Studies on synthesis and microstructure evolution of multiphase in-situ composites based on Mo-Cr-Si system

This paper presents the results on in-situ synthesis of refractory metal-intermetallic composites (RMICs), Mo-16Cr-4Si and Mo-11Cr-9Si (wt.%) multiphase alloys and their characterization. The alloys were prepared from the oxides of molybdenum and chromium by their coreduction with Si as reductant. Exothermic nature of the synthesis reactions resulted in the formation of consolidated composite as a product in a single step. As-reduced alloys were remelted by arc melting and heat treatment was given. The evolution of phases and the microstructure were studied by XRD, SEM, and EDS analysis. The multiphase microstructure consist of the silicide phases (Mo,Cr)₃Si + (Mo,Cr)₅Si₃ for hypereutectic and (Mo,Cr)₃Si phase distributed in bcc matrix comprising essentially a solid solution of (Mo,Cr) for hypo-peritectic composition. Comparative studies of the synthesized alloys were also carried out to the composition, phases, microstructure, hardness and their oxidation behavior.     

Effect of Melting Process on the Microstructure and Mechanical Properties of Fe–7 wt% Al Alloy

This article presents the effect of melting process on chemical composition, microstructure and mechanical properties of Fe–7 wt% Al alloy. The alloy ingot was prepared by air induction melting (AIM), air induction melting with flux cover (AIMFC) and vacuum induction melting (VIM) and cast into 50 mm diameter split cast iron mould. These cast ingots were hot-forged and hot-rolled at 1,373 K to 2 mm thick sheet. Hot-rolled alloys were characterized with respect to chemical composition, microstructure and mechanical properties. Ingots produced by AIM, AIMFC and VIM were free from gas porosity, however AIM ingots exhibited higher concentration of hydrogen as compared to AIMFC and VIM. The recovery of aluminium as well as reduction of oxygen during AIM is very poor as compared to AIMFC and VIM. AIMFC ingots exhibit low level of sulphur as compared to AIM and VIM ingots. The alloys produced by AIMFC and VIM exhibited superior tensile ductility compared to the alloys produced by AIM. The tensile properties of alloys produced by AIMFC are comparable to the alloys produced by VIM.     

Cu含量对Al-Cu合金板材组织及性能的影响

本文通过先熔炼铸锭,后轧制成板材的方法,制备了不同Cu含量的铝铜合金板材,研究了Cu含量变化(1.287%～9.806%)对合金板材显微组织、力学性能和成形性能的影响。结果表明,随着Cu含量的增加,合金中弥散析出的第二相质点逐渐增多;Cu含量在5.654%～9.806%范围时合金的力学性能较为理想,当Cu含量为5.654%时,合金的成形性能最好,此时板材的极限拉伸系数为0.75,制耳率低至3.8%。     

Solubility of nitrogen in liquid nickel and Ni‐Cr alloys under elevated pressure

The present work focuses on the experimental evaluation of the solubility of nitrogen during the melting process in nickel and binary Ni‐Cr alloys under elevated nitrogen partial pressure at 1550°C. In order to estimate the attainable nitrogen concentrations, the solubility of nitrogen in dependence of melt temperature and nitrogen partial pressure has been calculated by using Thermo‐Calc. Thermo‐Calc supported predictions of the achievable nitrogen contents referring to the investigated alloys show good agreement with the experimental data only up to nitrogen partial pressures of 0.1 MPa. The applicability of Sieverts law has been examined for nitrogen partial pressures up to 6 MPa and Ni‐Cr alloys with chromium mass contents of 15, 20, 30, 40 and 50 %. A deviation from Sieverts law was observed for the alloys with chromium mass contents higher than 20 % and a nitrogen partial pressure above 0.1 MPa. The effect of chromium and the nitrogen partial pressure on the solubility of nitrogen is described in terms of the Wagner's first and second order interaction parameters.     

