Au-Pt-Pd-Rh-Ni-Cu高熵合金相形成和相转变研究

The alloy of Au-Pt-Pd-Rh-Ni-Cu is a novel and outstanding material in the system of precious metals multicomponent alloy with the simple and clear phase structure applied in the electric contact field, and that can be analyzed easily. High-entropy alloy is a new material, which has broken the traditional idea of alloy designing of that as one or two elements as the main component. This project aims to combine the ideas of high-entropy alloy and precious metals to establishing an thought of designing and researching for precious metal multicomponent high-entropy alloy. The interactions between each element, formation and stability of phase structures and behaviors of phase transformation in the process of alloy formatting will be studied in project by means of typical (non)equal molar ratio modes and SPS, and get the descriptions of the model of thermodynamic state and the dynamic process in system. In addition, the corresponding relationships between the properties and phase structure, microstructure and energy state in material will be investigated carefully. Eventually, a new idea of precious metal multicomponent alloy for component designing, microstructure, phase structure and properties regulating and improving will be developed based on the thought, in which precious metal is the main component, the high-entropy alloy is the core idea. The breakthroughs of this project will effectively promote the developments in theory and technology of precious metal alloys.

Au-Pt-Pd-Rh-Ni-Cu合金是贵金属多元合金系中一种新型的、性能优异的电触点材料，其相结构简单明确，具有较好的可分析性；高熵合金是近年来新兴的合金材料，它打破了传统合金中主要组元为一或两种的设计方法。本项目拟将高熵合金的理念与贵金属合金材料相结合，确立一套贵金属多元高熵合金的设计与研究思路。项目拟通过典型等摩尔比和非等摩尔比两种配比方式，运用SPS技术，研究Au-Pt-Pd-Rh-Ni-Cu合金各元素在合金化过程中的相互作用，合金相结构的形成、稳定性以及相结构转变行为，对系统的热力学状态和动力学过程给出模型化描述。进一步考察合金材料的宏观性能与组织状态、相结构以及系统能量状态的对应关系。最终发展出一套以贵金属为基础组元，以高熵合金为核心理念的贵金属多元合金的成分设计，组织、结构和性能调控、改善的新思路。本项目的突破将有力推动贵金属合金化理论及技术的发展。

本项目运用真空烧结、放电等离子体烧结和电弧熔配制备等摩尔比和非等摩尔比Au-Pt-Pd-Rh-Ni-Cu高熵合金。使用热分析、X射线衍射、原位变温X射线衍射、扫描电镜、能谱、背散射电子衍射、透射电镜等手段对合金的成相/相变过程、结构特征、微观形貌进行了细致分析。.合金由两种FCC相结构组成，晶格参数为3.882 Å和3.796 Å，两FCC相以亚结构形式分布于基体中，两FCC相取向关系相同，界面为半共格匹配，由整齐排列的应变位错组态构成。 .体系在350 oC开始发生互溶反应，450 oC反应完成形成双FCC结构，在更高的温度下该结构特征不发生变化。合金铸态组织为发达的枝晶形态，枝晶间区域呈现层状、棒状或点状不连续形态。.原位变温XRD测试结果显示体系在较低温度下产生了瞬态的未知结构，随着温度的升高来自于这些结构的衍射峰逐渐增强，当样品重新冷却至室温时这些衍射反应消失。.经过等温热处理合金的显微硬度发生增长，两相的晶格参数变化至3.899 Å和3.784 Å，基体中出现了大量FCC结构析出物，其中充斥位错网格和缠结，导致了材料的硬化。.等摩尔比六元合金体系可用(Rh-Pt-Ni)-(Au-Pd-Cu)伪二元亚共晶平衡状态来进行描述，其中共晶线温度为1175 oC，液相线温度为1214 oC。.等摩尔比和非等摩尔比状态下均得到双FCC结构，这种结构特征一旦形成便能够相对稳定地存在，就本项目所涉及的六种元素来看，可以推断，多元素相互溶合反应最终是否形成单相结构是由各元素的本征性质所决定，而体系的热力学状态（高组态熵）仅是形成高熵合金（单相无序固溶体）的必要条件而非充分条件。.