Effect of Aging Heat Treatment on the Microstructure and Creep Properties of the Cast Ni-Based Superalloy at Low Temperature

Effect of aging heat treatment on the grain boundary microstructure and creep properties of a cast Ni-based superalloy was investigated. With increasing aging temperature from 750 to 1000 ℃, M_(23)C_6 carbides along the grain boundaries evolve from fine distributed block, continuous film into the coarse discrete block. Moreover, the M_(23)C_6 carbides are mainly enveloped within γ’ layers along grain boundaries during 1000 ℃ aging. Creep rupture lifetime and elongation at 760 ℃ and 645 MPa are improved with increasing the aging temperature. In particular, the creep rupture lifetime of the specimens aging at 1000 ℃ is one order of magnitude higher than that of the specimens aging at 750 ℃. The enhancement of ductility induced by the γ’ envelopes plays a significant role in the improvement of creep rupture lifetime.     

热障涂层高温抗氧化性能研究的现状与发展

从热障涂层(TBCs)的制备方式,长期高温氧化环境中服役的失效机制及高温抗热氧化性能的改善等方面,综述了近年来热障涂层(TBCs)中存在的热氧化生长(TGO)导致涂层失效及改善高温抗氧化性能研究的热点问题,并提出了作者的一些观点.     

SiC涂层对泡沫炭高温抗氧化性能的影响

采用包埋法在中间相沥青基泡沫炭表面生成了一层致密的高温抗氧化碳化硅涂层,研究了SiC涂层对泡沫炭高温抗氧化性能的影响.通过热重分析仪(TG)对有、无SiC涂层的泡沫炭的抗氧化性能变化进行了分析,采用扫描电子显微镜(SEM)分析了SiC涂层的结构和形貌特征变化,同时在1 200℃空气气氛中对SiC涂层的抗氧化性能进行了测试.结果表明:SiC涂层使泡沫炭的抗氧化性能有了显著的提高,并且随着SiC涂层厚度的增加,泡沫炭的抗氧化性能也随之增强.     

预氧化处理对钛合金抗高温氧化行为的影响

研究了预氧化处理对Ti06Al-4V合金在600℃空气中高温氧化行为的影响。利用XRD和SEM对氧化层表面形貌、相组成及氧化层断面组织结构进行分析。结果表明：预氧化处理的钛合金表面形成了较为致密的Al2O3和TiO2氧化膜，在氧化试验过程中，不仅改变合金的氧化机制，合金由高温氧化时氧向内部扩散为主转变为钛原子向外扩散为主，而且明显降低了合金的氧化速率，提高了氧化膜的粘附性和抗剥落能力。     

高温热处理对高磷Ni-P化学镀层耐蚀性的影响

对高磷（12.8%P）化学镀Ni-P合金镀层进行了750℃高温热处理，研究了经高温热处理后镀层的耐蚀性，结果表明，高温热处理后，镀层耐蚀性大大优于镀态。晶粒长大，晶界面积减少以及镀层表面生成较厚的，致密的氧化膜是耐蚀性提高的主要原因。     

Surface Chemistry of Oxide Scale on IN-738LC Superalloy: Effect of Long-Term Exposure in Air at 1173 K

The oxidation kinetics of IN-738LC at 1173 K in dry air up to 1500 hr followed parabolic law. Surface morphology and the oxide phases present in the scale were characterized by SEM, XRD, EDS, FIB, and XPS. FIB investigation exhibited a compact and adherent oxide layer. XRD analysis revealed the presence of NiO, NiAl₂O₄, NiCr₂O₄ spinel, and Al₂O₃ on the top scale surface formed at 1173 K in dry air. Extensive XPS analyses revealed the presence of Cr₂O₃, CrO₂, and CrO₃ on the top scale surface formed on IN-738LC after 10 hr of exposure. The presence of TiO₂, Al₂O₃, Cr₂O₃, NiO, and NiAl₂O₄ and NiCr₂O₄ spinels along with the oxides of Ta at the top surface of the scale was observed after 100 hr of oxidation. The TiO₂ content was high on the surface and the entire scale cross section was composed mostly of Cr₂O₃, NiO, TiO₂, and Al₂O₃ after 100 hr of exposure to dry air at 1173 K. The concentration of Al₂O₃ on the surface of the oxide scale was found to increase after 100 hr of exposure and remained constant thereafter. After 300 and 1500 hr of exposure, the surface oxide was mainly Al₂O₃ along with oxides of Ni, Ti, and Cr. The oxide scale cross section consisted mostly of Al₂O₃ along with other oxides such as Cr₂O₃, NiO, and TiO₂. The oxide-scale composition was found to vary significantly with the duration of exposure to dry air at 1173 K.     

