汽轮机钛合金末级叶片表面复合涂层原位制备及冲蚀行为研究

The aim of this project is to address the fabrication of one-step in-situ synthesized Ti3Al/TiN composite coating by using laser-gas assisted nitriding and its erosion resistance in high-temperature wet steam. This research can be used to ensure the long-life and reliable service of last stage blade which is fabricated by titanium alloy and used in low-pressure steam turbine. The following three issues will be focused in this project: (1) Identifying the formation mechanism and morphological evolution of TiN reinforced phase during laser nitriding process through analysis on Ti-N and Ti-Al phase diagrams and calculation according to thermodynamics. This research can provide an important insight into development of design methodology for environmental barrier coating on last stage blade fabricated by titanium alloy. (2) Developing the pore- and crack-free nitrided layer through multi-pass scanning on the basis of description of the formation mechanisms of micro-defects, residual stress and cracks. On the basis of modified shear-lag model, the fracture parameters, such as strength and fracture toughness, considering residual stress effect can be obtained. (3) Developing the prediction model of erosion resistance of composite coatings through investigating the competition between contact deformation and brittle fracture and their contributions on erosion rate. In this interdisciplinary program, the mechanical, chemical and material analyses will be included. Through the accomplishment of this project, the Synergetic evaluation system from material to fabrication and then to performance of coatings used for last stage blade could be established. Also, this project could provide some important insights on the improvement of the long-life design and manufacturing of the key components in ultra-super-critical power.

本项目以提高大型汽轮机的可靠性为目标，针对钛合金长叶片材料表面激光氮化Ti3Al/TiN复合涂层原位合成制备与高温湿蒸环境下冲蚀寿命预测展开研究。主要包括：（1）利用多元相图和热力学计算，研究涂层凝固成形过程中TiN增强相生成的动力学机制与形态演变规律，形成复合涂层材料/结构设计方法；（2）研究Ti3Al/TiN复合涂层微观缺陷及残余应力的形成机理及分布，建立考虑残余应力的涂层断裂力学参量模型，发展复合涂层多道搭接原位制备技术原型；（3）通过表征塑性接触形变和脆性断裂两种损伤机制对复合涂层冲蚀率的贡献，发展考虑残余应力的涂层冲蚀寿命预测模型。本项目体现了力学、化学和材料等多学科领域的交叉，可望突破构建钛合金表面涂层材料－结构－性能协同评价，为促进我国电力装备关键部件的寿命设计方法及制造水平提升提供科学支持。

项目开展以钛合金激光复合涂层抗冲蚀为目标，探究了激光复合涂层的制备工艺，表征了涂层的微结构、化学组分分布及力学性能，获得了抗冲蚀性能良好的涂层结构和制备工艺。采用等离子喷涂与激光合金化技术相结合，制备出两相均匀分布、无孔洞和裂纹的Ti3Al/TiN硬质复合涂层，主要由枝晶状的氮化物组织和非枝晶状的氮铝金属间化合物组成；该复合涂层能明显提高基体材料的表面硬度，且复合涂层中的两种物相均能不同程度的提高基材的弹性模量。复合涂层的抗冲蚀性能明显优于钛合金基体，冲蚀角度对复合涂层的抗冲蚀性能也有一定的影响，复合涂层的冲蚀失重随着冲蚀角度的增大而增加，表现出典型的脆性材料冲蚀特征。获基金资助发表论文11篇。