Magnetism and solid solution effects in NiAl (40% Al) alloys

The solid solution effects of ternary additions of transition elements in intermetallic Ni–40% Al were investigated by both experimental studies and theoretical calculations. Co solute atoms when sitting at Ni sublattice sites do not affect the lattice parameter and hardening behavior of Ni–40Al. On the other hand, Fe, Mn, and Cr solutes, which are mainly on Al sublattice sites, substantially expand the lattice parameter and produce an unusual solid solution softening effect. First-principles calculations predict that these solute atoms with large unfilled d-band electrons develop large magnetic moments and effectively expand the lattice parameter when occupying Al sublattice sites. The theoretical predictions were verified by both electron loss-energy spectroscopy (EELS) analyses and magnetic susceptibility measurements. The observed softening behavior can be explained quantitatively by the replacement of Ni anti-site defects (potent hardeners) by Fe, Mn, and Cr anti-site defects with smaller atom size mismatch between solute and Al atoms. This study has led to the identification of magnetic interaction as an important physical parameter affecting the solid solution hardening in intermetallic alloys containing transition elements.     

A new resource-saving,low chromium and low nickel duplex stainless steel 15Cr–xAl–2Ni–yMn

A new family of resource-saving, low Cr and low Ni duplex stainless steels, with compositions of 15Cr–xAl–2Ni–yMn (x = 1.2–2.8, y = 8–12, wt.%) has been developed by examining the effect of Al and Mn on microstructure, mechanical property and corrosion property. The results show that 15Cr–1.2Al–2.0Ni–8Mn and 15Cr–2.0Al–2.0Ni–10Mn alloys have a balanced ferrite–austenite relation and that 15Cr–2.8Al–2.0Ni–12Mn alloy has a primary ferrite phase structure. The ferrite volume fraction increases with the solution treatment temperature and Al content while decreases with Mn content. No precipitate was found after solution-treated at 750 °C for 30 min. 15Cr–1.2Al–2.0Ni–8Mn alloy has a strong strain hardening effect, and 15Cr–2.0Al–2.0Ni–10Mn alloy has a good TRIP effect. Both of the 15Cr–1.2Al–2.0Ni–8Mn and 15Cr–2.0Al–2.0Ni–10Mn alloys have excellent impact toughness at low temperature with the impact energy higher than 125 J at −40 °C. The pitting corrosions always occur in austenite phase. Among the designed alloys, 15Cr–1.2Al–2.0Ni–8Mn and 15Cr–2.0Al–2.0Ni–10Mn are found to be excellent alloys with a proper phase proportion and a better combination of superior mechanical property and good pitting corrosion resistance.     

Effect of Cr atoms on the formation of double kinks in screw dislocations in Fe and its correlation with solute hardening and softening in Fe–Cr alloys

In this work, we employed atomistic simulations to study the formation of a double kink (DK) on a screw dislocation in bcc Fe and to investigate how the presence of Cr affects it, using one of the most recent and reliable interatomic potentials for Fe and Fe–Cr systems (i.e. from Refs. [G.J. Ackland, M.I. Mendelev, D.J. Srolovitz, S. Han, A.V. Barashev, J. Phys.: Condens. Mat. 16 (2004) 1, P. Olsson, J. Wallenius, C. Domain, K. Nordlund, L. Malerba, Phys. Rev. B 72 (2005) 214119]). The formation energy of a DK of different lengths and structures, as well as the formation energies of each single kink and the interaction energies between them, have been obtained by performing large scale atomistic simulations and compared with the results obtained from elasticity theory. We show that the presence of Cr atoms, particularly Cr–Cr pairs, affects, sometimes significantly, the formation energy of DKs. The obtained results suggest a strong dependence of the effect of solute Cr atoms on dislocation motion in Fe–Cr alloys, depending on the actual Cr distribution, which in turn depends strongly on concentration and temperature. A possible framework to understand solute softening and hardening experimentally observed in Fe–Cr alloys is accordingly discussed.     

A first report on fracture toughness ofbcc iron alloys as influenced by solutes: opposite effects of silicon and cobalt

The effect of solutes on resistance to fracture of body centred cubic iron single-phase solid-solution alloys has been investigated. TheJ-integral method has been used for the measurement of ductile fracture toughness. TheJ _IC values so determined quantitatively indicate the extent of degradation in fracture toughness due to the addition of hardening solute silicon. Cobalt addition results in alloy softening. The measuredJ _IC values clearly demonstrate the toughening effect of cobalt addition as a solute, which result renders the case of Fe-Co solid-solution alloys interesting.     

