Untersuchung zur Gefügestabilität und Korrosionsbeständigkeit von Nickelbasislegierungen unter fertigungsüblichen Schweißbedingungen am Beispiel der Werkstofftypen NiMo28 und NiMo16Cr16Ti

Structure examinations and corrosion sensitiveness of welded nickel alloys NiMo28 and NiMo16Cr16Ti The sensitivity of NiMo 28 (Hastelloy B-2) and NiMo 16Cr 16Ti (Hastelloy C-4) to intercrystalline corrosion in the heat-affected zone of welded joints was investigated. The temperature-cycles in welded joints typically used in the construction of chemical equipment were experimentally determined. The effect of thermal stress on both the structural stability and corrosion sensitivity was then determined by metallographic examination. The results showed Hastelloy C-4 to have a distinctly improved structural stability over the previously available Hastelloy C-276. Under the test conditions we employed no negative effect on corrosion sensitivity in the area of the heat-affected zone of the welded joint is to be expected. Hastelloy B-2 shows – dependent on heat input – more or less significant structural changes of the grain boundary, the existence of droplet-like heterogenicity suggests the possibility of intergranular corrosion.     

Interfacial reactions between lithium silicate glass-ceramics and Ni-based superalloys and the effect of heat treatment at elevated temperatures

Two lithium silicate glasses (S- and BPS-glass) were sealed to four different Ni-based superalloys (Inconel 600, Inconel 718, Haynes 230, and Hastelloy C-276) and the effects of long-term heating at 700–900°C on the chemical, microstructural, and mechanical properties of sealed interfaces were studied. The presence of a small amount of ZnO in the BPS-glass leads to the formation of a thin interfacial second phase layer and a less rough alloy interface compared to the ZnO-free S-glass. Inconel 718 was found to be the most reactive of the alloys, with Cr and Nb diffusing into the glass and forming a coarse glass-ceramic microstructure at the interface. Heat treatment of all the reaction assemblies at 900°C for 100 h in air resulted in degradation of the seals and their spontaneous failure. Heat treatments at 700 or 800°C did not cause any interfacial coarsening in BPS sealed to Inconel 600, Haynes 230, and Hastelloy C-276 alloys and did not alter the bond strength of Haynes 230 bars, sealed with a thin layer of BPS-glass, demonstrating the potential of these material combinations for applications up to 800°C.     

Resistance characteristics to oxidation of the metal-catalyzer for Cat-CVD

In order to obtain oxide films using catalytic chemical vapor deposition (Cat-CVD), oxidation experiments for catalyzers of Alumel, Al Chrom-O, Chromel, Hastelloy C-276, Kanthal, Kovar, Inconel-600, Inconel-601, Inconel X-750, Iron Chrome 30, Moleculoy, Monel, Ni, Nickel Chrome, Pt, SUS-304, SUS-316, Super Invar, and Ti have been carried out. The electric resistance measured for each metal heated at 900 °C, exposed for 30 min in O₂ atmosphere, have revealed that Alumel, Al Chrom-O, Chromel, Hastelloy C-276, Kanthal, Inconel-600, Inconel-601, Inconel X-750, Iron Chrome 30, Moleculoy, Ni, Nickel Chrome, Pt, SUS-304, and SUS-316 are in resistance to oxidation.     

Vapour-phase siliconizing of some nickel-base alloys and transition metals using Si2Cl6 as a source of silicon

Some nickel-base alloys and transition metals were siliconized using hexachlorodisilane (Si₂Cl₆, b.p. 144° C) in the temperature range 500 to 1000° C, and subsequently their corrosion stabilities were examined. Using hexachlorodisilane as a silicon source, the siliconizing temperature could be lowered by 150° C for Monel, 200° C for Inconel (No. 600), 50° C for titanium and 150° C for molybdenum in comparison with that using silicon tetrachloride. The corrosion stability of Inconel plate against 1N H₂SO₄ and 1N HNO₃ were improved considerably by the siliconizing of the surface. On the other hand, that of Monel against 1N H₂SO₄ was improved outstandingly by the siliconizing of the surface, but not improved against 1N HNO₃.     

