先进变形高温合金中锯齿状塑性失稳时空特性的实验和机理研究

Serrated plastic instability, also called Portevin-Le Chatelier (PLC) and jerky flow, occurs in many metals and alloys when deformed at particular combinations of strain rates and temperatures. Previous studies on the mechanism of PLC mainly focus on the interaction between mobile dislocation and solute atoms. However, no complete theories have been estabilished to explain the formation and evolution of plastic instability and deformation and propagation of PLC band in Ni based wrought superalloy at high temperatures. Based on the our previous results on the mechanism of inverse dynamic strain aging (DSA) in advanced Ni-based superalloy with low stacking fault energy, which was funded by NSFS, the deformation and propagation of PLC bands in advanced Ni-based superalloy tensile tested at high temperature will be investigated by using the dynamic digital speckle correlation (DSC) method. The critical strain for serrations, decline range of serration and the deformation and propagation of PLC bands will be analyzed from a large number of experimental data. The effects of variation of solute atom concentration, size and distribution of precipitation,grain size and annealing twin size on the serrated plastic instability and the spatiotemporal features of PLC band will also be investigated. On the basis of the obtained results, the mechanism of serrated plastic instability in advanced Ni-based wrought superalloy will be explained. An effective model will be developed to explain the serrated plastic instability and the spatiotemporal feature of PLC band in advanced Ni-based wrought superalloy. Furthermore, the spatiotemporal features of PLC band will be simulated, according to the newly developed model. These obtained results will not only be help to clarify the mechanism of the spatiotemporal features of PLC band, but also provide the theory basis and technical support for the development and application of the new materials for aeroengine applications.

锯齿状塑性失稳(Portevin-Le Chatelier,PLC)是合金在变形过程中的一种重要现象，是合理和安全使用这些材料时必须考虑的因素。前期研究多集中在位错与溶质原子的相互作用方面，对塑性失稳的成因及与锯齿相伴随PLC带的演化与传播机理仍不清楚。本项目拟在上个基金项目的基础上，用动态数字散斑法研究先进变形高温合金在拉伸加载条件下发生的PLC带变形及其传播行为，分析锯齿状塑性失稳发生时的临界应变量、锯齿跌幅以及PLC带变形及传播规律；考察合金中溶质原子浓度变化，沉淀相的尺寸及分布状态、晶粒尺寸和孪晶尺寸对加载锯齿和PLC带时空特性的影响规律，揭示锯齿状塑性失稳和PLC带变形等复杂宏观现象所对应的微观机制；建立先进高温合金发生锯齿状塑性失稳的理论模型，模拟高温变形时PLC带的动态行为特征。研究结果有助于阐明先进高温合金发生锯齿状塑性失稳的内在本质，对提高合金的服役可靠性具有重要意义。

锯齿状塑性失稳(Portevin-Le Chatelier,PLC)是合金在变形过程中的一种重要现象，是合理和安全使用这些材料时必须考虑的因素。前期研究多集中在位错与溶质原子的相互作用方面，对塑性失稳的成因及与锯齿相伴随PLC带的演化与传播机理仍不清楚。本项目主要研究了新型镍基高温合金中大锯齿跌幅的成因、不同gamma prime相、时效过程中析出不同gamma prime相、溶质原子变化对合金中PLC现象的影响以及PLC现象的实验观察。建立了200度到600度温度范围内在线实时观察和数据采集处理系统；得到了低层错能的Ni-Co基高温合金在拉伸曲线上大应变阶段出现的大跌幅锯齿与合金变形时出现的微孪晶（层错）有关。高温合金中gamma prime相的含量对合金发生PLC效应的锯齿形貌有很大影响。同时gamma prime相含量的增加能够使发生PLC效应的区间向低温高应变速率移动，gamma prime相和温度、应变速率的作用一样都是合金发生动态应变时效的一个必要条件。基于动态应变时效理论中溶质原子、可动位错和林位错交互作用理论，对比研究了固溶状态Nimonic 263合金体系以及简单二元Ni-C、Ni-Cr、Ni-Mo合金的PLC效应，揭示了主导复杂高温合金体系中PLC效应的溶质原子类型；借助透射电镜观察了不同时效时间gamma prime相的析出和演化过程，分析了PLC效应发生过程中材料的变形机制；宏观观测方面，通过建立三维光学应变观测平台，首次利用数字图像相关法对室温不同拉伸速率下Ni-C合金以及高温合金中PLC变形带的形核、增殖以及时空演化行为进行了研究。上述研究结果丰富和发展了现有建立在位错与溶质原子作用基础上的动态应变时效模型，为航空发动机新材料的开发和应用提供理论依据和技术支持。相关结果已发表在J of Alloy&Compounds和Materials & Design等国内外核心期刊上。