磨损诱发激光熔覆层表层塑性区组织演变规律及其疲劳损伤行为研究

Laser cladding, a relatively new and effective method, has been successfully used to improve wear resistance of metals and alloys by creating composite coatings on their surfaces. Fatigue damage of the surface layer resulting from the wear-induced plastic-zone microstructure evolution becomes the main failure form of the coating in service. Based on the investigation of the wear-induced plastic zone of the surface layer in the TiB-TiC reinforced titanium matrix composite coating, the project will focus on the relationship between the plastic-zone microstructure evolution and fatigue damage behaviors. Moreover, fatigue damage behaviors will be monitored by the change regulation of some parameters (acoustic emission signal, accumulated dissipated energy, friction coefficient, wear volume) during sliding, and the fatigue life will be predicted effectively by building the mathematical model. The model involving the accumulated dissipated energy, wear volume and environmental factors (applied load and sliding speed) will be applicable in the running-in and stable-wear stages. Main research contents are followed: the microstructure evolution of the plastic zone under the reciprocating sliding, the relationship between the microstructure evolution and the strain hardening, the fatigue damage behaviors resulting from the microstructure evolution (including initiation, propagation and debonding of the cracks), dynamic monitoring of the fatigue damage behaviors and prediction of the fatigue lifes. This study will be expected to clarifying the fundamental law of the plastic-zone microstructure evolution of the surface layer in the laser-clad coating in service, revealing the mechanism of fatigue damage. It is very important for the regulation and control of original microstructure, selection of service conditions, evaluation of damage behaviors and prediction of fatigue lifes, when the coating is applied in the engineering fields.

通过激光熔覆技术获得复合涂层是提高金属和合金耐磨性非常有效的手段。磨损诱发的表层塑性区组织演变致其疲劳损伤成为涂层磨损失效的主要方式。本课题拟以往复滑动摩擦条件下磨损诱发TiB-TiC增强钛基复合涂层表层产生的塑性变形区为切入点，以塑性区组织演变-疲劳损伤行为两者映射关系为研究核心问题，通过参数（声发射信号、累积耗散能、摩擦因数、磨损体积）在磨损过程中的变化规律监控疲劳损伤行为，建立包含累积耗散能、磨损体积和环境因素（外加载荷和滑动速度）的数学模型，实现对涂层疲劳寿命的预测。主要研究内容：塑性区的组织演变规律；塑性区组织和应变硬化间关联；塑性区组织演变致其疲劳损伤行为（裂纹萌生、扩展、剥落）；涂层疲劳损伤行为监控及寿命预测。本研究有望阐明服役条件下熔覆层表层塑性区组织演变的基本规律，揭示其疲劳损伤机制，对涂层在工程中应用时原始组织调控、服役条件选择、损伤行为评价、服役寿命预测具有重要意义。

通过激光熔覆技术获得复合涂层是提高金属和合金耐磨性非常有效的手段。磨损诱发的表层塑性区组织演变致其疲劳损伤成为涂层磨损失效的主要方式。本项目以组织演变—磨损致疲劳损伤行为两者映射关系为研究核心问题，揭示了涂层的疲劳损伤机制，实现了对涂层疲劳损伤行为的有效监控及疲劳寿命的精确预测。主要研究内容及重要结果：熔覆材料组分（Mo、B4C、MoS2、TaC、NiCrBSi）、预置涂层厚度、工艺（功率、扫描速度）对涂层组织演变规律的影响；发明了一种新的预置涂层制备方法，提高了预置涂层的致密性并可精确控制其厚度，改善了组织重复性；设计了多种熔覆材料体系，如15 wt.%B4C+NiCrBSi、30 wt.%WC+49 wt.%NiCrBSi+21wt.%Ni、10 wt.%MoS2+NiCrBSi、40 wt.%TaC+NiCrBSi、CrCoAlNiMo；发明了高温熔覆及熔覆后高温处理的新方法；在钛合金Ti6Al4V表面制备了TiC与TiB2增强TiNi/Ti2Ni、WC/TiC增强(Ti)/TiNi/Ti2Ni、TiC/TiB2/TiS2增强TiNi/Ti2Ni、TaC/TiB2/TiC增强TiNi/Ti2Ni多种新型复合涂层，在45#钢表面制备了单一固溶体结构的高熵合金涂层(FeCrCoNiAlMo)；通过多种影响组织因素的优化组合，实现对组织的调控，有效降低了涂层中残余应力，解决了激光熔覆层工业化应用存在的易开裂的技术瓶颈，同时赋予其优异的服役性能；对目前预测平衡态加工条件下高熵合金物相预测判据进行了修正，使其适用于激光熔覆这种典型非平衡态下制备高熵合金涂层中物相的精确预测，并提出了一个新的判据；不同环境温度下（室温、高温）涂层中残余应力分布及磨损过程中疲劳损伤为的研究，建立了涂层表层组织-残余应力分布-疲劳损伤行为的映射关系；通过一些参数（累积耗散能、摩擦因数、磨损体积）实现了对疲劳损伤行为的有效监控；建立了包含累积耗散能、磨损体积和环境因素（滑动速度）的数学模型，实现对涂层疲劳寿命的预测。本研究系统阐明了服役条件下熔覆层表层塑性区组织演变的基本规律，揭示了涂层疲劳损伤机制，对其在工程中应用时原始组织调控、服役条件选择、损伤行为评价、服役寿命预测具有重要意义。