Texture, microstructure and magnetic properties of Fe-28Cr-15Co-3.5Mo permanent magnet

Crystallographic texture, microstructure and magnetic properties of Fe-28Cr-15Co-3.5Mo alloy were studied as a function of processing parameters. Texture studies revealed that thermo-magnetic aging leads to the development of ideal Goss type, {1 1 0} 〈0 0 1〉 and cube type {0 0 1} 〈0 1 0〉 textures. The orientation densities of these texture components become stronger after the step-aging treatments. Microstructural features show that improvement in magnetic properties were due to aligning and elongation of ferromagnetic Fe, Co-rich (α₁) particles in the preferred 〈1 0 0〉 directions. Magnetic analysis reveals that magnetic properties of the alloys are directionally dependent and influenced by the choice of thermo-magnetic treatment temperature or time. The maximum values of intrinsic coercive force, remanence and energy product, obtained in the textured magnetic alloy were 68.99 kA/m (867 Oe), 1.12 T (11.2 kG) and 43.2 kJ m³ (5.4 MG Oe), respectively.     

Nondestructive evaluation for remanent life of modified 9Cr-1Mo steel by reversible magnetic permeability

We present a magnetic and nondestructive method to evaluate the remanent life of modified 9Cr-1Mo steel by measuring the reversible magnetic permeability. Specimens with ten different kinds of aging periods were prepared using an isothermal heat treatment at 690 °C. The Larson-Miller parameter (LMP) was calculated and the peak interval of reversible magnetic permeability (PIRMP) was measured using the surface type probe. PIRMP was inversely proportional to LMP. We can evaluate the remanent life of modified 9Cr-1Mo steel using the relationship between PIRMP and LMP. Also, we present the possibility that the tensile strength and yield strength measured by destructive methods could be estimated by PIRMP measured nondestructively.     

Gradient structural-phase states of Fe-0.9C-1Cr-1V carburized steel

Quantitative analysis of changes in the structural composition, phase content, and dislocation substructure of surface layers of Fe-0.9C-1Cr-1V steel after high-temperature carburizing is performed by methods of optical and electron diffraction microscopy.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 33–37, October, 2004.     

Effect of domain variations on damping capacity of Fe-16Cr-2.5Mo alloy solution annealed at 1373 K and 1473 K

The damping capacity of Fe-16Cr-2.5Mo alloy heat-treated at different temperatures was investigated. A water-based magnetic fluid was used to analyze domain morphologies. The experimental results show that there is a maximum value of damping capacity when the solution annealing temperature of the material is 1373 K. When the annealing temperature is higher, the damping capacity of the alloy drops quickly. The change in damping capacity with the solution annealing temperature is believed to be due to different domain morphologies. The domains are larger and the domain-wall area is smaller in the alloy annealed at a higher temperature. The wedge-shaped domains acted as obstacles for pinning the domain-wall movement, even though movement of the 90° domains is easy. As a result, the damping capacity of the alloys drops when the annealing temperature is very high.     

Structural and magnetic transition in stainless steel Fe-21Cr-6Ni-9Mn up to 250 GPa

Stainless steel Fe-21Cr-6Ni-9Mn(SS 21-6-9),with ～21% Cr,～6% Ni,and ～ 9% Mn in weight percentage,has wide applications in extensive fields.In the present study,SS 21-6-9 is compressed up to 250 GPa,and its crystal structures and compressive behaviors are investigated simultaneously using the synchrotron angle-dispersive x-ray diffraction technique.The SS 21-6-9 undergoes a structural phase transition from fcc to hcp structure at ～ 12.8 GPa with neglectable volume collapse within the determination error under the quasi-hydrostatic environment.The hcp structure remains stable up to the highest pressure of 250 GPa in the present experiments.The antiferromagnetic-to-nonmagnetic state transition of hcp SS21-6-9 with the changes of inconspicuous density and structure,is discovered at ～50 GPa,and revealed by the significant change in c/a ratio.The hcp SS-21-6-9 is compressive anisotropic:it is more compressive in the c-axis direction than in the a-axis direction.Both the equations of states(EOSs) of fcc and hcp SS 21-6-9,which are in accordance with those of fcc and hcp pure irons respectively,are also presented.Furthermore,the c/a ratio of hcp SS 21-6-9 at infinite compression,R∞,is consistent with the values of pure iron and Fe–10Ni alloy.     

