X-ray photoelectron spectroscopy and electrochemical characterization of a FeCrMoNiRu alloy in 0.5 M HCl solution

The spontaneous passivation behaviour of a Fe-22Cr-3Mo-5Ni alloy system containing small amounts of ruthenium in 0.5 M HCl solution has been investigated by means of immersion tests, electrochemical measurements and the XPS technique. The weight loss and electrochemical measurements show that increasing amounts of ruthenium (up to 0.3 wt%) in Fe-22Cr-3Mo-5Ni substantially improve resistance to attack by hydrochloric acid. The XPS results show that the spontaneously formed passive film on this alloy with ruthenium mainly consists of Cr and Mo oxyhydrox-ides. Molybdenum is incorporated as Mo⁴⁺ and Mo⁶⁺, while neither ruthenium nor nickel are found in the passive film. The effects of ruthenium additions on the spontaneous passivation of FeCrMoNi alloys are discussed.     

Laser surface alloying of ferritic Fe-40Cr alloy with ruthenium

An investigation is made of the laser surface alloying of an experimental ferritic Fe-40Cr alloy with a rutherium powder coating using a continuous wave CO₂ laser. Themicrostructure and corrosion behaviour of the laser surface alloying layer and the Fe-40Cr bulk allyo were examined by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, microhardness, potentiodynamic and corrosion potential measurements. The results of the microstructural examination showed that fine cellular dendrites with a ruthenium content as high as 51.84wt.% were produced by laser surface alloying. The extended solubility of ruthenium in the cellular dendrites resulted in a dramatic increase of the hardness in the laser alloying layer. Potentiodynamic and open circuit corrosion potential measurements indicated that the ruthenium-containing surface layer spontaneously passivated in hydrochloric and sulphuric acid solutions, whereas the bulk Fe—40Cr alloy remained in the active state when exposed in these reducing acid solutions.     

Corrosion properties of Fe-24Cr stainless alloy modified by plasma immersion ion implantation in 0.5 M sulfuric acid solution

Ruthenium (Ru) and mixed Ru-Ti ions were implanted respectively into ferritic Fe-24Cr alloy using the plasma immersion ion implantation (PI³) technique. Potentiodynamic and potential-time response measurements were used to characterize the corrosion behavior of Fe-24Cr alloy exposed to a deaerated sulfuric acid solution. The results showed that the ferritic alloy does not passivate in dilute sulfuric acid. However, plasma-implanted Ru ions can induce spontaneous passivation of the alloy exposed to a sulfuric acid solution. X-ray photoelectron spectroscopy (XPS) analysis showed that Ru is incorporated as Ru⁴⁺ species in the hydrated chromium oxyhydroxide passive film formed on the Ru-implanted Fe-24Cr alloy.     

Caburisation of heat-resistant steels

The effects of alloying additions of silicon, molybdenum, reactive elements (Ti, Y, Ta, Hf, Nb, Zr), and aluminium, in cast, heatresistant steels on their carburisation resistance have been investigated at temperatures of 900 to 1150 °C. Under strongly reducing conditions, where neither silicon nor chromium oxidise, it is found that the alloying additions slow carburisation rates significantly. In the case of molybdenum and reactive elements, the beneficial effect is attributed to diffusional blocking of carbon flux due to the formation of carbide precipitates of these elements. Silicon operates by altering the solubility and diffusivity of carbon in the matrix. Aluminium appeared to exclude carbon almost completely from the alloy, probably by forming a tenacious external oxide scale. Comparison between a wrought and a cast alloy showed that the cast alloy was more resistant to carburisation. Under conditions oxidising to silicon and chromium, but not to iron and nickel, carburisation rates are slower. The most important factor is then alloy silicon content, which controls the formation of an external SiO₂ layer.     

The segregation of elements in high-refractory-content single-crystal nickel-based superalloys

Nickel-based superalloys are complex alloys that contain ten to 15 elements that are widely used in industries where high-temperature strength and corrosion resistance are required. Alloy additions commonly include Cr, Co, W, Ta, Al, Ti, Re, Mo, and, in some alloys, Ru. Each of these additions can affect the as-cast microstructure due to differences in elemental segregation. A better understanding of the effects of typical additions to nickel-based superalloys on the segregation of the elements in the alloy can help identify potential improvements in the processing of current alloys and the development of new alloys. Therefore, the effects of several common alloying additions on solidification segregation and defects were evaluated. In general, an increase in the degree of elemental segregation was observed with increases in each of the elements listed except cobalt and molybdenum. Increased levels of cobalt and molybdenum resulted in reductions in the segregation of most of the elements in the alloy. For more information, contact G.E. Fuchs, University of Florida, Department of Materials Science and Engineering, 116 Rhines Hall, Gainesville, FL 82611, USA; (352) 846-3317; fax (352) 392-7219; e-mail gfuch@mse.ufl.edu.     

