多场耦合下NiTi合金摩擦磨损特性的多尺度分析及跨尺度关联

NiTi shape memory alloy (SMA) exhibits excellent friction wear properties, which are closely owing to its thermoelastic martensitic transformation. Previous studies usually build qualitative theoretical assumptions and computational analysis based on experimental results. However, during contact friction, the process and the dynamic influences induced by martensitic transformation and plastic deformation on the friction wear properties are still not clearly revealed. In order to clarify the macro- and micro-mechanism of thermoelastic martensitic transformation on the friction and wear properties, the proposed project here plans to conduct multiscale analysis via the method integrating the macro/micro experimental characterization and the numerical simulation. Firstly, through the molecular dynamic simulation and micro-experimental investigation, the effects of martensitic transformation and dynamic dislocation evolution on the friction wear properties will be revealed in atomic scale. The micro interfacial mechanical behaviors and damage evolution characteristics will be obtained. A statistical mathematical model is to be established with the consideration of the micro scale influences. Then, we intend to build a numerical method on account of the micro contact effects and the thermo-mechanical coupling SMA constitutive relationship. Under the local effect of thermomechanical coupling, the key influencing factors affecting the friction wear properties are expected to be shed light on, and the tribological law contributed to engineering application will be established. Finally, through synthesizing the obtained macro and micro results, a design criterion for friction and wear based on thermoelastic martensitic transformation is to be proposed, providing theoretical basis for the performance improving and application of SMA.

NiTi形状记忆合金（SMA）优异的摩擦磨损特性与其热力耦合作用下特有的热弹性马氏体相变密切相关。已有研究多基于实验结果建立定性的理论假设和计算分析，对接触摩擦过程中马氏体相变及塑性变形的宏微观动态影响过程缺乏明确认知。为阐明热弹性马氏体相变对SMA摩擦磨损特性的影响机制，本项目拟采用宏-微观实验和数值方法进行多尺度分析，首先结合分子动力学模拟与微观实验表征，揭示原子尺度下马氏体相变及位错动态演化对摩擦磨损特性的影响规律，获取摩擦过程微观界面力学行为及损伤演化特征，并建立考虑微观影响的摩擦系数统计数学模型;进一步通过引入该数学模型，研究融合微观界面特性和SMA热力耦合本构关系的宏观数值分析方法，确立考虑微观接触和热力耦合相变作用的SMA摩擦磨损特性关键影响因素；最终建立基于热弹性马氏体相变的摩擦磨损设计准则，为SMA摩擦磨损物性改良及应用推广提供指导依据。

NiTi形状记忆合金(SMA)具有优良的耐磨性能。与传统耐磨材料的耐磨机理不同，其耐磨特性与应力诱发的热弹性马氏体相变具有密切联系。本项目从宏-微观多尺度出发，运用有限元模拟和分子动力学方法，对NiTi形状记忆合金的压痕和摩擦磨损力学行为进行多尺度仿真，揭示相变动态演化对其耐磨性能的影响机制。微观尺度上，基于第二次近邻MEAM势函数，再现了温度和应力诱发马氏体相变，确定马氏体变体重取向过程；研究了单晶和纳米多晶NiTi形状记忆合金的拉伸-压缩非对称性行为，通过不同载荷形式下激活马氏体体变体和孪晶形貌的不同，解释了形状记忆合金的拉伸-压缩非对称性的原子尺度物理机制；比较研究了纯镍和NiTi形状记忆合金纳米薄膜的纳米压痕和纳米划痕行为，发现划刻过程中，尽管纯镍薄膜法向力更小，但SMA薄膜的摩擦系数和磨损量更小；进一步的不同温度划痕模拟表明，随着温度的升高，NiTi的摩擦系数增大，耐磨性能降低，但由于应力诱发马氏体相变的存在，NiTi薄膜的摩擦系数和磨损率都低于纯Ni薄膜，值得注意的是，NiTi薄膜的摩擦系数随温度的升高逐渐增大，这与接触区域内马氏体相变体积以及相变导致的接触局部形貌显著相关。宏观尺度上，基于不可逆热力学框架，考虑塑性变形对逆向马氏体相变的影响，构建相变和塑性耦合的 SMA 唯象学本构模型，基于有限元软件 ABAQUS 二次开发功能，编译用户自定义子程序，对 SMA 管接头热机耦合作用过程进行数值模拟。基于该本构模型，构建了弹性+相变和弹塑性+相变的SMA纳米压痕有限元模型，研究了超弹性材料参数和塑性变形及其耦合作用对材料纳米压痕行为的影响特征，研究结果对理解SMA耐磨机理和超弹性接触力学理论具有指导意义。