高温金属材料晶体生长取向选择机理与控制

This project is targeted at advanced Ni-based single crystal superalloys and newly-developed titanium aluminide alloys, to carry out research on the selection of crystal growth orientation and solidification interface anisotropy, around the crystal orientation selection mechanism and its control during the preparation of high-performance aero-engine blades through directional solidification process. Through numerical simulation and experiments, the effect of thermal and solute fields in directional solidification on grain competitive growth and crystal selection behavior is to be clarified. The relationship among crystal growth direction, crystal preferred orientation and the main heat flow direction will be obtained as well as the influence of solidification parameters such as growth rate and temperature gradient will be investigated, in order to provide a theoretical basis for the realization consistency of those three directions during the crystal growth. The project will reveal the competitive growth mechanism between preferred orientation and non-preferred orientation in metallic materials, proved competitive growth process and mechanism for different oriented grains, establish stability conditions for the growth orientation to obtain optimal mechanical properties. We will also establish an accurate model of crystal growth orientation control under the variation of the thermal field, crystal preferential growth direction and solute field, prove the historical correlation among liquid-solid transformation, solid-solid transformation and crystal orientation, establish the precise control model of crystal orientation and technology base. The proposed project will develop theoretical and experimental basis for achieving the precise control of the crystal orientation of high-temperature metallic materials.

本项目以先进镍基单晶高温合金及新型TiAl合金为对象，围绕定向凝固技术制备高性能航空发动机叶片过程材料晶体取向选择机理及其控制的科学问题，开展晶体生长取向选择及凝固界面各向异性研究。通过模拟和实验，阐明定向凝固温度场和溶质场对晶粒竞争生长和选晶行为的影响，获得晶体生长方向、晶体择优取向和主热流方向之间的关系以及与生长速度和温度梯度等凝固参数的影响规律，为实现三个方向一致下的晶体生长提供理论依据；揭示金属晶体择优取向与非择优取向生长的竞争机制；探明不同取向晶粒竞争生长过程及机制，确立具有最优力学性能的晶体取向生长的稳定性条件；建立在热场、晶体择优生长方向和溶质场变化条件下的晶体生长取向控制的精确模型；探明液固相变、固固相变及晶体取向的历史相关性；构建晶体取向的精确控制模型及工艺技术基础。为实现高温金属材料晶体取向的精确控制提供理论和实验依据。

本项目以先进镍基单晶高温合金和新型钛铝合金为对象，采用定向凝固技术，研究选晶法和籽晶法晶体取向控制过程中晶体取向与凝固组织、析出相、界面稳定性之间的关系，选用不同结构的选晶器和不同取向的籽晶，结合不同结构尺寸的铸件，采用数值模拟、实验验证和理论分析相结合的方法，开展定向凝固高温金属材料晶体取向生长及界面各向异性研究，分析晶体取向、热场、流场、枝晶机械阻碍等在晶粒竞争长大中的作用规律，阐明凝固参数与晶粒竞争生长行为之间的内在联系，获得晶体生长方向、界面各向异性、晶体择优取向和主热流方向之间以及与生长速度和温度梯度之间的内在联系，探索定向凝固过程中的取向选择机制。.通过本项目的执行，建立了定向凝固条件下晶体生长方向、晶体择优取向和主热流方向之间以及与生长速度和温度梯度之间的唯象和函数关系，明确了凝固界面形态及其稳定性与界面各向异性对晶体择优取向的影响规律，有助于实现晶体生长方向、晶体择优取向、主热流方向三者一致。深化了对晶粒竞争生长行为、晶体取向选择机制和晶体取向控制方法的理解，奠定了高温金属材料晶体取向的精确控制的理论基础。研究了择优取向与非择优取向生长的竞争机制以及连续相变对晶体取向的影响机制，从源头上获得了晶粒竞争生长的演化规律及籽控取向的继承性，提出了晶体取向控制的有效方法。研究了复杂合金在变热场、变流场和变方向等条件作用下的晶体生长取向变化、籽控择优取向变化及竞争规律。.在项目执行期间，发表SCI论文148篇，出版专著1本，申请和授权国家发明专利34项，培养研究生14名。项目组骨干成员获得国家杰出青年基金资助一项，项目成果获教育部自然科学二等奖2项。研究成果已经在航空企业得到推广。