【作者】 龙运；

【导师】 刘其斌；

【作者基本信息】 贵州大学 ， 材料加工工程， 2009， 硕士

【摘要】 针对激光熔覆修复航空发动机制件报废高温锻压模具中使用热喷涂粉未开裂敏感性较大的缺点以及在高温（800℃以上）服役环境中,熔覆层容易开裂、脱落的问题,本文从材料合金化原理出发,综合考虑了激光熔覆过程中熔化与凝固的特点以及基材与粉末的物理化学特性,采用模具材料4Cr5W2SiV为基体,在不同工艺参数下激光熔覆HT-1合金粉末,对熔覆层组织和性能进行研究;最佳工艺下条件下,在HT-1合金粉末中添加不同含量稀土氧化物Y₂O₃研究Y₂O₃对激光熔覆HT-1合金粉末组织与性能的影响。借助OM,SEM、XRD、显微硬度计和磨损试验机等分析手段,对激光熔覆修复层的组织与性能进行研究,结果表明焦距f=330mm、激光功率P=3.5kW、扫描速度V=2mm/s、光斑尺寸D=15×2mm²为最佳工艺,得到的熔覆层表面光滑致密、组织细小均匀、稀释率小、硬度高且与基体实现了良好的冶金结合。微观组织分析表明,熔覆试样由表及里分为三个不同的组织区域:熔覆层、热影响区、基体。在最佳工艺条件下,熔覆层内组织过渡良好,结合区白亮带组织为平面晶,在熔覆层底部为胞状晶,熔覆层中部至表面的组织是从树枝晶→柱状晶→等轴晶。当Y₂O₃添加量在0～3.0 wt.%变化时,随着Y₂O₃含量的增加,熔覆层组织逐渐变细,当Y₂O₃含量在1.0 wt.%时,熔覆层组织最细,然而,当Y₂O₃含量大于1.0 wt.%时,熔覆层组织随着Y₂O₃含量的增加而变粗大;当未添加Y₂O₃时,熔覆层内除了基体相α—Fe外,还有Fe₅C₂、Fe₂B、FeSi等相以及一定量的非晶相,保证了熔覆层有良好的硬度,耐磨性能。添加稀土氧化物Y₂O₃后,熔覆层中出现了少量的尖晶石类矿物质FeFe₂O₁;Y₂O₃添加量为1.0 wt.%时,熔覆层具有最高的硬度和耐磨性,当Y₂O₃含量大于1.0 wt.%时,熔覆层的硬度和耐磨性随着Y₂O₃含量的增加反而降低。更多还原

【Abstract】 As to the problems for big cracking susceptibility caused by thermal spraying powders used in the failing aeroengine high-temperature forging mould repaired with laser cladding technology and easy abscission of coating caused in high-temperature service environment （>800℃） . In this paper, according to alloying principle of materials, the characteristics of melting and solidifying during laser cladding as well as physical and chemical character of substrate and powder are comprehensively considered. The mould steel 4Cr5W2SiV is used as substrate material under different technological parameters of laser cladding with alloy powder HT-1. The microstructure and properties of cladding coating have been invistigated. Under the condition of optimum technological parameters, the different contents of rare earth oxide Y₂O₃ added in the alloy powder HT-1, Effect of Y₂O₃ on microstructure and properties of alloy Powder HT-1 by laser cladding was studied.The microstructure and properties of coating prepared by laser cladding were studied by means of OM, SEM, XRD, Hardness Testmeter and Wear Testing Machine. The optimum technological parameter of broadband laser cladding is as followed: f=330mm, P=3.5kW, V=2mm/s, D=2×15mm². We obtained cladding coatings with good surface quality, fine microstructure, low dilution, high microhardness and good metallurgical combination interface with 4Cr5W2SiV substrate. The microstructure analysis results showed that, from the surface of the cladding specimen to the substrate, there are three distinct areas: the cladding area, the bonding area and the heat-affected zone in the substrate. Under the condition of optimum technological parameters, the transition of microstructure is smooth in cladding coating. The white bright band is plane crystals in the bonding zone. Cellular crystals are obtained in the bottom of cladding coating. The microstructure from the center to the surface of cladding coating transforms from dendrite crystals and columnar crystals to equia-xed crystals.The content of Y₂O₃ varies from 0 wt. % to 3 .0 wt. %, as the content of Y₂O₃ increases, the grain size in coating gradually becomes finer. When the content of Y₂O₃ is up to 1.0 wt. %, the finest grain size is obtained. However, when the content of Y₂O₃ exceeds 1.0wt. %, the grain size in coating is coarser with increase of Y₂O₃. Without Y₂O₃ in coating, there are some phases such as Fe₂B、Fe₃C、FeSi and an amount of amorphous besides the main phaseα-Fe in coating, so good hardness and wear resistance of the cladding coating can be guaranteed. When addition of Y₂O₃ into coating, a new kind of phase FeFe₂O₄ appears in coating. When the content of Y₂O₃ is 1.0 wt. %, the highest hardness and wear resistance are obtained in coatings, when the content of Y₂O₃ exceeds 1.0 wt. %, the hardness and wear resistance of the coating adversely decrease with increase of Y₂O₃.更多还原