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)。
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).
引文
[1]乐颂光.钴冶炼[M].北京：冶金工业出版社,1987
[2]丰成友,张德全,党兴彦.中国钴资源及其开发利用概况[J].矿床地质,2004,1(23)：23-26
[3]王德权,胡毅钧,李杰.阀门用钴基合金及堆焊工艺[J].阀门,2004,2：45-48
[4]孙晓刚.世界钴资源的分布和应用[J].有色金属,2001,1：56-59
[5]何清华,李爱强,邹湘伏.大洋富钴结壳调查进展及开采技术[J].金属矿山,2005,5：24-28
[6]Manheim.F.T. Marine Cobalt Resources[J]. Science,1986,232:600-603
[7]James Hein. Cobalt rich ferromanganese crusts:global distribution, composition, origin and research activities[J]. ISA Technical study,1998,2:43-49
[8]PeterA. Rona. Resources of the Sea Floor[J]. Science,2003,299:673-674
[9]Commeau.R.F,et al. Ferromanganese Crust Resources in the Pacificand Atlantic Oceans. In:IEEE. London,1984,421-429
[10]沈裕军,钟祥,贺泽全.大洋钴结壳资源研究开发现状[J].矿冶工程,1999,2(19)：11-13
[11]王素萍.我国钴矿供需形势分析及对策建议[J].世界有色金属,2008,(7)：34-35
[12]唐娜娜,莫伟,马少健.钴矿资源及其选矿研究进展[J].2006,(22)：5-7
[13]汪大林,徐君伍.口腔医学中金属与合金材料的应用现状和存在的问题[J].生物医学工程学杂志,1993,10(4)：364-367
[14]Douglass.C.W,Mjor.I.A,Munksgaard.E.C,etal. Advdent Res,1992,6(9):41-43
[15]Morris H F. Properties of Cobalt-Chromium Metal Ceramic Alloys After Heat Treatment[J]. J Protthet Dent,1990,63(4):426-433
[16]Cohen.S.M,Viswanadhan.T. Castability Optimization of Palladium Based Alloys. J Prosthet Dent,1996,76(2):125-131
[17]立石,哲也.金属系生体材料[J].金属,1989(1)：33-37
[18]汪大林,江中明.特种铸造及有色合金[J].1998,3：42-44
[19]黄乾尧,李汉康等编著.高温合金[M].北京：冶金工业出版社,2000
[20]C.T. Sims, N.S. Stoloff, W.C. Hagel(Eds.). Superalloys. New York:Wiley,1987, 145-174
[21]Y.Kimura, K.Sakai,Y.Mishima. Revolutionary microstructure control with phase diagram evaluation for the design of E21 Co3AlC-based heat-resistant alloys[J]. Journal of Phase Equilibria and Diffusion,2006,27(1):14-21
[22]Min Chena,ChongYu Wanga. First-principles investigation of the site preference and alloying effect of Mo, Ta and platinum group metals in γ'-Co3(Al,W)[J]. Scripta Materialia,2009,60:659-662
[23]D.H.Ping, C.Y.Cui, Y.F.Gu, et al. Microstructure of a newly developed γ' strengthened Co-base superalloy[J]. Ultramicroscopy,2007,107(9):791-795
[24]J.Sato,T.Omori,K.Oikawa,ect. Cobalt Base High Temperature Alloys[J]. Science, 2006,312:90-91
[25]Akane Suzuki,Garret C.DeNolf,Tresa M.Pollock. Flow stress anomalies in γ/γ'two phase Co-Al-W-base alloys [J]. Scripta Materialia,2007,56:385-388
[26]李相辉,甘斌,冯强,等.Co-Al-W三元合金热处理组织[J].北京科技大学学报,2008,30(12)：1369-1372
[27]CHAO Jiang. First-principles study of Co3(Al,W) alloys using special quasi-random structures [J]. Scripta Materialia,2008,59(10):1075-1078
[28]姚强,孙坚.(Co,I r)3(Al,W)析出相稳定性和弹性性质第一性原理的研究[J].材料研究与应用,2007,1(4)：282-285
[29]陈学定,韩文政.表面涂层技术[M].北京：机械工业出版社,1994
[30]宋武林.激光熔敷层热膨胀系数对其开裂敏感性的影响[J].激光技术,1998,22 (1) ： 34
[31]李春彦,张松,康煜平等.综述激光熔敷材料的若干问题[J].激光杂志,2002,23(3) ： 5
[32]徐滨士,刘世参.表面工程新技术[M].北京：国防工业出版社,2002：25-28
[33]徐大鹏,周建忠,郭华锋,等.激光熔敷裂纹产生机理及控制方法分析[J].工具技术,2007,(41)：45-46
[34]刘江龙,邹至荣,苏宝容.高能束处理[M].北京：机械工业出版社,1997：6
[35]孙盛玉,戴雅康.热裂纹分析图谱[M].大连：大连出版社,2002：4
[36]Linsong Wu, Peidi Zhu, Kun Cui. Effect of Ni content oncracking susceptibility and microstructure of laser clad Fe2Cr2Ni2B2Si alloy. Surface and Coatings Technology, 1996,80:279-282
[37]CHEN J,YANG H O,LI YM,et al. The research on two kinds of cracking behavior and mechanism of cladding in rapid laser forming process. Applied Laser,2002, 22(3):300-304