A study on the nickel-rich ternary Ti–Ni–Al shape memory alloys

The transformation sequence and hardening effects of 400 °C aged Ti47.5Ni50.65Al1.85 and Ti49.5Ni50.13Al0.37 shape memory alloys have been investigated by electrical resistivity tests, internal friction measurements, hardness tests and TEM observations. Both solution hardening and precipitation hardening are found to occur in these alloys. The hardening effects of Ti47.5Ni50.65Al1.85 alloy are obvious and much higher than those of Ti49.5Ni50.13Al0.37 alloy due to the former having the larger Ni/Ti ratio and a higher Al solute content in its matrix. The transformation sequence of 400 °C aged Ti47.5Ni50.65Al1.85 alloy shows B2↔R-phase only for an ageing time of more than 10 h and that of 400°C aged Ti49.5Ni50.13Al0.37 alloy shows the sequence B2↔R-phase↔B19′ or B2↔R-phase with different ageing times. All of these characteristics are associated with Ti11Ni14 precipitates during the ageing process. These aged Ti–Ni–Al alloys exhibit very good shape memory effects, in which the maximal shape recovery occurs at the peak of hardness. This revised version was published online in November 2006 with corrections to the Cover Date.     

Experimental analysis of the columnar-to-equiaxed transition in directionally solidified Al–Ni and Al–Sn alloys

Experiments were carried out to investigate the columnar-to-equiaxed transition (CET) during the upward vertical directional solidification of hypoeutectic Al–Ni and Al–Sn alloys. For the growth conditions examined both the thermal and solutal profiles inside the mushy zone and in the overlying melt ahead of the dendrite tips are expected to be stable, since the solute enrichment increases the melt density, and no solute movement induced by convection will affect the CET. From the experimental thermal profiles, tip cooling rates, tip growth rates and thermal gradients have been determined. It was found that the CET occurs for a critical value of cooling rate, with the columnar growth prevailing throughout the casting for cooling rates higher than such critical value, which for a particular binary alloy system is independent of the solute concentration in the hypoeutectic range. For Al–Sn and Al–Ni alloys the critical cooling rates were found to be 0.30 K/s and 0.16 K/s, respectively.     

Long-term leaching from MSWI air-pollution-control residues: leaching characterization and modeling

Long-term leaching of Ca, Fe, Mg, K, Na, S, Al, As, Ba, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Zn, Mo, Sb, Si, Sn, Sr, Ti, V, P, Cl, and dissolved organic carbon from two different municipal solid waste incineration (MSWI) air-pollution-control residues was monitored during 24 months of column percolation experiments; liquid-to-solid (L/S) ratios of 200-250L/kg corresponding to more than 10,000 years in a conventional landfill were reached. Less than 2% of the initially present As, Cu, Pb, Zn, Cr, and Sb had leached during the course of the experiments. Concentrations of Cd, Fe, Mg, Hg, Mn, Ni, Co, Sn, Ti, and P were generally bellow 1microg/L; overall less than 1% of their mass leached. Column leaching data were further used in a two-step geochemical modeling in PHREEQC in order to (i) identify solubility controlling minerals and (ii) evaluate their interactions in a water-percolated column system over L/S of 250L/kg. Adequate predictions of pH, alkalinity, and the leaching of Ca, S, Al, Si, Ba, and Zn were obtained in a simultaneous calculation. Also, it was suggested that removal of Ca and S together with depletion of several minerals apparently caused dissolution of ettringite-like phases. In turn, significant increase in leaching of oxyanions (especially Sb and Cr) was observed at late stage of leaching experiments.     

Density functional theory study of alloy element interstitials in Al

Density Functional Theory calculations were used to study Mg, Si, Cr, Mn, Fe, Co, Ni, and Cu interstitial configurations in Al. Energies of these elements in (100) dumbbell and octahedral configurations were determined. Results show that it is energetically favourable for metal alloying element atoms to replace Al selfinterstitials if the alloying atoms are smaller than the Al atoms, as expected. The system energy can thus be decreased by up to 2 eV. The difference between the energies of (100) dumbbell and octahedral configurations is only a few tenth eV for the alloys with metallic alloying elements. For Si, the difference can be up to 0.9 eV. This exceptional behavior of Si is most likely due to its angularly dependent bonding characteristics. Short ab-initio Molecular Dynamics simulations were performed on Mg and Si interstitials to allow these systems to evolve into different interstitial configurations rather than just the (100) dumbbell and octahedral configurations. For Si an alternative configuration with tetrahedral-like coordination was found. Consequences of the calculation results for radiation-induced segregation are discussed.     

