界的数量更多。另外，局部吹气和水蒸气气氛引起的部分氧化，以及水的快速冷却作用引起的较高强度的针状马氏体，都会导致焊接硬化。然而，调整焊接工艺参数，例如提高焊接速度，可以有效地降低焊接的显微硬度。我们的发现可以帮助您了解水环境对水下激光焊接的影响，