不同Ru含量的镍基高温合金热腐蚀研究

为了解Ru对高温合金热腐蚀性能影响规律,采用了浸盐方法研究了不同Ru含量镍基高温合金的热腐蚀过程,采用扫描电镜观察了合金腐蚀层截面的微观组织,并利用X-射线衍射仪确定相结构.结果表明:在900℃浸盐条件下,Ni基高温合金中加入质量分数3%的Ru可以显著提高合金自身的热腐蚀抗力,并且随着Ru含量增加,合金的热腐蚀抗力进一步增强;合金中加入Ru后,能促使合金表层腐蚀层变薄且与基体结合力好,从而提高了合金的热腐蚀抗力.     

高温镍基单晶合金NiCoCrAlYTa涂层的抗热腐蚀性能

以往,对高温镍基单晶合金上采用低压等离子喷涂制备的NiCoCrAlYTa涂层的热腐蚀性能研究较少.为此,采用低压等离子方法在镍基高温单晶合金上制备了NiCoCrAlYTa涂层,采用涂盐法研究了Na2SO4对试样在1 123 K空气中热腐蚀的影响,同时分析了NiCoCrAlYTa涂层的形貌及结构.结果表明:高温镍基单晶合金遭受了严重的热腐蚀,出现了内硫化和内氧化;NiCoCrAlYTa涂层由于表面生成了致密、保护性的Al2O3膜,以及涂层中Cr和Ta元素的作用而表现出优异的抗热腐蚀性能.结果证实,NiCoCrAlYTa涂层可以很好地提高单晶合金的抗热腐蚀性能.     

AlSi扩散涂层的制备及其在模拟燃煤环境中的热腐蚀行为

随着燃煤电站运行温度提高,会对电站耐热部件金属材料T91产生严重的高温热腐蚀,降低其设计使用寿命,因此,亟待开发耐热钢T91耐热腐蚀涂层。采用电弧离子镀技术在耐热钢T91表面制备一层Al5%Si镀层,然后在550℃真空热处理40 h形成Al Si扩散涂层;研究了该Al Si扩散涂层在650℃和750℃空气中典型燃煤环境中75%Na2SO4+25%NaCl盐膜下的热腐蚀行为。结果表明:耐热钢T91发生了快速热腐蚀,表面腐蚀产物主要是Fe和Cr的混合氧化物,易于剥落而不具有高温防护性能;而当T91表面施加Al5Si扩散涂层后,热腐蚀速度明显降低,表面腐蚀产物主要富含Al2O3,其抗热腐蚀性能较优,具有较好的高温防护性能。     

GH3030合金NiCrAlYSi涂层的高温防护性能

采用等离子喷涂法制备的航空发动机涡轮部件不能满足抗高温和热腐蚀需求。采用真空电弧离子镀技术(AIP)在GH3030镍基高温合金上制备170～180μm厚的NiCrAlYSi涂层,研究了该涂层700℃下的高温氧化行为和760℃下的燃气热腐蚀行为。结果表明:经过长时间的氧化,NiCrAlYSi涂层表面形成了以Al2O3,Cr2O3为主的氧化膜,提高了其抗高温氧化性能;经过760℃,100h燃气腐蚀试验后,NiCrAlYSi涂层主要由Ni3Al和α-Cr相组成,NiCrAlYSi涂层明显改善了GH3030合金的抗低温热腐蚀性能。     

DD421单晶高温合金在无SOx气氛下的低温热腐蚀硫化行为

采用涂盐法研究表面涂覆有90％(质量分数,下同)Na2 SO4+10％NaCl混合盐(750℃熔融态)和纯Na2 SO4盐(750℃固态)的第二代镍基单晶高温合金DD421在750℃大气环境下(无SOx气氛)的热腐蚀行为.结果表明:在熔融混合盐腐蚀介质中,硫化反应主要由液相熔融盐侵蚀所导致.热腐蚀100 h后合金腐蚀产物主要为典型的简单氧化物(Al2 O3,Cr2 O3,TiO2)以及Ni/Cr/Ti的硫化物.而在纯Na2 SO4固态盐热腐蚀实验中,热腐蚀100 h后合金腐蚀产物与混合盐实验中的产物基本相同,但其腐蚀层厚度相对更薄,硫化物尺寸相对更大.结合热力学和微观组织分析,本研究明确了在无SOx气氛的腐蚀环境下合金元素能够与固态Na2 SO4盐发生硫化反应.     

