【作者】 李宝增；

【导师】 刘其斌；

【作者基本信息】 贵州大学 ， 材料加工工程， 2008， 硕士

【摘要】 针对激光熔覆修复航空发动机叶片报废高温锻压模具中使用热喷涂粉末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,本文基于模具材料4Cr5W2SiV,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,研发出了专用于激光熔覆修复报废模具的铁基合金粉末。并对激光熔覆修复用合金粉末的最佳配比以及激光熔覆工艺参数对组织结构与性能的影响进行了研究。借助OM,SEM和XRD等分析手段,对激光熔覆修复层的组织结构与性能进行了研究,结果表明,当自制铁基熔覆粉末的重量百分比（wt.%）为:0.5C、25Cr、1.0Ni、1.5Si、1.5B、Fe为余量时,获得了无裂纹的熔覆层,熔覆层与基材实现了良好的化学冶金结合。熔覆粉末中造渣元素B的含量应严格控制:当B含量为1.5wt.%时,激光熔覆修复报废模具质量最佳;当B含量低于或高于1.5wt.%时熔覆层表面不平整、有裂纹或孔洞产生。窄带熔覆条件下,固定其它工艺参数,随着扫描速度的增大,熔覆层的平均显微硬度变化较大,P=2.5K W,V=5mm/s,d=3mm,f=300mm时,可以得到组织、硬度较好的熔覆层。但是,由于窄带激光熔覆搭接区太多,导致软化带较多,进而影响使用性能。宽带激光多层熔覆技术是获得较厚熔覆层的良好途径。这种方法对修复大尺寸的失效件非常有利。宽带激光熔覆修复的最佳工艺参数为:f=315mm,P=3kW,V=3mm/s,d=3mm×15mm。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+柱状晶到等轴晶;熔覆层稀释率小于10%,可以保证所配粉末的原有性能;熔覆层内除了基体相α—Fe外,还有一定量的非晶合相Fe₅C₂、Fe₂B、FeSi与金属间化合物Ni-Cr-Fe、Fe-Cr、Fe-Ni等,保证了熔覆层有良好的硬度,耐磨性能。熔覆层的硬度分布为最表层比较低,由表及里约0.3mm处,硬度明显升高;在0.3mm～0.9mm区域,硬度变化趋于平缓,在热影响区显微硬度最高达到了810HV0.2,在接近基材处,硬度明显下降。熔覆层的耐磨性能是基材的1.5倍。更多还原

【Abstract】 As to backwards for big cracking susceptibility caused by thermal spraying powders used in the failing aeroengine pieces high-temperature forging mould repaired with laser cladding technology and problems for easy abscission of coating caused in high-temperature service environment（＞800℃）,a kind of Fe-based alloy powder used in the failing forging mould repaired with laser cladding technology is researched and developed,through strain of thought of combination of alloying principle of materials with melting and solidifying characteristics during laser cladding and physical and chemical characteristics between substrate and powder,based on the mould steel（4Cr5W2SiV）.The optimum formulas of the powder and effect of the technological parameters on the microstructure and properties have been investigated.The microstructure and properties of coating prepared by laser cladding are studied by means of OM,SEM and XRD.The results indicate that no cracks coating and excellent chemical metallurgical bonding between cladding coating and substrate are obtained under condition of optimum formulas（wt.%:0.3C,25Cr,1.0Ni,1.7Si,1.5B,rest Fe）.The contents of slag agent B element must been controlled strictly:The optimum properties could been obtained under condition of 1.5wt.%B,Otherwise there may be many defects such as rough surface,cracks,holes and so on.Under condition of narrow laser cladding technology,other technological parameters are fixed,the hardness of the cladding coating changes within a certain of range with increase of the scaning speed.The cladding coating with good microstructure and properties ia obtained under condition of P=2.5KW,V=5mm/s,d=3mm, f=300mm,However,Since narrow laser cladding has more overlapping zones,leading to more soft band,furthermore,performance life is affected.Multi-cladding techenology of wide-band laser is a good approach to obtaining deeper cladding layers.This method is very suitable for repairing failure parts with serious wear.The optimum technological parameters of broadband laser cladding is as followed: f=315mm,P=3kW,V=3mm/s,d=3×15mm².Under the condition of optimum technological parameters,the transition of microstructure is smooth in cladding coating.The whitebright band is plane crystals in the bonding zone.Cellular crystals is obtained in the bottom of cladding coating.The microstructure from the center to the surface of cladding coating transformes from dendritic crystals and cylinder crystals to equiaxed crystals.The delution ratio is less than 10%and the character of the powder is preserved in the cladding coating. The matrix phase in cladding coating isα-Fe,a certain amount of amorphous alloys such as Fe₂B,Fe₃C,FeSi and intermetallics such as Ni-Cr-Fe,Fe-Cr,Fe-Ni are distributed on the matrix phase.Therefore,good hardness and wear resistance of the cladding coating can be guaranteed.The hardness of surface is relatively low,the hardness about 0.3mm distance from surface increases obviously,the hardness keeps smooth increase from 0.3mm to 0.9mm. The hardness has the maximum in the H.A.Z,up to 810HV0.2,then it drops quickly from H.A.Z to substrate.The wear resistance of cladding coating is 1.5 times greater than that of substrate.更多还原