A. Momeni K. Dehghani
材料科学技术（英文）
In this research, aging treatments at temperatures of 800 and 900°C for different aging time of 5{60 min were conducted on solution treated as well as hot worked samples of 2205 dual phase stainless steel. The effect of aging treatment on precipitation of intermetallic phases was investigated in undeformed specimens and those subjected to hot deformation with different strain rates of 0.001−1 s−1. It was found that σ precipitation increased by hot working. It was also concluded that the volume fraction of phase increased with deformation temperature and decreased with strain rate. The precipitation of intermetallic phases (i.e. σ and χ) was analyzed by an Avrami-type kinetics equation of %(σ+χ)=A(1-exp(-ktn)) and the values of n and ln k were estimated for different thermomechanical regimes. The values of n were assessed to increase from 0.4 to 1 with strain rate in the studied range. Otherwise, It was also understood that ln k decreased with strain rate. Microstructural observations by means of optical microscopy and scanning electron microscopy showed that σ particles mostly nucleated at the ferrite-austenite interfaces. But no sign of Â-phase could be seen. This fortified the idea of certain literature that Â-phase always forms at early stages of aging and consumes through the precipitation of σ.
关键词:
Duplex stainless steel
,
Hot Working
,
Sigma Phase
,
Secondary Phase
A. Momeni K. Dehghani
材料科学技术（英文）
In this research, aging treatments at temperatures of 800 and 900°C for different aging time of 5{60 min were conducted on solution treated as well as hot worked samples of 2205 dual phase stainless steel. The effect of aging treatment on precipitation of intermetallic phases was investigated in undeformed specimens and those subjected to hot deformation with different strain rates of 0.001−1 s−1. It was found that σ precipitation increased by hot working. It was also concluded that the volume fraction of phase increased with deformation temperature and decreased with strain rate. The precipitation of intermetallic phases (i.e. σ and χ) was analyzed by an Avrami-type kinetics equation of %(σ+χ)=A(1-exp(-ktn)) and the values of n and ln k were estimated for different thermomechanical regimes. The values of n were assessed to increase from 0.4 to 1 with strain rate in the studied range. Otherwise, It was also understood that ln k decreased with strain rate. Microstructural observations by means of optical microscopy and scanning electron microscopy showed that σ particles mostly nucleated at the ferrite-austenite interfaces. But no sign of Â-phase could be seen. This fortified the idea of certain literature that Â-phase always forms at early stages of aging and consumes through the precipitation of σ.
关键词:
Duplex stainless steel
,
Hot Working
,
Sigma Phase
,
Secondary Phase
Acta Chimica Sinica
Passive film formed on 304 stainless steel in 2.5 mol/L H2SO4 solution by using alternating voltage (A. V.) passivation have been investigated by measuring capacitance and photoelectrochemical parameters. The investigation of the effect of measure frequency on the slope of Mott-Schottky curve has been carried out. The photoelectrochemical measurements were consistent with the capacitance measurement. Analysis of the experimental results showed that the passive film formed 304 stainless steel by using A. V. passivation exhibits semiconducting properties. Using the simple model of semiconductor rather than the multi-donor level model can explain satisfactorily the semiconducting behavior of the film formed on 304 stainless steel by using A.V. passivation.
关键词:
A. V. passivation;passive film;semiconducting properties;stainless;steel;model;electrodes
Journal of Physics D-Applied Physics
A large magnetoresistance (MR) is observed in a double helical CoMnSi compound over the entire temperature region from 5 K to the maximum measuring temperature of 380 K, with the largest MR ratio of -18.3% at 245 K and the smallest MR ratio of -5.5% at 85 K at 5 T. This phenomenon is ascribed to two different mechanisms in different temperature regions. The suppressed spin fluctuations of the double helical structure are responsible for the MR below 110 K. However, in consideration of the natural multilayer superstructure of CoMnSi, the larger MR above 110 K is ascribed to the decrease in K-space restrictions when the change in magnetic structure from double helical order to fan order occurs.
