多场耦合作用下制备高性能粉末冶金TiAl合金板材的基础研究

TiAl alloy represents a new class of light-weight structural materials for high temperature, the powder metallurgy route offers an attractive alternative to the ingot rout for the preparation of TiAl alloy especially of TiAl sheet. In this project, aim at the foundation science problems about the fabrication of high performance of TiAl sheet by gas atomized prealloy powders, the delivery and atomization mechanism of TiAl alloy melt on the condition of cold crucible with electric, magnetic, temperature and flow multi- coupled fields was investigated, and the multi-phase fluid simulation was analyzed to evaluate the breakup mechanism during atomizing process. Gas atomization of prealloyed powder followedby hot isostatic pressing (HIP) to full density is viable approach for the production of forging and rolling performs, the forming and controlling mechanics of defects during the densification process for PM TiAl alloy was also studied. Through computer simulation combined with physical simulation of temperature, stress and velocity multi- coupled fields, the rolling deformation mechanism of TiAl alloy was analyzed. The subject is to break through the super refining, melt delivery, atomization nozzle design, oxygen controlling and high density hiped billets and high performance in large scale hot working technology, to supply the.foundation of development of TiAl alloy powder processing and meet the requirements of light structural materials for high-temperature applications in aerospace and other areas

TiAl合金是一种新型的轻质高温结构材料，在航空航天和汽车发动机等领域有广阔的应用前景，粉末冶金方法可以消除铸造缺陷，有望实现TiAl合金尤其是TiAl合金板材的工程化应用。本项目拟开展研究冷坩埚电磁场、温度场和流场多个物理场的耦合作用下TiAl合金液的导流与雾化行为，建立粉末冶金TiAl合金致密化过程中微缺陷形成和控制的基础理论，明确在温度场、应力场、速度场等多场耦合作用下板材轧制变形机理，突破TiAl合金纯洁熔炼、液态金属导流、雾化喷嘴结构设计、气雾化粉末氧含量和粒度控制以及高致密度大尺寸粉末冶金坯体制备和无缺陷板材轧制成形等技术关键，获得高纯低氧球形气雾化粉末和高性能粉末冶金板材的制备与加工技术基础，解决高性能大尺寸粉末冶金构件制备难题，满足以满足我国高超音速飞行器的研发用材的需求。

TiAl合金是一种新型的轻质高温结构材料，在航空航天和汽车发动机等领域有广阔的应用前景，粉末冶金方法可以消除铸造缺陷，有望实现TiAl合金尤其是TiAl合金板材的工程化应用。本项目完成了电场、磁场和流场多场耦合作用下冷坩埚感应熔炼和导流过程的数值模拟，对雾化过程中金属液滴与雾化气体的相互作用进行了分析，在两相流流动和雾化喷嘴气体动力学研究基础上，结合Fluent软件的数值模拟，研究了TiAl液滴的破碎过程，获得了雾化压力、熔体过热度等对金属液雾化作用规律，制备出了低氧球形的TiAl预合金粉末，明确了雾化工艺参数与粉末粒度和氧含量的关系，探明了TiAl合金粉末的氧化特性，粉末中的氧含量随着合金粉末的粒度变细而逐渐增大，粉末颗粒表面存在Al2O3和TiO2等氧化物，氧化程度与粒径大小呈反比关系，对所制备的合金粉末的微观组织和相组成进行了表征，SEM、EBSD和TEM研究表明，TiAl合金粉末相结构中Υ相的含量受粉末尺寸影响很大，随着粉末尺寸的增加而大幅增加，研究了TiAl 预合金粉末在温度场和应力场下固结成形中孔隙演变过程和致密化机理，获得了TiAl合金粉末致密化过程中热诱导孔洞(TIP)和原始颗粒边界(PPB)等缺陷形成理论和控制方法，以及热等静压温度对合金组织和性能的影响规律，研究了TiAl合金在热压缩状态下的变形机制，得到了材料在变形过程中的组织演变规律，通过包套热轧，采取合理的包套材料和结构设计，成功制备出外形完整、表面无缺陷的TiAl合金板材，经过室温和高温力学性能测试，TiAl板材的室温塑性可达3.62%，室温抗拉强度最高可达695MPa，800℃下拉伸塑性高达49.5%，同时抗拉强度高达462MPa，表现出了高的强度和良好的塑性。从而为改进TiAl 合金粉末与成形工艺提供科学依据，同时为粉末冶金TiAl合金的研制奠定坚实的理论和试验基础。