低成本高性能镍基高温合金中Hf与TCP相析出关联性研究

Nickel-base superalloy is a key material of aerospace engine. It has become a hot research topic to develop a new type of high temperature alloy of lower cost and high performance by replacing Re and Ru with suitable refractory elements. However, the complex interaction between the elements easily leads to the precipitation of TCP phase, thus reducing the mechanical properties of the alloy. No precipitation of TCP phase and good comprehensive mechanical properties have always been two major goals for researchers, however, the addition of a large number of refractory elements makes it difficult to coordinate the contradiction between the two. The applicant’s preliminary study shows that the interaction between Hf and carbide forming elements such as Cr, Ti, Nb, W can inhibit the precipitation of TCP phase in the alloy, which provides a new way to solve the contradiction between improving temperature bearing ability of alloy and of TCP phase. In this research, a novel high temperature alloy of lower cost and high performance was adopted as the research object. Based on experiment, thermodynamic calculation and theoretical analysis, this research studied the influence of additive Hf on alloy microstructure, revealed the influencing rule of Hf on element segregation and diffusion behaviors, illustrated the working mechanism of Hf on inhibition of TCP precipitation, and put forward the control strategy, in the hope of providing the theoretical basis and technical reserves for developing China's novel high temperature alloy of high performance and low cost.

镍基高温合金是航空航天发动机中关键材料之一，通过低成本难熔元素替代Re、Ru元素含量，发展低成本高性能的新型高温合金已成为研究热点，但大量难熔元素添加易导致TCP相析出，降低合金力学性能。尽管如此，无TCP相析出及良好综合力学性能一直是研究者们追求的目标，而大量难熔元素的添加使两者之间的矛盾难以协调。申请人前期研究表明，借助Hf与Cr、Ti、Nb、W等碳化物形成元素间的交互作用，可抑制合金中TCP相的析出，为协调合金承温能力的提高与抑制TCP相析出之间的矛盾提供了一条新的解决途径。本项目在已有工作基础上，以具有重大应用背景的新型低成本、高性能的高温合金为研究对象，结合实验、热力学计算，研究Hf元素的添加对合金微观组织的影响规律，揭示Hf对元素偏析行为和扩散行为的影响规律，阐明Hf元素抑制TCP析出的机理，并提出控制策略，为发展我国新型低成本、高性能的高温合金成分设计提供理论基础和技术储备。

进燃汽涡轮发动机对高温合金材料耐高温能力提出了更高的要求，合金化是提高合金高温性能的主要途径之一。但是，大量难熔元素的添加易导致合金析出有害TCP相，从而影响高温合金的服役性能。本项目通过第一性原理计算了碳化物晶体常数，研究了Hf元素对高温合金中碳化物晶体结构和相析出行为的影响，发现Hf元素的添加影响合金的凝固特征，从而影响合金微观组织结构。借助高通量制备技术，制备了微观组织连续变化的样品，研究了合金元素对微观组织的影响规律。研究了长期时效过程中，时效时间对MC6型碳化物及γ′相演化规律和元素扩散行为，揭示了Hf元素与Ti、W、Nb、Cr等碳化物形成元素之间的交互作用机制，发现Hf元素的添加可显著改变元素的偏析，促进MC6碳化物的析出，明晰了温度场作用下碳化物演化规律，以及MC6退化成M23C6的机制，建立了温度场作用下碳化物演化规律和元素扩散行为。研究了高温蠕变过程中微观组织的演变规律，探讨了热/力耦合作用下碳化物微观组织形貌演变的规律，提出Hf元素抑制TCP相析出的作用机制和策略。通过本项目的研究可为先进航空发动机用高温合金材料成分设计提供科学依据。