球磨时间对镍基ODS合金拉伸性能的影响

研究了球磨时间对Y2O3氧化物弥散强化(ODS)镍基高温合金机械合金化和拉伸性能的影响.镍基高温合金采用机械合金化和热压烧结方法制备.镍基ODS高温合金粉末是在行星式球磨机上进行球磨.采用扫描电镜及X射线衍射分析了球磨时间对镍基ODS合金粉末形貌和物相的影响.研究结果表明,Y2O3氧化物弥散强化镍基高温合金机械合金化粉末尺寸随研磨时间的增加先增大后减小,8h粉末颗粒尺寸达到最大,之后粉末颗粒尺寸逐渐减小,28h后,镍基ODS合金粉末尺寸稳定且均匀.拉伸结果表明,采用研磨28h的合金粉末制备的镍基ODS合金具有最高的抗拉强度(1300MPa).     

DD6单晶高温合金氧化物夹杂形成的热力学计算及分析EI北大核心CSCD

采用Thermo-calc热力学计算软件以及JMatPro分析软件对DD6镍基单晶高温合金真空感应熔炼过程中氧化物夹杂形成的热力学条件进行了计算分析。结果表明:DD6单晶高温合金熔化和凝固过程中形成的氧化物夹杂主要为Al2O3。热力学平衡状态下,熔化阶段和凝固阶段合金液中氧的活度分别在(3.21～14.0)×10-7,(1.63～4.89)×10-8范围内。在真空度为0.1Pa时,采用CaO坩埚熔炼DD6合金将会造成熔体增氧和Al2O3夹杂的产生。为了使Al2O3夹杂含量降低至10×10-6以下,合金化开始前应将氧的含量控制在4.709×10-6以内。     

DD6单晶高温合金氧化物夹杂形成的热力学计算及分析

采用Thermo-calc热力学计算软件以及JMatPro分析软件对DD6镍基单晶高温合金真空感应熔炼过程中氧化物夹杂形成的热力学条件进行了计算分析。结果表明:DD6单晶高温合金熔化和凝固过程中形成的氧化物夹杂主要为Al2O3。热力学平衡状态下,熔化阶段和凝固阶段合金液中氧的活度分别在(3.21～14.0)×10-7,(1.63～4.89)×10-8范围内。在真空度为0.1Pa时,采用CaO坩埚熔炼DD6合金将会造成熔体增氧和Al2O3夹杂的产生。为了使Al2O3夹杂含量降低至10×10-6以下,合金化开始前应将氧的含量控制在4.709×10-6以内。     

Ti_3Al金属间化合物的熔盐热腐蚀

采用电化学方法并结合扫描电镜、X 射线衍射、电子探针和能谱等物相分析技术研究了 Ti_3Al 金属间化合物在800℃熔融 NaCl-(Na,K)_2SO_4体系中的腐蚀行为。结果表明,Ti_3Al 合金耐熔盐腐蚀性能远低于 Ni 基 IN738合金。腐蚀时在合金表面形成外层为 TiO_2;内层为富 Nb 的Nb_2O_5,Al_2O_3,TiO_2的混合层和中间层为富 Al 的 TiO_2,Al_2O_3混合层的多层腐蚀层结构。Ti 快速向外扩散和氧向内扩散使合金表面腐蚀产物层迅速增厚。腐蚀产物内层的富 Nb 氧化物破坏了膜层与合金基体的粘附性。     

