粉末冶金高温合金原始颗粒边界的形成、演化及消除机制

Gas turbine disc produced by powder metallurgy superalloy was the critical key component of high performance aircraft engine. Prior particle boundaries (PPB) were regarded as weak interface composed of carbides and oxides etc along the powder particle profiles of PPB. Crack initiation and propagation induced by PPB could catastrophically lead to gas turbine disc failure. To date, the mechanism of formation, evolution and elimination of PPB were unclear. Focused researches will be carried out in this project, we emphasize: (1). The distribution and existence situation of main elements (especially for carbon and oxygen) of PPB will be characterized by fixed-point sampling, high accuracy and visualization analysis method. Thermodynamic and kinetic of carbides and oxides formation will be investigated to clarify the formation mechanism and evolution law of PPB. (2). The hot extrusion model of core-shell spherical object will be established. Elimination mechanism of PPB will be explained by combination of atomic diffusion equation under stress conditions and the parameters obtained by finite element method with characteristic boundary conditions. (3). The relationships between established quantitative classification method of PPB and key performance parameters will be used to gain the method of critical process for eliminating PPB. The expected results will provide a theoretical basis for controlling the defects and microstructure of powder metallurgy materials.

粉末冶金高温合金涡轮盘是高性能航空发动机的核心热端部件，原始颗粒边界是粉末冶金高温合金中碳化物、氧化物等沿颗粒轮廓形成的弱界面结合，其造成的裂纹萌生和扩展是导致涡轮盘失效的重要因素。目前，原始颗粒边界的形成、演化和消除机制尚不明确。本项目将重点开展以下研究：（1）采用定点取样、高精度、可视化分析方法，通过对原始颗粒边界组成主要元素（特别是C、O）的分布和存在形式进行定量表征，研究碳化物、氧化物形成的热力学条件和动力学过程，阐明原始颗粒边界的形成机制与演化规律；（2）通过建立基于原始颗粒边界存在和分布规律的核-壳球体挤压模型，引入特征边界条件的有限元模拟方法，结合应力条件下原子扩散方程，阐明原始颗粒边界的消除机理；（3）通过原始颗粒边界定量分级方法，及其与关键性能的映射关系，形成原始颗粒边界消除的关键工艺参数选择方法。预期成果将为粉末冶金材料的组织和缺陷控制提供理论依据。

本项目旨在分析原始颗粒边界的组成、形成机制，以及消除机理。结果表明：FGH96合金的PPB析出相主要为γ'相、MC型碳化物相和少量的Al2O3和ZrO2。γ'相的组成主要为fcc超晶格结构的Ni3(Ti/Al)；MC型碳化物主要为fcc型的(Ti/Nb)C；Al2O3的结构为六方结构；ZrO2的结构为面心立方结构。调节热等静压参数只能在较小程度上改善PPB的析出程度，不能消除PPB。结合Thermo-calc软件计算发现，原始颗粒边界析出相的形成机制是由于在温度场的作用下，碳化物和γ'相和氧化物易于在结合界面析出，因此选择在PPB处析出而形成弱结合界面。经热挤压后，原始颗粒边界已被破碎，合金的力学性能得到一定的提升。通过建立核-壳球体挤压模型，结合Deform软件模拟原始颗粒边界破碎过程，得到了原始颗粒边界降解、消除的物理模型。