钼合金燃料包壳激光深熔焊接头的合金化强韧机制与“寄生”钎焊同步增强效应

Molybdenum alloy, with excellent strength and toughness, is the next generation of accident tolerant fuel (ATF) cladding material in China. However, its application in the crucial places is limited severely due to the high gas content, the serious defects of blowhole and joint embrittlement. In this project, “cladding tube / plug" components of molybdenum alloy with high performance will be taken as the subject investigated. The approach of enhancing the joint’s strength and toughness and cleaning the gas is mixing Ti into the weld pool and carburizing the heat affected zone. And the method of combining the experiment with simulation will be employed ①to clarify alloying effects of gas cleaning, joint purifying, solution enhancement, dispersion strengthening and grain boundary enhancement, and to reveal the mechanism of enhancing the strength and toughness of the laser welded molybdenum alloy joint by combined alloying; ②to study the physical mechanism of the influence of the laser power modulation on the generation, motion and escaping of bubbles in the laser welding pool, and the mechanism of suppressing the blowhole defects in the laser welded molybdenum alloy joint though alloying and laser power modulation; ③to figure out the development and enhancement effect of the “parasitic” brazing interface in the heat affected zone of laser welded molybdenum alloy joint with the interlayer, and master the method of controlling the synchronous enhancement effect of the “parasitic” brazing interface. The expected result, having important theoretical significance and engineering application value, will help our country break through the bottle neck problem of welding the ATF cladding and enrich the laser welding system info for materials with high gas content and high melting point.

作为我国下一代事故容错燃料（ATF）包壳材料，高性能钼合金自身强韧性优异，但其含气量高、焊后气孔缺陷多、接头脆化严重，使其在核电等关键场合的应用受限。项目以高性能钼合金“包壳管/端塞”激光焊组件为对象，提出熔池掺Ti、接头渗C的合金化强韧、除气思路。采用试验和模拟结合的方法开展以下研究：①揭示“组合式合金化”的除气净化、固溶强化、弥散强化和晶界强化机制，阐明钼合金激光焊接头的强韧化机理；②揭示功率调制影响激光焊熔池气泡产生、运动及逸出行为的物理机制，阐明合金化和激光功率调制抑制钼合金激光焊气孔缺陷的机理；③揭示钼合金“套接接头”加中间层激光焊热影响区“寄生”钎焊界面的演变机制，掌握调控“寄生”钎焊界面同步增强效应的原理。预期研究结果将突破我国自主ATF包壳发展中遇到的焊接瓶颈问题，显著提高钼合金焊接质量，丰富高含气量材料、脆性难熔材料激光焊理论体系，具有重要的理论意义和工程应用价值。

高性能钼合金自身强韧性优异，但其含气量高、焊后气孔缺陷多、接头脆化严重，其熔焊接头抗拉强度通常只有100MPa左右（≤母材抗拉强度的20%）。项目选用Ti, C, N等元素进行合金化强化研究，研究掌握了合金化改善钼合金激光焊接头强韧性的机理，通过组合式合金化实现了焊缝和热影响区同步强化、晶内和晶界同步强化，使钼合金燃料包壳组件激光焊接头抗拉强度达到母材强度的95%以上；研究揭示了钼合金套接接头热影响区“寄生”钎焊界面演变机制，即随着到焊缝熔合线距离逐渐增大，“寄生”钎焊界面冶金结合形成机理依次为熔池液态金属在毛细作用下深入搭接缝隙实现熔接、钎料熔化润湿母材钎接、钎料与母材固相扩散连接三种形式；研究掌握了通过合金化和功率调制等抑制钼合金激光焊气孔缺陷的方法和机理，使焊缝孔隙率从1.10%减小到0.35%，最大气孔直径不超过50微米。项目焊接制备的核燃料包壳管进行了室温静载拉伸、水压爆破和泄漏率测试，各项指标均达到了行业技术标准的要求。研究结果对我国自主ATF包壳、高温热管技术发展起到了促进作用，并对高含气量材料、脆性难熔材料激光焊具有普遍指导意义。