The influence of minor alloying elements on the passivation behaviour of iron-chromium alloys in HCl

The influence on the polarization behaviour in 1 M HCl of different alloying elements added in equal atomic concentration to ferritic Fe-13Cr-X and Fe-24Cr-X (X = 6 at.% of Mo, W, V or Si) is investigated using rotating disk electrodes. The presence of these additional elements facilitates passivation and increases the resistance to pitting of the alloys but there is no correlation between their relative effect on passivation current density and on pitting potential. AES depth profiling of Fe-24Cr-6V alloys shows that the ratio V/(Fe + Cr + V) at the surface is lower on samples polarized in the high passive potential region than on a cathodically polarized standard.     

Hochlegierte korrosionsbeständige Stähle für Chemie‐, Energie‐ und Meerestechnik – Rückblick und Ausblick

High‐alloyed corrosion resistant steels for the chemical process industry, power engineering and marine technology – past and future Today's most common high‐alloyed corrosion resistant steels are in their majority characterised by very low contents of carbon and sulphur and, in many cases, by substantial amounts of nitrogen as an alloying constituent. Their broad use in the chemical process industry, power generation and marine technology has become possible when new metallurgical processes for steel making had been introduced in the 1960s. The time before had seen mainly stabilised grades, being highly alloyed with copper in many cases, which have disappeared to a large extent in our days. The superferritic grades (ferritic steels with ≥ 25% chromium) had been the materials of great expectations in the 1970s, but have found a very limited application only in the chemical industry since then, e.g. for the handling of hot concentrated sulphuric acid, due to the high risks of low ductility cracking of these materials at greater wall thickness. These risks can be managed better if the highly alloyed ferritic phase is present in a finely dispersed compound with an austenitic phase where the ferritic part is adding its advantages, higher strength and resistance to stress corrosion cracking, to the duplex compound. This can result in low weight and corresponding cost saving. The application of the corrosion resistant duplex grades will expand further as much as users will better learn the special requirements of manufacturing of these materials and to take advantage of their unique properties. However, the most important alloy developments since the 1960s have been seen in the field of the austenitic stainless steels being highly alloyed with chromium, molybdenum and nitrogen. Especially the austenitic 6% Mo grades as e.g. X1NiCrMoCuN25‐20‐7 – alloy 926 (1.4529) have found many applications in chemical process industry, power generation and marine technology. Higher alloyed grades as e.g. X1NiCrMoCu32‐28‐7 – alloy 31 (1.4562) are excelling in extraordinary resistance to corrosion by acids and pitting attack. In addition today's upper limits of alloying austenitic corrosion resistant grades have been explored with grade X1CrNiMoCu33‐32‐1 – alloy 33 (1.4591) for chromium additions up to about 33% and with grade X1NiCrSi24‐9‐7 – alloy 700 Si (1.4390) for additions of silicon up to about 7%, providing a high corrosion resistance mainly in oxidising acids. When considering the prospects of further development of the corrosion resistant duplex grades the ferritic phase within these materials is both offering chances and setting limits. The high‐alloyed austenitic corrosion resistant steels have a potential being unexplored so far in the alloy range where molybdenum and nitrogen are becoming more prominent compared to the chromium content.     

合金元素对Cu-Ag合金组织、力学性能和电学性能的影响

采用冷变形及中间热处理方法制备了具有双相纤维复合组织的Cu-Ag合金，研究了成分与组织，性能的关系，随着变形程度的增加，合金强度上升而电导率下降，合金中Ag含量由6％增加至24％时，铸态组织中第二相数量明显增多，变形后能够形成更多的Ag纤维复合相，因而合金强度明显上升，在Cu-6%Ag中添加1％Cr元素可以使合金基体得到进一步强化并在一定程度上细化了Ag纤维相，也可使合金度得到显著改善，在Cu－6%Ag-1%Cr合金中添加微量稀土元素可使Ag纤维分布更为弥散，因而使合金在不降低导电性的同时增加强度，尤其在高强度范围内这种作用更为显著。     

机械合金化Fe-40Al合金粉末工艺研究

以Fe粉、Al粉末为对象,采用机械合金化制备Fe-40Al合金复合粉末,研究球磨工艺参数对Fe-40Al合金粉末形貌及组织结构的影响规律,为机械合金化制备适合冷喷涂用Fe-40Al合金粉末提供最佳的工艺参数。研究结果表明,球磨后的Fe-40Al合金粉末具有独特的层状组织结构,随着球磨时间的延长,Fe-40Al合金粉末的平均粒径不断减小,由于Fe、Al相互扩散作用加强,粉末内部的层状结构不断细化而消失;随着球料比增加,机械合金化效率显著提高,相同球磨时间内Fe-40Al合金粉末粒径减小的幅度显著增大,同时粉末内部合金化过程加剧,导致层状结构快速消失。     

