界面反应对冷喷涂增材制造Ti-6Al-4V合金界面结合强度的影响机理

The advantages of cold spray technique are low deposition temperature and solid-state deposition. The active titanium alloy can be deposited by cold spray in the atmospheric environment, so it is suitable for additive manufacturing of titanium alloy. However, the bonding mechanism of cold-spraying deposition coating is not metallurgical bonding but mechanical interlocking, which have a severe impact on the mechanical property of deposition coating. Although many researchers have studied deposition theory which particles impacted on substrate by cold spray using numerical simulation and experiment, the research interest is focused on the bonding interface between coating and substrate and soft pure metals. Actually, it is still lack of adequate understanding for interface bonding, interfacial reaction and microcosmic mechanism inducing interfacial reaction of hard active metal materials. The Ti-6Al-4V alloy which has been widely applied in the aerospace industry is selected as the deposition powder material, the relations between dislocation, adiabatic temperature rise, stress distribution, metal jet and chemical activity of deformation Ti-6Al-4V particles in deposition coating and interfacial reaction are studied by finite element method and experiment, revealing the interface reaction and microcosmic mechanism inducing interfacial reaction, discussing the influence mechanism of interface reaction on interfacial bonding strength, confirming the microcosmic essence affecting the interfacial mechanical behavior of Ti-6Al-4V coating produced by additive manufacturing. Above studies can be rationally used to improve the mechanical property of additive manufacturing Ti-6Al-4V alloy.

冷喷涂技术具有低温固态沉积特性，可以在开放环境下进行活性金属钛合金的沉积制备，是一种适用于钛合金增材制造的技术。但冷喷涂沉积机制属于机械咬合，非冶金结合，结合界面已经成为影响沉积层力学性能的关键。尽管许多研究者通过数值模拟和实验的方法对冷喷涂的沉积机制进行了研究，但研究主要集中于沉积层与基体的结合界面，且研究材料以软质纯金属为主，对硬度较高的活性金属的沉积层内界面结合机制、界面反应特征、诱发界面反应的微观机理还不明确。本项目选择航空航天领域应用最广泛的钛合金Ti-6Al-4V为研究对象，利用数值模拟与试验结合的方式研究冷喷涂沉积层中形变Ti-6Al-4V颗粒内位错、绝热温升、应力分布、射流、化学活性与界面反应的关系，揭示冷喷涂增材制造Ti-6Al-4V层界面反应机制及其微观诱发机制，讨论界面反应对界面结合强度的影响机理，明确影响增材制造Ti-6Al-4V材料界面力学行为的微观本质。

冷喷涂技术依靠高速气流携带喷涂颗粒以超音速状态撞击基材发生塑性变形获得沉积涂层，具有能够在开放环境下沉积制备活性金属钛合金的优势，是一种适用于活性金属增材制造的独特技术。因此，沉积材料的硬度是制约冷喷涂技术应用的瓶颈问题，冷喷涂增材制造孔隙率低于1%的高致密钛合金沉积层是难点。针对上述问题，首先，借助微米级工业CT研究冷喷涂增材制造工艺优化与沉积层孔隙率的关系，研究氢化脱氢法制备不规则粉末和等离子旋转雾化球形粉末对沉积层显微组织、拉伸强度的影响规律，揭示不同类型颗粒特性对沉积层力学性能的影响机制，获得Ti-6Al-4V颗粒特性、冷喷涂工艺参数和沉积层质量的匹配性关系；其次，利用ABAQUS/Explicit中动力学显式塑性模型分析沉积层形变Ti-6Al-4V颗粒的Mises应力、等效塑性应变、温度场分布特性，对冷喷涂Ti-6Al-4V沉积中形变颗粒界面组织的微观演变进行预测，掌握法算法在本项目上的具体应用；然后，参考模拟结果，通过FIB技术和TEM技术相结合的方式，发现界面超塑性应变区存在板条马氏体原始组织向纳米等轴晶转变的特性，与真空退火颗粒界面组织对比发现纳米晶区与原始马氏体区存在明显的组织分界线，证明冷喷涂超音速冲击过程中颗粒组织以塑性流变区和原始组织区为特点的非传递性动态再结晶机制；最后，评价热处理对冷喷涂沉积层力学性能的影响规律，利用EBSD、纳米压痕分析对比研究热处理前后沉积层界面组织的晶粒取向、晶粒尺寸分布规律、织构特征、纳米硬度和弹性模量的变化规律，获得优化冷喷涂增材制造Ti-6Al-4V合金的热处理工艺窗口，阐述沉积层颗粒界面塑性流变引起的溅射咬合机制和绝热温升诱发动态再结晶组织纳米化引起的冶金结合机制的微观本质，从而为解决冷喷涂增材制造Ti-6Al-4V材料力学性能差的问题从界面调控方面提供基础理论指导。