退火温度对FeCuNbSiB纳米晶合金磁性能的影响

用熔体快淬法制备出3种FeCuNbSiB纳米晶合金带材,绕制成50 mm×32 mm×20 mm的环形磁环,随后在530~620℃下进行等温退火,研究退火温度对合金磁性能的影响。结果表明:随着退火温度的增加,合金内部晶化相的晶粒尺寸和体积分数有所增加。在550~600℃等温退火后合金具有相对较低的矫顽力(Hc为1.0~1.5 A/m,测试条件:Bm=100 mT,f=10 kHz)和损耗值(Pm为1.4~1.8 W/kg,测试条件:Bm=300 mT,f=10 kHz),特别是经过570~590℃退火后合金在1 kHz^50 kHz频率范围内具有最佳的磁导率。同时,在1 kHz^10 MHz频率范围内,不同测试频率下合金阻抗值对应的最佳退火温度也不同。     

High temperature oxidation behavior of FeCo‐based nanocrystalline alloys

This paper describes the dynamic and isothermal oxidation behavior of three different FeCo‐based Fe_38.5Co_38.5Nb₇Cu₁B₁₅, Fe₃₆Co₃₆Nb₇Si₁₀B ₁₁ and Fe_33.5Co_33.5Nb₇Si₁₅B₁₁ alloys and one traditional FINEMET Fe₇₃Nb₃Cu₁Si_15.5B_7.5 alloy. Dynamic and isothermal oxidation measurements in controlled oxidizing atmosphere were performed and the oxidation apparent energy as well as the oxidation behavior was obtained. SEM observations were carried out in order to characterize the oxide layer formed during the oxidation measurements. The apparent activation oxidation energy found for the Fe₃₆Co₃₆Nb₇Si₁₀B₁₁, Fe_33.5Co_33.5Nb₇Si₁₅B₁₁ and Fe₇₃Nb₃Cu₁Si_15.5B_7.5 alloys was about 35 kJ/mol and for the Fe_38.5Co_38.5Nb₇Cu₁B₁₅ alloy was about 70 kJ/mol.     

Abnormal changes in properties of alloys during structural transformations

Conclusions Electrical conductivity suffers an abnormal and significant rise, and the resistance to plastic deformation (hardness) a considerable fall, during the isothermal transformation of austenitic alloys, at the time when the transformation is occurring fastest.The anomalous changes in properties are evidence of a special condition in the alloy during transformation, with a weakening of interatomic bonds and an acceleration of plastic deformation and electron transfer. A cautious approach is therefore needed to the interpretation of resistivity curves, obtained during transformation rather than after stabilizing the alloy by quenching.     

Magnetic properties of nanocrystalline Finemet alloys with Co addition

This report focuses on ac magnetic properties of (Fe_0.5Co_0.5)_73.5Cu₁Nb₃Si_13.5B₉ alloy in the high temperature. The effects of replacing 50% Fe by Co in Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy on the static magnetic properties have also been studied. Addition of Co leads to an increase around 110 K of the Curie temperature of the amorphous phase, much higher than Ge-containing Finemet alloy. The material has much better ac magnetic properties than Hitperm alloy. An excellent stability of initial permeability in high temperature (up to 650 K) and high frequency (up to 5 × 10⁵ Hz) can be observed with respect to the Co-free alloy.     

Mechanical behavior of nanocrystalline metals and alloys

Nanocrystalline metals and alloys, with average and range of grain sizes typically smaller than 100 nm, have been the subject of considerable research in recent years. Such interest has been spurred by progress in the processing of materials and by advances in computational materials science. It has also been kindled by the recognition that these materials possess some appealing mechanical properties, such as high strength, increased resistance to tribological and environmentally-assisted damage, increasing strength and/or ductility with increasing strain rate, and potential for enhanced superplastic deformation at lower temperatures and faster strain rates. From a scientific standpoint, advances in nanomechanical probes capable of measuring forces and displacements at resolutions of fractions of a picoNewton and nanometer, respectively, and developments in structural characterization have provided unprecedented opportunities to probe the mechanisms underlying mechanical response. In this paper, we present an overview of the mechanical properties of nanocrystalline metals and alloys with the objective of assessing recent advances in the experimental and computational studies of deformation, damage evolution, fracture and fatigue, and highlighting opportunities for further research.     