Thermal oxidation induced during laser cleaning of an aluminium-magnesium alloy

During laser cleaning of metallic materials by pulsed lasers surface, modifications can be induced mainly by the transient thermal effect. In ambient conditions an oxidation of the cleaned surface can be detected. The aim of this work was to characterize this transient oxidation that can occur below the laser energy domain leading to any phase change (melting, ablation) of the cleaned substrate.A Q-switched Nd:YAG laser with pulse duration of 10 ns and wavelength of 1064 nm was used for the purposes of this study. For the surface analysis of the treated samples X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) were used.It was found that thermal oxidation took place on the aluminium-magnesium alloy during the irradiation in air with a laser energy ranged from 0.6 to 1.4 J cm^-2. It has been demonstrated that this thermal oxidation had the same mechanism as in the case of the steady state thermal oxidation of the aluminium-magnesium alloys even though the laser irradiation was applied only for the very short time of 10 ns. When the laser energy reached the value of 1 J cm^-2, the oxide formed by the thermal oxidation became in a large extent crystalline and its outer part was entirely covered by a continuous layer of magnesium oxide. PACS 61.82.Bg; 81.65.Mq; 61.80.Ba     

Dislocation driven chromium precipitation in Fe-9Cr binary alloy: a positron lifetime study

The influence of initial heat treatment on anomalous Cr precipitation within high temperature solubility region of the Fe–9Cr alloy has been investigated using positron lifetime studies. Air-quenched samples with pre-existing dislocations exhibited a distinct annealing stage in positron lifetime between 800 and 1100?K corresponding to Cr-precipitation. During this stage, Transmission Electron Microscopy showed fine precipitates of average size 4 nm, dispersed throughout the sample and from Energy-dispersive X-ray spectroscopy (EDS) analysis they are found to be Cr-enriched. The presence of dislocations is found to be responsible for Cr precipitation.     

Characterization of the ξ-carbide in ex-service 1Cr-0.5 Mo steels

The ξ-carbide, also described as Fe₂MoC and M_aC_b, has been identified at ferrite grain boundaries in 1Cr-0.5Mo steels exposed to elevated temperatures (500–530°C) for prolonged periods (65,000–170,000 hr). The structure and composition of the phase have been characterized using electron microdiffraction and energy-dispersive X-ray spectroscopy (EDXS) respectively. Analysis of microdiffraction patterns supports the proposal that the ξ-carbide has a monoclinic unit cell, rather than the orthorhombic unit cell first proposed. The ranges of metallic element concentrations in the ξ-carbide (i.e. 48–59 at.% Fe, 22–29 at.% Mo, 7–16 at.% Cr, 4–7 at.% Mn and 3–6 at.% Si) are unique compared to those of other carbide precipitates identified in the 1Cr-0.5Mo steels, which means that the ξ-carbide may be identified rapidly on extraction replicas using qualitative EDXS.     

基于声发射统计信息的2.25Cr-1Mo钢早期损伤判别方法

裂纹开裂是金属材料常见的损伤失效形式之一。而材料失效会经历从早期微小损伤到宏观变形的微观组织动态演化过程,如何在材料发生宏观变形之前,能够及早地发现损伤至关重要。该文基于对材料损伤失效过程不同声源的机理分析,提出了以不同声源信号数的统计占比值κ这一变量来判定表征材料早期损伤阶段的判别指标,制备6个含不同缺陷的不带堆焊层和带堆焊层的2.25Cr-1Mo钢试件,采用声发射技术对试件的弯曲损伤全过程进行在线测试,获得了6个试件早期损伤阶段的声学数据,通过对比分析以幅值和能量为主的单一参量以及基于支持向量机的多元参量κ值的统计结果,证明了利用κ值可以有效地对不带堆焊层和带堆焊层的2.25Cr-1Mo钢试件的早期损伤阶段进行判别,其中不带堆焊层试件的κ值范围为1:3.1～1:3.6之间,带堆焊层试件的κ值范围为1:2.2～1:2.6之间,具有明显的区分度。     

The influence of heat treatment conditions in an external magnetic field on the structure and magnetic properties of the Fe-25Cr-12Co alloy