含氮Fe-Mn合金的阻尼性能和抗腐蚀性能

通过内耗检测技术研究了氮对Fe-14．1Mn和Fe-16．5Mn合金阻尼性能及对Fe-Mn系合金相组成和抗腐蚀性能的影响。结果表明：Fe-14．1Mn比Fe-16．5Mn合金具有更高的阻尼性能;合金中加入质量分数为0．2%的氮,两种合金的阻尼性能略有改变,合金在固溶处理时,发生了γ-ε转变,转变生成的马氏体越多,合金的阻尼性能越好;并且含氮合金在1mol/L硫酸水溶液中的抗腐蚀性能提高2倍。     

The pitting corrosion of sputtered Fe base alloy films

Predominantly single phase Fe base alloy films were prepared by a DC sputtering method. The compositions of the alloy films, as determined by Auger electron spectroscopy (AES) were Fe-7 at% Cr and Fe-18 at% Cr, Fe-11 at% W and Fe-19 at% W, Fe-9, −13 and −27 at% Ta. The pitting potential of the sputtered alloys determined in chloride solutions was found to be strongly dependent on the nature and the concentration of the alloying element. The pitting potential of sputtered Fe-18 at% Cr and Fe-27 at% Ta alloy films were approximately 0.9 V higher than that of bulk Fe and 0.6 V higher than that of Fe-19 at% W alloy film. A very good correlation was found between the pitting potential of Fe alloy films and the solubility of an alloying element oxide in acidic solutions with a pH corresponding to that within the stable pits of pure Fe (pH = 2). The pitting potential of the Fe alloy was found to increase with a decrease in the solubility of the alloying element oxide in acidic solutions. The pitting potentials of the sputtered Fe-7 at% Cr and Fe-18 at% Cr alloy films were were significantly higher than those of the bulk materials with the same composition. The higher pitting potentials of these alloy films are tentatively attributed to the presence of very fine particles of the oxide phase that are homogeneously distributed in the sputtered alloys.     

What are the Effects of Residual Elements in Maraging Steels

The present state of knowledge on the compositional limits and the alloy purity requirements for maraging steels is reviewed. The effects of the principal alloying elements—nickel, cobalt, molybdenum, and titanium—on strengthening are described. The desired composition of the residual elements such as silicon, manganese, aluminum, and zirconium is discussed. In addition, the effects of interstitials and subversive elements on the strength of the alloys are discussed.     

Formation of Fe-19 wt%Cr-9 wt%Ni Nanocrystalline Alloy with Excellent Corrosion Resistance: Phase Transition and Microstructure

In this paper, microstructure characteristics and phase transitions of Fe-19 wt%Cr-9 wt%Ni nanocrystalline alloy are comprehensively studied during the mechanical alloying and hot pressing sintering processes. Corrosion resistance of the sintered Fe-19 wt%Cr-9 wt%Ni nanocrystalline alloy samples is further analyzed. During the mechanical alloying process, Fe-19 wt%Cr-9 wt%Ni nanocrystalline alloy powders mainly composed of metastable ferrite phase are obtained after mechanical alloying for 8, 16 and 24 h, respectively. In the subsequent hot pressing sintering process, the phase transitions(from ferrite to austenite) occur from 650 to 750 °C for Fe-19 wt%Cr-9 wt%Ni alloy powders milled for 24 h. When the sintering temperature is raised to 1050 °C for 1 h, the ferrite phase has transformed into austenite phase completely, and the obtained grain size of sintered Fe-19 wt%Cr-9 wt%Ni alloy is around 40 nm. Electrochemistry test of the sintered Fe-19 wt%Cr-9 wt%Ni alloy has been operated in 0.5 mol L~(-1) H_2SO_4 solution to show the corrosion resistance properties. Results show that the sintered Fe-19 wt%Cr-9 wt%Ni alloy exhibits excellent corrosion resistance, which is proved by higher self-corrosion potential, lower self-corrosion current density and larger capacitive reactance, compared with that of commercial 304 stainless steel.     

Microstructure and mechanical performance of a secondary cast aluminium piston alloy with minor element additions

The effect of individual and combined minor element additions (Sr, Sb, Mn, Cr and Al-5Ti-1B grain refiner) on microstructure and mechanical performance of a secondary cast aluminium piston alloy, with 1 wt-% Fe was investigated. It was observed that addition of Cr of up to 1% was better than a 0.53%Mn addition in improving tensile strength, impact energy and percent elongation of the alloy. The high mechanical performance recorded with addition of 1%Cr alloy was attributed to the significant reduction in porosity levels compared to all other minor element additions. It also resulted in a microstructure with fine compact intermetallic compounds. Other element additions also resulted in improved mechanical properties with 0.53%Mn performing better than 0.3%Mn + 0.2%Cr. Marginal improvements in mechanical performance were recorded with addition of 0.02%Sr (or 0.05%) and 0.02%Sb individually or in combination with 0.53%Mn. This was attributed to general increase in porosity and volume fraction of intermetallics.     

