Cyclic oxidation behavior of glass-ceramic composite coatings on superalloy K38G at 1100 °C

The SiO₂-Al₂O₃-ZrO₂-CaO-ZnO glass-ceramic composite coatings (GC), nanocrystalline NiCoCrAlY coating, and their combinations (bi-layer GC/NiCoCrAlY) were prepared on K38G specimens. The thicknesses of the glass-ceramic coatings and the NiCoCrAlY coatings were about 10 μm and 20 μm, respectively. Cyclic oxidation tests were carried out at 1100 °C for 120 cycles. Microstructures of the specimens before and after oxidation tests were characterized by SEM, EDS and XRD. The glass-ceramic coatings with or without a NiCoCrAlY intermediate layer improved the isothermal and cyclic oxidation resistance of the Ni-base superalloy K38G at 1100 °C, and performed better than the NiCoCrAlY coatings. An alumina layer formed at the glass/metal interfaces of the specimens coated by the glass-ceramic coatings with or without a NiCoCrAlY intermediate layer. The NiCoCrAlY intermediate layer was beneficial to the cyclic oxidation resistance of the glass-ceramic coatings.     

Effect of post heat-treatment on the microstructure and high-temperature oxidation behavior of precipitation hardened IN738LC superalloy fabricated by selective laser melting

The present study investigated the effect of as-built and post heat-treated microstructures of IN738LC alloy fabricated via selective laser melting process on high temperature oxidation behavior.The as-built microstructure showed fine cell and columnar structure due to high cooling rate.Ti element segrega-tion was observed in inter-cell/inter-columnar area.After post heat-treatment,the initially-observed cell structure disappeared,instead bimodal Ni3(Al,Ti)particles formed.High temperature(1273 K and 1373 K)oxidation test results showed parabolic oxidation curves regardless of temperature and initial microstructure.The as-built IN738LC fabricated via the selective laser melting process displayed oxida-tion resistance similar to or slightly better than that of IN738LC fabricated via wrought or cast process.Heat-treated SLM IN738LC,although had similar oxidation weight-gain values to those of the SLM as-built material at 1273 K,showed relatively better oxidation resistance at 1373 K.Bimodal Ni3(Al,Ti)precipitate formed in the post heat treatment changed the local chemical composition,thereby led to changes in alumina former/chromia former location and fraction on the alloy surface.It was concluded that in heat-treated IN738LC increased alumina former fraction was found,and this resulted in excellent oxidation resistance and relatively low weight-gain.     

Protective Properties of High Temperature Oxide Films on Ni-based Superalloys in 3.5% NaCl Solution

The electrochemical behaviors of high temperature oxide film formed on the sputtered microcrystalline coating of M38 alloy （mc-M38） were investigated by potentiodynamic and electrochemical impedance spectroscopy （EIS） techniques in 3.5% NaCl solution. Mott-Schottky analysis was used to study the semi-conductive properties of the surface oxide. The results of the capacitance measurements showed that the oxide films on both the coating and the cast alloy were p-type semiconducting characteristics. Both the carrier density （Na）and the flat band potential （Efb） were obviously frequency-dependent, and the optimal frequency range was from 1000 to 1500 Hz. The oxidized coating exhibited higher protectivity than the oxidized cast alloy due to the lower carrier density compared with that of the oxidized cast alloy. The EIS data of the long-term immersing tests suggested that the oxide film served as an inner-barrier layer against chloride ions. The penetration of the aggressive ions into the surface oxide resulted in the decreased polarization resistance as a function of the immersion time.     

