基于晶格热动力学的“洋葱C”深渗强化层微观耐磨机制研究

Heavy duty gears are the core drive components in modern industry. The fatigue crack in deep sub-surface due to pulsating cycle stress is the key to its friction damage. The traditional alloy carburized steel surface has limited space for performance enhancement. It is the key to restricting the independent high-end manufacturing of heavy-duty gears in China. On the issue, the principle of special affinity and catalytic adsorption effects of Onion-Like Carbon on the surface of nanodiamonds with Group VIII metals are applied skillfully to the deep surface reinforcement of heavy gear materials. And by introducing the Onion-Like Carbon effect associated parameters, a new idea to study the mechanism of strengthening wear resistance from the perspective of lattice thermal-dynamics are put forward. It mainly including: Study on the lattice thermodynamic behavior of the solute atom of Onion-Like Carbon effect, and elucidation of the intrinsic enhancement mechanism of deep-penetration strengthening layer; based on the dislocation shielding theory, a coupled mechanical model of lattice stress field and fatigue crack dislocation stress field was established, deducing the critical shear stress that forms the cyclic slip zone of the fatigue crack source, constructing the mapping function of the Onion-Like Carbon effect associated parameter and the origin of fatigue crack initiation. Furthermore, the micro wear mechanism of the Onion-Like Carbon deep penetration strengthening layer will be revealed. The research results of this project have important scientific significance and application value for fully exploiting the application of multi-dimensional nanostructure “carbon” in the field of surface strengthening and expanding direction of the simplified alloying of heavy-duty gear wear.

重载齿轮作为现代工业中的核心传动部件，其损伤的关键在于次表层深部因脉动循环应力产生疲劳裂纹。传统合金渗碳钢表面强化性能提升空间有限，是制约我国重载齿轮自主高端制造的关键。针对该问题，本项目将金刚石表面的“洋葱C”与Ⅷ族金属产生特殊亲和力与催化吸附作用的原理巧妙运用于重载齿轮表面深层强化，引入“洋葱C”效应关联参数，提出从晶格热动力学角度研究微观耐磨机制的新思路。主要内容包括：探析“洋葱C”效应溶质原子的晶格热动力学行为，阐明深渗强化层本征强化机理；依据位错屏蔽理论，建立晶格应力场与疲劳裂纹位错应力场的耦合力学模型，推演形成疲劳裂纹源循环滑移带的临界分切应力，构建“洋葱C”效应关联参数与疲劳裂纹源萌生的映射函数，揭示“洋葱C”深渗强化层的微观耐磨机制。本项目研究成果，对充分发掘多维度纳米结构“碳”在表面强化领域的应用，拓展重载齿轮耐磨强化的简化合金化新方向具有重要的科学意义和应用价值。

传统重载轴齿类合金渗碳钢表面强化性能提升空间有限，是制约我国重载齿轮自主高端制造的关键，其损伤的关键在于次表层深部因脉动循环应力产生疲劳裂纹。本项目以重载工况下轴齿类零部件的长寿命运行为切入点，将金刚石表面的“洋葱C”与Ⅷ族金属产生特殊亲和力与催化吸附作用的原理巧妙运用于轴齿材料深渗层的组织调控，着重解决重载齿轮表面深渗层强韧性匹配的精准控制，采用实验分析、理论计算、计算模拟相结合的方法，围绕碳的晶格热动力学行为对重载轴齿类材料深渗层的亚结构演变、强韧化机理、宏观服役行为、疲劳损伤机制等进行了系统的研究。取得了以下重要研究结果：基于亚稳碳化物的热动力学特性，实现了OLC深渗强化层组织调控；明释了强化层的晶格演变经历了“晶格固溶-马氏体与残余奥氏体中的配分-共格析出-沉淀硬化-碳化物粗化长大”的过程；引入硬化因子m调节析出相转变和有效晶粒尺寸的对应关系，实现了对未知热力学条件下，特定碳浓度渗层的应力-应变曲线较准确的预测；基于深渗层梯度应力应变特性，阐明了动态服役过程的应变再分配机制，建立了深渗层强韧性匹配与裂纹尖端损伤模型；解释了OLC深渗层晶格热动力学与位错运动能力及位错应力场的关联关系，对深渗梯度层弹塑性变形致疲劳损伤过程的位错演变与强韧性的关联关系进行了建模，明晰了OLC深渗强化层的微观耐磨机制。本项目研究中碳化物演变热动力学模型的研究结果可应用于重载齿轮热加工工艺的精准控制，可充分发挥材料亚结构组织的调控能力，指导制定高端零部件提质降碳的生产工艺；应变再分配模型、裂纹尖端模型的研究结果可为长寿命服役的重载设计提供理论支持与应用指导，对实现长寿命深渗强化层的组织调控与抗疲劳磨损具有重要的科学意义。项目研究成果在某重载齿轮生产企业进行了生产工艺小试，显示了较好的应用技术拓展空间，为基础理论研究向工程实际运用做了良好的铺垫。