关键词:
giant magnetoresistance;magnetic-structure;crystal;metals
Journal of Physical Chemistry C
alpha-K(x)MnO(2) nanotubes with x = 0.10, 0.12, 0.15, and 0.17 have been synthesized through acid and alkali treatments of the precursor alpha-MnO(2) nanotubes. For the samples with x = 0.10 and 0.12, a large divergence of the ZFC and FC susceptibilities and pronounced hysteresis at low temperature are observed. However, the samples with x = 0.15 and 0.17 are antiferromagnetic with Neel temperatures of 25.4 and 25.3 K, respectively. The reciprocal susceptibility and electrical conductivity indicate that the samples with x = 0.15 and 0.17 undergo a charge separation transition from mixed/averaged valence state manganese ions to Mn(3+) and Mn(4+) between 250 and 300 K. Below half occupancy of the K(+) site (x <= 0.125), the strong geometrical frustration due to the triangular lattice configuration and the mixture of Mn(3+)/Mn(4+) result in the spin-glass behavior of the samples with x = 0.10 and 0.12. Above half occupancy of the K(+) site, the samples with x = 0.15 and 0.17 exhibit an antiferromagnetic feature due to the charge separation of Mn(3+) and Mn(4+). Our experiments display that the magnetic properties of alpha-K(x)MnO(2) can be tuned by varying the K(+) content.
关键词:
hydrothermal synthesis;manganese-dioxide;hollow urchins;tunnel;phase;transitions;nanowires;growth;oxides
李丽荣
,
赵娟
,
王贵
金属功能材料
采用非晶态多核配合的方法在800℃制备出La0.85K0.15MnO3纳米颗粒,用XRD、HRTEM和PPMS等手段对纳米颗粒的微观结构和磁性能进行研究.XRD和ED分析表明,所有样品都具有单相钙钛矿结构;样品的M-丁曲线研究结果表明,La0.85K0.15MnO3纳米颗粒的居里温度Tc为242.65 K.
关键词:
居里温度
,
纳米颗粒
,
La0.85K0.15MnO3
Oxidation of Metals
The corrosion of four Fe-Cr commercial steels with different tents in a simulated waste-gasification atmosphere containing 0.5 vol.% H-2, 0.5 vol.% HCl, balance CO2 has been investigated at 773 and 873 K. The same materials have also been tested in the same gas mixture free from HCl at both temperatures for comparison. The results show that the materials with low-chromium content (2.25 CrMoV and NF616) undergo accelerated corrosion in the presence of HCl, while the stainless steel SS304 suffers very little corrosion. On the contrary a steel containing 12 wt.% Cr (12 CrMoV) corrodes rather rapidly at 773 K but quite slowly at 873 K. The beneficial effect of chromium on the corrosion resistance of the steels increases with the chromium content at both temperatures. The steels tested show corrosion rates generally decreasing with time, having kinetics which are approximately parabolic at 773 K but intermediate between parabolic and linear at 873 K Only little or even no chlorine can be detected at the scale/metal interface at both temperatures for all materials corroded in HO-containing atmospheres. The corrosion mechanism can be explained by the so-called "active-oxidation, model.
关键词:
Cr steels HCl;reducing atmosphere;corrosion;high-temperature corrosion;fe-cr alloys;hydrogen-chloride;chromium-alloys;gas-mixtures;oxygen;800-degrees-c;oxidation;metals;fuels
Journal of Materials Research
The morphology of the dark and bright regions observed by transmission electron microscopy for the Zr(64.13)Cu(15.75)Ni(10.12)Al(10) bulk metallic glass strongly depends on the ion beam parameters used for ion milling. This indicates that the ion beam could introduce surface fluctuation to metallic glasses during ion milling.
关键词:
room-temperature
Nanoscale Research Letters
The linear thermal expansions (LTE) of bulk nanocrystalline ingot iron (BNII) at six directions on rolling plane and conventional polycrystalline ingot iron (CPII) at one direction were measured from liquid nitrogen temperature to 300 K. Although the volume fraction of grain boundary and residual strain of BNII are larger than those of CPII, LTE of BNII at the six measurement directions were less than those of CPII. This phenomenon could be explained with Morse potential function and the crystalline structure of metals. Our LTE results ruled out that the grain boundary and residual strain of BNII did much contribution to its thermal expansion. The higher interaction potential energy of atoms, the less partial derivative of interaction potential energy with respect to temperature T and the porosity free at the grain boundary of BNII resulted in less LTE in comparison with CPII from liquid nitrogen temperature to 300 K. The higher LTE of many bulk nanocrystalline materials resulted from the porosity at their grain boundaries. However, many authors attributed the higher LTE of many nanocrystalline metal materials to their higher volume fraction of grain boundaries.
关键词:
Linear thermal expansion;Bulk nanocrystallined materials;Severe;rolling technique;electrochemical corrosion behavior;different grain sizes;microstructure;diffraction;selenium;metals
