【作者】 蒋松林；

【导师】 王新林；

【作者基本信息】 南华大学 ， 机械电子工程， 2010， 硕士

【摘要】 激光熔覆原位生成技术是通过在基体表面添加熔覆材料,利用高能密度激光束辐照加热,使熔覆材料与基材表层发生熔化,在熔池中熔覆材料元素与基体元素发生化学冶金反应,从而在基体表层形成冶金结合的熔覆层,达到改善基体表面性质为目的一门新型改性技术。为了改善TC4钛合金耐磨性能差缺陷,本文采用激光熔覆原位生成技术,在TC4钛合金表面预涂覆高纯度C与BN粉末,原位生成Ti-C、TiN、TiB₂、TiB和AlN等陶瓷增强相。通过对不同工艺参数下熔覆层宏观、微观质量的对比分析,选出了最佳的激光熔覆工艺参数范围。利用SEM、XRD和EDXs等测试手段对熔覆层的显微组织和相成份进行分析。利用HXD-1000B型显微维氏硬度计测试了熔覆层的硬度。实验结果表明,激光熔覆层的宏观、微观质量与激光熔覆工艺参数密切相关。在最佳激光工艺参数范围为激光功率P=1900-2000W,光斑尺寸为3×2mm²,预涂层厚度h=0.3-0.5mm,扫描速度V=4-6mm/s时,获得的激光熔覆层表面连续均匀,内部无裂纹的熔覆层,且与TC4钛合金基体实现冶金结合。激光熔覆试样沿层深方向存在三个不同的组织区域,由表及里依次为:熔覆层、结合区及基体热影响区。显微组织成分分析表明,在激光熔覆的过程中,基体中的Ti和Al元素与预置涂层的C、N、B等元素发生化学反应,原位生成TiC、TiN、TiB₂、TiB和AlN等陶瓷增强相。TiC、TiN、TiB₂、TiB和AlN相是以树枝晶和枝晶形式存在。经显微硬度测试,TC4钛合金表面熔覆层的显微硬度相对TC4钛合金有了明显的提高。熔覆层显微硬度(857HV_0.5-1454 HV0.5)比钛合金基材硬度(330HV_0.5-340HV_0.5)提高到2-4倍。更多还原

【Abstract】 In-situ formation by laser cladding is a new modified technique forimproving the surface properties of the substrate. It is using the highdensity energy of laser beam to irradiate the cladding material which isadded on the surface of substrate, resulting in the cladding material andthe surface of substrate melted, and the element of cladding materialreacting with the element of the substrate for formatting cladding layerwhich join to the substrate with metallurgical bonded. In the paper, forimproving the poor tribological properties of TC4 titanium alloy, it is aprocess of in-situ formed composite coating by laser cladding on TC4titanium alloys substrate with preplaced the high purity C and BN powder,in-situ producing TiC, TiN, TiB₂, TiB and AlN ceramic reinforcementphases. Through the comparison analyses of the macroscopic andmicroscopic qualities for the cladding layers, the range of laser claddingparameters were optimized. Microstructure of the cladding layers wascharacterized by XRD, SEM and EDXs. The microhardness of thecladding layers was measured by HXD-1000B type micro-sclerometer.The experimental results show that the macroscopic and microscopicquality is related to process parameters of laser cladding. Under theoptimized laser cladding parameters range of P=1700-2000W，S=3×2mm², h=0.3-0.5mm, V=4-6mm/s, the cladding layers are obtained, inwhich no cracks appear and surface is distributed uniformly. the lasercladding layers are metallurgically bonded with TC4 titanium alloyssubstrate. The microstructure structure analysis shows that three regionswith different microstructure existed in the surface of laser cladding zone:the cladding layer, the bonded zone of the cladding layer with the substrate, and the heat-affected zone in the substrate. The microstructurecomposition analysis shows that there is a reaction between C, B, N andTi, in-situ producing TiC, TiN, TiB₂, TiB and AlN ceramic reinforcementphases. The in-situ produced TiC, TiN, TiB₂, TiB and AlN shows themorphologies of fine dendrite. The average microhardness of lasercladding layer is remarkably improved. The microhardness is857HV_0.5-1454 HV0.5 in the laser cladding layer，which is 2-4 times thatof the TC4 substrate (330HV_0.5-340 HV0.5).更多还原