【摘要】：本文使用半導(dǎo)體激光器對鈦合金進(jìn)行激光表面改性,在不同鈦合金基體材料上制備得到了具有高承載性能的氮化層和TiC+Ti熔覆層。使用掃描電子顯微鏡(SEM)、能譜儀(EDS)和X射線衍射儀(XRD)對制備得到的硬化層微觀組織進(jìn)行了研究,分析了硬化層的開裂機(jī)理,使用電化學(xué)工作站測試了激光表面改性后樣品在3.5%NaCl溶液中的耐蝕性能,使用顯微硬度計測量了樣品的硬度分布,使用摩擦磨損試驗(yàn)機(jī)對所制備試樣進(jìn)行滾壓承載實(shí)驗(yàn),使用三維形貌儀對試樣的壓痕深度進(jìn)行測量以表征其承載性能,且通過觀察滾壓實(shí)驗(yàn)后試樣的形貌分析了其磨損機(jī)理,最后使用COMSOL對激光氣體氮化TC4合金過程中的溫度場分布進(jìn)行了模擬,并預(yù)測了激光氮化工藝參數(shù)一定時氮化層的厚度大小。實(shí)驗(yàn)結(jié)果表明,TC4和TC11合金表面所制備硬化層均可有效提高基材的硬度、腐蝕性能與承載性能。TC4合金和TC11合金表面氮化層硬度值分別為1392HV和923HV,TC4合金表面TiC+Ti熔覆層顯微硬度平均值隨熔覆粉末中TiC含量的增加而提高,顆粒相的硬度在1000~1500 HV波動;激光功率600W的氮化樣品與TiC含量低于60%的熔覆樣品均比原始樣品腐蝕電流小,而其余工藝參數(shù)的樣品由于硬化層氣孔、裂紋等缺陷的存在,耐蝕性能較差,且在鈦合金表面硬化層中TiC含量60%的樣品腐蝕電流(I=1.145×10-7A)最小,耐蝕性能最優(yōu);單珠接觸應(yīng)力為8.5GPa條件下,滾珠在所制備硬化層表面滾壓120次后,TC4合金、TC11合金表面氮化層和TC4合金表面熔覆層最淺壓痕深度平均值分別為9.6um、13.1um和20.45um,與相同載荷下原始樣品壓痕深度56.4um相比,承載性能顯著提高,其中鈦合金表面激光制備硬化層壓痕深度最淺,承載性能最優(yōu)的工藝為:激光氣體氮化TC4合金,激光功率700W,掃描速度300mm/min,搭接率40%。另外,激光功率1000W,掃描速度300mm/min工藝條件下激光氮化TC4合金熔池溫度場的模擬結(jié)果所預(yù)測出的氮化層厚度與實(shí)驗(yàn)所測結(jié)果相符,熱應(yīng)力大多集中于靠近熔池兩側(cè)邊緣,且使鈦合金板發(fā)生塑形形變,最大形變量為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.
【學(xué)位授予單位】：北京工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：TG174.4

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