钼基难熔金属电子束焊接冶金过程能量-合金化耦合控制及接头强韧化机理研究

Molybdenum alloys have excellent high temperature mechanical properties and relatively low cost, making their widely application in high temperature structures of aerospace industry. Attributed to the embrittlement of welded joint, fusion welding of molybdenum alloy becomes a technology bottleneck for the gas jet valve development of a new generation solid rocket divert and attitude control motor. For its advantages such as vacuum atmosphere, low heat input and limited heat affected zone, electron beam welding is recognized as a preferred welding method of molybdenum alloy. Focused to the demand and existing problem, an alloying system of welding filler metal was designed and a kind of integrated thermal control method was proposed for electron beam welding of molybdenum alloy. So that, non-equilibrium metallurgical process of electron beam welded molybdenum alloy joint was adjusted through energy - alloying coupling means. As a result, grain configuration and grain boundary microstructure were optimized. Finally, the strengthening and toughing mechanism of the welded joint was revealed. Research achievements of this project can not only solve the electron beam welding technology problem of molybdenum alloy used in high temperature gas jet valve, promote independently design and manufacture ability of propulsion system for the new generation air defense weapon in our country, also can enrich basic welding metallurgy theory of refractory metal, have important scientific and engineering significance.

钼合金具有优异的高温综合性能及相对较低的原料成本，在航空航天领域高温结构得到广泛应用。由于存在接头脆化问题，钼合金熔焊成为我国新一代固体姿轨控发动机燃气射流阀研制的技术瓶颈。电子束焊接因真空保护气氛、焊接热输入小及接头热影响区小等优点，是钼合金高质量焊接最有前景的焊接方法。本项目针对钼合金焊接的技术需求与存在问题，设计钼合金电子束焊接材料合金元素体系，提出钼合金电子束焊接一体化热控方法，通过能量-合金化耦合手段调控钼合金电子束焊接非平衡冶金过程，优化接头内晶粒形态与晶界微结构，解明接头强韧化机理。研究成果不仅可以解决我国高温燃气射流阀用钼合金的真空电子束焊接技术难题，提升我国新一代防空武器推进系统自主设计与制造能力，还可以丰富难熔金属焊接冶金基础理论，具有重要的科学与工程意义。

项目针对钼合金焊接时焊缝晶粒长大和晶界偏析引起的焊接接头脆化问题，开展钼基难熔金属电子束焊接技术研究。通过对接头组织与性能的研究，揭示了接头组织演变与冶金调控机理。 . 项目通过数值模拟方法分析了焊接束流及焊接速度的变化对接头温度场及应力场的影响规律，并确定了TZM合金电子束焊接试验的参数范围为：焊接束流33-40mA，焊接速度330-390mm/min。焊缝区由粗大的柱状晶及等轴晶组成。而热影响区在焊接热循环的作用下发生再结晶，并且该区的晶粒尺寸明显小于焊缝区的晶粒尺寸。焊缝区的Mo2C的含量明显高于热影响区。MoO2及TiO2熔点较低，易于向晶界偏析，产生非共格关系的相界，进而造成焊缝晶界上拉应力的集中，造成接头焊缝区晶界脆化及沿晶断裂的发生。. 采用焊缝中添加Zr元素的TZM电子束焊接试验，当焊缝中Zr的理论质量分数为1.32%时，由于Zr与O的优先反应并在焊缝晶粒内部沉淀析出。接头焊缝区的晶界得到了净化，接头的断裂形式由焊缝区的沿晶断裂与穿晶断裂的混合断裂形式，转变为焊缝区完全的穿晶断裂，接头的强度较对照组显著提高，达到452MPa。焊缝中Re元素含量升高时，接头的抗拉强度也随之升高。当焊缝Re的质量分数为21.6%时，接头的抗拉强度升至408MPa。Re含量升高到48.7%时，在焊缝区晶内形成大量的小角度晶界提高位错开动的门槛值，而且由于Re的固溶作用，造成钼的晶格常数的降低，原子间结合力的升高，阻碍了氧元素向晶界上的扩散，抑制了沿晶断裂的形成。接头断裂转移至热影响区，抗拉强度提高到524MPa，达到一定的应用要求。. 项目研究成果不仅突破我国高温燃气射流阀用钼合金的真空电子束焊接技术瓶颈，提升我国新一代防空武器推进系统自主设计与制造能力，还可以丰富难熔金属焊接冶金基础理论，具有重要的科学与工程意义。