Relating the Debye temperature and structural stability of rapidly solidified Al alloys

The work described in this article was undertaken in an attempt to explain the high-temperature stability of rapidly solidified, face-center ed-cubic Al-8Mn-2Ni alloys by the change in Debye characteristic temperature (Θ). The Θ has been determined from the x-ray diffraction intensities by evaluating Debye Waller factor B. It was found that Θ remains almost unchanged on annealing up to 623 K, thus predicting its high-temperature stability.     

Grain growth in nanocrystalline iron and Fe-Al alloys

The effects of the annealing temperature and time, cryomilling in liquid nitrogen, and the addition of aluminum powder on the thermal stability and grain growth behavior of nanocrystalline iron were modeled using the Artificial Neural Network (ANN) technique. The developed model can be used as a guide for the quantification of the grain growth by considering the effects of annealing temperature and time. The model also quantified the effect of Al on the thermal stability of cryomilled nanocrystalline Fe. The model results showed that the cryomilling of Fe has a tangible effect on the stabilization of the nanostructure.     

掺Cr纳米晶Mg_2Ni合金的气态储氢性能

纳米晶Mg2 Ni1-xCrx(x =0 ,0 .1,0 .2 ,0 .3)合金由纯Mg、Ni、Cr粉在 5 0 0℃经 3h烧结后机械球磨而成。在 2 10℃吸氢、2 5 0℃放氢的条件下 ,添加Cr后合金的最大吸放氢量明显提高 ;纳米Mg2 Ni0 .8Cr0 .2 合金的气态储氢量和吸氢动力学性能较好 ,第一次放氢量就达到 3.0 % ,并且循环稳定性良好 ,吸氢后生成Mg2 NiH4 、Mg2 NiH0 .2 4 相。纳米Mg2 Ni0 .7Cr0 .3 合金的放氢量在不经过活化的条件下便达到最大值 ,然而循环稳定性差 ,这是由于循环过程中有MgH2 生成而造成的     

掺Cr纳米晶Mg2 Ni合金的气态储氢性能

纳米晶MgNi1-xCrx(x=0,0.1,0.2,0.3)合金由纯Mg、Ni、Cr粉在500℃经3h烧结后机械球磨而成。在210℃吸氢、250℃放氢的条件下，添加Cr后合金的最大吸放氢量明显提高；纳米Mg2Ni0.8Cr0.2合金的气态储氢量和吸氢动力学性能较好，第一次放氢量就达到3．0％，并且循环稳定性良好，吸氢后生成Mg2NiH4、Mg2NiH0．24相。纳米Mg2Ni0.7Cr0.3合金的放氢量在不经过活化的条件下便达到最大值，然而循环稳定性差，这是由于循环过程中有MgH2生成而造成的。     

Transformation temperature changes due to second phase precipitation in NiTi-based shape memory alloys

This study investigated changes in the martensite start temperature (M_s) of NiTi-based shape memory alloys as a result of second phase precipitation. Precipitation of the second phase leads to a change in the matrix chemical composition and may alter the electron concentration (c_v) of the matrix. When the electron concentration of the matrix increases, the transformation temperature decreases, whereas the M_s temperature rises when the c_v of the matrix decreases. Additionally, if the precipitation does not result in a significant variation of the c_v of the matrix, the variation in M_s is small (<15 °C). In the present work it is shown that alteration of the M_s temperature as a result of precipitation is mainly due to the change in electron concentration of the matrix. The extrinsic effect of the precipitates on M_s is also discussed on the basis of their quantities in the as-quenched and aged microstructures and the strain energy induced in the matrix.     

