铌基合金高温强化的研究

研究了一种用于高温结构材料的铌基合金及其高温强化方法.经过试验,总结出两种强化方法:一是固溶强化,通过添加高熔点的W,Mo元素,形成合金化固溶体,从而提高了材料的高温蠕变性能;二是时效强化,通过加入C和Zr元素生成碳化物强化相.并研究C,Zr元素含量、热处理工艺及压力加工方法对时效强化的影响,分析得知,C含量控制在0.01%～0.13%,可以得到适量的碳化物强化相,在1600～1900℃下保温6～18 h热处理,可以使碳化物均匀分布.大变形量的压力加工方法可以使碳化物强化相进一步破碎,从而细化.经上述方法强化处理后的材料,其高温性能测试结果证实,此方法效果较为显著.     

Structure and Texture of Oxide Dispersion Strengthened Alloy 617 for Very High Temperature Applications

High energy mechanically milled Alloy 617 ODS powder was consolidated by Spark Plasma Sintering (SPS) technique and subsequently annealed at 650 °C and 1050 °C (923 K and 1323 K). Microstructure and microtexture evolution during SPS and annealing have been investigated. SPS consolidated sample exhibited heterogeneous microstructure with ultra-fine grains surrounded by coarse grains. Inhomogeneous distribution of plastic deformation induced during ball milling resulted in heterogeneous nucleation and further grain growth during consolidation. The bimodal microstructure is advantageous with coarse grains providing ductility and fine grains providing strength by the Hall–Petch relationship. The bimodal grains structure was also retained during annealing. As-sintered specimen showed 〈100〉 texture parallel to the compression axis due to dynamic recrystallization during the SPS process. At 650 °C, annealed sample exhibited 〈111〉 annealing texture parallel to compression axis. The texture was randomized in sample annealed at 1050 °C. Precipitation analysis by SEM, XRD and TEM showed the presence of M₂₃C₆, M₆C and Al₂O₃ in both As-sintered and annealed samples. Dispersoids analysis showed the presence of fine and uniform Y₃Al₅O₁₂, Y₄Al₂O₉ and a complex oxide rich in Ni, Y, Al and O. Stress–strain analysis from instrumented indentation test shows higher yield strength for Alloy 617 ODS in comparison with conventional Alloy 617.

     

Precipitate Redistribution during Creep of Alloy 617

Nickel-based superalloys are being considered for applications within advanced nuclear power generation systems due to their high-temperature strength and corrosion resistance. Alloy 617, a candidate for use in heat exchangers, derives its strength from both solid solution strengthening and the precipitation of carbide particles. However, during creep, carbides that are supposed to retard grain boundary motion are found to dissolve and reprecipitate on boundaries in tension. To quantify the redistribution, we have used electron backscatter diffraction (EBSD) and energy-dispersive spectroscopy (EDS) to analyze the microstructure of 617 after creep testing at 900 °C and 1000 °C. The data were analyzed with respect to the location of the carbides (e.g., intergranular vs intragranular), grain boundary character, and precipitate type (i.e., Cr rich or Mo rich). We find that grain boundary character is the most important factor in carbide distribution; some evidence of preferential distribution to boundaries in tension is also observed at higher applied stresses. Finally, the results suggest that the observed redistribution is due to the migration of carbides to the boundaries and not the migration of boundaries to the precipitates.     

Characterization of Creep-Damaged Grain Boundaries of Alloy 617

Intergranular cracking and void nucleation occur over extended periods of time in alloy 617 when subjected to stress at high temperatures. Damage occurs inhomogeneously with some boundaries suffering failure, while others are seemingly immune to creep. Crack propagation associated with grain size, and grain boundary character was investigated to determine which types of grain boundaries are susceptible to damage and which are more resistant. Electron backscatter diffraction and a stereological approach to obtain the five-parameter grain boundary distribution were used to measure the proportions of each type of boundary in the initial and damaged structures. The samples were crept at 1273.15 K (1000 °C) at 25 MPa until fracture. It was found that in addition to low-angle and coherent twin boundaries, other low index boundary plane grain boundaries with twist character are relatively resistant to creep.     

合金元素对Cu—P合金高温性能的影响

用Gleeble1500高温拉伸试验机研究了添加元素Ag，Sb，Sn对Cu－P合金高温性能的影响．研究结果表明，Ag能显著提高Cu－P合金在室温下的综合性能，Sb和Sn能显著提高Cu－P合金在150～280℃时的强度，其中的Sn强化效果最好．但当合Sn＞5％时，会使Cu—6．5P合金的室温脆性增大．     