Ti_2AlNb合金表面渗镀Al层的抗热腐蚀性能

目前,鲜见对Ti_2AlNb合金表面渗镀Al层在高温熔盐环境中耐腐蚀性能的报道。采用加弧辉光等离子渗镀技术在Ti_2AlNb合金表面渗镀Al层。采用扫描电镜、X射线衍射仪分析了渗镀Al层的形貌、结构及相组成;采用涂盐热腐蚀试验研究了渗镀Al层在750℃的Na_2SO_4熔盐中的热腐蚀行为。结果表明:渗镀Al层由外层纯Al沉积层和内层Al-Ti-Nb扩散层组成,其组织均匀致密,与基体结合良好;在750℃的Na_2SO_4熔盐中,Ti_2AlNb合金基体腐蚀增重显著,腐蚀产物出现明显的层状剥落现象,耐热腐蚀性较差,而渗镀Al层试样仅发生微小的增重,腐蚀100 h后,内部扩散层还比较完整,未出现氧化和硫化的现象,仍拥有足够的Al源来抵抗接下来的腐蚀进程。     

Effect of Nb,Mo, V contents on oxidation resistance of Ti3Al based alloys

In the present paper, the effect of the contents of Nb, Mo, V on the oxidation properties (700°C, in air) of Ti₃Al based alloys has been studied. It has been shown that the alloys were oxidized rapidly as exposed at 700°C in the air. After 100 h exposure, oxygen-affected alloy surface layer of about 10 thickness has been formed on account of the poor protection of the oxide film. An addition of (11–13%)¹ Nb enhanced the oxidation resistance. The addition of Mo and V in the Ti₃Al–Nb system alloy reduced the oxidation resistance significantly.     

氟盐-氧化物体系电解制备Al-Cu-Y合金的电极还原过程研究

采用Na_3AlF_6-AlF_3-LiF-MgF_2为基础电解质,Al_2O_3-CuO-Y_2O_3为原料的氟盐-氧化物体系熔盐电解制取Al-Cu-Y合金。重点通过循环伏安分析Y(Ⅲ)在阴极的电极还原过程,利用扫描电镜(SEM)及能谱(EDS)表征并对比分析热还原产物及电解产物的成分及物相组成。结果表明:AlF_3-NaF-5%LiF-5%MgF_2(质量分数,下同)(n(NaF)/n(AlF_3)=2.2)体系在温度1 208K、电压3.0V、阴极电流密度0.7A/cm~2、电解时间2h条件下能够制取Al-Cu-Y合金。Cu(Ⅱ)在碳质电极表面可一步直接还原为零价态Cu(0);Y(Ⅲ)不能在体系内直接还原为零价态Y,而是在预先形成的Al-Cu活性阴极表面还原并合金化,从而形成强化相Al_3Y,并与Al_2Cu强化相同时富集于铝基体相晶界。通过在熔盐底部的液态铝热还原CuO及Y_2O_3也可形成Al-Cu-Y合金,但铝基体相晶界富集AlCu相及AlY相,Cu及Y含量不易控制,且存在较多O、C杂质元素。     

Optimization of annealing treatment and comprehensive properties of Cu-containing Ti6Al4V-xCu alloys

The Ti6Al4V-Cu alloy was reported to show good antibacterial properties, which was promising to reduce the hazard of the bacterial infection problem. For the purpose of preparing Ti6Al4V-Cu alloy with satisfied comprehensive properties, it’s important to study the heat treatment and the appropriate Cu content of the alloy. In this study, high Cu content Ti6Al4V-xCu (x = 4.5, 6, 7.5 wt%) alloys were prepared, and firstly the annealing heat treatments were optimized in the α+β+Ti₂Cu triple phase region to obtain satisfied tensile mechanical properties. Then the effect of Cu content on the tribological property, corrosion resistance, antibacterial activity and cytotoxicity of the Ti6Al4V-xCu alloys were systematically studied to obtain the appropriate Cu content. The results showed that the optimal annealing temperatures for Ti6Al4V-xCu (x = 4.5, 6, 7.5 wt%) alloys were 720, 740 and 760 °C, respectively, which was resulted from the proper volume fractions of α, β and Ti₂Cu phases in the microstructure. The additions of 4.5 wt% and 6 wt% Cu into the medical Ti6Al4V alloy could enhance the wear resistance and corrosion resistance of the alloy, but the addition of 7.5 wt% Cu showed an opposite effect. With the increase of the Cu content, the antibacterial property was enhanced due to the increased volume fraction of Ti₂Cu phase in the microstructure, but when the Cu content was increased to 7.5 wt%, cytotoxicity was presented. A medium Cu content of 6 wt%, with annealing temperature of 740 °C make the alloy possesses the best comprehensive properties of tensile properties, wear resistance, corrosion resistance, antibacterial property and biocompatibility, which is promising for future medical applications.     