某凝析气田异种不锈钢偶对在不同NaCl溶液中的腐蚀行为

为了考察某凝析气田现场新投用的3种合金钢材316L、双相不锈钢2205以及Inconel 625在现场出现耦合后是否会发生电偶腐蚀,对Inconel 625/316L、Inconel 625/2205偶对在不同Cl~-浓度下的电偶腐蚀特性进行了电化学试验,研究了耦合前各自的开路电位随时间的变化、耦合后的耦合电流随时间的变化、耦合(闭路)电位随时间的变化、耦合电流及耦合(闭路)电位的稳定值大小。结果表明:不同影响因素(电偶、Cl~-浓度)下,电位差均为50 mV左右,电偶电流密度约为1×10~(-6)A/cm~2,由此计算出材料偶接后的均匀腐蚀速度为0.002 mm/a,按照腐蚀速度划分标准(NACE RP0775-2005),均属于轻度腐蚀,因此625/316L、625/2205异种不锈钢之间耦合不会引起明显的电偶腐蚀问题。本方法对在油气田上使用类似异种钢耦合后出现的腐蚀研究具有一定的指导意义。     

Ni-Cr-Mo-Nb超音速火焰喷涂层在模拟烟气中的热腐蚀行为

选用适量的Ni,Cr,Mo和Nb的配比,在20钢表面超音速火焰喷涂了Ni-Cr-Mo-Nb合金层,以期提高其耐蚀性。采用XRD,SEM/EDS技术对Ni-Cr-Mo-Nb合金层及其高温腐蚀产物成分、形貌进行了分析;对Ni-Cr-Mo-Nb合金层涂覆75%Na_2SO_4+25%NaCl(质量分数)混合熔盐后于600,650℃烟气中的热腐蚀行为进行了研究。结果表明:Ni-Cr-Mo-Nb合金层结构致密,孔隙率低;Ni-Cr-Mo-Nb合金层在涂覆75%Na2SO4+25%Na Cl盐膜后的烟气中600,650℃时先增重后失重,其腐蚀产物分为2层,外层富含Ni,内层富含Cr且S含量较高,具有良好的耐蚀性能。     

Corrosion behaviors of amorphous and nanocrystalline Fe-based alloys in NaCl solution

Amorphous Fe(73.5)Si(13.5)B9Nb3Cu1 alloy was prepared by the chill block melt-spinning process and nanocrystalline Fe(73.5)Si(13.5)B9Nb3Cu1 alloy was obtained by annealing. The crystallization behaviors were analysed by DSC, XRD and TEM. The electrochemical corrosion behaviors in different annealed states were performed by linear polarization method and electrochemical impedance spectroscopy in 3.5% NaCl solution. The results show that the crystallization of amorphous alloy occurs in the two steps. Some nanometer crystals appear when annealing in 550 degrees C and 600 degrees C, respectively with grain size 13 nm and 15 nm. The nanocrystalline alloy has a tendency to passivation and lower anodic current density than amorphous alloy. It indicates that nanocrystalline alloy has a higher corrosion resistance. Amorphous Fe(73.5)Si(13.5)B9Nb3Cu1 alloy consisted of only single semi-circle. When the alloy was annealed in 600 degrees C, its EIS consisted of two time constants, i.e., high frequency and low frequency capacitive loops. The charge transfer reaction resistances increases as annealing temperature rises.     

Determination of J-integral R-curves for Hastelloy X and inconel 617 up to 1223 K using the potential drop technique

For Hastelloy X (T = 308 K and T = 1223 K) and for Inconel 617 (T = 308 K, 473 K, 673 K, 873 K, 973 K, 998 K, 1023 K, 1048 K, 1073 K, 1173 K, and 1223 K) the J-integral R-curves have been determined. For Hastelloy X at 308 K the multispecimen technique has been compared with the single specimen method using the potential drop technique. At 1223 K Hastelloy X delivered a low J₀-integral value. Inconel 617 showed a smooth increase in J₀ with increasing temperature, up to 998 K; above this temperature even for large loadline displacements only blunting behaviour has been observed. The same tendency has been found for the evaluation of the tearing modulus. With increasing temperature the tearing modulus increases. In the temperature range from 998 K to 1223 K the tearing modulus increases by about one order of magnitude. For both alloys the onset of stable crack growth in most cases is earlier than the load maximum is reached in the load versus load-line displacement curves.     

