【作者】 张小彬；

【导师】 刘常升；

【作者基本信息】 东北大学 ， 材料学， 2008， 博士

【摘要】 0Cr13Ni5Mo马氏体不锈钢(CrNiMo)具有良好的抗空蚀性能、耐蚀性能和抗冲刷磨损性能,是常用的水轮机部件材料。但是,CrNiMo不锈钢在作为制造大型水轮机转轮的材料时,容易出现裂纹。为降低开裂趋势,提高材料性能,对合金成份进行了调整,增加真空精炼冶炼工艺,开发出了M-CrNiMo不锈钢。本文将二者与0Cr13Ni4Mo不锈钢相对照,研究了这三种不锈钢材料的抗空蚀损伤、空蚀与腐蚀交互作用损伤和冲刷磨损行为,并对其抗空蚀机理进行了探讨。为了进一步提高M-CrNiMo不锈钢的抗空蚀能力,利用激光表面合金化和激光熔覆技术在M-CrNiMo不锈钢材料表面制备具有冶金结合界面、无裂纹等缺陷、组织致密和抗空蚀性能优良的涂层,进而改进水轮机转轮表面处理技术。采用超声振荡空蚀实验设备对三种不锈钢材料进行了超声空蚀实验；利用电化学测试系统测量了不锈钢材料在静态和空蚀条件下的极化曲线；并采用旋转圆盘仪装置对不锈钢材料进行了冲刷磨损实验。实验结果表明,M-CrNiMo不锈钢在单相液体介质中的抗空蚀和抗冲刷磨损性能明显高于CrNiMo不锈钢和0Cr13Ni4Mo不锈钢。不锈钢微观组织中的各相在空蚀作用下产生塑性变形和破坏。破坏从铁素体薄弱区开始,而后扩展到马氏体,产生空蚀微坑；到了空蚀稳定期,在整个材料表面,空蚀微坑随空蚀的继续而加宽、加深,发展成尺寸较大的空蚀坑。腐蚀与冲刷磨损因素对三种不锈钢的空蚀破坏都有显著促进作用,M-CrNiMo不锈钢在含砂水中的抗冲刷磨损性能略高于CrNiMo不锈钢和0Cr13Ni4Mo不锈钢。不锈钢的显微组织尺寸与硬度因素对抗空蚀性能的提高起决定作用。以M-CrNiMo不锈钢材料作为基体,采用激光表面技术,通过优化各项激光工艺参数,在M-CrNiMo不锈钢表面制备出了的抗空蚀性能更强的WC合金化涂层和NiCrSiB熔覆层。利用光学显微镜(OM)、扫描电镜(SEM)及附带能谱仪(EDAX)、透射电镜(TEM)、X-射线衍射分析(XRD)、超声振荡空蚀试验机以及测定显微硬度等分析手段,对所制备涂层的组织结构、界面结合、空蚀失重、空蚀形貌及相关机理进行了系统的研究。选取纯WC粉末作为合金化材料,利用脉冲Nd:YAG激光器,优化激光工艺,在M-CrNiMo不锈钢材料表面制备出的激光表面合金化WC涂层的表面光滑均匀,内部组织细小且致密、无气孔和裂纹等微观缺陷。X-射线分析结果表明,WC合金化层的基体由Fe-Ni-Cr固溶体构成,内部有W2C、Ni4W、MoNi4、Fe6W6C、Fe7W6和CrC等硬质相生成。合金化工艺使表面的显微硬度得到大大提高,并增强了M-CrNiMo不锈钢的抗蚀性能。WC合金化层表面空蚀破坏形貌与M-CrNiMo不锈钢相比明显轻微,空蚀过程没有大的空蚀坑出现。WC合金化层抗空蚀性能增强的原因归结于其与基体的界面处呈良好的冶金结合、合金化层中的硬质析出相和激光表面处理时的快速冷却。分别采用脉冲Nd:YAG激光器和CO2连续激光器在M-CrNiMo不锈钢材料表面制得了NiCrSiB熔覆层。熔覆层表面光滑,内部组织细小、均匀,与不锈钢基体具有良好的冶金结合,在涂层以及界面处均没有裂纹和气孔等缺陷存在。X-射线分析结果表明,NiCrSiB熔覆层的基体由CrNiFe构成,内部有M23[CB]6(M=Cr、Fe)、CrB、CrSi和Fe2B等硬质相生成。超声空蚀实验结果表明,激光熔覆NiCrSiB涂层空蚀破坏损伤降低,熔覆层的空蚀失重率仅为M-CrNiMo不锈钢的1/3,且低于WC表面合金化层。熔覆层的硬度有显著的提高,表面有明显的加工硬化效应。此外,NiCrSiB熔覆层表面的空蚀破坏与M-CrNiMo不锈钢相比显著轻微,空蚀3小时后仍有完整表面存在；空蚀6小时后仍然没有大的空蚀坑出现。NiCrSiB熔覆层的强化机制包括细晶强化、第二相强化和加工硬化等,涂层与基体的界面处呈良好的冶金结合,NiCrSiB自熔合金自身的良好性能与激光熔覆过程中的急冷因素都是熔覆层抗空蚀性能的提高原因。与脉冲Nd:YAG激光器制备的NiCrSiB熔覆层相比,CO2激光器制备的NiCrSiB熔覆层更厚,更均匀。更多还原