Effect of microstructure on corrosion behavior of low carbon high chrome steel

The two types of microstructure of low carbon and high chromium steel (5Cr) were obtained through the test smelting, rolling and quenching after rolling.Corrosion performance of 5 mass%Cr steel and Q235 steel were researched by means of cyclic wetting and drying corrosion test in 2 mass% NaCl solution.Corrosion behavior and corrosion rust layers were analyzed by OM, SEM, EDS, XRD, cyclic wetting and drying corrosion tester and electrochemical testing. The results show that after the specimens were immersed and etched in 2 mass% NaCl solution for 72h, the different microstructures of 5Cr steel have great influence on the resistance to chloride ion corrosion. B+F+M microstructure of 5Cr steel shows lower corrosion rate than Q235 steel, 5Cr steel with martensite microstructure also shows lower corrosion rate than Q235 steel. Corrosion susceptibility of 5Cr steel with martensite structure is weaker than complex organization.The stratification of chromium oxide, oxyhydroxide, and iron oxide exists in the chromium- containing steel rust layer, in which the Cr enrichment maximum value is 17 mass%, and the lowest is 1 mass%.Lath martensite formed by quenching process makes the corrosion potential rise, ??- FeOOH and ??- FeOOH form. Bainite+ferrite phase and adverse phenomenon of Cr steel may cause the poor corrosion resistance.     

Microstructures and mechanical properties of rapidly solidified CuCr alloys

Rapidly-quenched CuCr alloys have been prepared by melt-spinning and the microstructures and mechanical properties examined as a function of alloy content and subsequent annealing treatment. Mechanical properties have been successfully measured by tensile testing on the ribbon samples and it is shown that this method is more suitable than hardness testing for a proper evaluation of the materials. An alloy containing 2% Cr has been prepared in the totally solid-solution state, whilst a 5% Cr alloy contains large chromium particles distributed uniformly throughout the ribbon and fine-grain-sized CuCr solution. These large chromium particles are deduced to arise by a uniform, primary-solidification mode prior to, and independent of, the nucleation and growth of the copper from the lower ribbon surface. The increased solid solubility obtained allows extensive precipitation and strengthening following ageing: the primary chromium particles play an important role both in strengthening and in restricting grain coarsening.     

Effect of alloying additions on the structure and mechanical properties of Fe<Subscript>3</Subscript>Al -1C intermetallic alloy

Effect of titanium and nickel on the structure and properties of Fe₃Al intermetallic alloy containing about 1.0wt.% C have been investigated. The composition of the alloying element was substituted for Iron. The alloys were prepared by melting commercial grade raw materials iron, aluminum, titanium or nickel in air induction furnace with flux cover (AIMFC). Further these ingots were refined by electroslag refining (ESR) process. These ingots could be successfully hot-worked using conventional hot-forging and hot-rolling techniques. The hot-worked material was sound and free from cracks. ESR hot-rolled alloys were examined using optical microscopy, X-ray diffraction (XRD), scanning electron micrograph (SEM) to understand the microstructure of these alloys. The electron probe micro analysis (EPMA) studies were carried out to determine the matrix and precipitate compositions and to identify the phases present in the alloys. The base alloy and the alloy containing Ni exhibited a two-phase microstructure of Fe₃AlC_0.5 precipitates in Fe₃Al matrix. The alloy containing Ti exhibits three-phase microstructure, the additional phase being TiC precipitate. Ti addition resulted in no improvement in strength at room temperature and at 873 K whereas Ni addition has resulted in greater improvement in strength at room temperature and at 873 K and also improved the creep life significantly from 66 hrs to 111 hrs.     

Effect of vanadium addition on microstructure and properties of Alo.sCro.gFeNi2.s multi-principal alloys

Al0.5Cr0.9FeNi2.5Vx (x =0,0.2,0.4,0.6,0.8,1.0) multi-principal alloys were prepared by vacuum arc melting.The effect of vanadium addition on its microstructure ...     