Surface damages and tool wear mode in end milling of hastelloy‐C276 under dry and wet conditions

Hastelloy‐C276 is a nickel based superalloy that is widely used in chemical, petro‐chemical, environmental and nuclear industries due to its outstanding performance in a wide range of corrosive mediums. The superior properties of nickel based superalloys impair their machinability which increases the difficulty in obtaining a good surface finish. Because most of the components' failures are initiated from surface defects, several researchers have been concerned about surface integrity in machining aerospace superalloys particularly Inconel‐718. Due to the lack of studies done on machining corrosion‐resistant superalloys, this study aims to investigate surface damages and tool wear modes in milling Hastelloy‐C276 under dry and wet conditions. The absence of cooling and lubricating actions in dry machining resulted in the formation of craters, severe plastic deformation, voids, debris re‐deposition and materials drag. The breakage of the nucleated carbide phases resulted in the formation of nucleated cavities on the machined surface in both wet and dry machining. Adhesive tool wear was less in dry machining due to the formation of oxide layers on tool faces which suppressed the formation of built‐up edges due to the weak adhesion properties of oxide compounds which resulted in less surface roughness at v_c = 50 m/min. On the other hand, the higher temperature and friction in dry machining resulted in severer tool coating delamination.     

316L和Hastelloy C合金在不同温度循环废酸中的耐蚀性能

为了解316L和HastelloyC合金在不同温度的循环废酸中的耐蚀性能,利用静态挂片试验、电化学试验和扫描电镜研究了2种合金在不同温度循环废酸中的腐蚀速率及形貌。结果表明：在50℃的循环废酸中,316L和HastelloyC合金均具有优异的耐蚀性,且耐蚀性相当;316L和HastelloyC合金的腐蚀速率均随循环废酸温度的升高而增加,316L合金的增加缓慢,HastelloyC合金的增加急剧;当温度由50℃升高到80℃时,循环废酸的氧化性增加,Mo含量较高的HastelloyC合金在循环废酸中不能形成完整、致密的钝化膜,从而使其耐蚀性急剧下降。     

AZ91镁合金表面MgFe_2O_4薄膜的溶胶-凝胶法制备及其耐蚀性能

MgFe2O4耐酸耐碱,但目前还未见将其制成镁合金防腐蚀涂层的报道。采用溶胶-凝胶法在AZ91镁合金表面制备了MgFe2O4薄膜,利用正交试验研究了镀膜层数、溶胶中Mg2+与Fe3+的摩尔比、烧结温度、烧结时间对AZ91镁合金膜试样自腐蚀电流密度的影响,得出最优方案,并研究了优化条件制备的膜试样的组织结构及耐蚀性。结果表明:各因素对AZ91镁合金膜试样自腐蚀电流密度的影响程度由大到小依次是镀膜层数、烧结温度、nMg2+/nFe3+、烧结时间;最优条件是镀膜1层,nMg2+/nFe3+=0.35,烧结温度400℃,烧结时间5 h;与AZ91镁合金基体相比,优化条件制备的MgFe2O4薄膜的自腐蚀电流密度降低了1个数量级,自腐蚀电位正移了690 mV,耐腐蚀性能得到很大提高。     

