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1.
《Intermetallics》2005,13(3-4):373-376
A series of nano-grained B2-structured RuAl-based intermetallics and corresponding composites are synthesized by mechanical alloying. These RuAl-based materials include stoichiometric RuAl, B2-structured ternary (Ru,Ni)Al and (Ru,Ir)Al, eutectic RuAl–Ru and particle reinforced RuAl–ZrO2 composite. The accumulation of impurities, mainly Fe, in grain boundaries and the structural evolution during grain growth are found to be the controlling factors for the grain growth stagnation in nano-grained B2-structured binary RuAl and ternary (Ru,Ni)Al and (Ru,Ir)Al intermetallics. Ternary alloying element forming iso-structured pseudo-binary compounds, eutectic in situ and ceramic particle reinforced composites are explored to be the effective routes to enhance the stability of single-phase RuAl. The thermal stability of microstructure in various RuAl-based materials are found to decrease in a sequence from pseudo-binary RuAl–IrAl, RuAl–NiAl, eutectic RuAl–Ru composites, ceramic particle reinforced RuAl–ZrO2 composites to binary stoichiometric RuAl. 相似文献
2.
低温退火温度对Laves相Cr2Nb固相热反应合成的影响 总被引:7,自引:0,他引:7
研究了退火时间为3h时,退火温度对Cr-Nb机械合金化(MA)粉的Laves相Cr2Nb固相热反应合成的影响规律,获得了30hMA粉在退火时间为3h时能使Laves相Cr2Nb固相热反应合成充分进行的最低退火温度。优化出的cr2Nb固相热反应合成低温退火温度,可为通过MA+热压(或烧结)工艺路线制备具有微/纳米晶结构的高强高韧Cr2Nb合金或Cr2Nb基复合材料提供理论指导。 相似文献
3.
Nano-crystalline RuAl was synthesised by mechanical alloying. The evolution of the nano-crystalline RuAl phase during the
mechanical alloying process using ruthenium and aluminium powders was studied. During the milling process, the peaks corresponding
to reflections from the aluminium planes disappeared. The variation of crystallite size and microstrain with milling time
was evaluated using X-ray diffraction (XRD) patterns. though the XRD results showed the formation of a RuAl phase after 7h
of milling, scanning electron microscopy studies revealed that the RuAl phase was formed after 2h of milling. The analysis
revealed that average crystallite sizes of 17 and 120 nm were obtained for RuAl and Ru phases, respectively, during the milling
process. Density value of 97 % of the theoretical value was obtained for the milled powder mixture after cold compaction and
sintering. 相似文献
4.
《Acta Materialia》2001,49(3):395-403
The thermal stability of as-milled nano-RuAl has been studied by isothermal annealing at high temperatures. All three kinds of structural evolutions in as-milled powders upon high temperature exposure, namely reordering, strain relaxation and grain growth, show signs of stagnation. The total quantity of impurities, mainly 15 at.% Fe has been analyzed as being dissolved substitutionally in RuAl and also segregated to grain boundaries. Upon grain growth, lattice diffusion and segregation of impurity atoms in grain boundaries have been verified by the lattice parameter variation. The incremental apparent activation energy for grain growth at different temperatures is related to the accumulation of impurities in grain boundaries. Reordering and strain relaxation processes that accompany grain growth could consume a certain part of the driving force for grain growth. 相似文献
5.
S. Praveen B. S. Murty Ravi S. Kottada 《JOM Journal of the Minerals, Metals and Materials Society》2013,65(12):1797-1804
In the current study, the phase evolution of multicomponent equiatomic CoCrCuFeNi, CoCuFeNi, CoCrCuNi, and CoCrFeNi alloys synthesized by mechanical alloying (MA) followed by annealing was studied. From the phase evolution studies, CoCrFeNi, CoFeMnNi, CoCuFeNi, and CoFeNi were chosen to correlate the densification together with phase evolution during spark plasma sintering (SPS). MA resulted in a major face centered cubic (fcc) phase and a minor body centered cubic (bcc) phase in Cr-containing alloys, and a single fcc phase in all other alloys. After SPS, CoFeMnNi and CoFeNi remained as single fcc phase. However, CoCuFeNi transformed to two fcc phases, and CoCrFeNi had a major fcc phase with minor sigma phase. From densification studies, it was evident that CoCrFeNi showed delayed densification, albeit maximum final densification in comparison to other alloys. This behavior was attributed to distinctly different phase evolution in CoCrFeNi during SPS as compared to other alloys. Detailed phase evolution studies were carried out on CoCrFeNi by annealing the powders at different temperatures followed by conventional x-ray diffraction (XRD) and in situ high-temperature XRD of mechanically alloyed powders. The results obtained from the annealing and in situ high-temperature XRD studies were correlated with the densification and alloying behavior of CoCrFeNi alloy. 相似文献
6.