Mechanisms of plastic deformation in microcrystalline and nanocrystalline TiNi-based alloys

Mechanisms of plastic deformation of a high-temperature B2 phase that act upon tension, compression, and high-pressure torsion in TiNi-based single crystals have been studied depending on the crystal orientation. For the crystals with orientations located near the [$ \bar 1 $ \bar 1 11] and [$ \bar 1 $ \bar 1 12] poles in the standard stereographic triangle, multiple dislocation slip prevails upon both compression and tension. In “hard” crystals with the deformation axis close to the [001] direction, in which the Schmid factors for dislocation slip are close to zero, the main deformation mechanisms are the mechanical twinning in the B2 phase and the stress-assisted B2 → B19′ martensitic transformation. All the above listed mechanisms take part in the formation of the {111}〈hkl〉 texture. The mechanism of the change in the orientation of “hard” polycrystalline grains upon the formation of a nanocrystalline and amorphous-crystalline state has been demonstrated on the example of the evolution of the structure of [001] crystals upon severe plastic deformation in a Bridgman cell.     

Modern structural titanium alloys

Conclusions Further research to increase the strength, service life, and ductility of titanium alloys should be directed toward studying the possibility of heat treatment and thermomechanical treatment, utilization of the metastable structural condition, and intermetallic hardening of the and solid solutions.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 29–34, July, 1980.     

Tailoring and patterning the grain size of nanocrystalline alloys

Nanocrystalline alloys that exhibit grain boundary segregation can access thermodynamically stable or metastable states with the average grain size dictated by the alloying addition. Here we consider nanocrystalline Ni–W alloys and demonstrate that the W content controls the grain size over a very broad range: ∼2–140 nm as compared with ∼2–20 nm in previous work on strongly segregating systems. This trend is attributed to a relatively weak tendency for W segregation to the grain boundaries. Based upon this observation, we introduce a new synthesis technique allowing for precise composition control during the electrodeposition of Ni–W alloys, which, in turn, leads to precise control of the nanocrystalline grain size. This technique offers new possibilities for understanding the structure–property relationships of nanocrystalline solids, such as the breakdown of Hall–Petch strength scaling, and also opens the door to a new class of customizable materials incorporating patterned nanostructures.     

非晶纳米晶软磁合金的研究进展

介绍了非晶纳米晶软磁合金的最新研究进展,简要分析和总结了添加合金元素以及晶化退火工艺对非晶纳米晶合金结构和性能的影响.最后,根据现有非晶纳米晶合金的研究现状以及实际应用中对其性能的要求,指出了未来非晶纳米晶软磁合金的发展方向.     

Room-temperature and high-temperature magnetic permeability of Co-doped nanocrystalline alloys

Influence of composition and annealing temperature on structure and magnetic properties of amorphous and nanocrystalline Fe_(78.4—x)Co_xSi_9 B_9 Nb_(2.6)Cu_1(x=27.4,40.0,51.0,78.4) alloys was investigated by X-ray diffraction(XRD) and the temperature dependence of permeability. According to the initial crystallization temperature(T_(x1)) from differential scanning calorimetry(DSC) curves of as-quenched amorphous alloys,490-700 ℃ isothermal annealing was carried out to obtain the characteristic nanocrystalline structure. Furthermore,the soft magnetic properties were measured by temperature evolution of magnetic permeability to obtain the correlation between Co content, annealing temperature and magnetic permeability. The results show that, on the one hand,the annealing temperature exerts a significant effect on phase structure and initial permeability(μ_i). The highertemperature(from 550 to 610 ℃) annealed Co content nanocrystalline samples can remain higher μ_i at elevated temperature. On the other hand, partial substitution Fe by Co can improve the high-temperature magnetic stability;however, the room-temperature permeability of higher Co content alloys decreases obviously at the same time. This phenomenon was analyzed from the viewpoint of the saturation magnetic induction(B_s), magnetic anisotropy(K) and magnetostriction(λ_s).