激光裂解含二茂铁的聚硅氧烷制备SiOC(Fe)陶瓷涂层研究

激光裂解聚合物先驱体在金属表面制备性能优异的陶瓷涂层,解决了金属本身存在的耐磨防腐蚀性能不足的问题,已成为一种行之有效的方法。采用激光裂解含二茂铁的聚硅氧烷制备了SiOC(Fe)陶瓷涂层,采用电子显微镜(SEM)、X射线衍射仪(XRD)和X射线光电子能谱(XPS),分析了激光裂解含二茂铁的聚硅氧烷生成物的组成与结构,并初步研究了其裂解机理。结果表明:在激光作用下,含二茂铁的聚硅氧烷在激光裂解过程中会发生非平衡态的自由基化学反应,生成的陶瓷涂层主要由晶态的SiC、Fe_3C,非晶态的SiO_2、Fe_2O_3、Fe_3O_4以及C单质、C_6H_(18)OSi_2等物质组成,由二茂铁激光裂解生成的Fe_2O_3、Fe_3O_4、Fe_3C相对制备的陶瓷涂层孔隙具有填补作用。二茂铁质量分数越大,陶瓷涂层表面越平整致密,孔隙越少。     

Phase transformations in the alloy hastelloy B

The alloy Hastelloy B undergoes phase transformations in the temperature range of 600°–800° C. These phase transformations were studied in some detail by electron microscopy. The essential result of this study was the observed formation of the DO₂₂ structure as an intermediate phase. The DO₂₂ structure is relatively stable in Hastelloy B and its further transformations are easily observable. At 600°C it is transformed to Ni₄ Mo followed by a partial transformation to Ni₃ Mo, whereas at 700°C Ni₃ Mo is formed from DO₂₂ directly.     

Study on Ductility Dip Cracking susceptibility in Filler Metal 82 during welding

In this paper, Ductility Dip Cracking (DDC) susceptibility in Inconel600 companion Filler Metal 82 (FM82) under different stress states is investigated. Inconel600 is a Ni-Cr-Fe alloy with excellent resistance to general corrosion, localized corrosion, and stress corrosion, which has been widely used in nuclear power plants. However, the companion FM82 has been shown to be susceptible to DDC in welding process. To resolve the problem, this work is mainly focused on evaluating DDC susceptibility in FM82 in welding process. First of all, Strain to Fracture (STF) test is used to achieve the DDC criterion under simple stress state, and the formation mechanism of DDC was explained. Real welding is a process with complex stress state. Later, to get the DDC susceptibility under complex stress state, models about multi-pass welding were built up by means of finite element method. According to numerical simulation results, relationship of deformation and temperature history is achieved. Moreover, susceptible locations and moments could be determined associated with STF results. The simulation results fairly agree with welding experiment from another research.     

Synthesis of carbon nanotubes using mesoporous Fe-MCM-41 catalysts

MWNTs (multi-walled carbon nanotubes) were made by catalytic CVD process using iron-containing mesoporous silica, Fe-MCM-41, with 4 mol% Fe loading prepared by direct synthesis route. Uniform 5 nm size Fe2O3 nano-particles impregnated onto a mesoporous silica support, SBA-15 were also prepared for CNTs synthesis. The catalysts were characterized using XRD, SEM/TEM, N2 physisorption, UV-vis diffuse reflectance and FT-IR spectroscopies. Acetylene gas was introduced as a carbon source, and the gas mixture of Ar:H2:C2H2 = 14:5:1 pyrolyzed at 750 degrees C for 60 min was found to be the optimum synthesis condition. Fe-MCM-41 due to higher dispersion of nano-sized Fe-species was efficient as catalyst for MWNTs with more uniform size distribution. Cobalt-impregnated Fe-MCM-41 (Co/Fe = 1) produced a small fraction of SWNTs of ca. 2 nm diameter mixed with MWNTs.     

Formation of a highly oriented FeO thin film by phase transition of Fe3O4 and Fe nanocrystallines

A highly oriented FeO thin film was formed from a Fe₃O₄ thin film containing Fe nanocrystallines by post-annealing at 600°C. Fe₃O₄ thin films were grown on Si(100) substrates by ion beam sputter deposition under oxygen ambient. The stoichiometry of the iron oxide thin film could be precisely controlled by in situ X-ray photoelectron spectroscopy (XPS). X-ray diffraction (XRD) pattern of the Fe₃O₄ thin film grown at substrate temperature of 300°C showed a mixed phase of Fe₃O₄ and Fe nanocrystallines with a preferred orientation (110). However, the mixed phase was converted to a highly oriented FeO(200) phase by post-annealing at 600°C. This could be inverted as a result of Ostwald ripening of the Fe₃O₄ and Fe nanocrystallines.     