617合金的组织稳定性

 对先进超超临界燃煤发电机组锅炉高温部件候选材料617合金在750℃下时效1000,2000,3000和5000h后试样的组织稳定性进行了研究。通过OM,SEM,TEM和X射线衍射等方法对时效后晶界及晶粒内的析出物进行了分析。研究发现,时效后试验材料的晶界析出M23C6碳化物;晶内析出γ′相,且γ′相呈颗粒状弥散分布,γ′相尺寸随时效时间的延长而增长。经1000h时效后,试验材料的强度开始增加,并且随着时效时间的延长,强度开始呈现平稳趋势。随着时效时间的延长,试验材料的韧性呈下降趋势。     

高温电连接器用导电弹性合金的研究

为满足承受175～200℃高溫电连接器的需要,作者研制出了一种Ni含量小于5％,并加入少量Al,Si,Cr,Mg等元素的高强度高导电铜合金(CE-4合金)。试验了时效温度,时效时间及变形度对该合金机械性能的影响,测定了室温电阻率和弹性模量以及它们与温度的关系,并测试了几种温度下的应力松弛性能。结果表明,在36％～50％变形度下,430～450℃时效1小时,合金具有最高的强度,σ_b:940～1000N/mm~2,σ_(0.2):800～850N/mm~2,良好的延性(δ:～5％),有与铍青铜相当的高的弹性模量(E:139000～140000N/mm~2)和高的导电性(20～23％IACS),以及优于铍青铜的抗应力松弛能力。将该材料加工装配成Y11型高温电连接器,经200℃,1000小时的例行试验,各项指标均能满足军用标准的要求。     

High-Temperature Oxidation of Alloy 617 in Helium Containing Part-Per-Million Levels of CO and CO<Subscript>2</Subscript> as Impurities

The objective of this study was to determine the mechanisms of carburization and decarburization of alloy 617 in impure helium. To avoid the coupling of multiple gas/metal reactions that occurs in impure helium, oxidation studies were conducted in binary He + CO + CO₂ gas mixtures with CO/CO₂ ratios of 9 and 1272 in the temperature range 1123 K to 1273 K (850 °C to 1000 °C). The mechanisms were corroborated through measurements of oxidation kinetics, gas-phase analysis, and surface/bulk microstructure examination. A critical temperature corresponding to the equilibrium of the reaction 27Cr + 6CO ↔ 2Cr₂O₃ + Cr₂₃C₆ was identified to lie between 1173 K and 1223 K (900 °C and 950 °C) at CO/CO₂ ratio 9, above which decarburization of the alloy occurred via a kinetic competition between two simultaneous surface reactions: chromia formation and chromia reduction. The reduction rate exceeded the formation rate, preventing the growth of a stable chromia film until carbon in the sample was depleted. Surface and bulk carburization of the samples occurred for a CO/CO₂ ratio of 1272 at all temperatures. The surface carbide, Cr₇C₃, was metastable and nucleated due to preferential adsorption of carbon on the chromia surface. The Cr₇C₃ precipitates grew at the gas/scale interface via outward diffusion of Cr cations through the chromia scale until the activity of Cr at the reaction site fell below a critical value. The decrease in activity of chromium triggered a reaction between chromia and carbide: Cr₂O₃ + Cr₇C₃ → 9Cr+3CO, which resulted in a porous surface scale. The results show that the industrial application of the alloy 617 at T > 1173 K (900 °C) in impure helium will be limited by oxidation.     

铁铬铝合金脆断

研究了Fe-25Cr-5Al电热合金断裂原因及断裂方式.高于1000℃合金晶粒急剧长大,当晶粒大小(相似文献   

GH648合金高温抗氧化性能的研究

GH648是一种时效硬化型镍基高温合金,主要用作航空发动机的启动机900℃以下的抗氧化承力件.在高温下,该合金不仅要有较高的强度,而且还要有较好的抗氧化性能.为此,本文探讨了GH648合金高温氧化机理并简单分析了C元素对合金抗氧化性能的影响.结果表明,GH648合金在空气中氧化时,其氧化膜主要为Cr2O3,该合金的氧化是以Cr在Cr2O3中的扩散为控制因素的;合金在低于900℃的空气中氧化时属于完全抗氧化级.随C含量的升高,合金的抗氧化性能降低.     

7B04铝合金断裂韧性研究

本文测定了7B04铝合金各时效工艺状态下的常规拉伸性能，通过标准三点弯试验方法测定了合金的断裂韧性，并对其断口进行了宏观分析，从而研究时效工艺对常规力学性能与断裂韧性的影响，结果得出一种强度和断裂韧性均比T73和T76高的过时效工艺。     

铝合金变形抗力的热模拟研究

根据汽车热交换器用铝合金复合箔的生产过程中热轧焊合和冷轧所要求的不同变形条件，设计了不同的变形温度、应变、应变速率，进行热轧过程的模拟实验，分析了在不同热变形条件下的变形抗力及典型变形状态的显微组织，提出了提高复合箔质量的方法。     

化学镀Co-P合金耐腐蚀性能的研究

主要探究了在不同含磷量镀态和不同温度下热处理对合金腐蚀性的影响.极化曲线测定结果表明,热处理温度为400℃时,腐蚀电位达到最大,腐蚀电流最小,镀层耐腐蚀性能最好.     