Large,low-field and reversible magnetostrictive effect in MnCoSi-based metamagnet at room temperature

TiNiSi-type MnCoSi-based alloys show large magnetostriction during the magnetic-field-induced meta-magnetic transition.However,the high critical field required to drive the transition directly hinders their potential applications.In this work,we systematically investigate the tricritical behavior and mag-netostrictive effect in substituted MnCoSi alloys.Replacing Si with Sb or In,Co with Fe or Cu,and Mn with Co,which can simultaneously reduce the critical field and the temperature of tricritical point,are explored.Among the substituted MnCoSi alloys,Mn0.983Co1.017Si displays a temperature of a tricritical point of 250 K and a room-temperature critical field of 0.60 T,which is the lowest up to now.Profited from these optimizations,a large reversible magnetostrictive effect under low field is successfully realized at room temperature.In a field of 1 T,the magnetostriction of Mn0.983Co1.017Si alloy is close to 1000 ppm.Besides,a strong relation between critical field and valence electron concentration is revealed in the transition-metal-substituted MnCoSi alloys.Our work greatly enhances the low-field magnetostrictive performance of MnCoSi-based alloys and make them be of interest in potential applications.     

Atomic Structures of Precipitates in Al–Mg–Si Alloys with Small Additions of Other Elements

In Al–Mg–Si alloys, additions of only a few weight percent of Mg and Si enable formation of hardening precipitates during heat treatment. The precipitation is complex and is influenced by chemical compositions and thermo‐mechanical treatment. Structural analysis at the atomic scale has played an important role for understanding the Al–Mg–Si system. This review paper gives a summary of the influence of elements on the precipitate structures of Al–Mg–Si alloys at the atomic scale. The structures are modified by small additions of different elements, but all the encountered precipitates are structurally connected with the Si network, except for the main hardening phase which exhibit a partially discontinuous Si network. The influence of the selected elements (Li, Cu, Zn, Ge, Ag, Ni, Co, and Au) is discussed in detail.

     

代位原子在Fe3Al亚点阵中的占位与合金的塑性

采用中子衍射法测定了Ｃｒ、Ｍｏ、Ｔｉ、Ｎｉ、Ｍｎ、Ｓｉ等代位原子在ＤＯ３结构Ｆｅ３Ａｌ亚点阵中的原子占位，并从解离能角度探讨了原子对之间的相互作用及合金室温塑性的影响，结果表明：Ｃｒ、ＭＯ、Ｔｉ都占据了Ａｌ原子的次近邻位置，替代Ｆｅ原子；Ｎｉ、Ｍｎ占据Ａｌ原子的最近邻位置，（Ｓｉ＋Ａ）当量成分以内的Ｓｉ原子替代占据Ａｌ原子的位置，由于Ａｌ－Ｃｒ原子对的结合能低于Ｆｅ－Ａｌ，ＡＬ－Ｍｏ用Ａｌ－Ｔｉ对     

1Cr18Ni9不锈钢高温单轴时相关棘轮行为研究

在室温、250℃、500℃和650℃四种温度下对1Cr18Ni9不锈钢材料的单轴应变循环特性及其时相关棘轮行为进行了实验研究,以讨论不同加载速率、加载波形和峰值应力保持时间对材料棘轮行为的影响。实验结果表明:在室温下,材料呈现出弱的循环软化特性和渐进型棘轮变形行为,并对加载速率和峰值应力保持时间具有强烈依赖性;在250℃、650℃下,因材料的循环硬化加快而使其棘轮行为较快趋于安定,但棘轮变形大小仍一定程度依赖于加载速率和保持时间;在500℃温度下则由于动态应变时效的影响没有明显的棘轮行为发生。研究得到一些有助于后续建立时相关本构模型的结论。     

Enhancement of mechanical properties of Al–Mg–Si alloys by means of manganese dispersoids