Zn-Al-Sr-Cu合金在NaOH溶液中的腐蚀行为

为研究合金元素Sr对ZA35合金耐腐蚀性能的影响,采用电化学工作站测试ZA35和ZA350.15Sr两种合金在20,40,60℃NaOH溶液中的开路电位和极化曲线,结合合金组织和表面腐蚀形貌,探讨了Sr对ZA35合金电化学腐蚀性能的作用规律.结果表明:两种合金的开路电位均随NaOH溶液温度升高而降低,相同温度下,ZA3...     

合金化阻燃镁合金的研究进展

综述了合金化阻燃镁合金的研究进展和现状，重点介绍了Be、Ca、RE、Zn等合金阻燃元素以及复合添加阻燃元素对镁合金的阻燃性、组织和力学性能的影响，指出了开发合金化阻燃镁合金存在的问题及展望。最终得出结论；复合添加2种或3种以上阻燃元素是舍金化阻燃镁合金的未来发展趋势。     

Development of Fe−12%Cr mechanical-alloyed nano-sized ODS heat-resistant ferritic alloys

The development of mechanical alloying (MA)-oxide dispersion strengthened (ODS) heat-resistant ferritic alloys of Fe?12%Cr with W, Ti and Y₂0₃ additions were carried out. Fe?12%Cr alloys with 3%W, 0.4%Ti and 0.25% Y₂0₃ additions showed a much finer and more uniform dispersion of oxide particles among the alloy system studied. Nano-sized oxides dispersed in the alloys suppress the grain growth during annealing at a high temperature and resulted in the remarkable improvement of creep strength. The oxide phase was identified as a complex oxide type of Y?Ti?O.     

Effect of aluminum and titanium additions to Fe-21%Cr-32%Ni on the oxidation behavior in an impure helium atmosphere at high temperatures

The effects of aluminum and titanium additions on the oxidation and carburization behavior of Fe-21%Cr-32%Ni in an HTGR-simulated impure helium environment at high temperatures were studied. Intragranular and intergranular oxidation were the principal forms of degradation, with the effect of aluminum being major and that of titanium relatively minor. As the aluminum content in the alloy increased, the mode of degradation changed from both uniform intragranular and intergranular oxidation, to one involving only uniform intragranular oxidation. This transition in the degradation mode was explained by the volume changes in the alloy resulting from a combination of both a volume increase due to internal-oxide precipitation and shrinkage due to the condensation of vacancies formed as a result of selective removal of alloying elements to the external scale. Intergranular oxidation was observed only when the resultant volume change was due to shrinkage. When the resultant volume change was positive, only uniform intragranular oxidation occurred and at the same time, extensive carburization was observed probably due to the deterioration of the surface scale caused by the deformation of the alloy substrate. A small amount of titanium, ca. 0.4%, appeared to modify the phenomena caused by aluminum additions, e.g., causing increased intergranular penetration for the 0.4% Al alloy and internal-to-external transition for the 2.1% Al alloy. External scale formation without any internal oxidation was observed for alloys containing more than 1.9% Al at 973 and 1023 K and for an alloy containing 2.1% Al and 0.4% Ti at 1073 and 1123 K. In these cases, carburization was almost completely eliminated.     

Effects of temperature variations on oxidation of iron–20% chromium alloys at 1200 K in Ar–20% O2- Cl2 gas mixtures

Oxidation of an Fe-20%Cr alloy has been investigated at 1200 K in gas mixtures of Ar-20%O₂ with additions of 0.05 to 1.0%Cl₂ with temperature cycles to room temperature at 12 h intervals. The metals experience accelerated oxidation which proceeds via a chloride vapor transport mechanism and produces a porous oxide scale. The temperature cycles trigger accelerated oxidation in gas mixtures which would not produce accelerated oxidation under isothermal conditions. The results indicate that chlorine and temperature cycles have a synergistic effect on the oxidation rates.     

The model of deformation-induced segregation near a moving grain boundary in the Fe-Cr-Ni alloy

A model is proposed of diffusion-induced segregation at a moving grain boundary in a three-component alloy upon severe plastic deformation with allowance for generation and absorption of point defects and their mutual recombination. Redistribution of atoms of alloying elements and formation of near-boundary segregates during severe plastic deformation in stable austenitic alloys of the Fe-12Cr-30Ni type is studied. It has been shown by numerically solving an appropriate set of equations that the motion of a grain boundary leads to the formation of a deformation-induced segregation with an asymmetrical profile of the component concentrations. The boundary is being enriched with nickel and depleted of the other components.