This work presents an attempt to define the qualitative and quantitative changes in microstructural parameters of Fe-Cr-Co alloy microstructure depending on the parameters of heat isothermal high-temperature aging and magnetic treatments. Two alloys of nominally similar Cr and Co contents, but containing differing impurities, were tested for the determination of the influence of impurities on the values of B_r, H_c and (BH)_max. High-temperature aging was carried out by two methods: (i) an isothermal process and (ii) continuous cooling in an external magnetic field; values of their magnetic properties were compared. Changes in particle size of the ferromagnetic phase ₁ as well as its surface content, specific surface and structure anisotropy coefficient were defined for the material as function of the temperature of isothermal high-temperature aging. The results obtained enabled discussion of individual influence of microstructural parameters during magnetic hardening of Fe-Cr-Co type alloys. Results from TEM examinations show that microstructural parameters are sensitive functions of isothermal heat-magnetic treatment and in this process a very precise control of its parameters is required. On the grounds of investigations performed, magnetic aging with continuous cooling is found to be the most favourable treatment, since owing to the wider range of the admissible parameters of treatment it allows for higher tolerance as regards the technological parameters.     

Electron spectroscopic study of passive oxide layer formation on Fe-19Cr-18Ni-1Al-TiC austenitic stainless steel

Surface oxidation of a TiC-enriched austenitic stainless steel alloy was investigated at 50 °C by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). It was found that a passive oxide layer started to form on the alloy surface after 5 L of oxygen exposure. Further oxidation of the alloy was suppressed after 500 L of oxygen exposure when a stable passive layer was formed. It was found also that Ti and Ni did not oxidize and Ti remained in a carbide form during whole oxidation. The oxidation kinetics of different metals were investigated as well.     

Effect of various lanthanum sol-gel coatings on the 330Cb (Fe-35Ni-18Cr-1Nb-2Si) oxidation at 900 °C

The influence of a lanthanum sol-gel coating on the oxide scale adherence has been studied during the 330Cb (Fe-35Ni-18Cr-1Nb-2Si) oxidation at 900 °C, in air. The alloy oxidation is performed in order to generate a protective chromia scale acting as a good barrier against carburization. Argon annealing of lanthanum sol-gel coatings have been performed at various temperatures in order to find the best conditions to insure the scale adherence. Kinetic results show that lanthanum sol-gel coatings lead to a lower oxidation rate compared to blank specimens. Thermal cycling tests on lanthanum the sol-gel coated specimen show that the oxide scale formed at 900 °C, in air, is adherent.     

Thermal and optical studies of an amorphous InSe9 alloy produced by mechanical alloying

In this paper we investigated thermal and optical properties of an amorphous alloy of the In–Se system. The amorphous InSe₉ alloy was produced by mechanical alloying and it was studied using Differential Scanning Calorimetry and microPhotoluminescence spectroscopy techniques, and from them several properties, such as glass transition and crystallization temperatures and energies and the optical gap energy were determined and compared to the values found in other alloys of the In–Se system. This comparison revealed some differences among our alloy produced by mechanical alloying and alloys produced by other techniques, which is a clear indication of the influence of the fabrication technique in their physical properties. The main differences occur in the activation energies associated with the glass transition and crystallization processes and also in the optical gap energy.     

X-ray photoelectron spectroscopic analysis of oxidized Fe-16Cr-16Ni-2Mn-1Mo-2Si austenitic stainless steel

Depth profile analysis (argon ion etching/X-ray photoelectron spectroscopy) was conducted on a series of Fe-16Cr-16Ni-2Mn-1Mo-2Si austenitic stainless steel samples oxidized at 973 and 1073 K with exposure times of 25, 100, 193, 436 and 700 h. Surface and near surface rearrangement following oxidation resulted in a region of high Cr concentration on all oxidized samples. Temperature and time dependence to O₂ penetration depth was observed. In general, O₂ penetration depth was found to increase with increasing exposure up to 436 h. No increase in depth was observed between 436 and 700 h exposure time.     

