高冲击韧性Cu-Ni合金低温微观结构演变原位研究

Generally, there is no theoretical ductile-brittle transition during cooling of the metals having a face-centered-cubic (FCC) structure. However, for some FCC metals, the impact energy (impact toughness) can have a substantial dropping during cooling. The present project chooses Cu-Ni alloys which show a big difference in the impact energy between room temperature and lower temperature as the objects, and gives an in-situ study on the microstructure evolution during decreasing temperature and its influence on the impact toughness of the alloy. First, the influence of alloy composition and deformation process on the impact toughness of the alloy will be investigated, in order to find out suitable objects. The microstructure study will be conducted mainly based on the Synchrotron X-ray and Neutron Diffraction and Small-angle Scattering techniques. The in-situ diffraction and small-angle scattering techniques applied to microstress as well as structural defects of Cu-Ni alloys will be developed. The relative quantitative analytical models will also be constructed. Based on the study, the influence of temperature on the microstress and structural defects of Cu-Ni alloys during cooling will be revealed. And the coupling effects of microstress and structural defects on the impact toughness will be demonstrated. Finally, the intrinsic correlations between the alloy composition & deformation process, low temperature microstructure evolution and impact toughness of Cu-Ni alloys will be built.

某些具有面心立方结构的金属虽然在温度降低过程中不发生理论意义上的韧－脆转变，但其冲击功数值随温度降低可发生大幅下降。本项目拟以高、低温冲击功相差较大的Cu-Ni合金为研究对象，主要依托基于同步辐射和中子散射的衍射及小角散射技术，围绕温度降低过程中微观结构演变及其对合金冲击韧性的影响规律和机理，探明合金成分和变形工艺对合金冲击韧性演变规律的影响，构建衍射及小角散射技术应用于Cu-Ni合金低温微观应力和结构缺陷演变的原位研究方法及其数据定量解析方法，揭示微观应力、结构缺陷随温度的演变规律，查明微观应力和结构缺陷对合金低温冲击韧性演变的耦合影响机理，建立合金成分和变形工艺－低温微观结构演变－冲击韧性演变之间的关联性。

本项目通过调整Cu-Ni系合金的成分、加工工艺及热处理工艺参数，对不同合金的室温和液氮温度冲击功进行了系统研究，最终选取了一种高、低温冲击功数值相差较大（室温和液氮温度冲击功相差50J）的热锻态CuNi30Fe(0.5-0.8)Mn(0.2-1)Zn(0.2-0.5)合金为研究对象，利用同步辐射高能X射线原位衍射技术，对温度降低过程中该合金的微观结构进行了原位追踪，构建了通过衍射谱形、峰宽、峰位等信息模拟计算合金微观应力和位错密度的数据解析方法，通过研究发现：随着温度从室温降低到液氮温度，该合金的位错密度和微观应力不断降低。这说明，随着温度降低，热锻态铜镍合金的冲击功随着位错密度和微观应力的降低而降低；研究还发现，该合金中不同晶面对微观应力承受能力的差距也可能是合金高低温冲击功相差较大的一个原因。本项目还针对热锻态铜镍合金在大风洞实验装置和液氧煤油发动机部件的应用背景，开展了该合金在室温和液氮温度的高周疲劳性能、低温尺寸稳定性研究。