High Nitrogen Austenitic Stainless Steels Manufactured by Nitrogen Gas Alloying and Adding Nitrided Ferroalloys

 A simple and feasible method for the production of high nitrogen austenitic stainless steels involves nitrogen gas alloying and adding nitrided ferroalloys under normal atmospheric conditions. Alloying by nitrogen gas bubbling in Fe Cr Mn Mo series alloys was carried out in MoSi2 resistance furnace and air induction furnace under normal atmospheric conditions. The results showed that nitrogen alloying could be accelerated by increasing nitrogen gas flow rate, prolonging residence time of bubbles, increasing gas/molten steel interfaces, and decreasing the sulphur and oxygen contents in molten steel. Nitrogen content of 069% in 18Cr18Mn was obtained using air induction furnace by bubbling of nitrogen gas from porous plug. In addition, the nickel free, high nitrogen austenitic stainless steels with sound and compact macrostructure had been produced in the laboratory using vacuum induction furnace and electroslag remelting furnace under nitrogen atmosphere by the addition of nitrided alloy with the maximum nitrogen content of 081%. Pores were observed in the ingots obtained by melting and casting in vacuum induction furnace with the addition of nitrided ferroalloys and under nitrogen atmosphere. After electroslag remelting of the cast ingots, they were all sound and were free of pores. The yield of nitrogen increased with the decrease of melting rate in the ESR process. Due to electroslag remelting under nitrogen atmosphere and the consequential addition of aluminum as deoxidizer to the slag, the loss of manganese decreased obviously. There existed mainly irregular Al2O3 inclusions and MnS inclusions in ESR ingots, and the size of most of the inclusions was less than 5 μm. After homogenization of the hot rolled plate at 1 150 ℃×1 h followed by water quenching, the microstructure consisted of homogeneous austenite.     

不锈钢高铬铁液的脱磷

讨论和分析了高铬铁液氧化脱磷和还原渣系脱磷的特点以及碳的影响，提出高铬铁母液用氧化法脱磷，废钢返回法冶炼不锈钢用还原法脱磷。     

Structure and properties of Cu-Cr alloys subjected to shear under pressure and subsequent heating

The effects of the chromium content (0.75, 9.85, 27%) in Cu-Cr alloys, their initial state, and the heating temperature on their thermal stability after severe plastic deformation are studied by microhardness and electrical resistivity measurements and metallography. The microhardness and electrical resistivity of Cu-Cr alloys are determined as functions of the heating temperature in the range 50–600°C, and microhardness distributions over the diameter of samples differing in the chromium content are plotted. The difference in the strengthening and softening of low- and high-alloy copper-chromium alloys subjected to high-pressure torsion is shown to be related to the initial structure of the material.     

钇含量对CoNiCrAlY合金微观组织的影响

分别采用真空感应熔炼及真空惰气雾化的方法制备了CoNiCrAlY铸锭及粉末,并对其铸态组织进行了研究。结果表明:随着钇含量的增加,钇偏聚程度也逐渐增大,在铸锭铸态组织中存在明显的枝晶组织,钇含量较低时其形貌呈现细长条状。而当钇含量达到1.40%时,铸锭中枝晶开始呈现鱼骨状。另外,研究表明粉末中的显微组织与铸锭中相似,但当钇含量为0.61%时,钇的偏聚不明显。     

