钙钛矿氧化物La0.65(Ca,Ba)0.35Mn1-xFexOy的磁电阻效应

本工作制备了La065(Ca,Ba)035Mn1-xFexOy(x=0～02)氧化物系列样品。发现在常温附近,含Ba样品的磁阻变化率远比相应含Ca样品的高。在x=0时,样品电阻随温度的变化曲线存在金属—半导体转换峰,随着Fe对Mn的部分替代,该转换峰向低温区移动,当替代量x达到一定程度时,在实验温区观察不到金属—半导体转换峰。磁阻效应在高铁含量时只能在低温观察到。Fe替代Mn对大磁阻效应的影响,可能主要因为:随着Mn3 被Fe3 所替代,样品La065(Ca,Ba)035Mn1-xFexOy中的铁磁相互作用受到抑制,反铁磁相互作用得到加强。     

Boron extended solubility and strengthening potency in rapidly solidified Ni3Al

The strengthening of the intermetallic compound Ni₃Al by boron addition has been investigated via the rapid solidification technique of melt spinning. Using X-ray diffraction, differential thermal analysis and transmission electron microscopy it is shown that by rapid solidification up to 1.5 at.% boron can be held in solution in the aluminide without formation of boride. The lattice parameter results further show that the boron atoms in solution tend to occupy the interstitial sites, generate large lattice strain, and thereby strengthen the Ni₃Al substantially. For example, addition of 1 at.% boron increases the room temperature yield strength of rapidly solidified Ni₃Al from ∼480to∼750MPa. This represents a strengthening potency significantly larger than that of substitutional solutes.     

Sulfides and oxides in Fe−Mn alloys: Part I. Phase relations in Fe−Mn−S−O system

This is a critical review of available equilibrium data between phases involving Fe, Mn, S, and O. Using the Morey-Williamson theorem, and that modified by Darken, the sulfur and oxygen potential diagrams are constructed for the Fe?S?O system involving nine univariant and three invariant equilibria. The solubility of sulfur in wustite-saturated iron is evaluated; the sulfur content of iron in equilibrium with wustite and liquid oxysulfide reaches a maximum of 143 ppm at 1200°C; this is about one half of that corresponding to the solidus of the Fe?S system. An estimate is made of the phase equilibria in the Fe?Mn?S?O quaternary system involving gamma iron and Mn(Fe)O phases. There is a eutectic invariant at ～900°C, and the liquid miscibility gap invariant is estimated to be at ～1225°C. From the expected phase relations and equilibria, it is deduced that if sufficient oxygen and sulfur,i.e. Mn(Fe)O and Mn(Fe)S phases, are present in Fe?Mn alloys, there may be a liquid oxysulfide phase present at temperatures above 900°C, depending on the concentration of manganese in solution. The higher the manganese content in solution, the higher is the temperature above which a liquid phase is present,e.g. for 10 ppm Mn, 900°C and for ～90 pct Mn, ～1225°C. A mechanism is suggested for the precipitation of sulfides and oxysulfides near the surface of steel during heating in an oxidizing atmosphere. In the Appendix by Darken and Gurry, results are given of the melting temperatures of mixtures of wustite and pyrrhotite in equilibrium with iron, from an investigation carried out about thirty years ago.     

An investigation of the lattice parameters of α-(Fe,P) alloys

In this investigation the lattice parameters of α-(Fe, P) alloys are measured very accurately. By comparison with literature it is concluded that the distribution of P-atoms in Fe is not always random and varies with heat treatment.     

Deformation substructure and slip systems in directionally solidified Ni3Al(γ’)-Ni3Nb(δ)

Metallurgical and Materials Transactions A - At strains ?5 x 10-3, the 2 μmγ’ lamellae deformed by dislocation multiplication on those few slip systems with unobstructed paths...     

Effect of WFe substitution on microstructures and electrochemical hydrogen storage properties of LaNi3.70Co0.2-xMn0.30Al0.15Cu0.65(W0.42Fe0.58)x alloys

W0.42Fe0.58 alloy, instead of pure W and Fe, was used to substitute Co in LaNi3.70Co0.2Mn0.30Al0.15Cu0.65 alloy to improve the overall electrochemical properties with the decrement of the cost. Microst...     

