-
试验中所用基材为300mm×150mm×12mm 2Cr25Ni20钢板,基体常温平衡组织为奥氏体,而所用的激光熔覆合金粉末为NiCrFeMo高温合金粉末,其粒度为:100目~300目, 粉末流动性:10g/s~100g/s,硬度: 25HRC~30HRC, 使用温度:1000℃。试验前,粉末在烘干机内静置烘干,烘干时间为2h,温度为150℃。基材与高温合金粉末成分如表 1所示。
Table 1. Compositions of substrate and Ni-based superalloy alloy powder(mass fraction)
element C Si Cr Nb+Ta Mn S P Mo Fe Ni 2Cr25Ni20 ≤0.0025 ≤0.0150 ≤0.2400 — ≤0.0200 ≤0.00030 ≤0.00035 — balance ≤0.1900~0.2200 powder 0.0003~0.0005 0.006~0.015 0.20~0.23 0.04~0.06 — — — 0.08~0.1 0~0.05 balance -
试验在激光快速成型系统上进行,该试验系统由德国IPG公司YLS-4000-S2光纤激光器,中国KUKA公司KR30HA机器人,中国新松公司1000mm伺服旋转工作台,中国新松公司XSL-PF-01A-2负压式气载送粉器及中国东露阳实业有限公司PH-LW296-TH2P冷却系统组成, 如图 1所示。激光波长:1070nm ~1080nm;激光聚焦头(PLFDH0125)使用抛物聚焦镜,焦距f=600mm, 焦点光斑直径3mm。配置侧向送粉喷嘴及调整机构, 载气与保护气为氩气。在熔覆过程中,氩气不仅被用作保护熔覆层被空气氧化,还被用作保护激光加工头内的光学元件免受烟尘氧化。
Figure 1. Laser cladding experiment equipments(1—fiber laser YLS-4000-S2;2—KR30HA robot; 3—servo rotating worktable; 4—XSL-PF-01A-2 negative pressure type powder feeding system; 5—PLFDH0125 laser head; 6—lateral powder-feed nozzle; 7—cooling system)
该系统送粉方式为气压驱动侧向同步送粉,为了提高基材对激光的吸收率,成形性能优良的熔覆层,前期通过正交试验选出最佳工艺参量,具体试验工艺参量设定为:激光功率1.6kW,扫描速率8mm/s,送粉量15g/min,光斑直径3mm,送粉载气流量150L/h。
为了评估NiCrFeMo高温合金涂层与基材2Cr25Ni20钢板间的结合强度与常温力学性能,设计常温拉伸试验,将板件垂直于长边开V型坡口,坡口尺寸如图 2所示。
采用上述激光试验系统在2Cr25Ni20钢板上进行Ni基高温合金粉末激光熔覆成形试验,研究在上述工艺参量下,粉末在激光作用下熔化,形成致密Ni基高温熔覆层,冷却至室温,经过多层堆积,将上述钢板上的通槽填充完整,并使用磨光机磨削熔覆层多余部分,用不同目数的砂纸先后打磨该部分,然后使用酒精擦拭熔覆层及其周围表面,静置晾干。
处理完成后,利用电火花线切割机沿熔覆板件对处理后板件熔覆区域中心横截面方向进行线切割,并对切割后样品进行标准金相制样。清理表面铁屑,用砂纸将试样棱角打磨平滑。然后进行抛光、腐蚀,采用Kalling试剂(C2H5OH 100mL, HCl 100mL, CuCl2 5g)腐蚀熔覆层与基材,使用Zeiss Sgma 500扫描电子显微镜(scanning electron microscope, SEM)对基材区、热影响区、基材区与熔覆层结合处以及熔覆层截面显微组织晶粒形态进行观察。
利用理学D/max2500 X射线衍射仪(X-ray diffraction, XRD)分别测试熔覆层、基材与熔覆层结合处中的物相,然后利用牛津200 X射线能量色散光谱仪(energy dispersive spectrometer, EDS)测试熔覆层和垂直界面方向各层各元素的分布。
采用HVS-1000Z型维氏显微硬度计沿基材区-热影响区-熔覆层直线方向测量各层区显微硬度值,测量距离为相邻两点间距200μm,载荷为300g(2.942N),加载时间为15s。
将熔覆完成的试样依据GB/T 228.1-2010金属材料拉伸试验第一部分:室温试验方法标准进行试验,先用线切割在处理好的板件上切制出标准力学拉伸试样,然后使用不同目数的砂纸对力学试样进行打磨抛光,最终通过CMT 5205常温力学试验机测试修复试样力学性能。
镍基高温合金激光熔覆涂层组织及性能研究
Study on microstructure and properties of laser cladding coating for base superalloy
-