Effect of heat-treatment on the nanostructural change of W-Cu powder prepared by mechanical alloying
Sung-Soo Ryu Jung-Taik Lim Jin-Chun Kim Young Do Kim In-Hyung Moon 《Metals and Materials International》1999,5(2):175-178
W-30wt.%Cu powder prepared by mechanical alloying (MA) was annealed at various temperatures to investigate the structural
change of MA W-Cu powder. From differential scanning calorimeter analysis and transmission electron microscope observation,
it was revealed that the recovery of W in MA W-30wt.%Cu powder occurred at 700°C and the W grain started growing also at this
temperature. The W grain had grown significantly after annealing at 900°C, and the Cu phase in the MA powder was found to
act as liquid melt near 900°C. The microstructure of the sintered specimen was similar to that of the W-Cu alloy via liquid
phase sintering. This microstructure, even at temperatures below Cu melting, was the new feature observed in the MA W-Cu powder.
This suggests that such a microstructure is closely related to the inherent high diffusivity of the nanosized W crystallites
as well as the liquid-like behavior of the Cu phase. 相似文献
7.
《Intermetallics》2005,13(1):5-21
The structure, physical properties, processing and the related microstructure of RuAl and its alloys are presented in Part I of this overview, with a particular emphasis on the recent studies. The structure and physical properties reviewed include electronic structure, bonding, crystal structure, phase stability, as well as thermodynamic, elastic, electrical and thermal properties. Crystal defects are also covered and special attention is given to constitutional point defects, dislocations and planar faults. Ingot and powder metallurgy, mechanical alloying and thin film deposition are considered as processing techniques for the production of single or multiphase RuAl alloys. The typical characteristics of the microstructure related to different processing methods are presented. The entire overview is completed in Part II where mechanical properties, deformation and fracture behavior, environmental resistance and applications are discussed. 相似文献
8.
1.IntroductionInrecelltyears,MoSiZhasattractedconsiderableattentionasapotentialhigh-temperaturestructuralmaterial.Thecombinationofhighmeltingpoint(2030"C),moderatedensity(6.24gcm--'),excellentoxidationresistance,andhighmodulusatelevatedtemperaturemakesMoSiZoneofthemostpromisingmatrixphasetobeusedattemperaturesupto1600oC[l].Anothermolybdenumsilicide,Mo5Si3,hasbeenproposedasapotentialreinforcementforMoSt,[1,2].AmongawidevarietyofprocessingtechniquesutilizedtosynthesizeMoSt2,mechanicalalloy… 相似文献
9.
采用纯Al粉和纯Ru粉通过机械合金化(MA)和热处理制备了含Ru50%(质量分数, 下同)的铝钌合金.利用扫描电镜、差热分析和X-射线衍射等手段观察了复合粉体在MA和热处理后粉体的相组成和晶粒尺寸的变化.结果表明,MA30 h后Al溶入Ru中形成无序过饱和固溶体,晶粒尺寸细化到了20 nm左右.经550 ℃退火处理后,发生烧结现象,固溶体发生有序转变生成以Al2Ru为主的合金相,晶粒尺寸在50~60 nm,保温时间对合金组成和晶粒尺寸没有太大影响. 相似文献
10.
11.
目的研究RuAl的金属合金化及其氧化物Al_2O_3和RuO_2两相组的氧化关系,揭示其抗氧化性能机理。方法采用密度泛函理论的第一性原理,建立RuAl掺杂金属原子X及其间隙添加O原子的RuAl-X-O晶胞模型与其氧化产物Al_2O_3和RuO_2的晶胞模型。结果计算的Al_2O_3和RuO_2氧化能结果显示,Al_2O_3的氧化能(-11.43 eV/O_2)比RuO_2的氧化能(-2.28 eV/O_2)小,RuO_2的氧化能值与0值较为接近,在高温下结构稳定性较差,比较容易发生分解,RuAl的抗氧化能力主要依靠氧化产物Al_2O_3来进行。金属X合金化后,RuAl的氧化产物Al_2O_3和RuO_2的氧化能都增加,氧化能差值(eV/O_2)从大到小依次为Zr(0.29)Ce(0.28)Sn(0.22)Sr(-0.49),其中,金属Zr合金化对提高RuAl抗氧化能力的效果最好。计算的氧间隙形成能和电荷密集数等结果显示,金属X原子对RuAl的合金化降低了RuAl中的O固溶度,从而导致RuAl中内氧化速度降低。结论金属X原子对RuAl的合金化,阻碍RuAl表面的O向其内部扩散,障碍"内氧化"的生成条件,在RuAl表层界面的横向方向上容易形成连续、致密的Al_2O_3氧化层,提高RuAl的抗氧化性能。 相似文献
12.