无氰镀银层高温防变色性能初步探究

目的探寻无氰镀银层高温变色的原因,以增强无氰镀银层的防高温变色性能。方法采用硫代硫酸盐体系在紫铜片上镀银,并进行无惰性气体保护的300℃×1 h烘烤。借助扫描电镜(SEM)观察镀层高温烘烤后的微观形貌,采用能谱仪(EDS)检测镀层中各元素的含量与分布,探讨银层厚度、供电方式、后处理工艺对镀层防高温变色性能的影响。结果当直流电镀层厚度达到9μm,脉冲电镀层厚度达到6μm时,镀层经高温烘烤后不变色。而经水溶性银保护剂、重铬酸钾、PMTA处理后的镀层(厚6μm)均在高温烘烤后发生了变色情况。扫描电镜观察显示,高温变色镀层表面有凸起状裂纹,能谱仪检测到有铜原子外渗现象。结论高温下铜原子的外渗导致了镀层变色。采用脉冲方式进行电镀,可以使镀银层孔隙率降低。通过增加镀银层厚度和采用脉冲电镀,能够提高镀银层的防高温变色性能。     

Inhibition of the Corrosion of Grey Cast Iron in Ethanediol/Water Solutions by Benzoate/Benzotriazole Mixture: A Synergistic Effect

Abstract

The synergistic effects of sodium benzoate and benzotriazole in inhibiting the corrosion of grey cast iron in 50% ethanediol/water solutions are described. Good inhibition can be obtained in the presence of both inhibitors at concentrations of eachwhich are ineffective when either inhibitor is present alone. The results also showthat the inhibitors are effective on both ‘as-cast’ and machined surfaces. Limited information is presented to demonstrate a similar synergistic effect for the inhibition of corrosion of an aluminium alloy. Some possible adsorption mechanisms to explain these effects are considered briefly.     

Studies on the Surface Chemistry of Oxide Films Formed on IN-738LC Superalloy at Elevated Temperatures in Dry Air

The oxidation behavior of IN-738LC was studied to develop high-temperature materials for low cost and highly efficient turbine systems. The present study was undertaken to investigate the kinetics and the surface chemistry of the oxide films formed during isothermal oxidation of IN-738LC superalloy in the temperature range 1123–1223 K in dry air. The oxidation kinetics followed the parabolic law. The activation energy of oxidation was 264 kJ mol–1. The scaling process is controlled mainly by the diffusion of chromium ions through the intermediate chromia layer in the scale. The surface morphology and the oxide phases of the scale were characterized by SEM, XRD, and EDS studies. XRD analysis revealed the presence of NiO, NiAl₂O₄, NiCr₂O₄ spinel, Al₂O₃, and Cr₂O₃ on the top-scale surface. The scale surface and cross section were further characterized using X-ray photoelectron spectroscopy (XPS), which revealed the presence of NiO, Ni₂O₃, NiAl₂O₄, Al₂O₃, and TiO₂ on the top-oxide surface. The chromia layer was found to be underneath the top scale. The chromia layer also contains NiCr₂O₄ and NiAl₂O₄ spinels along with Al₂O₃. Application of XPS was found to be successful to understand the oxide-scale chemistry in terms of the oxide-growth mechanism of IN-738LC at elevated temperatures.     

