【作者】 闫健强；

【导师】 夏天东；

【作者基本信息】 兰州理工大学 ， 材料学， 2010， 硕士

【摘要】 传统的钴基高温合金中γ′相不稳定或与γ-Co基体的错配度较大,不能像镍基合金中那样主要依靠γ′相来强化,因此钴基高温合金的高温强度主要依靠固溶强化和碳化物强化来增强,这就使得它的高温强度不如镍基合金,限制了其使用范围。新型Co-Al-W高温合金是由高温稳定的L12型γ’-Co3(Al,W)相强化的合金,其高温强度高于传统的镍基高温合金,将会成为下一代高温材料的候选。本文在新型Co-Al-W高温合金已有的研究基础上,通过优化合金成分设计,利用真空电弧熔炼的方法制备该合金。采用激光熔敷技术和TIG堆焊技术两种表面熔敷工艺在304不锈钢基材表面制备Co-Al-W合金熔敷层,对熔敷层宏观形貌、稀释率、相组成、微观组织特征、成分和硬度进行了分析。得出的主要研究结果如下：(1)真空电弧熔炼制备的Co-Al-W合金在900℃经时效处理72小时的相由γ-Co基体及与其共格的γ’-Co3(Al,W)强化相和少量碳化物共同组成。由γ’-Co3(Al,W)相沉淀强化Co-Al-W合金的液相线温度比传统钴基高温合金的高50-100K。钨含量增加,合金液相线温度升高,γ′相数量和体积分数也增加。加入合金元素铌可提高合金中γ′相的固熔温度,对γ′相起稳定作用。(2)激光输出功率、扫描速度对熔敷层成形的影响显著,而搭接率的影响程度较小。对于Co：Al：W(原子比)为78：12：10的混合粉末而言,本实验条件下能够获得较好成形的激光熔敷工艺参数是输出功率3kW、扫描速度3mm／s、搭接率10%。(3)熔敷层组成相主要为面心立方的γ-Co基体及金属间化合物CoxAl和碳化物(Cr23C6,Co6W6C和CoCX)等相。(4)激光熔敷层稀释率较低,大约为17%；而TIG熔敷层的稀释率较大,大约为32%。通过激光和TIG熔敷均获得了高硬度的熔敷层,硬度最高可达1050(HV0.1)。更多还原

【Abstract】 Conventional Co-based superalloys lack effective precipitation strengthening by intermetallic compounds with the L12 structure as the case in the Ni-based superalloys, and depend on solid-solution elements and precipitation of low volume fraction of carbides for their high-temperature strength. The novel Co-Al-W superalloys are strengthened by a ternary compound with the L12 structure,γ′-Co3(Al,W), which precipitates in the disordered y face-centered cubic cobalt matrix with high coherency and with high melting points. And the novel alloys showing a high-temperature strength greater than those of conventional nickel-base superalloys, will become the candidates for next-generation high-temperature materials.Optimizing the alloy composition design on the basis of existing research.The novel Co-Al-W superalloy were prepared by vacuum arc melting (VAM). Laser cladding technology and Tungsten Inert Gas (TIG) welding was used to deposit Co-Al-W alloy on 304 austenite stainless steel substrate and cladding layer shape, dilution, Vickers hardness, microstructure and distribution of alloying elements were investigated. The main results as follows:(1) The microstructure of Co-Al-W alloy annealed at 900℃for 72 hours after solution treatment at 1300℃for 2 hours prepared by vacuum arc melting is composed of richγ-Co matrix,γ′Co3(Al,W) phase and few carbides.The novel Co-Al-W alloy is strengthened by a ternary compoundγ′-Co3(Al,W) phase with precipitation strengthening, which is 50 to 100℃higher than those of Ni-base superalloys. Tungsten stabilizeγ’ phase with effect ofγ’precipitation strengthening, the melting temperatures gradually increasing with the increasing of tungsten concentration. The solvus temperatures of theγ’phase increased because of the addition of Nb.This result showed that Nb stabilized theγ’phase.(2) Laser power and scanning speed affect the performance of coating shaping significantly,while overlapping has less influence on shaping. Under the experimental conditions and when Co:Al:W proportion is 78:12:10(atom rate),the optimized parameters are as follows:laser power is 3kW,scanning speed is 3mm/s,overlapping-is 10%.(3) The phases in the cladding layer were composed ofγface-centered cubic cobalt matrix and intermetallics CoxAl and carbide (Cr23C6, Co6W6C and CoCx). (4) Laser cladding layer with lower dilution rate, about 17%; and TIG cladding layer with higher dilution rate, approximately 32%. We obtained high hardness cladding layer through the laser and TIG cladding. The maximum hardness up to 1050 (HV0.1).更多还原