钛合金表面激光制备高承载硬化层工艺与组织性能研究

发布时间：2018-10-11 09:09

【摘要】：本文使用半导体激光器对钛合金进行激光表面改性,在不同钛合金基体材料上制备得到了具有高承载性能的氮化层和TiC+Ti熔覆层。使用扫描电子显微镜(SEM)、能谱仪(EDS)和X射线衍射仪(XRD)对制备得到的硬化层微观组织进行了研究,分析了硬化层的开裂机理,使用电化学工作站测试了激光表面改性后样品在3.5%NaCl溶液中的耐蚀性能,使用显微硬度计测量了样品的硬度分布,使用摩擦磨损试验机对所制备试样进行滚压承载实验,使用三维形貌仪对试样的压痕深度进行测量以表征其承载性能,且通过观察滚压实验后试样的形貌分析了其磨损机理,最后使用COMSOL对激光气体氮化TC4合金过程中的温度场分布进行了模拟,并预测了激光氮化工艺参数一定时氮化层的厚度大小。实验结果表明,TC4和TC11合金表面所制备硬化层均可有效提高基材的硬度、腐蚀性能与承载性能。TC4合金和TC11合金表面氮化层硬度值分别为1392HV和923HV,TC4合金表面TiC+Ti熔覆层显微硬度平均值随熔覆粉末中TiC含量的增加而提高,颗粒相的硬度在1000~1500 HV波动;激光功率600W的氮化样品与TiC含量低于60%的熔覆样品均比原始样品腐蚀电流小,而其余工艺参数的样品由于硬化层气孔、裂纹等缺陷的存在,耐蚀性能较差,且在钛合金表面硬化层中TiC含量60%的样品腐蚀电流(I=1.145×10-7A)最小,耐蚀性能最优;单珠接触应力为8.5GPa条件下,滚珠在所制备硬化层表面滚压120次后,TC4合金、TC11合金表面氮化层和TC4合金表面熔覆层最浅压痕深度平均值分别为9.6um、13.1um和20.45um,与相同载荷下原始样品压痕深度56.4um相比,承载性能显著提高,其中钛合金表面激光制备硬化层压痕深度最浅,承载性能最优的工艺为:激光气体氮化TC4合金,激光功率700W,扫描速度300mm/min,搭接率40%。另外,激光功率1000W,扫描速度300mm/min工艺条件下激光氮化TC4合金熔池温度场的模拟结果所预测出的氮化层厚度与实验所测结果相符,热应力大多集中于靠近熔池两侧边缘,且使钛合金板发生塑形形变,最大形变量为24um左右。
[Abstract]:In this paper, laser surface modification of titanium alloy was carried out by using semiconductor laser. Nitride and TiC Ti cladding layers with high bearing capacity were prepared on different titanium alloy substrates. The microstructure of the hardened layer was studied by scanning electron microscope (SEM) (SEM), energy spectrometer (EDS) and X-ray diffractometer (XRD), and the cracking mechanism of the hardened layer was analyzed. The corrosion resistance of laser surface modified samples in 3.5%NaCl solution was tested by electrochemical workstation, the hardness distribution of samples was measured by microhardness meter, and the rolling load bearing test was carried out by friction and wear tester. The indentation depth of the specimen was measured by three dimensional topography instrument to characterize its bearing capacity, and the wear mechanism of the specimen was analyzed by observing the morphology of the specimen after rolling test. Finally, the temperature field distribution of laser nitrided TC4 alloy was simulated by COMSOL, and the thickness of nitride layer was predicted when the parameters of laser nitriding process were fixed. The experimental results show that the hardness of the substrate can be improved effectively by the hardening layer prepared on the surface of TC4 and TC11 alloys. The hardness of nitride layer on TC4 alloy and TC11 alloy is 1392HV and 923HVTC4 alloy respectively. The average microhardness of TiC Ti cladding layer increases with the increase of TiC content in the cladding powder, and the hardness of particle phase fluctuates from 1 000 to 1 500 HV. The corrosion current of the nitrided sample with laser power 600W and the cladding sample with TiC content less than 60% is smaller than that of the original sample, while the other process parameters have poor corrosion resistance due to the defects such as hardening layer porosity and cracks. The corrosion current (I _ (1) 1.145 脳 10 ~ (-7) A) of the sample with 60% TiC content in the surface hardening layer of titanium alloy is the smallest, and the corrosion resistance is the best, and the contact stress of single bead is 8.5GPa. After 120 times rolling on the surface of the hardened layer, the average depth of the superficial indentation on the surface of TC4 alloy, TC11 alloy surface nitride layer and TC4 alloy was 9.6 umn 13.1 um and 20.45 umum, respectively, compared with the indentation depth 56.4um of the original sample under the same load. The bearing capacity of titanium alloy is obviously improved. The best technology for preparing hardened layer indentation on titanium alloy surface is laser gas nitrided TC4 alloy, laser power 700W, scanning speed 300mm / min, lap ratio 40mm / min. In addition, the predicted thickness of nitride layer in laser nitride TC4 alloy molten pool temperature field under laser power 1000W and scanning rate 300mm/min process is in agreement with the experimental results, and the thermal stress is mostly near the edge of both sides of the molten pool. The titanium alloy plate is shaped and deformed, and the maximum deformation is about 24um.
【学位授予单位】：北京工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG174.4

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