Abstract

The effects of Mn dispersoids on the enhancement of mechanical properties in Al–Mg–Si(–Mn) alloys have been studied to develop a new high Mn alloy which does not need an aging heat treatment after a shaping process (i.e. extrusion process). By adding Mn to Al–Mg–Si alloys, sphere- or rod shaped Mn dispersoids of a size ranging from 0·05 to 0·5 μm are formed by the use of proper heat treatments. The as extruded alloys containing 1·0 wt-%Mn are measured to have higher tensile properties with good ductility, as compared with those of the commercial Al alloy 6N01 (Al–0·69Mg–0·79Si–0·48Cu–0·27Zn–0·37Mn–0·3Cr– 0·11Ti, wt-%). These phenomena are obtained from the dispersion hardening effect and homogeneous deformation by Mn dispersoid particles acting as obstacles to dislocation movement. Comparing the fatigue crack growth behaviour between the high Mn alloys and the commercial 6N01 alloy in the as forged condition, high Mn alloys are shown to have higher fatigue crack growth resistance and show a more tortuous crack path. This result can be explained by the increasing energy absorption through crack deflections and tortuous crack paths by the Mn dispersoids.     

Alloying element additions to Ni3Al: Site preferences and effects on elastic properties from first-principles calculations

First-principles calculations were performed to study the effects of alloying elements (Mo, Re, Ta, W, Ti, Co, Nb, Ru, Cr, Y) on the elastic properties of Ni₃Al. The site preferences of the alloying elements in Ni3Al at different temperature and concentrations were predicted. The influence of alloying elements on the lattice parameters of Ni₃Al were calculated and compared with the values fitted from experimental data. The effects of alloying elements on the elastic constants of Ni₃Al were present. The directional shear and Young’s moduli for single-crystal Ni₃Al alloys with alloying elements were estimated. The bulk, shear, and Young’s moduli of polycrystalline alloys were obtained. It is found that all the alloying elements occupy Al sites except Ru and Co, which may occupy both sites depending on concentration and temperature. All the elements increase shear and Young’s moduli of single-crystal Ni₃Al in all orientations except Cr, Co and Y. All the elements increase both bulk and shear moduli of polycrystalline Ni₃Al except Co and Y. The solute atoms with higher bulk modulus tend higher bulk modulus of Ni₃Al alloys, and the bulk modulus is related to the mole volume either.     

Aging behaviour of cobalt free chromium containing maraging steels

Abstract

This paper reports an investigation of the aging behaviour of two Co free Cr containing maraging steels (Fe–1·0Si–11·2Cr–1·3Mo–9·1Ni–1·2Al–1·0Ti and Fe–0·8Si–17·2Cr–6·1Ni–0·4Al–0·9Ti, all at.-%), using hardness measurements, electron microscopy of replicas and thin foils, atom probe field ion microscopy (APFIM), and thermochemical calculations. Two different families of intermetallic phases (Ti₆Si₇Ni₁₆G phase and η Ni₃Ti) have been found to contribute to age hardening. The composition and morphology of these precipitates were studied in deformed and undeformed alloys after aging at 420–570°C for various times. In addition, reverted austenite has been found in the aged structure. Results obtained using APFIM are compared with equilibrium thermodynamic calculations and previous APFIM studies of conventional Cr free low Al and Si maraging steels having higher Mo contents.

MST/1558     

Mechanical and chemical properties of Ni3Si and Ni3(Si,Ti) alloys multiphased by chromium addition

Abstract

The alloying behaviour and microstructure of Ni–Si–Cr ternary and Ni–Si–Ti–Cr quaternary alloys were first characterised by optical microscopy, X-ray diffraction, and scanning electron microscopy with electron probe analysis. The microstructures of the Ni–Si–Cr ternary alloys consisted of large dispersed Ni₅Si₂ phase and finely precipitated Ni₃Si phase in nickel solid solution, while the Ni–Si–Ti–Cr quaternary alloys consisted of finely precipitated Ni₃(Si,Ti) phase and nickel solid solution. Then, the high temperature mechanical properties, bend strength, and oxidation and corrosion properties of the alloys were investigated. The Ni–Si–Cr ternary alloys showed significant strengthening over a wide range of temperatures, and also large compressive plastic deformation at high temperatures. The strength and fracture toughness at ambient temperatures were correlated with the volume fraction of Ni₅Si₂ phase. The Ni–Si–Ti–Cr quaternary alloys did not show increased yield strength, but exhibited improved tensile ductility and plasticity over a wide range of temperatures. Both Ni–Si–Cr ternary and Ni–Si–Ti–Cr quaternary alloys showed substantially improved oxidation resistance in air at 1173 K, compared with Ni₃Si and Ni₃(Si,Ti) alloys. Also, the Ni–Si–Cr ternary and Ni–Si–Ti–Cr quaternary alloys showed corrosion resistance comparable to that of the Ni₃Si and Ni₃(Si,Ti) alloys.     

