Synergetic effects of impurities and alloying element Cr on oxidation and dissolution corrosion of Ni (111) surfaces: A DFT study

Using density-functional calculations, we studied the interactions between interstitial impurities (H, O, N, S, and P) and Ni (111) surfaces doped, or not, with Cr, and studied the effect of Cr doping on the dissolution corrosion resistance of Ni(111) surfaces. The aim of this work was to study, at the atomic scale, the effects of Cr on the segregation behaviors of impurities and the synergetic effects between co-doped atoms on the resistance to dissolution corrosion of Ni (111) surfaces. The results indicate that impurities S, P, O, and H prefer to be trapped at near-surface sites, that Cr was uniformly distributed in the Ni crystal and can affect the segregation behavior of impurities S and P to move toward the surface, and it affects impurities N and O such that they shift from the surface to the subsurface. The formation of near-surface Cr nitrides (speculated to be Cr₂N based on the results obtained for particular co-doped surfaces) was also noted. Introducing Cr enhances the structural stability of the Ni (111) surface and protects it from being corroded when impurities are present. The elementary processes studied afforded microscopic insights into the formation of a Cr-depleted zone, a phenomenon that leads to local corrosion of the Ni alloy surface. The results of our theoretical calculations explain some of the experimental results previously observed at the atomic scale.     

Cu50Ni50合金快速凝固的分子动力学模拟

采用分子动力学模拟的方法研究了Cu₅₀Ni₅₀合金在不同冷却速度下的凝固过程,利用均方位移、径向分布函数和结构可视化等方法分析其微观结构.并对凝固模型进行拉伸模拟,通过应力应变曲线和直观结构变化分析其性能.研究表明：冷却速度对Cu₅₀Ni₅₀合金凝固形成的结构有较大影响,随着冷却速度的升高,凝固形成的结构中晶体含量减少,在较低的冷却速度下,如冷却1×10¹²K/s时,Cu₅₀Ni₅₀合金凝固形成晶体结构;在较高的冷却速度下,如1×10¹⁴K/s时,Cu₅₀Ni₅₀合金凝固形成非晶体结构,且非晶Cu₅₀Ni₅₀合金的抗拉性能要优于晶体Cu₅₀Ni₅₀合金.     

High temperature corrosion behaviour of some Fe-, Co- and Ni-base superalloys in the presence of Y2O3 as inhibitor

High temperature corrosion is accelerated degradation of materials at higher temperatures of operation caused by the presence of a deposit of salt or ash. Inhibitors and fuel additives have been investigated with varying success to control this type of corrosion. In this work, effect of an oxide additive namely Y₂O₃ on the hot corrosion behaviour of some superalloys viz Superfer 800H (alloy A), Superco 605 (alloy B) and Superni 75 (alloy C) has been investigated in an Na₂SO₄-60%V₂O₅ environment at 900 °C for 50 cycles. Each cycle consisted of 1 h heating in a Silicon Carbide Tube Furnace followed by 20 min cooling in ambient air. Weight data were taken by an electronic balance having an accuracy of 0.01 mg after each cycle. Subsequently, the exposed alloys were characterized by XRD, SEM and EPMA analyses to evaluate the role of the oxide additive. In the Na₂SO₄-60%V₂O₅ environment, the corrosion rate for the Co-base alloy was found to be highest, whereas that for the Ni-base Superni 75 the lowest. Superficially applied Y₂O₃ was observed to be useful in reducing the high temperature corrosion of the alloys. It was found to be most effective for the alloy A for which the oxide scale was continuous and rich in protective Cr. Alloy B showed the formation of medium size scale rich in Cr and Co. The oxide scale for the alloy C contained mainly Cr and Ni.     

Continuous flame oxidation in supercritical water

Abstract

Continuous flames have been observed in Supercritical water oxidation (scWO) of isopropyl alcohol (IPA), using a vertical continuous reactor with sapphire windows and a mixing nozzle. Two types of continuous flame were confirmed: the one was long pale blue colored and the other was red short cone shaped, changing blue to red at around air ratio 2.0. The flame was strongly influenced by IPA concentration, air ratio and design of the mixing nozzle. Results for decomposition of PA are presented for IPA concentrations ranging from 600 up to 28260 ppm as TOC and initial reactor temperatures, were mostly around 490°C, at 25 MPa. Decomposition rate at steady state was over 99.9%. Experimentally measured CO₂ and O₂ concentrations at the flue gas were in good agreement with theoretically calculated values. Even for low air ratio as 1.1, high decomposition rate without CO, NO, NO₂ was achieved.     