Microstructure and Residual Stress of Alumina Scale Formed on Ti2AlC at High Temperature in Air

Ti₂AlC ternary carbide is being explored for various high temperature applications due to its strength at high temperatures, excellent thermal-shock resistance, and high electrical conductivity. A potential advantage of Ti₂AlC over conventional Al₂O₃-forming materials is the near-identical coefficient of thermal expansion (CTE) of Ti₂AlC and α-Al₂O₃, which could result in superior spallation resistance and make Ti₂AlC a promising option for applications ranging from bondcoats for thermal barrier coatings to furnace heating elements. In this study, isothermal and cyclic oxidation were performed in air to examine the oxidation behavior of Ti₂AlC. Isothermal oxidation was performed at 1000, 1200 and 1400 °C for up to 25 h and cyclic oxidation consisted of 1,000 1-hour cycles at 1200 °C. Characteristics of the oxide scale developed in air, including mass change, residual stress in the α-Al₂O₃ scale, phase constituents and microstructure, were examined as functions of time and temperature by thermogravimetry, photostimulated luminescence, x-ray diffraction, scanning electron microscopy, and transmission electron microscopy via focused ion beam in situ lift-out. Above a continuous and adherent α-Al₂O₃ layer, a discontinuous-transient rutile-TiO₂ scale was identified in the oxide scale developed at 1000 and 1200 °C, while a discontinuous-transient Al₂TiO₅ scale was identified at 1400 °C. The continuous α-Al₂O₃scale thickened to more than 15 μm after 25 h of isothermal oxidation at 1400 °C, and after 1,000 1-hour cycles at 1200 °C, yet remained adherent and protective. The compressive residual stress determined by photoluminescence for the α-Al₂O₃ scale remained under 0.65 GPa for the specimens oxidized up to 1400°C for 25 hours. The small magnitude of the compressive residual stress may be responsible the high spallation-resistance of the protective α-Al₂O₃ scale developed on Ti₂AlC, despite the absence of reactive element additions.     

镍基高温合金GH4049高温疲劳小裂纹扩展规律

对镍基高温合金GH4049在相同载荷、不同温度下疲劳小裂纹扩展规律进行了试验，利用复型技术和光学显微镜观测了裂纹尺寸演化全过程，发现小裂纹扩展速率的趋势是先快后慢，且温度升高，扩展速率反而下降。这与小裂纹的闭合效应有关，在700％小裂纹的氧化诱发闭合效应比650％时明显。     

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 高温电阻测量通常采用直流补偿法完成,在具体操作（数据处理）中,普遍取工作电流正、反向过程中测得的电位差值的绝对值数据平均值作为测量结果简称“绝对值法”。实践证明,传统方法在寄生温差电势大的情况下,将导致错误的结果;从理论、实践两方面进行了分析,提出的“代数平均值处理法”;简称“代数值法”,为高温电阻检测方法的重要改进。     

等离子熔化沉积TiC增强Inconel 718基原位自生复合材料显微组织及高温耐磨性

为改善镍基高温合金Inconel 718的高温耐磨性,利用同轴送粉等离子熔化沉积快速成形技术原位合成了TiC增强Inconel 718高温合金基高温耐磨复合材料。分析了复合材料的显微组织结构和原位自生过程,探讨了增强相TiC的含量对复合材料的显微硬度及高温干滑动摩擦磨损性能的影响规律,研究了复合材料的高温磨损机理。结果表明:复合材料组织细小致密,显微硬度随TiC增强相体积分数增加而相应提高;在高温干滑动磨损实验条件下,复合材料表现出优异的耐磨性。     

陶瓷／石墨复合材料的制备及高温氧化性能

通过热压法制备了陶瓷／石墨复合材料。采用热分析仪考察了复合材料在1400℃～1600℃温度范围内的抗氧化行为；利用扫描电镜分析样品在1400℃和1600℃恒温氧化后的表面形貌。结果表明；陶瓷／石墨复合材料在1400℃氧化时有优良的自愈合抗氧化性能。在1600℃氧化时，对于粘度较高的样品来说，氧化新形成的玻璃膜可以弥补挥发形成的表面孔道，仍能形成均匀的、连续的玻璃膜覆盖在基体表面，从而有效地抑制氧气的进入。     

中温酸性化学镀Ni-P合金耐蚀性能研究

为提高化学镀Ni-P合金耐蚀性能,以Q235钢为待镀基体,在中温的酸性条件下,采用正交试验方法得到镀层耐蚀性最佳的工艺条件为:镀液pH值 5.2;Ni2 与H2PO2-的摩尔比为0.48;复合络合剂乳酸15mL/L 丙酸5mL/L;加速剂NaF 0.4g/L;热处理温度500 ℃.在此条件下,腐蚀电流为2.166×10-5A,可较好地提高镀层耐蚀性.     

