Effects of adding nano-sized ZrC in the fusion zone (FZ) on the microstructures and properties of laser-welded joints of pure molybdenum (Mo) and underlying mechanisms were explored. Compared with the joints without ZrC, the average microhardness of the FZ increases from 180 HV to 330 HV, the tensile strength of joints grows from 32 MPa to 386 MPa, and the fracture mode of joints switches from intergranular fractures to that dominated by cleavage fractures, after adding ZrC. ZrC, ZrO2, and Mo2C are detected in the FZ after adding ZrC. ZrC and ZrO2 is mainly found on grain boundaries (GBs). ZrC is able to deplete O in the FZ, thus decreasing the amount of harmful molybdenum (Mo) oxides on GBs, so it plays a role in purifying and strengthening GBs. ZrC, ZrO2, and Mo2C particles not only hinder dislocation movement and GB movement, but also serve as effective heterogeneous nucleation cores and therefore can refine grains in the FZ. The average grain size in the FZ of the joint without ZrC is 47.6 μm, while it is 28.4 μm after adding ZrC, which reduces by 40.3 % compared with the former. The significant improvement of the joint strength after adding ZrC is a result of joint action of dispersion strengthening, fine-grain strengthening, and GB purification.

中文翻译：

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在熔池中添加纳米级 ZrC 的激光焊接钼接头的微观结构和机械性能


探讨了在熔融区 （FZ） 中添加纳米级 ZrC 对纯钼 （Mo） 激光焊接接头微观结构和性能的影响及其潜在机制。与未添加ZrC的节理相比，加入ZrC后，FZ的平均显微硬度从180 HV提高到330 HV，节理的拉伸强度从32 MPa提高到386 MPa，节理的断裂模式由晶间断裂转变为以解理断裂为主的断裂模式，加入ZrC后，在FZ中检测到ZrC、ZrO2和Mo2C，ZrC和ZrO2主要存在于晶界（GBs）上。ZrC 能够消耗 FZ 中的 O，从而减少 GB 上有害钼 （Mo） 氧化物的数量，因此它在净化和强化 GB 方面发挥着净化和强化 GB 的作用。ZrC、ZrO2 和 Mo2C 颗粒不仅阻碍位错运动和 GB 运动，而且还作为有效的非均相成核核心，因此可以在 FZ 中细化晶粒。不含 ZrC 的接头 FZ 中的平均晶粒尺寸为 47.6 μm，而加入 ZrC 后为 28.4 μm，与前者相比减小了 40.3 %。添加 ZrC 后接头强度的显著提高是分散强化、细粒强化和 GB 净化共同作用的结果。