超细Ni80Cr20合金丝冷拉拔烧头及穿模工艺

采用冷拉拔技术制备超细Ni80Cr20合金丝,探索了电化学法烧头和超景深显微镜辅助穿模方法,开展了直径25.60μm的超细丝拉拔至21.14μm的烧头和穿模工艺研究。实验结果表明:采用电解电压为5V,0.2mol/L的HCl溶液,烧头时间为1s,超景深显微镜200倍放大模式,成功拉制直径为21.14μm的微丝;电化学法可以精确控制烧头电压和时间,同时超景深显微镜可以放大金刚石模具孔径,解决了烧头时间控制不准确和人工穿模的难题,显著提高了穿模效率和成功率。     

Investigation on the undercooling and crystallization of Ni–Fe alloy coating melt by DSC

The undercooling of Ni–Fe alloy coating melt was in situ investigated by differential scanning calorimeter with flux processing technique. The highest undercooling of Ni–Fe alloy with 426 K was obtained as the thermal treatment temperature of the melt being 1904 K and the cooling rate being 50 K min^?1. When cooling rate is fixed, the undercooling depends on the melt processing temperature, and increases rapidly at the first stage. The effects of thermal treatment temperature and cooling rates on the undercooling were discussed.     

硫原子在镍基合金825(001)面吸附的第一性原理研究

元素硫在镍基合金表面吸附产生严重的电化学腐蚀,为从原子尺度研究硫腐蚀机理,采用第一性原理方法,构建并优化了镍基合金825的晶胞结构模型,计算分析了S原子在镍基合金825耐蚀性较差面(001)晶面的吸附及电子转移情况.结果表明:Ni原子占据顶角, Cr原子和Fe原子对称占据面心是镍基合金825稳定的晶胞结构;原子S在镍基合金825(001)面上最稳定的吸附位为四重穴位,吸附能为-6.51 eV; S吸附前后的态密度(DOS)和二维电荷差分密度图(DCD)对比发现,镍基合金825中Fe与S之间电荷偏移明显,形成离子键,易生成腐蚀产物Fe_xS_y. S的吸附对镍基合金825中Cr原子的电子分布影响不大,且合金中Cr和Ni抑制了合金中Fe与S之间的相互作用,从而提高了合金耐蚀性.     

Laser welding of thin foil nickel-titanium shape memory alloy

In this study, two L27 Taguchi experiments were carried out to study the effect of fibre laser welding parameters and their interactions upon the weld bead aspect ratio of nickel-titanium thin foil. The optimum parameters to produce full penetrated weld with the largest aspect ratio and desirable microstructure were successfully obtained by the Taguchi experimental design. The corrosion property of the optimized NiTi weld in Hank’s solution at 37.5 °C was studied and compared with the as-received NiTi. To improve the corrosion properties of the weld, the effect of post-weld-heat-treatments ranging from 573 to 1173 K was investigated. The corrosion properties, surface morphology, microstructure and Ti/Ni ratio of the heat-treated NiTi weld were analysed. It was found that a post-weld heat treatment at 573 K for 1 h provided the best pitting corrosion resistance at the weld zone.     

Heusler合金Mn50–xCrxNi42Sn8的相变、磁性与交换偏置效应

研究了Mn50–xCrxNi42Sn8 (x=0, 0.4, 0.6, 0.8)多晶样品的相变、磁性和交换偏置效应.结果表明,该系列合金在室温下都具有非调制的四方马氏体结构.马氏体逆相变温度随Cr含量增加而逐渐降低. 20 k Oe磁场下的M-T曲线表明,该系列合金的磁性比较弱.两相之间的磁性差最大为△M=7.61 emu/g.磁性的变化主要与Mn-Mn间距的变化以及Ni(A位)-Mn(D位)间杂化作用的强弱有关.在低温下,马氏体相的磁性随着Cr含量增加而增强.在500 Oe的外加磁场作用下,从室温冷却到5 K,在Mn50Ni42Sn8合金中观察到高达2624 Oe的交换偏置场.随着Cr含量的增加,交换偏置场逐渐减小.当Cr含量x=0.8时,随着冷却场的增加, 5 K时的交换偏置场先迅速增加然后逐渐减小.当冷却场为500 Oe时,交换偏置场最大.这主要归因于自旋玻璃态与反铁磁性区域的界面交换耦合作用的变化.     