[38]SINGH,MAZUNDERJ. Microstructure and wear properties of laser clad Fe2Mn2C alloys. Metallurgical Transactions,1987,18 (5):313-318
[39]陈静,林鑫,王涛,等.316L不锈钢激光快速成形过程中熔敷层的热裂机理[J].稀有金属材料与工程,2003,32：23-28
[40]孙会来.激光熔敷研究现状与发展趋势[J].激光杂志,2008,1(29)：33-34
[41]董世运,马运哲,徐滨士,等.激光熔敷材料研究现状[J].材料导报,2006,6(20)：45-49
[42]洪永昌,夏正文.激光扫描速度对Co基合金堆焊重熔层组织和硬度的影响[J].热处理,2006,21(1)：31-35
[43]王新林,李必文,郑启光.核阀密封面激光熔敷层耐磨性能研究[J].应用激光,2003,23(6)：261-264
[44]张松,张春华,孙泰礼,等.激光熔敷Co基合金组织及其抗腐蚀性能[J].中国激光,2001,28(9)：860
[45]李明喜,袁晓敏,何宜柱,等.Ni基合金激光熔敷Co基合金的组织与性能[J].安徽工业大学学报,2003,20(2)：106
[46]夏正文,洪永昌.激光重熔Co基合金堆焊层的组织和性能[J].电焊机,2005,35(7)： 26-29
[47]W.C.Lin,C.Chen.Characteristics of thin surface layers of cobalt-based alloys deposited by laser cladding[J]. Surface & Coatings Technology,2006,200:4557-4563
[48]A.S.C.M.d'Oliveira, R.Vilar,C.G. Feder.High temperature behaviour of plasma transferred arc and laser Co-based alloy coatings[J]. Applied Surface Science, 2002,201:154-160
[49]H.Hugel. New solid-state lasers and their application potentials[J]. Optics and Lasers in Engineering,2000,34:213-229
[50]Qi Yunlian, Deng Ju, Hong Quan,et al. Electron beam welding, laser beam welding and gas tungsten arc welding of titanium sheet[J]. Materials Science and Engineering,2000,A280:177-181
[51]Achim Mahrle,Jurgen Schmidt. The influence of fluid flow phenomena on the laser beam welding process[J].International Journal of Heat and Fluid Flow, 2002,23:288-297
[52]L.Quintino,A.Costa,R.Miranda,ect.Welding with high power fiber lasers preliminary study[J]. MaterialsandDesign,2007,28:1231-1237
[53]Li Mingxi,He Yizhu,Yuan Xiaomin. Effect of nano-Y2O3 on microstructure of laser cladding cobalt-based alloy coatings[J]. Applied Surface Science,2006,252: 2882-2887
[54]Li Mingxi,He Yizhu,Yuan Xiaomin. Microstructure of Al2O3 nanocrystalline cobalt-based alloy composite coatings by laser deposition[J]. Materials and Design,2006,27:1114-1119
[55]Li Mingxi,He Yizhu,Sun Guoxiong. Microstructure and wear resistance of laser clad cobalt-based alloy multi-layer coatings[J].Applied Surface Science,2004,230: 201-206
[56]Rafal Jendrzejewski,Carmen Navas,Ana Conde,et al.Properties of laser-cladded stellite coatings prepared on preheated chromium steel[J].Materials and Design, 2006,1-6
[57]T.Omoria, Y.Sutou a, K.Oikawa, et al. Shape memory and magnetic properties of Co-Al ferromagnetic shape memory alloys [J]. Materials Science and Engineerings 2006,440:1045-1049
[58]郭建亭著.高温合金材料学[M].北京：科学出版社,2008
[59]张庆茂,刘文今,杨森,钟敏霖.送粉式激光熔敷稀释率的分析模型及其影响因素.钢铁研究学报,2002, (14)：25-29
[60]徐洲,姚寿山主编.材料加工原理[M].北京：科学出版社,2003
[61]郭晓琴,李晓玲,张锐,等.TiB2/Cu激光熔敷工艺研究[J].郑州航空工业管理学院学报,2009,27(5)：141-144
[62]孙宽,姚继蔚,徐忠锦,等.影响激光熔敷质量的主要因素[J].农业装备与车辆工程,2007,(7)：36-42
[63]JB／T7510-1994,工艺参数优化方法-正交试验法[S]
[64]《正交试验法》编写组.正交试验法[M].北京：国防工业出版社,1976
[65]关振中主编.激光加工工艺手册[M].北京：中国计量出版社,1998
[66]单际国,谭稳达,任家烈.交流TIG电弧粉末堆焊层成形特点的研究[J].电焊机,2005,35(7)：27-29
[67]董巍,单际国,谭稳达,等.Ni-Al粉末直流T IG电弧堆焊层的稀释率及其控制[J].金属热处理,2007,32(7)：41-43
[68]Kazuya Shinagawa,Toshihiro Omori,Katsunari Oikawa,et al. Ductility enhancement by boron addition in Co-Al-W high-temperature alloys [J]. Scripta Materialia,2009, 61:612-615