Preparation and mechanical properties of bulk ultrafine (W0.5Al0.5)C0.65 with minor Fe binder by reactive hot-pressing

Binderless (W_0.5Al_0.5)C_0.65 produced by reactive hot-pressing (RHP) has high hardness but low bending strength and fracture toughness. In this work, bulk ultrafine (W_0.5Al_0.5)C_0.65 with minor addition of Fe as the binder phase has been prepared by RHP. Rapid synthesis and high densification can be achieved for the (W_0.5Al_0.5)C_0.65 with 0.4–1.0?wt-%Fe by RHP at a relatively low temperature. Pure (W_0.5Al_0.5)C_0.65 without sub-carbide phase or brittle η-type phase can be synthesised due to the fact that the carbon vacancy in (W_0.5Al_0.5)C_y can reach 50%. And thanks to the combined effect of nanoscaled initial powders, low temperature, rapidly reactive sintering and pressure, bulk ultrafine (W_0.5Al_0.5)C_0.65-Fe with a grain size of about 0.2?μm can be obtained by RHP. Thus, with an appropriate amount of Fe (about 0.8?wt-% in this work), the bending strength and fracture toughness of (W_0.5Al_0.5)C_0.65 can be highly improved.     

Al-Fe-Si合金基体及强化相Al12(Fe,X)3Si价电子结构分析

基于EET理论,计算了Al-Fe-Si合金基体与强化相Al12Fe3Si,Al12(Fe,X)3Si的价电子结构,探讨了价电子结构与合金强化、合金相稳定性的关系及合金元素X对强化相稳定性的影响.结果表明:与基体α-Al相比,强化相Al12Fe3Si,Al12(Fe,X)3Si的n(A)值分别增强了248%,208%～231%,位错运动阻力分别增大2.48倍和2.08～2.31倍,从合金相价电子结构参数n(A)看,溶质原子固溶强化作用弱于析出相的强化作用;合金元素V,Cr,W,Mo,Mn的加入改变了Al12FeSi的价电子结构,使其原子状态组数σ(N)增加了2个数量级,使合金相的稳定性增强,进而延缓了粗化速度;V,Cr,W,Mo,Mn对Al12Fe3Si相稳定性影响的强弱顺序为Cr(Mn)→W(Mo)→V.     

Physicochemical properties of coconut husk activated carbon modified by Fe(NO3)3 and Mn(NO3)2

Fe-loaded activated carbon (AC) has high surface acidity and more active sites,while manganese-loaded AC has high oxygen content.Coconut husk AC modified by Fe-...     

Environmental embrittlement in Ll2-ordered (Co,Fe)3 V alloys

Environmental effects on mechanical properties and fracture behavior of Ll₂-ordered (Co, Fe)₃V alloys with compositions (Co₇₈Fe₂₂)₃V and (Co₈₅ Fe₁₅)₃V were studied by tensile test in the strain range of 3.3 × 10⁻⁵ to 3.3 × 10⁻¹s⁻¹ at ambient temperatures. The (Co, Fe)₃V alloys were found to be susceptible to environmental embrittlement. The yield and flow stresses were insensitive to the test environment, while the ductility and ultimate tensile strength decreased according to the sequence of dry oxygen, vacuum, air, and distilled water. The ductility loss was closely associated with intergranular fracture, and the propensity for intergranular fracture increased in the same environmental sequence. Lower strain rate resulted in more intergranular fracture and hence lower ductility. A beneficial effect of grain refinement was observed. All these results suggest that the embrittlement was caused by moisture-induced hydrogen which diffused to grain boundaries, resulting in reduced grain-boundary cohesion and increased intergranular fracture. Grain boundaries were more intrinsically brittle in (Co₈₅Fe₁₅)₃V than in (Co₇₈Fe₂₂)₃V. A possible reason was suggested to explain the grain-boundary brittleness in (Co, Fe)₃V alloys, based on consideration of phase stability.     

Sulfur segregation to grain boundaries in Ni3Al and Ni3(AI,Ti) alloys

The segregation of S to grain boundaries in Ni₃Al and Ni₃(Al, Ti) has been studied using Auger electron spectroscopy. The S concentration at the grain boundaries decreases more slowly with increasing temperature than would be predicted by segregation models based on a single solute binding energy to the grain boundaries. This behavior, which can be interpreted as an increase in the effective solute binding energy for a grain boundary as a function of temperature, is consistent with predictions of a model based on the existence of a spectrum of solute binding energies for grain boundaries. Formerly Professor and Head of the Department of Metallurgical Engineering, Michigan Technological University     

Stacking faults in gamma prime Ni3(Al,Ti) precipitation hardened nickel-base alloys

Most high temperature nickel-base alloys are strengthened by a coherent, orderedγ′ precipitate of Ll₂ structure. Examination of thin foils of these materials after various thermal and/or mechanical treatments has shown the presence of stacking faults in a variety of forms. Stacking faults are developed in conjunction with certain phase reactions, and during plastic deformation. The experimental evidence indicates that stacking fault energy is an important parameter determing the slip mode and strength at low and intermediate temperatures.