粉末冶金铁素体超合金中纳米析出相演变与协同强化机制

Due to the lack of effecive strengthening mechanisms at high temperature, conventional heat-resistant ferritic alloys can not meet the demand of increasingly higher service temperature and high temperature mechanical properties. In view of these problems, the idea of the comprehensive utilization of several kinds of nanosized strengthening phases, such as Y-Ti-O oxide nanocluster, B2-NiAl and L21-Ni2TiAl intermetallic nanoprecipitates, is proposed. The comprehensive control of population, particle size, distribution, phase constituents and interfacial structure of the nanoprecipitates is realized through the methods of mechano-chemistry synthesis, addiiton of alloying elements and the optimization of heat treatment parameters. The thermodynamics and kinetics of mechano-chemistry synthesis are investigated in order to reveal the formation condiions of the nanoprecipitates, and the evolution of particle size and interfacial structure of these nanoprecipitates. The main focus is put on solving the difficulties in the control of impurity oxygen, the refinement and uniform distribution of the oxide nanocluster, as well as the enhancement of thermal stability of intermetallic compounds. Finally, the processing theory of the collaborative strengthening mechanisms of multi-phase and multi-scale precipitates is established, and the key controlling parameters and technical principles of the match between strength and ductility of the ferritic superalloy is grasped. The objective is to further enhance the high temperature mechanical properties and service temperature limit of powder metallurgy ferritic superalloy. This project is expected to provide theoretical and technical guidance for the development of light-weight high performance ferritic superalloy with complicate shape，and for the design of the other highly alloyed materials strengthened by multi-phase nanoprecipitates.

本项目针对传统铁素体耐热合金高温下缺乏有效的强化机制，不能满足日益提高的使用温度和高温力学性能要求的问题，提出综合利用Y-Ti-O氧化物团簇、B2-NiAl和L21-Ni2TiAl金属间化合物几种纳米析出相进行协同强化的思路，通过机械化学反应、添加微合金元素和控制热处理条件等协作手段综合调控纳米析出相的数量、粒径、分布、相组成及界面结构。研究机械化学反应热力学和动力学，揭示各种纳米析出相的形成条件以及粒径和界面结构的演变规律。重点解决杂质氧含量控制、氧化物团簇细化和均匀化、金属间化合物热稳定性的提高等难题。建立多元、多尺度纳米析出相协同强化的工艺原理，掌握合金强韧性匹配的关键控制因素和技术基础，旨在进一步提高粉末冶金铁素体超合金的高温力学性能和使用温度极限。该研究能够为轻质、复杂形状和高性能粉末冶金铁素体超合金结构件的研制和其它多相协同强化高合金化材料的设计提供理论和技术借鉴。

本项目针对传统铁素体耐热合金高温下缺乏有效的强化机制的问题，提出综合利用氧化物团簇、B2相和L21相进行协同强化的思路，通过机械化学反应、添加微合金元素和控制热处理条件等协作手段综合调控纳米析出相的数量、粒径、分布、相组成及界面结构。通过真空烧结+热等静压、以及选区激光熔化工艺制备出接近全致密的铁素体ODS合金，有效提高了合金的高温力学性能。. 优化设计出三种氧化物和金属间化合物共强化的铁素体ODS合金，分别为高β′相含量铁素体ODS合金（Fe-12.5Al-21.5Ni-10Cr-3.4Mo-0.4YH2-0.22TiH2-0.35Fe2O3）、含Cu型铁素体ODS合金（Fe-5Ni-1Al-1.5Cu-0.2Ti-0.3Y2O3）和含Mn型铁素体ODS合金（Fe-10Cr-5Ni-1Al-2Mn-0.3Y2O3）。高β′相含量合金中的β'相呈近球形，粒径为100~200nm，氧化物粒径仅3~5nm，β'相沉淀强化和氧化物弥散强化对强度的贡献率分别为49%和23%，硬度达852HV，但塑性较低。为了改善合金韧性，基于热力学计算设计了铁素体-奥氏体双基体ODS合金，有效提升了合金的高温强度和塑性，700℃的压缩屈服强度达498MPa，延伸率为4.6%。含Cu型合金中析出NiAl/Cu沉淀和氧化物弥散相，富Cu/B2-NiAl共沉淀相和氧化物颗粒的平均粒径分别为4.76±1.58nm和13.19±3.25nm，数量密度分别为3.5×1023m-3和1.9×1021m-3；析出初期，富集Ni、Al和Mn的bcc-Cu析出相首先在bcc-Fe/氧化物的界面处偏析。随着沉淀反应的继续，Ni、Al和Mn元素向富Cu团簇外迁移，导致B2-Ni(Al,Mn)在富Cu纳米相附近的异质成核。随着B2-Ni(Al,Mn)的生长，形成了氧化物/B2-NiAl复合析出相。含Cu型合金在700℃的抗拉强度和屈服强度分别为214MPa和147MPa。通过纳米氧化物的添加，合金在700℃时的抗拉强度提高约46%。含Mn型合金中析出沉淀强化相为平均粒径为3.0±0.6nm的B2-Ni(Al,Mn)和平均粒径为8.6±1.2nm的长条型L21-Ni2AlMn。采用选区激光熔化制备的含Mn铁素体ODS合金的室温抗拉强度从1267MPa提高到1352MPa；600℃的抗拉强度提高了46.1%。