Chromium vaporisation from Fe,Cr base alloys used as interconnect in fuel cells

Fe,Cr base alloys protected by Cr₂O₃ base oxidation scales are candidate materials for the metallic interconnect of solid oxide fuel cells (SOFC). The operating temperatures of such cells range between 800 and 950 °C. Cr₂O₃ base oxide scales are necessary since they show sufficient electrical conductivity unlike Al₂O₃ or SiO₂ scales. It is, however, disadvantageous that Cr₂O₃ base oxide scales form the volatile chromium(VI) species CrO₃(g) and CrO₂(OH)₂(g) under operating conditions at the cathode side of SOFC. The electrochemical reduction of these species forming solid Cr(III) oxides at the three‐phase boundary electrolyte/cathode/oxidant leads to a rapid degradation of the electrical properties of SOFC. The study of the chromium vaporisation of different Fe,Cr base alloys under SOFC operating conditions and its reduction by the coating of the alloy surface are, therefore, of topical interest in SOFC development. The commercial alloys Fe18Cr1Al (DIN 1.4742), Fe25Cr0.7Mn0.5Si (AISI 446), Fe20.4Cr5.7A10.3Si (DIN 1.4767) and the oxide dispersion strengthened (ODS) alloy Cr5Fe1Y₂O₃ as well as the model alloy FeCrMn (HNA) were investigated. These alloys form the following oxide scales under operating conditions on the cathode side: iron rich chromium oxides (DIN 1.4742), Cr,Mn spinel (AISI 446 and HNA), Al₂O₃ (DIN 1.4767), and Cr₂O₃ (Cr5Fe1Y₂O₃). The alloys DIN 1.4742 and Cr5Fe1Y₂O₃ were coated with a perovskite layer (25 to 30 μm thickness) made of La_0.90Sr_0.10CrO₃ (LSC) and La_0.8Sr_0.2MnO₃ (LSM) by the use of vacuum plasma spraying (VPS). The vaporisation studies were carried out under non‐equilibrium conditions using the vapour transportation method. The carrier gas consisted of synthetic air with a relative humidity of rH = 60%. Alloy plates of the dimensions 80 · 30 · 5 mm³ with rounded edges and a surface area of 48.5 cm² were used as samples in the vaporisation experiments carried out at 850 and 950 °C. Typical time periods of the vaporisation measurements were between 20 and 350 h. Alloy Cr5Fe1Y₂O₃ with Cr₂O₃ scale showed the highest chromium vaporisation rate among the uncoated samples. The latter showed the following factors for the reduction of the chromium vaporisation rate as compared to Cr5Fe1Y₂O₃ at 850 °C: 23 for AISI 446, 10 for HNA, 5 for DIN 1.4767, and 2 for DIN 1.4742. The different factors are explained by the different oxide scales mentioned above. The alloys with VPS coatings showed a reduction of chromium release by up to a factor of > 100. Investigations of the microstrucure of the perovskite coating revealed its densification during the transpiration experiments which in turn reduces the chromium vaporisation. Moreover, the Cr₂O₃ vaporisation was re‐determined under equilibrium conditions by the vapour transportation method leading to new results.     

热压烧结法制备石墨/铜铬自润滑复合材料的组织性能

将机械合金化所制得的铜铬合金粉末,采用热压烧结法制备成石墨/铜铬复合材料,并着重分析了其组织性能。结果表明,随着铬含量的增加,复合材料的相对密度和电导率逐渐降低,硬度逐渐升高,抗弯强度先升后降且于铬含量为1%时达到最大。其中含1%Cr和2%C复合材料的相对密度为99.82%,电导率为85.57%IACS,硬度为HBS 69.34,抗弯强度为330MPa。与常规冷压烧结法相比,热压烧结法所制备复合材料的晶粒更加细小,增强相分布更加均匀,故其综合性能更加优异。     

Investigation of Pt-Dy co-doping effects on isothermal oxidation behavior of （Co,Ni）-based alloy

A Co32Ni21Cr8Al0.6Y (wt.%) alloy with and without doping 3 wt.% platinum, or co-doping 3 wt.% platinum and 0.1 wt.% dysprosium was produced by arc melting. The hardness of both base alloy and composition-modified alloy was measured by using a Vickers hardness tester. Isothermal oxidation tests at 1000 ℃ in static air atmosphere were conducted to assess the isothermal oxidation behavior of the alloys. The microstructure and composition of the tested alloys before and after oxidation were investigated by means of X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM) equipped with energy dispersive spectroscopy (EDS) and back scatter detector. Results showed that platinum had significant influence on microstructure of the tested alloy by the formation of β-(Ni,Pt)Al phase. Addition of 3 wt.% platinum could slightly increase the hardness of the tested alloy. Platinum accelerated phase transformation of alumina from metastable θ-Al 2 O 3 to stable α-Al 2 O 3 and suppressed the consumption of β-phase. Co-doping both 3 wt.% platinum and 0.1 wt.% dysprosium induced the fastest transformation of θto αalumina and the formation of a fine-grained oxide scales. The most effective reduction of oxidation rate was achieved by the Pt-Dy co-doping effects.     