【Abstract】 0Cr13Ni5Mo stainless steel (CrNiMo) has good structural strength, cavitation resistant, corrosion resistant capabilities and has been widely applied in hydro turbines. However, seriously cracks and cavitation erosion damages were found in CrNiMo large size hydro turbines. In order to decrease its crack tends and to improve its mechanical properties, M-CrNiMo stainless steel was developed by modifying the composition and vacuum refine procedure. In this paper, cavitation erosion damage, cavitation erosion and corrosion interaction damage behaviors of 0Cr13Ni5Mo, M-CrNiMo and 0Cr13Ni4Mo stainless steels were investigated.Supersonic cavitation erosion experiment was tested by supersonic vibration cavitation erosion experiment system. Polarization curves of three kinds of stainless steels in static state and in cavitation erosion condition were obtained by electro-chemistry test system. The erosive wear behaviors were completed by rotating disk equipment.The results show that M-CrNiMo stainless steel has better cavitation resistance property and erosion abrasion resistance property than those of CrNiMo and 0Cr13Ni4Mo stainless steels. During the cavitation erosion, the microstructure phases in stainless steel were plastic deformed and destroyed. At the first incubation period the micro cracks begin in ferrite weak area, then extend to martensite and come into micro-pit. During the static period the micro-pits get wider and deeper and finally the big size cavitaion erosion pits are produced in the entire surface. Corrosion and erosion abrasion strongly accelerate the cavitation erosion damages in three stainless steels. The erosion abrasion resistance properties of M-CrNiMo stainless steel are better than those of CrNiMo and 0Cr13Ni4Mo stainless steels. Micro-structure and hardness were decisive effects for high cavitation resistance properties of M-CrNiMo stainless steel.In order to increase the cavitation erosion of M-CrNiMo stainless steel, complete dense coating with an excellent metallurgical bonding at the interface can be achieved by laser cladding, therefore, the surface treatment technique in hydro turbine can be improvedWC laser alloying layer and NiCrSiB laser cladding layer were made on surface of M-CrNiMo by laser alloying and cladding techniques respectively. Their micro-structure, interface, cavitation erosion mass loss and surface morphologies etc were investigated by optical microscope, Scanning Electron Microscope (SEM and EDAX), Transmission Electron Microscope (TEM), X-ray diffractometer (XRD), supersonic vibration cavitation erosion experiment setup and digital vision Micro-Vickers etc systemly.WC Alloying layer was achieved on surface of M-CrNiMo stainless steel by Nd:YAG pulse laser. The alloying layer was flat, uniform and metallurgical bonded with the substrate, no defect such as crack, air hole was found. The matrix of the WC Alloying layer is Fe-Ni-Cr solid solution. WC alloying layer was strengthened by hard precipitated phases such as W2C, Ni4W, MoNi4, Fe6W6C, Fe7W6, CrC, etc. The surface alloying treatments increase the hardness apparently and strengthen the erosion resistance. Cavitation erosion morphologies of the alloying layer is notably slight compareing to that of the M-CrNiMo stainless steel, with little erosion pits after cavitation erosion test for 6 hours. It is due to the closing metallurgy band with interface and hard phase precipitation as well as the quenching in laser surface alloying treatment.NiCrSiB cladding layer was obtained on the surface of M-CrNiMo stainless steel by Nd:YAG pulse laser and CO2 LASER. The laser cladding layer was uniform, compact and no defect as gas hole, crack and metallurgical bond with the substrate. The substrate of cladding layer are composed by CrNiFe solid soltuion, with precipitated phases such as M23[6P-CB]6 (M=Cr、Fe)、CrB、CrSi、Fe2B, etc. The supersonic cavitation erosion test shows that the cumulative mass rate of NiCrSiB cladding layer is 4.2mg/h, which is only 1/3 of the M-CrNiMo stainless steel and lower than that of WC cladding layer. Hardness of cladding layer increased obviously, which means the work hardening occurring on the surface during the test. The cavitation erosion surface damage of NiCrSiB cladding layer was slighter than that of M-CrNiMo stainless steel, with e polished surface after being cavitation eroded for 3 hours and no big cavitation erosion pits after being cavitation eroded for 6 hours.The strengthening mechanism of NiCrSiB coating is a mixture of fine grains strengthening, second phase strengthening and work hardening effect during cavitation erosion process, and the coating has excellent bonding at the interface. In comparison with NiCrSiB coating prepared by CO2 laser cladding, the NiCrSiB cladding layer by LASER shows thicker and more uniform.更多还原