Threshold Stress Creep Behavior of Alloy 617 at Intermediate Temperatures

Creep of Alloy 617, a solid solution Ni-Cr-Mo alloy, was studied in the temperature range of 1023 K to 1273 K (750 °C to 1000 °C). Typical power-law creep behavior with a stress exponent of approximately 5 is observed at temperatures from 1073 K to 1273 K (800 °C to 1000 °C). Creep at 1023 K (750 °C), however, exhibits threshold stress behavior coinciding with the temperature at which a low volume fraction of ordered coherent γ′ precipitates forms. The threshold stress is determined experimentally to be around 70 MPa at 1023 K (750 °C) and is verified to be near zero at 1173 K (900 °C)—temperatures directly correlating to the formation and dissolution of γ′ precipitates, respectively. The γ′ precipitates provide an obstacle to continued dislocation motion and result in the presence of a threshold stress. TEM analysis of specimens crept at 1023 K (750 °C) to various strains, and modeling of stresses necessary for γ′ precipitate dislocation bypass, suggests that the climb of dislocations around the γ′ precipitates is the controlling factor for continued deformation at the end of primary creep and into the tertiary creep regime. As creep deformation proceeds at an applied stress of 121 MPa and the precipitates coarsen, the stress required for Orowan bowing is reached and this mechanism becomes active. At the minimum creep rate at an applied stress of 145 MPa, the finer precipitate size results in higher Orowan bowing stresses and the creep deformation is dominated by the climb of dislocations around the γ′ precipitates.     

Inconel690合金高温高速热变形行为研究

在Gleeble-3800热模拟试验机上,采用热压缩实验研究了不同变形条件下Inconel 690合金的高温变形行为与组织演变特点.实验中采用的变形温度为1000～1200℃,变形量为70％,变形速率为1.0 ～80.0 s-1.根据实验结果获得了该合金的应力-应变关系,并对峰值应力进行了线性回归,由此得到了该合金的高温材料常数,激活能Q =417.6 kJ.mo1-1,α =0.003196 MPa-1,n=7.51,并最终得到了Incone1690合金的高温变形本构方程.通过金相显微镜研究了合金动态再结晶规律与温度和应变速率的关系,结果表明:变形温度对Inconel 690合金组织的影响很大,随温度的升高,动态再结晶百分数逐渐增加,且伴随着晶粒的长大;而提高应变速率,变形的时间缩短,位错密度迅速增大,动态再结晶的驱动力增加,也可以使再结晶后的晶粒细化;当温度为1150℃左右,应变速率50～80 s-1时,能够得到均匀细晶组织.     

Fracture Resistance of Nanocrystalline Ni

Atomic level simulations are used to study crack propagation mechanisms in nanocrystalline Ni. Digital samples with a mean grain size of 5 and 8 nm containing 125 grains were used. For both grain sizes, the mechanism of crack propagation involves the formation of nanocracks along grain boundaries in the vicinity of the main crack. Crack resistance curves for the two grain sizes indicate that the smaller grain sizes are more ductile, requiring higher stress intensities for crack propagation. This result is consistent with softer behavior for smaller grain sizes in the inverse Hall–Petch regime, where deformation is accommodated by grain boundary mechanisms. The present simulations specifically show that grain boundary sliding also plays an important role in crack blunting observed in these materials. In many cases, the crack is arrested as it encounters grain boundaries in its path, showing increased resistance to propagation. Increased ductility for smaller grain sizes in this regime indicates that there is a minimum in ductility as a function of grain size in these materials, located around the 10- to 12-nm grain size. This article is based on a presentation given in the symposium entitled “Deformation and Fracture from Nano to Macro: A Symposium Honoring W.W. Gerberich’s 70th Birthday,” which occurred during the TMS Annual Meeting, March 12–16, 2006, in San Antonio, Texas, and was sponsored by the Mechanical Behavior of Materials and Nanomechanical Behavior Committees of TMS.     

Development and Evaluation of Dissimilar Gas Tungsten Arc-Welded Joint of P92 Steel/Inconel 617 Alloy for Advanced Ultra-Supercritical Boiler Applications

Metallurgical and Materials Transactions A - In the present research work, an effort has been made to examine the effect of the ERNiCrCoMo-1 filler on solidification mechanism, microstructural...     

高强度ZA合金焊缝的耐腐蚀性术

借助于电子分析仪、光学显微镜等分析手段,以高强度zA合金为母材,通过对氧-乙炔气焊焊缝、TIG焊缝及母材的耐腐蚀性试验,对不同焊缝在NaCl溶液中的耐腐蚀件进行了研究.结果发现焊缝的耐腐蚀性高于母材,其中TIG焊缝的耐腐蚀性高于氧-乙炔气焊焊缝,两种焊接方法的焊缝耐蚀性完全能够达到使用性能要求.