Studies on Synthesis and Characterization of Mo Based <Emphasis Type="Italic">In Situ</Emphasis> Composite by Silicothermy Co-reduction Process

The results of an in situ synthesis of refractory metal–intermetallic composite (RMIC), Mo-16Cr-4Si (wt pct) multiphase alloy and its characterization, are presented in this study. The alloy was prepared from the oxides of molybdenum and chromium by their co-reduction with Si metal powder as a reductant. The exothermic nature of these reactions resulted in the formation of consolidated composite as a product in a single step. The thermodynamic aspects of exothermic reactions were studied by thermogravimetry/differential thermal analyzer. As-reduced alloys were remelted by arc melting and heat treated to obtain a homogenous microstructure. The evolution of phases and microstructures qA studied by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectrum analysis. The multiphase alloy consisted of Mo₃Si and discontinuous (Mo, Cr) (ss) phase with a volume percentage of 28 pct. The synthesized alloys were characterized with respect to composition, phases, microstructure, hardness, and oxidation behavior.     

Obtaining of copper-chromium alloys for cast electrodes of contact welding

The possibility is considered of obtaining copper-chromium bronze BrKh1 in conditions of open melting and cast electrodes made from this alloy. It is found that the use of Cu-10% Cr base metal prepared by the method of mechanical doping allow one to fabricate the alloy of the specified composition without substantial losses and additional operations in conditions of open melting. The obtained characteristics of properties of cast and thermally treated alloys are not lower than the characteristics of deformed alloys of the same composition. The effect of phosphorus used for deoxidation of the melt on the microstructure and properties of cast bronze BrKh1 is determined.     

铜铬系合金研究和发展现状

铜及铜合金材料广泛应用于电子信息、电气控制、电力传输及轨道交通等领域,随着科技进步和社会发展,对高强度、高导电同时兼备耐热、耐蚀、抗应力松弛等高性能铜合金材料的需求十分迫切。目前,铜铬系合金被认为是综合性能最优异的铜合金之一。本文简要回顾了铜铬系合金的发展历史,总结了其应用现状,重点探讨了稀土元素以及Hf, Ag, Ti, In, Mg, Zr和Sn的添加对铜铬系合金组织及性能的影响规律,并按照单一元素添加、复合元素添加、稀土元素添加的方式,分别讨论了稀土元素以及Ti, Mg, Mg与Si, Ni与Si等对铜铬锆合金组织和性能的影响。通过对文献的整理发现,微量合金元素的添加可明显改善铜铬合金强度与导电匹配性,并提高合金抗软化温度。此外,添加多元微量元素对性能的提升要优于单一元素,若匹配以合适的变形加工和热处理工艺,更易获得理想材料。今后,可以在铜铬锆合金基础上添加稀土元素,找到适宜的添加量以达到在最大化提高强度与抗软化温度的同时最小化影响其导电率。     

Nonmetallic inclusions in a chromium steel intended for the power engineering industry

The behavior of oxygen in the course of manufacturing large steel ingots containing 1.5–20% Cr, the formation of oxides depending on the contents of deoxidizing agents and oxygen, and the composition of the oxide phase in ingots and forgings made of the steel are considered. The steel is manufactured using an arc steel-melting furnace and unit for complex treatment of steel (ASF-ACSPU technology) and the ASF-ACSPU technology and electroslag remelting (ESR). It is shown that the oxide phase composition depends on the contents of strong deoxidizing agents and oxygen and the development of secondary oxidation. Chromium- and manganese-containing spinels are characteristic species of the secondary and tertiary oxides in the chromium steel in the case of deficient aluminum and silicon.     

变温超固相线液相烧结工艺对15Cr系高铬铸铁显微组织及性能的影响

为解决常规定温超固相线液相烧结出现的烧结温度窗口狭窄和产品力学性能对烧结温度波动敏感的问题,采用变温超固相线液相烧结工艺制备了粉末冶金高铬铸铁,研究了变温超固相线液相烧结的高温阶段工艺参数对15Cr系高铬铸铁显微组织和力学性能的影响,并与定温超固相线液相烧结制备的合金进行了对比.研究发现,变温超固相线液相烧结制备的合金...