高温碳氢气氛下Cr5Mo钢的尘化腐蚀状况

金属渗碳腐蚀(即尘化)是高温碳氢环境下常发生的灾难性腐蚀。Cr5Mo钢的工程应用量大面广,过去对其渗碳腐蚀研究不够。为此,研究了炉管材料Cr5Mo钢在600℃,50%CO-H2-3%H2O气氛下的尘化腐蚀行为,采用X射线衍射分析了腐蚀试样的物相组成,采用扫描电镜对试样进行了微观形貌分析。结果表明:Cr5Mo钢在试验条件下呈现均匀腐蚀,材料自表面向内依次析出Fe5C2和Fe3C脆性腐蚀产物,经560h尘化腐蚀后的试样平均腐蚀深度约为200μm,而基体材料性质无明显改变。因此Cr5Mo钢在尘化过程中出现的腐蚀减薄是由脆性碳化物层的析出引起的。     

The metallurgical behaviour during brazing of Ni-base alloy Inconel 600 to Si3N4 with Ag71Cu27Ti2 filler metal

Detailed observations were carried out on the metallurgical behaviour of joint-brazing of nickel based alloy Inconel 600 to Si₃N₄ with Ag71Cu27Ti2 filler metal, with emphasis on the interface between the filler metal and the Inconel 600 and the effects of nickel which was the predominant element in the base metal. Based on the experimental results, the mechanism of bonding Inconel 600 to the filler metal is attributed to the diffusion of silver and copper along the grain boundaries of the Inconel 600, which results in mechanical anchoring. The effects of nickel on the metallurgical behaviour of filler metal are summed up as enhancing the separation of silver- and copper-rich liquid phases from the molten filler metal; combining titanium and decreasing its activity in the reaction with Si₃N₄ at the interface with ceramics; promoting the diffusion of silver and copper into Inconel 600; and facilitating the flow of filler metal over the surface of Inconel 600.     

Sodium vanadate-induced corrosion of nickel and MCrAIY coatings on Inconel 600

The vanadate-induced corrosion of M Cr AIY coatings (M = Ni/Fe) on Inconel alloy 600 has been studied by using samples with preformed vanadate deposits. The samples were exposed to oxygen at 650 to 800°C for a maximum of 25 h in a thermobalance. The presence of molten vanadate ((Na₂O)_x·V₂O₅) on the surface causes accelerated corrosion. The corrosion rates increase with increasing V₂O₅ content of the vanadates. In the presence of molten vanadate, protective scales of Cr₂O₃-Al₂O₃ fail to develop; rather the oxide layer next to the coating consists of the oxides of all components in the coating and of vanadium both as vanadate and as vanadium sesquioxide. In most cases the molten vanadate phase fluxes the oxide scale and particularly the NiO phase in the oxide layer. Under these conditions the corrosion is probably governed by inward transport of oxygen (or oxygen species) in the vanadate melt. When the NiO concentration in the oxide layer next to the metal is high (as on nickel-base coatings with more than 75 wt-%Ni) a Ni₃(VO₄)₂ layer gradually develops between the oxide and the melt. This is accompanied by compositional changes in the oxide layer beneath the vanadate and results in a slow oxidation rate. MST/510     

Grain boundary character distribution and its effect on corrosion of Ni–23Cr–16Mo superalloy

Grain boundary character distribution (GBCD) of the Hastelloy C2000 alloy (Ni–23Cr–16Mo) and the effect of coincidence site lattice (CSL) grain boundaries on corrosion resistance were examined by electron backscattered diffraction and electrochemical experiments. Various deformation followed by annealing was applied to optimise the GBCD of the alloy. After grain boundary engineering (GBE) treatment, the proportion of CSL boundaries increased from 37.7% to 62.4% and the corrosion current density of the specimens decreased in NaCl solution. The results indicated that GBE treatment is responsible for preferable corrosion resistance due to the increase of the fraction of special low energy grain boundaries with perfect grain boundary atom arrangement after thermomechanical process.