Effect of aluminium content on the anodic behaviour of copper-aluminium alloys in 3.5 wt% NaCl solution

Anodic behaviour of heterogeneous Cu-Al alloys in 3.5 wt% NaCl solution has been investigated as a function of aluminium content by potentiodynamic polarization, cyclic voltammetry and potentiostatic current transient experiments and compared to pure Cu and homogeneous Cu-Al alloys. The specimens were subjected to various anodic potentials and subsequent analyses by scanning electron microscopy (SEM) supplemented with energy dispersion spectroscopy (EDS). The pure Cu and single -phase Cu-Al alloys showed that a relatively thick protective CuCl film forms at active-passive transition potentials and transforms into CuO or Cu(OH)₂ at the passivation potential, resulting in high limiting current densities. However, the Cu-10 wt% Al alloy is passivated to Al(OH)₃, impeding the transformation of the thick CuCl layer which contains AlCl or Al(OH)₂Cl salt into CuO or Cu(OH)₂. At high applied anodic potential, the Cu₂(OH)₃Cl phase forms on the deteriorated passive film Al(OH)₃.     

On the tensile creep behaviour of a directionally-solidified Ni3Al-based alloy

High temperature tensile creep behaviour of a directionally-solidified Ni₃Al-based alloy is presented. The study involved selection of nine alloy systems based on Ni₃Al. The alloys contained varying amounts of Cr and Ta, fixed amounts of 1·5 at.% Hf and 0·5 at.% Zr and doped with 0·2 at.% each of C and B. The alloys were vacuum arc-melted into buttons and homogenized at 1050°C for 68 h. The test pieces of the alloys were hot compression tested at 600, 700, 800 and 900°C. The yield strength data of some of the alloys were superior to conventionally cast Mar-M 200, a cast nickel-base superalloy widely used in gas turbine structural applications. The best alloy system was chosen based on consistent performance in the hot compression studies. The alloy so chosen was directionally solidified and vacuum-homogenization-treated for 20 h at various selected temperatures. Optimum creep properties were observed at 1120°C, 20 h treatment. The minimum creep rate data of the DS alloy showed relatively higher values even at lower temperatures and stress levels as compared to Mar-M 200. Hence, the alloy is less promising in replacing nickel-based superalloys used as structural materials in gas turbine applications.     

稀土对Al-Zn-M g-Cu/Al2O3陶瓷界面润湿性的影响

采用真空座滴法和熔铸法研究了在Al-Zn-Mg-Cu 合金中加入稀土(Ce、Y) 对Al2Zn2M g2Cu/Al₂O₃陶瓷界面润湿性的影响。结果表明,Al-Zn-Mg-Cu 合金中加入稀土可有效降低铝合金/Al₂O₃界面的接触角, 改善界面结合状态; 稀土改善界面润湿性存在一最佳含量范围, 添加Ce 的最佳含量约为0. 5w t% , Y 约为0. 7w t%。稀土改善润湿性的作用主要是稀土与Al₂O₃膜、Al₂O₃陶瓷发生反应。Mg、Zn、Cu 等合金元素在界面富集并参与界面反应对润湿性有利; 稀土与Mg、Zn、Cu 等合金元素适当组合改善润湿性的效果比单一稀土明显。      