草酸阳极氧化法制备铝合金氧化膜及其防腐蚀性能

为了改进铝合金的防护性能,扩展铝合金应用范围,需要对铝合金进行表面处理。利用草酸电解液阳极氧化法在2A12铝合金表面制备了一层氧化膜,通过扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、X射线衍射仪(XRD)、原子力显微镜(AFM)等手段分析其表面形貌、组织结构、物相和表面粗糙度。微观表征结果表明,阳极氧化法能使铝基体表面生成非晶态的氧化铝薄膜,并且该薄膜是多孔结构,具有优异的屏蔽作用。利用电化学方法、中性盐雾试验评价了阳极氧化膜的防腐蚀性能,证实了阳极氧化后铝合金的防腐蚀性能优于铝合金基体。     

The electrochemical corrosion behavior of K38G nanocrystalline thin film in 3.5% NaCl solution

The electrochemical corrosion behavior of a K38G nanocrystalline (NC) thin film fabricated by magnetron sputtering technique has been investigated in comparison with cast K38G alloy in 3.5% NaCl solution. The results indicated that compared with the cast K38G alloy, the NC thin film had a higher occurring frequency of metastable pits and lower rates of stable pitting nucleation and growth. The influence of nanocrystallization on the pit initiation and pit growth processes has been discussed, respectively.     

K52合金及其涂层的涂盐热腐蚀行为

研究了合金及其涂层的热腐蚀行为,测定了它们的氧化动力学曲线。用扫描电镜和电子探针观察了合金及涂层腐蚀后的表面形貌和横截面显微组织。结果表明:溅射K52纳米晶涂层在含有NaCl的盐中腐蚀10 h,氧化膜就大面积剥落,涂层遭受很大的破坏。而铸态合金腐蚀50 h后,产生已基本连续的内氧化铝层,这层氧化铝对阻止O、S和Cl的进入起到一定的作用,提高了合金的抗氯盐腐蚀。     

Oxidation of Ion Plated Ni—Cr Alloy Film at 300℃

Investigation by using LAS 3000 surfaceanalysis system showed that the oxide of Fe,Cr,Al formed during oxidation were Cr_2O_3,Fe_2O_3and Al_2O_3,but only small amount of nickel oxidewas found.The composition of oxide layers for differentoxidation durations varied in a similar way.In all cases,there exists an oxygen concentrationpeak in the composition profile of oxide layer.There is a transitional zone between oxide layerand alloy film.The thickness of oxide layerincreases logarithmically with the time of oxida-tion.The ion plated Ni-Cr alloy film has verydense oxide layer and good oxidation resistance.     

金属陶瓷涂层耐蚀性能研究

采用溶胶 凝胶浸渍提拉法在不锈钢、纯铜及铝合金基底上制作了连续的ＳｉＯ２ 、ＴｉＯ２ 、Ａｌ２Ｏ３ 及ＳｉＯ２ ＴｉＯ２ 陶瓷涂层。通过阳极极化曲线、循环动电位极化曲线、点蚀电位、三氯化铁腐蚀试验、５ ％ 硫酸腐蚀试验以及氧化试验检测了陶瓷涂层对金属的保护能力。分析试验结果表明,这些陶瓷涂层大幅度提高了基底金属在腐蚀介质及氧化环境中的寿命。     

Ceramic Films Containing Ca,P and Al Formed on Surface of TC4 Alloy by Micro-Arc Oxidation

Ceramic films containing Ca, P and Al were prepared on surface of TC4 alloy by micro-arc oxidation using direct current supply to enhance its seawater and plankton corrosion resistance. XRD, EDS, SEM and EPMA were employed to characterize the microstructure and the phase composition. The results showed that 15 μm-ceramic films which was uniform and compact were formed on TC4 . The mass proportion of Ca, P and Al is about 2 : 3 : 4. There was AlPO4 crystal but Ca was not crystal. Cyclic Volt-Ampere test showed that the corrosion resistance of theceramic films was much better than that of the TC4 substrate.     

Protective Effect of the Sputtered TiAlCrAg Coating on the High-Temperature Oxidation and Hot Corrosion Resistance of Ti-Al-Nb Alloy

The effect of a sputtered Ti-48AI-8Cr-2Ag (at. pct) coating on the oxidation resistance of the cast Ti-46.5AI-5Nb (at. pct) alloy was investigated in air at 1000-1100℃. Hot corrosion in molten 75 wt pct Na2SO4+25 wt pct K2SO4 was investigated at 900℃. The scale on the cast TiAINb tends to spall in air, while the scale on coating is very adherent. The sputtered Ti-48AI-8Cr-2Ag coating remarkably improved high temperature oxidation resistance of the cast Ti-46.5AI-5Nb alloy because of the formation of an adherent Al2O3 scale. Due to the inward diffusion of Cr, Kirkendall voids were found at the coating/substrate interface. TiAICrAg coating provided excellent hot corrosion resistance for TiAINb alloy in molten 75 wt pct Na2SO4+25 wt pct K2S04 at 900℃ due to the formation of a continuous Al2O3 scale.     