Effects of Cr,Mn, Si,Cu and Zr on microstructure and mechanical properties of high carbon Fe–16Al alloy

Abstract

Effects of alloying elements Cr, Mn, Si, Cu and Zr on the microstructure and mechanical properties of Fe₃Al (Fe–16Al) based alloy containing ～0·5 wt-%C have been investigated. Six alloys were prepared by a combination of air induction melting with flux cover and electroslag refining (ESR). ESR ingots were hot forged and hot rolled at 1373 K and were further characterised with respect to microstructure and mechanical properties. The base alloy and the alloys containing Cr, Mn, Si and Cu exhibit a two phase microstructure of Fe₃AlC_0·5 precipitates in Fe₃Al matrix whereas the alloy containing Zr exhibits a three phase microstructure, the additional phase being Zr rich carbide precipitates. Cr and Mn have high solubility in Fe₃AlC_0·5 precipitates as compared to Fe₃Al matrix whereas Cu and Si have very high solubility in Fe₃Al matrix compared to Fe₃AlC_0·5 precipitate and Zr has very low solubility in both Fe₃Al matrix and Fe₃AlC_0·5 precipitate. No significant improvement in room and high temperature (at 873 K) strengths was observed by addition of these alloying elements. Furthermore, it was observed that addition of these alloying elements has resulted in poor room and high temperature ductility. Addition of Cr, Mn, Si and Cu has resulted in marginal improvement in creep life, whereas Zr improved the creep life significantly from 22·3 to 117 h.     

Assessment of trace element levels in Rhododendron honeys of Black Sea Region, Turkey

Rhododendron and multi-flower honeys obtained from Black Sea Region of Turkey (12 Rhododendron and 8 multi-flower honeys) were studied to determine the presence of the 14 trace elements such as Cu, Cd, Pb, Co, Cr, Ni, Al, Se, Zn, Mn, Fe, K, Ca and Mg. Trace element determination was performed by atomic absorption spectrometry (AAS) after microwave digestion. The results revealed that Rhododendron honeys exhibited higher concentrations of Cu, Co, Cr, Ni, Se, Zn, Ca and Mg but lower concentrations of Al, Mn, Fe and K than in the multi-flower honeys. Trace element levels in analyzed honey samples were generally lower than literature values.     

Microstructure of In-Situ composites

In this paper, the results of several years of research work by the authors on the microstructure of In-Situ composites are reviewed. Alloy systems investigated are the fibrous Al? Ni and cobalt-base superalloy Co? Cr? C, and the lamellar Al? Cu and Co? W. The effect of solidification variables and off-eutectic compositions on the micro-structure of Al? Ni Co? W and Al? Cu systems was studied. The influence of heat flow direction on the microstructure of Al? Ni was examined. Post solidification isothermal annealing was performed for Al? Cu and Co? Cr? C alloy and thermal cycling regimes were imposed on the Co? Cr? C alloy and the microstructure variations were examined. Computer simulation of directional, solidification to study the heat flow pattern in the metal and mould was also performed. It was found that low growth rates, high temperature gradients, eutectic composition and pure materials favor a planar solidification front and an aligned structure. Increasing the growth rate resulted in finer structures. The thermal stability of In-Situ composites was found to be reasonably good due to the strong interfacial bond between matrix and reinforcement in this class of composites.     

Fe基非晶纳米晶喷涂粉末的制备及性能

利用氩气雾化方法制备出了Fe48Cr15Ni15Si5.8B2.7Mo6W4Al2Co非晶合金粉末,利用扫描电镜、透射电镜、X射线衍射仪、粒度分析仪和差示扫描量热仪对粉末的微观结构、相组成、粒径分布以及热稳定性进行了分析。研究表明,所制备的粉末结构为非晶纳米晶结构,纳米晶的尺寸约为20～40nm;粉末颗粒形貌呈球形或椭球形,流动性很好。差热试验表明,粉末具有很强的非晶形成能力并且热稳定性非常好;筛分出来的小于47!m目的粉末粒度正态分布比较窄。