NiAl based oxide dispersion strengthened (ODS) intermetallic alloys have been produced by mechanical alloying (MA) and consolidated by hot extrusion. Subsequent isothermal annealing was carried out to induce normal grain growth (NGG), and a thermomechanical treatment was performed to induced secondary recrystallization (SRx). SRx resulted in pronounced elongated grain growth without dispersoid coarsening, whereas concurrent equiaxed coarsening of grains and dispersoids occurred in NGG specimens. Creep properties of grain coarsened ODS MA NiAl were investigated, and the associated creep mechanisms were evaluated. The creep properties of SRxed MA NiAl are compared with those of as-consolidated MA NiAl and other counterparts. It has been shown that SRx results in improved creep resistance compared to NGG mechanism. The apparent activation energy and the stress exponent for creep indicate that SRx MA NiAl exhibits intermediate creep behavior of the two limiting dislocation creep modes; climb, controlled and viscous glide controlled. However, a grain size dependent creep has been shown, indicating that grain boundary sliding mechanism contributes to the overall deformation in MA NiAl. 相似文献
13.
《Acta Materialia》2002,50(10):2747-2760
The microstructural evolution of multicomponent Fe70-x-yCoxNiyZr10B20 (x = 0, 7, 21; y = 7, 14, 21, 28) alloys during mechanical alloying (MA) has been studied using XRD, SEM and TEM. Mixtures of elemental and pre-alloyed powders have been transformed initially into the single supersaturated bcc α-Fe solid solution phase for the alloys investigated. Subsequently, an amorphous phase has been obtained in Co-free alloys and Co-containing alloys with high Ni/Co ratios of 1 and 3. However, no amorphous phase was detected in another Co-containing alloy with a lower Ni/Co ratio (e.g. 0.33). The thermal stability of the as-milled powders has been investigated by a combination of DSC and the Pendulum magnetometer experiments. The DSC studies provide information on the thermodynamics and kinetics of crystallization of amorphous structure as a function of alloying contents. The Pendulum magnetometer studies reveal the phase transformation from nanocrystalline bcc α-Fe solid solution to amorphous structure during MA and the thermomagnetization behavior of the as-milled powder. 相似文献
14.
Microstructure evolution and thermal stability of nanocrystalline Cu-Nb alloys during heat treatment
The microstructure evolution and high thermal stability of the mechanically-alloyed supersaturated nanocrystalline Cu-10%Nb alloy during subsequent heat treatment were investigated by X-ray diffractometry and transmission electron microscopy (TEM). The results show that no significant change of the microstructure of the solid solution can be detected after annealing at 300-400 ℃. The pronounced phase separation can be detected at 700 ℃. After annealing for 30 min at 900 ℃, almost all the Nb atoms precipitate from the solid solution, and the average Cu grain size is about 37 nm. As the solute atoms hinder the migration of fcc phase, at Cu grain boundaries, no significant grain growth occurs before large amount of Nb atoms precipitates from Cu matrix, and the decrease of internal strain and density of dislocation is small. Furthermore, the nanosized Nb precipitates can also help to reduce the Cu grains growth through precipitating pinning effect. Therefore, the mechanically-alloyed nanocrystalline Cu-Nb alloys have a high thermal stability. And the contaminations brought into the Cu matrix by milling can influence the phase formation and the thermal stability of Cu-Nb alloys during heat treatment. 相似文献
15.
Structure and magnetostriction of Tb0.4Nd0.6(Fe0.8Co0.2)1.90 alloy prepared by solid-state synthesis
Mechanical alloying (MA) and subsequent solid sintering process was used to prepare the Nd-containing magnetostrictive Tb0.4Nd0.6(Fe0.8Co0.2)1.90 alloy. The structure, thermal stability and phase transformation were investigated as functions of composition, milling process and annealing temperature. An amorphous phase was formed by high-energy ball milling for 5 h with the ball-to-powder weight ratio of 20:1, which crystallized into MgCu2-type and PuNi3-type crystalline structure with different annealing temperatures. The magnetoelastic properties were investigated by means of a standard strain technique. The high Nd-content (Tb,Nd)(Fe,Co)2 Laves phase for the composition Tb0.4Nd0.6(Fe0.8Co0.2)1.90 was synthesized by MA process plus annealing at 500 ℃ for 30 min. 相似文献
16.