Effect of addition of Al and Cu on the properties of Sn–20Bi solder alloy

This study investigates the effect of the composite addition of Al and Cu on the microstructure, physical properties, wettability, and corrosion properties of Sn–20Bi solder alloy. Scanning electron microscopy and X-ray diffraction were used to identify the microstructure morphology and composition. The spreading area and contact angle of the Sn–20Bi–x (x?=?0, 0.1 wt% Al, 0.5 wt% Cu, and 0.1 wt% Al–0.5 wt% Cu) alloys on Cu substrates were used to measure the wettability of solder alloys. The results indicate that the alloy with 0.1 wt% Al produces the largest dendrite and the composite addition of 0.1 wt% Al and 0.5 wt% Cu formed Cu₆Sn₅ and CuAl₂ intermetallic compounds in the alloy structure. And the electrical conductivity of Sn–20Bi–0.1Al is the best, which reaches 5.32 MS/m. The spread area of the solder alloy is reduced by the addition of 0.1 wt% Al and 0.5 wt% Cu, which is 80.7 mm². The corrosion products of Sn–20Bi–x solder alloys are mainly lamellar Sn₃O(OH)₂Cl₂ and the corrosion resistance of 0.1 wt% Al solder alloy alone is the best. The overall corrosion resistance of Sn–20Bi–0.1Al–0.5Cu is weakened and the corrosion of solder alloy is not uniform.

     

The effect of H2-anneal on the adhesion of Al2O3 scales on a Fe3Al-based alloy

Abstract

The cyclic (1,100°C, air) and isothermal (1,000°C, O₂) oxidation behavior of a Fe-28Al-5Cr (at%) alloy, with and without a prior H₂-anneal heat treatment at 1,200°C for 100 h, was studied. Changes in interfacial chemistry were evaluated using Scanning Auger Microscopy after removal of the oxide film in ultra high vacuum. This was achieved by making a scratch on the specimen surface, which caused spallation of the film at various locations along the scratch. The scale thickness and the temperature drop at which spallation took place during cooling were utilized to semi-quantitatively compare the adherence of the scales. Porosity at the scale–alloy interface and the scale microstructure were determined from scanning electron microscope observations. It was found that H₂-anneal greatly improved scale adhesion and resulted in a pore-free and sulfur-free interface. The effects were similar to that of a 0.1 at% Zr-containing alloy, except that the improvement in scale adhesion was not as great as that from Zr doping. This implies that oxide/alloy interfaces are not intrinsically strong and the effect of reactive elements, such as Zr, is more than preventing impurity from segregating to the interface. Results are also compared with the effect of H₂-anneal on other model alloys, such as NiCrAl, FeCrAl and NiAl, and on single crystal superalloys.     

The sintering densification and microstructure evolutions of Ti-1Al-8V-5Fe alloy with Si additions

The cost-efficient Ti-1Al-8V-5Fe-xSi (denoted Ti-185-xSi hereafter, x = 0, 0.15, 0.3, 0.45, 0.6, 0.75) alloys are synthesized by cold compaction and sintering powder metallurgy (PM) technology using TiH₂ and high-pure FeV₈₀ powders. The sintering densification, microstructural evolutions and mechanical behavior of Ti-185-xSi alloys sintered at 1350°C are investigated. The results show that the Si element is favorable to enhance the sintered density of Ti-185 alloys, which should be limited to ≤0.3%. The amount and average size of precipitate Ti₅Si₃ increase in the Ti-185 alloys with increasing Si content. Meanwhile, the Rockwell hardness of Ti-185 alloy also displays an increasing tendency, suggesting the Si element can improve the hardness of Ti-185. The Ti-185–0.15Si alloy possesses a better comprehensive mechanical property of strength (937 ± 8 MPa) and elongation (3.5%). The high-performance Ti-185 alloy is successfully prepared using low-cost FeV₈₀ master alloy with slight Si impurity instead of costly V.     

Influence of carbides and microstructure of CoCrMo alloys on their metallic dissolution resistance

CoCrMo alloys are passive and biocompatible materials widely used as joint replacements due to their good mechanical properties and corrosion resistance. Electrochemical behaviour of thermal treated CoCrMo alloys with different carbon content in their bulk alloy composition has been analysed. Both the amount of carbides in the CoCrMo alloys and the chemical composition of the simulated body fluid affect the electrochemical properties of these biomedical alloys, thus passive dissolution rate was influenced by the mentioned parameters. Lower percentage of carbon in the chemical composition of the bulk alloy and thermal treatments favour the homogenization of the surface (less amount of carbides), thus increasing the availability of Cr to form the oxide film and improving the corrosion resistance of the alloy.