Nickel-base corrosion-resistant alloys

In this article the effect of the base (Mo, Cr), alloying (V Nb, Fe, W, Ti), and impurity (C, Si, P, Fe) elements on phase and structural transformations in Ni-Mo and Ni-Cr alloys are considered. Their corrosion and electrochemical behavior, and mechanical properties after various heat treatments related to commercial practice or the conditions of use are reviewed. Based on the regularities observed, general rules are formulated for the development of corrosion-resistant, deformable, and weldable nickel-base alloys with a required combination of properties.I. P. Bardin Central Scientific Institute of Ferrous Metallurgy. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 9–13, September, 1994.     

High-temperature high-pressure SCC testing of corrosion-resistant alloys

Stress corrosion cracking test methods of corrosion-resistant alloys are reviewed. The interest to write a review on this topic was drawn by demands for oil country tubular goods applicable in deep wells with high pressures, high temperatures, and the presence of H₂S, where stress corrosion cracking is one of the most critical failure modes. All conventional methods for determining the stress corrosion cracking resistance of an alloy, mainly slow strain rate testing, constant load testing (tensile, 4-PB), constant strain testing (U-bend, C-ring), and fracture mechanics (double cantilever beam sample) are covered. Considering the variety of testing solutions, the field of search is narrowed to hot (up to 250°C) aqueous chloride solutions with dissolved H₂S and CO₂ gases under high pressure (up to 200 bar total pressure).     

Diffusion welding of nickel-based creep-resisting alloys

Special features of the diffusion welding of creep-resisting alloys were investigated to evaluate the possibilities and prospects of using these alloys in aviation engine construction.     

弥散型高强度镍基高温弹性合金

采用真空中频熔炼、轧制加工及热处理研制出符合航空要求的高温镍铍钛合金带,各项性能达到了美国同类产品水平.     

304不锈钢与C-276镍基耐蚀合金的真空钎焊

采用铜箔对C-276镍基耐蚀合金和304不锈钢的真空钎焊工艺进行研究。通过金相显微镜、扫描电镜及能谱分析、显微硬度机和万能材料试验机等手段研究钎焊温度对钎焊接头的微观组织和力学性能的影响。结果表明,钎焊温度对接头的组织和性能有明显影响。钎缝中心区为Cu基固溶体,两侧界面反应区分别为Fe基固溶体和Ni基固溶体。钎焊温度过低时,冶金作用较弱,接头强度较低;钎焊温度过高时,钎料流失较多,接头强度也较低。当钎焊温度为1 125℃时,接头的拉剪强度最高,为105.7 MPa,且接头的断裂方式为韧性断裂。     

Characteristics of passivity of extremely corrosion-resistant amorphous iron alloys

The amorphous FeCrPC alloy was compared with the crystallized alloy having the same composition in potentiodynamic polarization curves and with an 18Cr8Ni stainless steel in current decay after abrading the specimens under anodic polarization. Through these results along with the previous ESCA study, the extremely high corrosion-rseistance of the amorphous iron alloys containing 8 at.% or more chromium has been interpreted in terms of the rapid formation of thick, uniform, highly corrosion-resistant passive film due to the characteristics of the amorphous alloys.     

Oxidation and hot corrosion of nickel-based alloys containing molybdenum

The oxidation of Ni-15% CrMo alloys has been studied at 900°C in flowing and static oxygen atmospheres. In flowing atmospheres, molybdenum has no effect: all the alloys oxidize in a protective manner. However, in static atmospheres the oxidation rate of alloys with > 3% Mo eventually accelerates, and catastrophic destruction of the alloy takes place. Under these circumstances a molybdenum-rich oxide layer is detected adjacent to the alloy.When specimens are coated with Na₂SO₄ prior to oxidation, alloys containing > 3% Mo again suffer catastrophic degradation, in either flowing or static atmospheres, and again a molybdenum-rich oxide layer is observed. This suggests that the principal role of the salt coating is to prevent the escape of MoO₃ to the atmosphere.The morphology of the attack in the rapid propagation region is very similar to that obtained in pre-sulphidation/oxidation experiments in the absence of salt and that particular aspect of the reaction is not greatly affected by molybdenum; the aluminium content is more important in determining the nature of the propagation.Attack similar to that exhibited by molybdenum-containing alloys can be obtained with Ni-15%Cr binary alloys in the presence of MoO₃ vapour in the atmosphere, and this might suggest that the MoO₃ reacted with the Na₂SO₄ to produce an acid (SO₃-rich) salt, leading to acidic fluxing. However, very similar types of attack were obtained when Na₂MoO₄ was added to the Na₂SO₄, and this should not have affected the acidity of the salt at all.These experiments suggest that acidic fluxing may not be important in the hot corrosion of alloys of this type (molybdenum-containing) and that when catastrophic corrosion is observed, its initiation is probably due to the formation of a molybdenum-rich oxide layer, molten during the reaction. There appears to be a threshold molybdenum content below which attack does not occur, and this seems insensitive to an increase in the chromium content from 15 to 25%.     

A nickel-based brazing alloy for brazing creep-resisting alloys and steels

The main types of brazing alloys used for brazing creep-resisting alloys and steels are investigated and their characteristics and main special features described. The aspects of the selection of brazing alloys for brazing different materials depending on the brazing conditions and the operating conditions of the components are discussed. Examples of the application of the technology of high-temperature brazing in the manufacture of aviation technology components are presented.     