ICP法测定超临界水氧化设备腐蚀液中铜、铬、铝、镍、钛

采用光谱法研究了超临界水氧化设备腐蚀液中Cu,Cr,Al,Ni和Ti元素的含量,分析判断不锈钢设备腐蚀状况及其因素。结果表明,超临界设备不锈钢材料主要成分元素Cr在超临界水中有不同程度的溶解,并且溶解程度随温度和压力升高而增大。     

Cr-Ni-Mo-Co surface alloying layer formed by plasma surface alloying in pure iron

Using double glow plasma alloying technique, a multi-elements alloyed layer containing elements of Cr, Ni, Mo and Co was formed on the surface of pure iron. After undergoing suitable aging treatment followed solid solution treatment, the formed alloying layer keeps a good combination of corrosion resistance and wear resistance. The relationship between the process parameters of heat treatments and the properties of the formed Cr-Ni-Mo-Co alloying layer, such as the chemical composition, hardness, corrosion resistance and wear resistance, was investigated in this study. It was revealed that the formed alloying layer exhibits a better behavior than that of 304 stainless steel and pure iron by employing a suitable heat treatment system. The temperature employed in solid solution treatment is 1453 K (1180 °C) followed by water quenching and the aging temperature is 813 K (540 °C) followed by water cooling.     

Effect of superficially applied ZrO2 inhibitor on the high temperature corrosion performance of some Fe-, Co- and Ni-base superalloys

High temperature corrosion is an acute form of corrosion occurring at elevated temperature in the presence of an oxidizing gas and is associated with a thin electrolytic deposit (salt or ash) on alloy. Inhibitors and fuel additives have been used with varying success to combat oil ash corrosion. In this paper, the effect of an oxide additive namely ZrO₂ on the hot corrosion behaviour of some superalloys, viz. Superfer 800H (alloy A), Superco 605 (alloy B) and Superni 75 (alloy C) has been investigated in an Na₂SO₄-60%V₂O₅ environment at 900 °C for 50 cycles. Each cycle consisted of 1 h heating in a Silicon Carbide Tube furnace followed by 20 min cooling in ambient air. Weight change measurements after each cycle were taken by an electronic balance having an accuracy of 0.01 mg. XRD, SEM and EPMA analyses of the exposed specimens were carried out to characterize the oxide scales. In the Na₂SO₄-60%V₂O₅ environment, the corrosion rate for the Co-base alloy was found to be highest, whereas that for the Ni-base Superni 75 a lowest. Whereas, with ZrO₂ superficial coating, the overall weight gains got reduced for the alloys B and C, however the inhibitor was marginally effective in the alloy A. A thick scale was observed in the latter case, which was rich in Cr, Ni, Fe and V. Absence of protective continuous chromia layer and presence of less protective NiO was probably the main reason for more corrosion rate in this case.     