包铝层和氧化时间对2E12铝合金硫酸阳极氧化及膜层性能的影响

对保留表面包铝和去除包铝的2E12-T3铝合金采用硫酸阳极氧化处理工艺,研究了包铝层和氧化时间对铝合金阳极氧化行为及膜层耐蚀性的影响。采用扫描电子显微镜观察氧化膜的表面以及截面形貌,应用动电位扫描极化曲线和电化学阻抗谱对膜层的电化学性能进行分析。结果表明:两种铝合金表面均能形成具有防护性能的阳极氧化膜,膜层随氧化时间延长而增厚。富铜的第二相颗粒会使得不带包铝的2E12铝合金氧化膜具有更多孔洞缺陷,甚至出现微裂纹。保留包铝的2E12铝合金表面氧化膜更厚,孔洞缺陷少,耐蚀性更好。阳极氧化30min和45min的2E12铝合金阳极氧化膜具有较低的腐蚀电流和较高的多孔层阻抗,耐蚀性好。     

Cr/Cr2O3多层膜的研究

用真空蒸镀及自然氧化方法在玻璃基底上制备纳米量级的4、5、6、7对层的Cr／Cr2O3多层膜。采用称重法测定薄膜的厚度；在常温和低温下使用三点法测定多层膜的电特性；用扫描电镜（SEM）观察薄膜的表面和截面的形貌及成分；用X射线衍射仪检测相结构。结果表明：制备的是纳米量级非晶态的Cr／Cr2O3多层膜，在常温和低温（77K）下均具有类似负阻的特性。     

磁控溅射镀Al对NiCrAlY合金层循环氧化性能的影响

通过磁控溅射手段在NiCrAlY合金表面成功制备了1层Al膜,并比较了镀Al粘结层和不镀Al粘结层在1200℃循环氧化的性能.结果表明,磁控溅射镀Al,制得表面Al膜厚度在2μm左右,NiCrAlY合金层内部的组分并无变化.这层Al膜有助于在表面形成1层分布连续、排列紧密的α-Al_2O_3层,降低了合金层的循环氧化增重速率,延长了涂层开裂脱落时间,使NiCrAlY合金表现出了比较好的抗循环氧化性能.     

Morphology and Microstructure of Sputtered Superalloy Coating

The morphology and microstructure of magnetron sputtered coating of superalloy K38G on cast al-loy K38G have been investigated by means of SEM, TEM and XRD. The results indicate that thesputtered coating is identical to the substrate in chemical composition but it is composed only of γphase without γ'. The sputtered superalloy coating presents columnar structure and the grain size isin the range of 20-100 nm. There are a great number of planar defects such as stacking faults andmicrotwins in the coating. The morphology and microstructure of the sputtered coating may haveclose relation to the remarkable increase of oxidation resistance of the coating.     

镁合金无铬微弧氧化新工艺

利用正交试验对MB2镁合金无铬、磷、镁微弧氧化成膜工艺进行了研究,同时利用表面分析技术,分析了氧化膜层的显微硬度、截面形貌和相结构,采用动电位扫描法考察了氧化膜的耐腐蚀性能.研究的最佳工艺条件为:30 g/L KOH,45g/L Al(OH)3,2 g/L K2SiO3,2g/L添加剂M,电流密度65 mA/cm2,温度45℃.该微弧氧化新工艺能在镁合金上形成银灰色的氧化膜层,其显微硬度值及耐腐蚀性远优于传统含铬工艺DOW17所形成的膜层;微弧氧化膜主要由MgO,MgAl2O4,Al2O3组成,具有多孔结构,孔径较为均匀,分为内外两层,外层为疏松层,内层为与基体结合牢固的致密层;在成膜过程中,电解液的铝盐浓度和微弧氧化电流密度是影响性能的主要因素.     