Nd对Al2O3f/AZ91D复合材料高温蠕变性能的影响

利用高温压缩蠕变实验研究了Nd对复合材料的高温蠕变性能以及压应力对濡变应力指数的影响.结果表明稀土元素Nd的加入可以明显改善复合材料的高温蠕变性能,试验中添加0.8％Nd的Al2O3f/AZ91D复合材料的抗高温蠕变性能最好;当应力为60～90 MPa与156～180MPa时复合材料的蠕变机理为基体和增强体之间的载荷传递,纤维的开裂和破断是其失效的主要机制;应力为90～156 MPa时复合材料的蠕变机理为位错滑移与位错攀移共同作用.     

热处理对TiC_p/Fe复合材料组织和性能的影响

研究了热处理对液态等温反应合成的TiCp/Fe复合材料的组织和性能的影响。指出热处理可以使在凝固过程中产生的少量TiFe2 和Fe3 C等相溶解消失 ,并得到一定数量的细小的二次TiC增强相。热处理过程能完全改变复合材料的基体组织。通过不同的热处理工艺 ,可以获得具有不同基体组织的复合材料 ,合金元素钼可有助于基体组织的调整。热处理过程对复合材料的性能也有较大的影响 ,二次TiC对基体的强化作用使复合材料的抗拉强度上升和冲击值下降     

铝硅复合对Fe32Mn7Cr3Al2Si钢氧化改性层耐蚀性的影响

利用XRD、EPMA、阳极极化和电化学阻抗技术研究了铝硅复合合金化对Fe32Mn7Cr3Al2Si钢高温氧化诱发转变层的组织、成分及电化学腐蚀性能影响.在700和800℃空气中对Fe32Mn7Cr3Al2Si奥氏体钢进行循环氧化表面改性,形成的氧化层由内层Al2O3、中间层Mn2SiO4,外层Mn2O3组成.经800℃...     

腐蚀产物MgO对Fe基合金在固态和熔融NaCl-MgCl2 中高温耐蚀性能的影响

熔融氯化盐是下一代聚光式太阳能热发电站（第3代CSP）候选传热和储热介质,含MgCl₂的熔融氯化盐对金属传热管道和储热容器腐蚀后在其表面形成MgO,MgO对管道耐腐蚀性能影响尚不清楚。通过对比碳钢和3种Fe-Cr-Ni合金在固态（345 ℃）和熔融NaCl-MgCl₂（445和545 ℃）中的腐蚀行为,分析了MgO对4种试样在不同温度下的腐蚀行为机理。结果表明,在固态NaCl-MgCl₂中,碳钢表面MgO壳致密且连续,可以保护试样免受腐蚀。在熔融NaCl-MgCl₂中,4种试样表面也生成了致密的MgO壳,但它因热应力作用而开裂和剥落,熔融盐沿着氧化膜裂纹渗入MgO/基体界面,发生化学-电化学联合腐蚀反应,不能保护试样免受该熔盐腐蚀。     

高温热压法制备La(Fe, Si)13Hy系磁制冷材料的磁热性能研究

La(Fe, Si)₁₃H_Y系合金是一种极具发展潜力的室温磁制冷材料,但该材料易粉化,如何成型并保持大磁热效应成为了亟需解决的问题。本文采用中频感应炉熔炼La_0.8Ce_0.2Fe_11.51Mn_0.19Si_1.3母合金并退火,之后制备成粉末。合金粉末在650 ℃, 850 ℃和1050 ℃不同温度下热压成型,将热压块体合金加工成薄片后进行饱和氢化。利用X射线衍射仪、扫描电子显微镜、VersLab对样品的相组成、微观结构、磁热性能进行了研究。在1050 ℃下热压样品的孔隙率最低,最大体积磁熵变最高,达到了144.7 mJ/cm^₃?K。1050 ℃热压样品氢化后居里温度提高至室温附近,仍保持了一级磁相变的大磁热效应,且没有裂痕产生,保持了完整性。