Phase composition at surface of Fe-3%Si alloy

The structure, phase and chemical compositions of surface layers in different depths of Fe-3%Si alloy were investigated. According to the X-ray Photoelectron Spectroscopy (XPS) spectrum (penetration depth of up to ∼ 1nm) of the as-prepared sample, a layer of SiO₂ was present on the top. After the subsequent Ar⁺ sputtering (removing the SiO₂ layer), a segregation of Si atoms and two other phases were observed. The phases were described as the cubic c-FeSi and Fe₃Si. The emission⁵⁷Fe M?ssbauer spectra confirmed a presence of these phases. The α-Fe and solid solution of α-Fe + 1wt.%Si were recognized in the Conversion Electron M?ssbauer spectra (penetration depth ∼ 300nm) while the M?ssbauer spectra taken in scattering geometry with detection of 14.4 keV gamma radiation (scanning depth of ∼ 30 μm) indicate Fe-3wt.%Si solid solution as a main phase. Presented at International Colloquium “M?ssbauer Spectroscopy in Materials Science”, Všemina, Czech Republic, June 1–4, 2004. This work was supported by the Grant Agency of the Academy of Sciences of the Czech Republic (Contract No. IAA1041404).     

Phase change behaviors of In-Ge-Sb-Te alloy

Phase change behaviors of In₂Ge₈Sb₈₅Te₅ material were studied. Thermal analysis shows the phase change occurs around 160 °C and melting at 572 °C. Isothermal reflectivity-time measurement of In₂Ge₈Sb₈₅Te₅ shows a growth-dominated crystallization mechanism. A high crystallization speed of 30 ns is realized upon irradiation by blue laser beam of 405 nm. It has face-centered-cubic NaCl-type and rhombohedral Sb crystal structures. The weaker binding energy of In and In-Sb bond energy are believed to be the reasons for fast crystallization speed of In₂Ge₈Sb₈₅Te₅. PACS 61.05.cp; 68.55.Nq; 68.60.Dv; 78.66.Jg; 78.20.-e     

Electronic properties of austenite and martensite Fe-9%Mn alloys

We calculate the electronic properties of austenite and martensite Fe-9%Mn alloys using the self consistent full-potential linearized-plane-wave method under the generalized gradient approximation full lattice relaxation. By minimizing total-energy, the lattice constants in their ground states were determined. We discuss the total energy dependence of the volume, and density of states (DOS).      

Wet oxidation behaviors of Hi-Nicalon fibers

Wet oxidation behaviors of Hi-Nicalon fibers were investigated in environment of PH₂O:O₂:Ar=14:8:78 kPa with a slow gas flow rate of 3.5 cm s⁻¹ above 1300 °C for 1 h. Experimental results indicated that oxidized Hi-Nicalon fibers were covered by silica. The weight gains and surface micromorphologies were strongly affected by temperature. Below 1500 °C, the surface of the oxidized fibers were rough-hewn and cracked, and there were no changes detected in fiber diameter. After oxidation at 1600 °C, the silica locally spalled and the fiber swelled in diameter. The Young-Laplace equation was applied to interpret surface micromorphologies change during wet oxidation of the specimens. The cracks in silica produced by oxidation and the microcrystal growth of the fibers at high temperature were considered for the strength degradation of the fibers.     

Plastic behaviour of Fe-3% Si alloy single crystals

Fe-3% Si alloy single crystals of single slip and double slip orientation have been tested in tension at temperatures between 113 K and 473 K. The stress-strain curves exhibit a yield drop followed by inhomogeneous yielding (yield propagation stage), a parabolic and an approximately linear parts. The slip line observations carried out in various stages of deformation show that only at the beginning of the parabolic part of stress-strain curve the specimen is completely filled out with slip bands and the deformation becomes relatively homogeneous. With both single slip and double slip orientations deformation takes place predominantly in one slip system only. At higher temperatures ageing occurs during deformation.Na Slovance 2, Praha 8, Czechoslovakia.The authors would like to thank Dr. B. esták for suggestion of the problem and for his interest in discussion of the results. We are also grateful to Mr. J. Poucha for help with some experimental work and to Miss G. Výborná for help with specimen preparation. To Dr. S. Libovický and Dr. F. Kroupa we thank for helpful discussions.     

Study of ageing effects of a low-interstitial 18Cr-2Mo ferritic steel

The phase transformations which occur in the 18Cr-2Mo ferritic steel by annealing in the temperature range 603–1093 K have been studied using Moessbauer spectroscopy and X-ray diffraction. It is found that the 748 embrittlement is to be ascribed to Cr redistribution and/or to the formation of an intermetallic R-type phase. Precipitation of an h.c.p. Laves phase Fe (Mo,Nb) of MgZn₂-type takes up at about 850 K and Nb to Mo substitution goes on by increasing the annealing temperature.