C. H. Lee T. Fukunaga Y. Yamada U. Mizutani H. Okamoto 《Journal of Phase Equilibria and Diffusion》1993,14(2):167-171
The mechanism for the amorphization induced by mechanical alloying (MA) has been studied in the immiscible Cu- Ta system.
A mixture of copper and tantalum powders at a composition ratio of Ta: Cu = 7:3 was used. The first 30 h of milling essentially
results in the reduction in Ta and Cu grain size down to ∼10 nm without measurable formation of an amorphous phase. The thermally
assisted amorphization (TAA) becomes noticeable after 60 h of milling. The higher the ambient temperature, the faster the
amorphization proceeds. The TAA effect is also observed by annealing a partially amorphous MA powder. The microstructure after
30 h of milling is such that fine Cu crystallites are embedded in a fine- grained Ta matrix. Here an interfacial energy contribution
is large enough to raise the Gibbs energy to that of an amorphous phase. Now high temperature milling or annealing allows
an energetically downhill process to occur. This is most likely responsible for the observed TAA effect in the Cu- Ta system
characterized by a positive heat of mixing. 相似文献
17.
T. A. Sviridova A. P. Shevchukov E. V. Shelekhov P. A. Borisova 《The Physics of Metals and Metallography》2011,112(4):356-370
The possibility of obtaining a “line” (narrow-homogeneity-range) intermetallic compound CuAl2 with the use of mechanical alloying (MA) and subsequent annealing has been investigated by X-ray diffraction and scanning
electron microscopy. Regimes (composition of a charge mixture, time of preliminary MA, time and temperature of annealing)
allowing one to obtain a virtually single-phase compound have been determined. The low-temperature annealings in a temperature
range of 100–250°C have shown that the most probable mechanism of mass transfer upon heating of layered composites obtained
by MA is grain-boundary diffusion, which can be explained by a large fraction of grain boundaries in mechanically alloyed
powders. 相似文献
18.
The binary Fe?Si elemental powders mixture (1∶2 in atomic proportion) has been milled for different milling times in an attrition mill. The phase characterization of mechanically alloyed powder was investigated using the chemical method of differential dissolution (DD) and the X-ray diffraction (XRD) method. In powder specimens milled for more than 15 hr, ∈-FeSi and unreacted Si were observed. The formation of a supersaturated solid solution of Si in ∈-FeSi induced by mechanical alloying (MA) was also verified. The lattice parameter of the ∈-FeSi of as-milled powders changed from 4.4876 Å to 4.4668 Å according to the increase of MA time. Based on the results of the DD analysis, unreacted Si could be classified as (1) crystalline Si, (2) Si supersaturated in ∈-FeSi, or (3) amorphous Si. Therefore formation of the β-FeSi2 after annealing could be explained by the reaction between the ∈-FeSi and the Si classified into types (1) and (2). It seemed that the amorphous Si induced by MA did not react with the ∈-FeSi during annealing at 700°C. 相似文献
19.
20.
F. Ali S. Scudino S.M. Gorantla V.C. Srivastava H.R. Shahid V. Uhlenwinkel M. Stoica G. Vaughan N.K. Mukhopadhyay J. Eckert 《Acta Materialia》2013,61(10):3819-3830
In this work the effect of mechanical milling on the structure, thermal stability and hardness of single phase Al62.5Cu25Fe12.5 icosahedral quasi-crystals has been investigated for different milling intensities. The results indicate that, irrespective of the milling intensity used, the quasi-crystals transform to a body-centered cubic (bcc) phase during milling. This transformation starts when the grain size of the QC phase is about 10 nm, which represents the critical grain size initiating the phase transformation. Upon heating the milled powder displays grain growth of the bcc phase at low temperatures, followed by transformation to the original icosahedral QC phase at higher temperatures. The phase transformations occurring during milling and subsequent annealing have a remarkable effect on the indentation hardness, which can be tuned within a wide range (7–10 GPa) as a function of the volume fractions of the different phases. This suggests that a composite material with optimized mechanical properties can be produced by appropriate thermo-mechanical treatments. 相似文献