Q235基体上CMT-TWIN技术堆焊镍基合金

以Q235为基体,以镍基合金Inconel625(φ1.0 mm焊丝)为堆焊材料,采用CMT-TWIN焊接技术进行堆焊,试验结果表明最佳参数为:电弧电压14.7 V,焊接电流98 A,焊接速度4 mm/s,摆宽10 mm(双丝参数一致),能够获得致密美观、无缺陷的镍基合金堆焊层。从熔合线附近到堆焊层中心,组织为树枝晶形态的奥氏体;EDS表明元素含量在熔合线附近发生突变的区域较窄(10~20μm),而在堆焊层中分布较均匀,说明熔合比较小;剪切试验表明基体与堆焊层结合界面的抗剪强度大于326 MPa,断口形貌表明为韧性断裂。     

Degradation of zirconium-containing nickel-based alloys in a hydrogen-hydrogen sulfide environment

The modes of degradation experienced by a Ni-15Cr and three Ni-15Cr-xZr alloys (where x=1, 5, or 10 wt. %) after exposure to a 1% H₂S/H₂ gas mixture at 1000° C have been examined, with particular reference to the morphological features. The addition of Zr at about the 1% level has been shown to have a beneficial effect, in terms of reduced weight gain relative to the Ni-15Cr control, explained by a thinner more protective external CrS scale, and a decreased tendency for CrS subscale formation (internal sulfidation). Zr additions beyond 1%, up to 5 and 10%, become increasingly detrimental principally on account of extensive internal ZrH_x formation, associated with the selective attack of the increasing amounts ofNi₅Zr in the alloy microstructures. The mode of action of Zr at about the 1% level in these alloys is considered in the light of earlier studies concerning the performance of similar alloys in O/S atmospheres.     

Inconel 601 Ni基合金的焊接工艺性分析

为了解决Inconel 601 Ni基合金的焊接问题,针对该合金的成分特点和焊接性,确定其焊接工艺参数并进行焊接试验,提出Inconel 601 Ni基合金在焊接过程中防止焊接热裂纹产生、提高焊接质量的难点及注意事项,并提出无损检测后焊接质量评定及处理方法。     

Post-fabrication vapor phase strengthening of nickel-based sheet alloys for thermostructural panels

High-temperature metallic systems for use in thermostructural sandwich panels are important for many hypersonic flight systems. The complex three-dimensional geometry of these structures poses fabrication challenges for high-strength, high-temperature alloys. A new processing technique involving post-fabrication strengthening via pack aluminization has been investigated. Aluminization produces a β-NiAl surface layer, which is decomposed in subsequent annealing treatments, distributing Al through the sheet thickness. Microstructural development through the stages of processing is discussed along with mechanical properties of the post-fabrication, precipitation-strengthened sheet. Additionally, the benefit of this process to the oxidation behavior of these structures is discussed.     

Surface integrity of nickel-based alloys subjected to severe plastic deformation by abusive drilling

Surface integrity of nickel-based superalloys after machining operations has become a topic of major interest in the aerospace sector. In the present work, the characteristics of nickel-based alloys (Alloy 718, Waspaloy, Alloy 720Li, and RR1000) subjected to abusive drilling conditions have been investigated using experimental methods such as FEG-SEM, EBSD, XRD, TEM and nano-indentation. The results indicated the presence of nano-sized grains typical of severe plastic deformation in the machined surface while the presence of plastic slip bands was observed in the sub-surface layers. Correlations between the thermo-mechanical properties of the nickel-based alloys and the severe plastic deformation features of the machined surfaces are presented.     

Effect of alloying elements on the properties of corrosion-resistant high-temperature single-crystal alloys on a nickel base

The need to provide high values of short-term mechanical properties in a wide temperature range, including ones exceeding the operational temperatures of turbine blades of gas turbine engines, is in the “shadow” of such characteristics as long-term strength and resistance to high-temperature salt corrosion. However, the attainment of high mechanical properties in corrosion-resistant high-temperature alloys cannot be treated as a requirement of secondary importance. The present paper is devoted to the properties of single-crystal nickel alloys alloyed with Cr, Co, W, Mo, Ti, Al, and Nb in various amounts. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 8–10, March, 1998.     

High-temperature oxidation of nickel-based alloys and estimation of the adhesion strength of resulting oxide layers

The kinetics of isothermal oxidation (1100°C) of commercial nickel-based alloys with different content of sulfur (0.22–3.2 wt ppm) is studied. The adhesion strength in a metal/oxide system is estimated as a function of sulfur content and duration of high-temperature exposure. The scratch-test technique is proposed to quantitatively estimate the work of adhesion of resulting oxide films. It is found that the film microstructure is composed of an inner α-Al₂O₃ layer and an outer NiAl₂O₄ spinel layer, which are separated by discrete inclusions of TiO₂. Residual stresses in the oxide film are experimentally determined by X-ray diffraction.     

Corrosion of a stainless steel and nickel-based alloys in high temperature supercritical carbon dioxide environment

Corrosion of four alloys has been studied in supercritical carbon dioxide at 650 °C and 20 MPa, specifically AL-6XN stainless steel and three nickel-based alloys, PE-16, Haynes 230, and Alloy 625. The tests were performed for exposure durations of up to 3000 h with samples being removed for analyses at 500 h intervals. The corrosion performance of the alloys was evaluated by weight change measurements, and the surface oxide layers were characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Weight gain measurements showed that the Al-6XN stainless steel exhibited the least corrosion resistance while the weight gains were nearly similar for the other alloys. The oxide layer in AL-6XN stainless steel was composed of large equiaxed grained outer layer of Fe₃O₄ (magnetite) and an inner layer of FeCr₂O₄. Oxide spallation was observed in this stainless steel even after 500 h exposure. In all alloys, Cr-rich oxides phases of Cr₂O₃ and Cr_1.4Fe_0.7O₃ were identified as the protective layers. In alloy PE-16 a thin layer of aluminum oxide formed that promoted the corrosion resistance of the alloy. Cr₂O₃ was identified as the main protective oxide layer in nickel base alloys Haynes 230 and 625.