600℃铸造高温钛合金的组织演变规律及强化机制研究

With the development of aerospace titanium alloy component towards large size, complex, thin-walled direction, Titanium alloy precision casting technology has a wide application prospect. 600℃ high temperature titanium alloy precision casting technology represents for the highest level of the titanium alloy casting. At present, the 600℃ high temperature titanium alloy precision casting technology prepared in our country is far below the level of the developed countries, which can be mainly ascribed to the indistinction of the alloy composition, the formation and control mechanism of microstructure, and the key factors controlling the mechanical behavior. Hence, the project takes the conventional high temperature titanium alloy Ti-1100 as the investigated object, to study the effects of the Zr, Nb, B content on the microstructure of the as-cast and heat treatment alloys. And the formation and control mechanism of the silicide phase, α2 phase, and TiB phase in high temperature titanium alloys will be revealed. The mechanical properties of the alloys are invesitigated under the room temperature and high temperature conditions, and the relationships between the composition, microstructure and the macroscopic mechanical properties are established. Finally, the strengthening mechanism and the fracture mechanism of the high temperature titanium alloys under the room temperature and high temperature conditions are revealed. This project will lay the theoretical foundation for the composition design, promoting the development of the cast high temperature titanium alloy, and expanding its application area.

随着航天用钛合金构件向大尺寸、复杂、薄壁方向发展，钛合金精密铸造成形技术应用前景广阔。600℃高温钛合金的铸造技术代表着钛合金铸造的最高水准。目前我国600℃高温钛合金的铸造技术较国外差距很大，其主要原因是没有找到适合铸造成形的高温钛合金成分，对合金的组织形成机理及调控机制不清晰，尤其是对控制力学行为的关键因素仍缺乏深刻认识。鉴于此，本项目拟以常用的Ti-1100合金为研究对象，研究Zr、Nb、B元素及复合添加对Ti-1100合金凝固组织和热处理态组织的影响规律，揭示高温钛合金中硅化物及α2相的形成及调控机制，阐明TiB相在凝固过程中的形成机制以及热处理条件下TiB相内部结构的演化机制；研究合金的室温和高温力学性能，建立高温钛合金成分—组织—宏观力学性能之间的关系，揭示高温钛合金室温及高温强化机制与断裂机理，为铸造高温钛合金的成分设计，促进铸造高温钛合金的发展，扩大其应用领域奠定理论基础。

研制开发能耐600 ℃及更高温度的铸造钛合金是国家急需攻克的难题。本研究从600 ℃铸造高温钛合金的成分设计着手，系统研究了Zr、Nb元素对铸造Ti-1100合金的组织形成机理、高温抗氧化性能、高温摩擦磨损性能、高温力学性能的影响，为解决国家在航空航天等方面的重大需求具有重要的科学意义和实际应用价值。研究结果发现：Zr、Nb元素的添加均没有改变铸造Ti-1100合金的显微组织，仍为具有网篮特征的魏氏组织。随Zr、Nb含量的增加，合金组织具有一定的细化作用并有硅化物析出。Nb元素可以有效地提高铸态合金的高温抗氧化性能，氧化动力学曲线服从抛物线法则。Ti-1100-1.0Nb合金在650 ℃，700 ℃，750 ℃温度下均表现出最佳的高温抗氧化性能，且在三个氧化温度下氧化100小时后的增重分别为0.44 mg/cm2，0.54 mg/cm2，1.46 mg/cm2，增重增幅分别为23 %和232 %。而随着Zr含量的增加，铸态和热处理态合金的高温抗氧化性能均降低。铸态和热处理态Ti-1100-xZr合金磨损率均随着温度的升高而降低，铸态合金在600℃磨损率较室温磨损率降低了77.9%-91.3%，较500℃磨损率较低了38.1%-72%。同时随着Zr含量增加，铸态和热处理态Ti-1100合金室温磨损率呈增加趋势，而高温磨损率呈降低趋势。而铸态Ti-1100-xNb合金的室温磨损率随着Nb含量的增加先增高后降低，其耐磨性随磨损温度的升高显著提高，与铸态合金相比，1000 ℃退火处理后的合金耐磨性显著降低。不同Zr、Nb含量合金的磨损机制均由室温时的磨粒磨损，黏着磨损向高温时的氧化磨损转变。Nb可以提高铸态Ti-1100合金的室温和高温抗拉强度，但导致延伸率降低。室温最高抗拉强度可达到1084 MPa，延伸率为2.5%，600 ℃抗拉强度可达591 MPa，延伸率为3.07%，铸态力学性能基本达到了预期目标。