摘要: 为了研究高温合金激光熔覆涂层组织演变及力学性能,采用激光熔覆技术在2Cr25Ni20耐热奥氏体不锈钢表面制备镍基NiCrFeMo高温合金涂层。使用扫描电子显微镜、X射线衍射仪、能量色散光谱仪、显微硬度计等微观分析测试手段对该镍基高温合金涂层的微观组织形貌、物相种类、界面元素分布与偏析、各区域的硬度进行分析。结果表明, 基材与熔覆层结合位置至熔覆层顶部,依次由多种晶粒形态生成;Nb与Mo元素在熔池金属液体对流作用下向基材发生扩散,其它元素基本无扩散;熔覆层存在物相有γ-Ni和Cr2Fe14C,熔覆层结合位置包含物相Fe2Ni3, γ-(Fe, Ni)和Ni0.9Nb0.1;基材显微硬度平均值为252HV0.3左右,熔覆层显微硬度平均值为285HV0.3左右;经常温拉伸试验,与2Cr25Ni20钢力学性能比较,2Cr25Ni20钢修复件抗拉强度升高,强度增大,断后伸长率明显下降,塑性降低。此研究为后续钢炉转轴修复提供了可行性方案。Abstract: In order to study the microstructure evolution and mechanical properties of laser cladding coatings of high temperature alloy, a nickel-based NiCrFeMo high temperature alloy coating was prepared on the surface of 2Cr25Ni20 heat-resistant austenitic stainless steel using laser cladding technology. The cladding technology prepares a nickel-based NiCrFeMo high-temperature alloy coating on the surface of 2Cr25Ni20 heat-resistant austenitic stainless steel. Scanming electron microscope, X-ray diffraction, energy dispersive spectrometer, micro-hardness tester and other micro-analysis test methods were used to analyze the microstructure morphology, phase types, interface element distribution and segregation, and hardness of each area of the nickel-based superalloy coating. The results show that the bonding position of the base material and the cladding layer to the top of the cladding layer is sequentially generated from a variety of crystal grain morphologies. The Nb and Mo elements diffuse to the substrate under the action of the molten metal liquid convection, and the other elements basically have no diffusion. The cladding layer has phases: γ-Ni and Cr2Fe14C, while the bonding position of the cladding layer contains phases: Fe2Ni3, γ-(Fe, Ni), and Ni0.9Nb0.1. The average microhardness of the substrate is about 252HV0.3, and the average microhardness of the cladding layer is about 285HV0.3. In normal temperature tensile test, compared with the mechanical properties of 2Cr25Ni20 steel, the tensile strength of 2Cr25Ni20 steel repaired parts increases, the strength increases, the elongation after fracture decreases significantly, and the plasticity decreases. Therefore, this study provides a feasible plan for the subsequent repair of the steel furnace shaft.