基于团簇模型设计的Cu-Cu_(12)-[M_(x/(12+x))Ni_(12/(12+x))]_5(M=Si,Cr,Cr+Fe)合金抗高温氧化研究

文章在稳定固溶体团簇模型的指导下,对白铜合金进行微合金化,将Cu元素在合金中的含量固定为72.22 at.%,改变Ni与M(M为Si,Cr,Cr+Fe)的比例,设计了系列合金成分,并对其抗高温氧化性能及其机制进行了研究.同时加入基体中的Ni-Si元素可以从两方面提高合金的抗氧化性能:以团簇形式加入,形成稳定固溶体结构,可以降低Cu-Ni-Si合金的化学反应活性;Si/Ni比增大后,合金在少量固溶的基础上能析出抗氧化性能优于基体的析出相,且析出越多,抗高温氧化性能越好.所以其抗氧化能力的来源并不是形成致密Si氧化物薄膜.Ni-Cr的同时加入可以明显抑制Cu合金在800?C以下的中温氧化,但其抗高温氧化能力主要与外氧化层中是否形成连续的Cr氧化层有关,因而该系列合金的抗高温氧化能力与Cr/Ni比有密切联系,合理选择团簇内Cr/Ni比例,才能够提高Cu合金的抗高温氧化能力.第四组元Fe和第三组元Cr相比较,不能够起到优先氧化、生成保护性氧化皮的作用,所以Cr,Fe同时添加只能抑制Cu在800?C以下的中温氧化,却不能够提高Cu合金的抗高温氧化能力.     

液态三元Fe-Cr-Ni合金中快速枝晶生长与溶质分布规律

采用落管方法实现了液态三元Fe-Cr-Ni合金的深过冷与快速凝固,合金液滴的冷却速率和过冷度均随液滴直径的减小而迅速增大.两种成分合金近平衡凝固组织均为粗大板条状α相.在快速凝固过程中,不同直径Fe_(81.4)Cr_(13.9)Ni_(4.7)合金液滴凝固组织均为板条状α相,其固态相变特征很明显,随着过冷度增大,初生δ相由具有发达主干的粗大枝晶转变为等轴晶.Fe_(81.4)Cr_(4.7)Ni_(13.9)合金液滴凝固组织由α相晶粒组成,随着过冷度增大,初生γ相由具有发达主干的粗大枝晶转变为等轴晶,其枝晶主干长度和二次分枝间距均显著下降,晶粒内溶质的相对偏析度也明显减小,溶质Ni的相对偏析度始终大于溶质Cr.理论计算表明,与γ相相比,δ相枝晶生长速度更大.在实验获得的过冷度范围内,两种Fe-Cr-Ni合金枝晶生长过程均由热扩散控制.     

Effects of ultrasonic waves on the interfacial forces between oil and water

The effect of ultrasound on flow through a capillary using the pendant drop method was investigated. Water was injected into a 0.1 mm Hastelloy C-276 capillary tube submersed into several mineral oils with different viscosity, and kerosene. The average drop rate per minute was measured at several ultrasonic intensities. We observed that there exists a peak drop rate at a characteristic intensity, which strongly depends on oil viscosity and the interfacial tension between water and the oil. The semi-quantitative results reveal that the remarkable change in the interfacial forces between oil and water could be the explanation to the enhancement of oil recovery when the ultrasonic waves are applied.     

Microstructure evolution and mechanical property of pulsed laser welded Ni-based superalloy

For evaluating the microstructure evolution and mechanical property of Ni-based Hastelloy C-276 weld joint by the pulsed laser welding, the influence of pulsed laser welding on the microstructure and mechanical property of the weld joint is investigated by the analysis of the microstructure morphology, microhardness, phase structure and tensile property. The results indicate that, in the fusion zone three sections are divided on the basis of the patterns of grain structures. In the weld joint, the element segregation is found, but the trend of brittle phase׳s formation is weakened. The weld microhardness presents just a little higher than that of base metal, and there is no obvious the softened heat affected zone. Meanwhile in the weld joint, the phase structure is still the face-center cubic with the tiny shift of peak positions and widened Full Width at Half-Maximum. The yield strength of weld joint is the same as that of base metal, and the tensile strength is nearly 90% of that of base metal. The decreased tensile strength is mainly attributed to the dislocation piling-up.     

Electrochemical corrosion and oxidation resistances of Zr_(60)Ni_(21)Al_(19) bulk amorphous alloys

Electrochemical corrosion and oxidation resistances of Zr 60 Ni 21 Al 19 amorphous alloy were studied. The ternary amorphous alloy exhibits greater positive potential than its crystalline counterpart and 0Cr19Ni9Ti stainless steel. Its weight loss result measured in 2 mol/L HCl solution is in agreement with the potentiodynamic curve. But there is no obvious difference in the oxidation resistances between Zr 60 Ni 21 Al 19 amorphous and its crystalline alloys. They both exhibit high oxidation resistance.     

