【作者】 宋兴奎；

【导师】 刘政军；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2011， 博士

【摘要】 阀门在国民经济建设中占有十分重要的地位,而阀门密封面在使用过程中,极易受到介质的腐蚀和冲刷,使阀门密封面受到损伤,因此开展相关技术将耐磨合金粉末堆焊到铁基阀门密封面上,起到延长阀门的使用寿命、提高经济效益的目的,十分有意义。本文采用反极性弱等离子弧将铝青铜堆焊到20g和HT200表面,并在堆焊过程中施加横向磁场,3对不同堆焊电流和磁场电流下堆焊层的硬度、耐磨性、耐蚀性和显微组织进行对比分析,并对堆焊界面的结合机理进行研究,明确堆焊电流和磁场电流对堆焊层组织性能的影响规律和作用机理。得到主要结论如下:(1)在送粉量Q=17g/min,堆焊速度V=120mm/min,焊接电流I=110A时,铝青铜与低碳钢/铸铁堆焊层的成型性及堆焊层的组织性能得到最佳。对于铝青铜与低碳钢堆焊层而言,硬度为259HV,磨损量为0.008g,摩擦系数为0.3;对于铝青铜与铸铁堆焊层而言,硬度为233.7HV,磨损量为0.128g,摩擦系数为0.35;此时铝青铜堆焊层中的显微组织以α-Cu为主,并伴有少量弥散分布的γ2、β′和κ相,起到第二相强化;但是由于γ2相的极化电位较低,耐蚀性较差,在腐蚀介质中将优先腐蚀而致堆焊层的耐蚀性下降,因此在堆焊电流为110A时堆焊层的耐蚀较差。(2)在堆焊电流合适情况下,堆焊层界面结合良好,熔合线清晰可见,无杂质存在,而且在堆焊层界面有一定的元素扩散现象存在,当堆焊电流较大时,扩散加剧,使得部分铜溶入堆焊层中,产生成分偏析。铝青铜堆焊层界面的结合方式主要为层状结合,堆焊层通过物理接触、表面激活和内部扩散三个过程实现堆焊层金属与基材之间的原子结合。(3)在堆焊电流I=110A,磁场电流I_m=1A,铝青铜与碳钢/铸铁堆焊层组织性能得到最佳匹配。铝青铜/铸铁堆焊层的磨损量达到0.0063g,硬度为284HV,摩擦系数变化幅度较小为0.3左右;铝青铜/铸铁堆焊层的硬度达到252.9HV,磨损量达到0.0088g,摩擦系数变化幅度较小为0.35左右。堆焊层中的显微组织以α-Cu为基体,在晶界弥散分析着K相及β相的,起到第二相强化作用,此时堆焊层的力学性能达到最佳值,耐蚀性最好(腐蚀极化电位最高,腐蚀电流最小),界面结合最为理想(形成具有一定宽度成分较为均匀的过渡层,而且界面无明显的金属化合物出现)。(4)外加磁场产生的电磁搅拌对堆焊层形成“M搅拌”、“S搅拌”和“F搅拌”,其中以“F搅拌”作用效果最为明显,可以细化堆焊层中的显微组织,改善组织分布形态,球化杂质,提高堆焊层的综合力学性能;但是磁场电流不易过大,此时电磁阻尼作用增强,会使堆焊层组织粗化、性能恶化。更多还原

【Abstract】 Valves are very important in national economic construction,but sealing faces of valves are easy to be corroded and abraded,which were vulnerable to be damaged. So,it is significance to research the way how the wearable alloy powders were surfacing on sealing face, which would prolong the lifetime of valves and increase the economic performace.Albronze alloy powers were surfaced on 20g and HT200 with weak plasma arc under different welding parameters and DC transverse direction magnetic field. The hardness, wearing resistance, erosion resistance, microstructure and interfacing bonding mechanism of surfaing layer were tested and studied. The influence rule and acting mechanism of magnetic field currents and welding currents on properties and microstructure of surfacing layer were researched. The main results are as following:(1)The optimal value of forming, properties and microstructure of albronze with low carbon steel & cast iron surfacing layer are obtained when Q=17g/min, V=120mm/min, I=110A. For albronze and low carbon steel, the hardness is 259HV,wear extent is0..0088g,fraction factor is 0.3;For albronze and cast iron, the hardness is 233.7HV, wear extent is 0.128g, fraction factor is 0.35. The microstructure of albronze surfacing layer consists ofα-Cu and second phaseγ2,β′&κ,which has second phase invigoration effect. The polarization potential ofγ2 phase is low, so erosion resistance ofγ2 phase is not good and will erode at first. The erosion resistance of surfacing layer is not good when I=110A.(2)The interface bonding of surfacing layer is good when surfacing current is proper, fusion line is clear and clean, the phenomenon of element diffusion appears along surfacing layer interface. The component segregation will appear when surfacing current is too big, when the diffusion of element iaggravate. The bonded mode of albronze surfacing layer is lamellar bond. Through physical contact, face activation and inter diffusion, the surfacing layer bonds with based metal for atom size. (3)The optimal microstructure and properties of surfacing layer are obtained when I=110A and I_m=1A. For albronze and low carbon steel surfacing layer, hardness is 284HV, the wear extent is 0.0063g, fraction factor is 0.3;For albronze and cast iron surfacing layer, hardness is 252.9HV, wear extent is 0.0088g, fraction factor is 0.35. The microstructure of surfacing layer consists ofα-Cu and second phase K andβ,which has second phase invigoration effect. The erosion resistance of surfacing layer is best at this time, the corrosion potential is highest and corrosion current is lowest. The best state of interface bond also appears at this time, the breadth of transition layer is proper and metallic compound hasnot been found.(4)The“M stirring”,“S stirring”and“F stirring”will affect the solidifaction and crystallization of surfacing layer metal, which are induced by extra magnetic field. The effect of“F stirring”is best, which can refine the microstructure, nodulare impurity and improve the distribution of phae and the properties of surfacing layer. But the magnetic field current is too big to properties of surfacing layer because of the electromagnetic damping.更多还原