-
Figure 4. a—overall microstructure morphology of cladding layer b—the distribution of network structure on the surface of cladding layer c—enlarged local view of reticular distribution d— equiaxed crystal distribution on the upper layer of the cladding layer e—columnar crystal distribution in cladding layer f—the cellular crystal distribution at the lower end of the cladding layer
Table 1. Compositions of substrate and Ni-based superalloy alloy powder(mass fraction)
element C Si Cr Nb+Ta Mn S P Mo Fe Ni 2Cr25Ni20 ≤0.0025 ≤0.0150 ≤0.2400 — ≤0.0200 ≤0.00030 ≤0.00035 — balance ≤0.1900~0.2200 powder 0.0003~0.0005 0.006~0.015 0.20~0.23 0.04~0.06 — — — 0.08~0.1 0~0.05 balance -
[1] LIU B Ch, HUANG T Y. China materials engineering [M]. Beijing: Chemical Industry Press, 2005: 204(in Chinese). [2] CHEN Sh M. Research on high temperature properties of Al2O3/20Cr25Ni20 composite material or roll [D]. Kunming: Kunming University of Science and Technology, 2013: 5-10(in Chinese). [3] WANG E Z, XU Y P, BAO Ch G, et al. Preparation of Al2O3 particles/heat-resistant steel composite material and high-temperature abrasive wear properties[J]. Journal of Composite Materials, 2004, 21(1): 56-60(in Chinese). [4] HAO Y B, WANG J, YANG P, et al. Research on microstructure and properties of laser cladding tin-based babbitt alloy [J]. Chinese Journal of Lasers, 2020, 47(8): 0802009 (in Chinese). doi: 10.3788/CJL202047.0802009 [5] CHEN Zh J, DING Y M, DONG G, et al. Analysis of microstructure and Cr content of low Cr alloy modified layer prepared by laser cladding on 9%Cr steel [J]. Surface Technology, 2020, 49(2): 281-287(in Chinese). [6] DONG Sh Y, MA Y Zh, XU B Sh, et al. Research status of laser cladding materials [J]. Material Guide, 2006, 20(6): 10-14(in Chin-ese). [7] SONG X H, ZOU Y F, XING J K, et al. Performance comparison of 35CrMo laser cladding iron-based alloy and nickel-based alloy coating [J]. Laser Technology, 2015, 39(1): 39-45(in Chinese). [8] LU H F, PAN Ch Y, QIN E W, et al. Microstructure and properties of laser cladding WC/Ni-based alloy composite coating on 45 steel [J]. Metal Heat Treatment, 2019, 44(12): 19-25(in Chinese). [9] LIU P L, SUN W L, WANG G D, et al. The effect of scanning rate on the performance of laser cladding nickel-based alloy coating [J]. Laser Technology, 2018, 42(6): 845-848(in Chinese). [10] DENG D W, SUN J H, WANG X L, et al. Effect of laser power on the structure and properties of laser cladding nickel-based alloy coating [J]. Rare Metals, 2016, 40(1): 20-25(in Chinese). [11] GONG Ch, WANG L F, ZHU G X, et al. Influence of laser additive manufacturing process parameters on residual stress of cladding layer [J]. Laser Technology, 2019, 43(2): 263-268(in Chinese). [12] ZHANG D Q, ZHANG J Q, LI J H, et al. Effect of defocusing amount on laser cladding of self-fluxing Ni-based WC on 45# steel surface[J]. Surface Technology, 2015, 44(12): 92-97(in Chinese). [13] LIU P L, SUN W L, HUANG Y. The effect of temperature gradient on cracks in laser cladding layer [J]. Laser Technology, 2019, 43(3): 392-396(in Chinese). [14] LI C, WHITE R, FANG X Y, et al. Microstructure evolution characteristics of Inconel625 alloy from selective laser melting to heat treatment[J]. Materials Science & Engineering, 2017, A58(8): 20-31. [15] PAVITHRA E, SENTHILKUMAR V S. Microstructural evolution of hydroformed Inconel625 bellows[J]. Journal of Alloys and Compounds: An Interdisciplinary Journal of Materials Science and Solid-state Chemistry and Physics, 2016, 669(5): 199-204. [16] CHUNG K H, RODRIGUEZ R, LAVERNIA E J, et al. Grain growth behavior of cryomilled Inconel625 powder during isothermal heat treatment[J]. Metallurgical & Materials Transactions, 2002, A33(1): 125-134. doi: 10.1007/s11661-002-0011-y [17] JEYAPRAKASH N, YANG C H, RAMKUMAR K R. Microstructure and wear resistance of laser cladded Inconel625 and Colmonoy 6 depositions on Inconel625 substrate[J]. Applied Physics, 2020, A126(6): 1-11. doi: 10.1007/s00339-020-03637-9 [18] XU F J, LV Y H, Y, LIU Y X, et al. Microstructural evolution and mechanical properties of Inconel625 alloy during pulsed plasma arc deposition process[J]. Journal of Materials Science & Technology, 2013, 29(5): 480-488. [19] WANG X, XU X, GAO Y, et al. Research on microstructures and properties of Inconel625 coatings obtained by laser cladding with wire[J]. Journal of Alloys & Compounds, 2017, 715(8): 362-373. [20] DINDA G P, DASGUPTA A K, MAZUMDER J. Laser aided direct metal deposition of Inconel625 superalloy: Microstructural evolution and thermal stability[J]. Materials Ence and Engineering, 2009, 509(1/2): 98-104. [21] ROMBOUTS M, MAES G, MERTENS M, et al. Laser metal de-position of Inconel625: Microstructure and mechanical properties[J]. Journal of Laser Applications, 2012, 24(5): 2575-2581.