Corrosion development between liquid gallium and four typical metal substrates used in chip cooling device

The limitation of the currently available thermal management method has put an ever serious challenge for computer chip designers. A liquid metal with low melting point around room temperature was recently identified as a powerful coolant of driving heat away because of its superior thermo-physical properties and the unique ability to be driven efficiently by a completely silent electromagnetic pump. However, the adoption of gallium, one of the best candidates as metal coolant so far, may cause serious corrosion to the structure materials and subsequently affect the performance or even dangerous running of the cooling system. To address this emerging critical issue, here the compatibility of gallium with four typical metal substrates (6063 Aluminum-Alloy, T2 Copper-Alloy, Anodic Coloring 6063 Aluminum-Alloy and 1Cr18Ni9 Stainless Steel) was comprehensively investigated in order to better understand the corrosion mechanisms and help find out the most suitable structure material for making a liquid metal cooling device. To grasp in detail the dynamic corrosion behavior, an image acquisition and contrasting method was developed. Moreover, corrosion morphology analyses were performed by means of scanning electron microscope (SEM). The chemical compositions of the corroded layers were evaluated using energy dispersive spectrometry (EDS). According to the experiments, it was found that, the corrosion of the 6063 Aluminum-Alloy was rather evident and serious under the temperature range for chip cooling. The loose corrosion product will not only have no protection for the inner substrate, but also accelerate the corrosion process. Compared to the 6063 Aluminum-Alloy, T2 Copper-Alloy showed a slow and general corrosion, but part of the corrosion product can shed from the substrate, which will accelerate corrosion action and may block the flowing channel. Anodic Coloring 6063 Aluminum-Alloy and 1Cr18Ni9 Stainless Steel were found to have excellent corrosion resistance among these four specimens. No evident corrosion phenomena were found under the examination of SEM and EDS when exposed for 30 days at the temperature of 60°C, which suggests their suitability as structure materials for the flow of liquid metal. However, as for the Anodic Coloring 6063 Aluminum-Alloy, surface treatment and protection are of vital importance. The present study is of significance for making a liquid metal chip cooling device which can actually be used in the future computer industry.     

Laser texturing of Hastelloy C276 alloy surface for improved hydrophobicity and friction coefficient

Laser treatment of Hastelloy C276 alloy is carried out under the high pressure nitrogen assisting gas environment. Morphological and metallurgical changes in the laser treated layer are examined using the analytical tools including, scanning electron and atomic force microscopes, X-ray diffraction, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. Microhardness is measured and the residual stress formed in the laser treated surface is determined from the X-ray data. The hydrophibicity of the laser treated surface is assessed using the sessile drop method. Friction coefficient of the laser treated layer is obtained incorporating the micro-tribometer. It is found that closely spaced laser canning tracks create a self-annealing effect in the laser treated layer and lowers the thermal stress levels through modifying the cooling rates at the surface. A dense structure, consisting of fine size grains, enhances the microhardness of the surface. The residual stress formed at the surface is compressive and it is in the order of −800 MPa. Laser treatment improves the surface hydrophobicity significantly because of the formation of surface texture composing of micro/nano-pillars.     

Measurements of bulk-to-surface segregation of impurities in electrodeposited NiCr alloys by auger electron spectroscopy

Auger Electron Spectroscopy (AES) measurements of the non-equilibrium segregation of K to the surface of an electrodeposited NiCr alloy of 20%Ni-80%Cr composition are reported. It is shown that a surface enrichment of K takes place on the surface to a maximum of 8% coverage in the temperature range 400–550°C. The process is initially diffusion-connrolled, with an activation energy of 17 ± 3 kJ/mol. An electrodeposited alloy of approximately 80%Ni-20%Cr composition showed a considerable C-enrichment at the surface in the temperature range 300 to 600°C. A cast alloy of the same composition showed a similar C-enrichment in the temperature range 300 to 455°C. The electrodeposited alloy of 20%Ni-80%Cr showed no such C-enrichment, due to the segregation of both K and Cr to the surface in the range 300 to 600°C and the formation of chromium carbide precipitates.