钛合金着色技术的研究

利用正交试验法研究了在磷酸-冰乙酸体系中磷酸、冰乙酸、添加剂、氧化电压、电解液温度、氧化时间等对钛阳极氧化膜的影响,确定了最佳工艺条件.结果表明,在采用以Ce作为添加剂的电解液中处理后所得到的钛合金着色膜呈蓝色、光亮美观,具有优良的耐蚀性、耐磨性和良好的附着力.     

Improvement of high temperature oxidation resistance of rare earth metal-added Fe–20%Cr–5%Al alloys by pre-annealing treatment

Abstract

Fe–20mass%Cr–5mass%Al alloy foils have recently been used as a catalytic converter substrate for automobiles because of their good oxidation resistance. In this study, the effect of pre-annealing on the oxidation behaviour of Fe–20mass%Cr–5mass%Al alloy foils containing a small amount of La–Zr and La–Hf was examined by a cyclic oxidation test at 1373K in air. The Al₂O₃ scale formed by oxidation was analyzed with a scanning electron microscope (SEM) and transmission electron microscope (TEM) equipped with an energy-dispersive X-ray spectrometer.

The oxidation rate of these alloys was reduced by pre-annealing in a reducing atmosphere. The Al₂O₃ scale which formed on the pre-annealing alloys was characterized by a thinner outer equiaxed grain layer and larger inner columnar grain size than the scale layer which formed on as-cold rolled alloys of the same material.

It is inferred that, with the pre-annealed alloys, the low-density of grain boundaries in the Al₂O₃ limited oxygen diffusion along the Al₂O₃ grain boundaries, resulting in a decreased growth rate of Al₂O₃ scale.     

Effect of sputtered TiAlCr coatings on oxidation and hot corrosion resistance of Ti-24Al-14Nb-3V

The effect of sputtered Ti-50Al-10Cr and Ti-50Al-20Cr coatings on both isothermal and cyclic oxidation resistance at 800 similar to 900 degreesC and hot corrosion resistance at 850 degreesC of Ti-24Al-14Nb-3V was investigated. Results indicated that Ti-24Al-14Nb-3V alloys exhibited poor oxidation resistance due to the formation of Al2O3+TiO2+AlNbO4 mixed scales in air at 800 similar to 900 degreesC and poor hot corrosion resistance due to the spallation of scales formed in Na2SO4+K2SO4 melts at 850 degreesC. Both Ti-50Al-10Cr and Ti-50Al-20Cr coatings remarkably improved the oxidation and hot corrosion resistance of Ti-24Al-14Nb-3V alloy.     

High‐temperature low‐cycle fatigue behaviour of a cast Al–12Si–CuNiMg alloy

The low‐cycle fatigue behaviour of a cast Al–12Si–CuNiMg alloy, with a high content of Si, is investigated at 200, 350 and 400 °C. The fatigue test results show that the alloy exhibits symmetrical hysteresis loops, moderate cyclic softening and higher fatigue resistance at higher temperature. The fracture surface analysis reveals that more tear ridges are formed at higher temperature, which strongly affect the fatigue resistance. Furthermore, evaluation of the material fatigue resistance using an energy‐based Halford–Marrow model indicates that the material's ability to absorb and dissipate plastic strain energy is enhanced as temperature increases.     

The effect of micro-structure on the oxidation behavior of a Ni-based superalloy in water vapor plus oxygen

The oxidation behavior of a Ni-based superalloy with polycrystalline, single-crystalline (SC) and nanocrystalline (NC) structures was studied at 1000 °C in water vapor (20.12 vol.%) plus oxygen. The oxidation behavior of the SC alloy was similar to that of the cast alloy, while nanocrystallization increased the corrosion resistance. The oxides scale on the SC alloy and cast alloy consisted of external TiO₂, Cr₂O₃ and internal Al₂O₃, while only external Al₂O₃ scale formed on the NC coating in water vapor plus oxygen. Meanwhile, the morphologies of oxides scale on three samples are significantly different from one another. The effect of micro-structures on the oxidation behavior of this Ni-based superalloy is discussed.