首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Co70 Fe8 Si9B13 amorphous ribbon, crystallized ribbon and a mixture of pure crystalline powders were mechanically alloyed by milling and nanocrystalline structures were obtained. The structural changes were monitored By X-ray diffraction and differential scanning calorimetry measurements. The thermal behaviour on heating the alloys prepared by ball milling was studied and the influence of the high-energy ball milling on the resulting phases was found.  相似文献   

2.
Ti-Al intermetallics have been produced using mechanical alloying technique. A composition of Ti-48Al-2Nb at % powders was mechanically alloyed for various durations of 20, 40, 60, 80 and 100 h. At the early stages of milling, a Ti (Al) solid solution is formed, on further milling the formation of amorphous phase occurs. Traces of TiAl and Ti3Al were formed with major Ti and Al phases after milling at 40 h and beyond. When further milled, phases of intermetallic compounds like TiAl and Ti3Al were formed after 80 hours of milling and they also found in 100 h milled powders. The powders milled for different durations were sintered at 785°C in vacuum. The mechanically alloyed powders as well as the sintered compacts were characterized by XRD, FESEM and DTA to determine the phases, crystallite size, microstructures and the influence of sintering over mechanical alloying.  相似文献   

3.
Mechanically alloyed Co-20wt%Ni-10wt%Mo and Co-70wt%Ni-10wt%Mo (nominal compositions) alloy powders were produced by milling of pure elemental powders. Mechanically alloyed powders were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. MA powder specimens were tested electrollitically in a 30% KOH aqueous solution at 298 K. X-ray diffraction analysis and transmission electron microscopy of milled powders showed the presence of two phases, an fcc solid solution and intermetallic compounds of Ni or Co with Mo. These phases showed a nanometric size. The linear sweep voltammograms confirmed also the presence of two phases in both mechanically alloyed alloy powders. The Co-20wt%Ni-10wt%Mo alloy powders showed the best electrocatalytic activity for hydrogen evolution reaction.  相似文献   

4.
Mechanically alloyed Ni60Ti40 amorphous powders were further milled in argon, nitrogen and oxygen atmospheres. X-ray diffraction, differential scanning calorimetry and transmission electron microscopy analyses were made to investigate the structural changes during each process. No distinguishable structural changes during further milling of the amorphous powders in argon or nitrogen atmospheres were observed. However, in an oxygen atmosphere, the amorphous phase was crystallized into intermetallic compounds and was accompanied by the occurrence of titanium oxides in the initial stage. On further milling in an oxygen atmosphere, the intermetallic compounds decomposed and only the nickel saturation solution and titanium oxides remained. A thermodynamic explanation of the crystallization and decomposition has been proposed.  相似文献   

5.
《Advanced Powder Technology》2021,32(10):3826-3844
Mechanical milling presents an effective solution in producing a homogenous structure for composites. The present study focused on the production of 0.5 wt% yttria nanoparticle reinforced 7075 aluminum alloy composite in order to examine the effects of yttria dispersion and interfacial bonding by ball milling technique. The 7075 aluminum alloy powders and yttria were mechanically alloyed with different milling times. The milled composites powders were then consolidated with the help of hot pressing. Hardness, density, and tensile tests were carried out for characterizing the mechanical properties of the composite. The milled powder and the microstructural evolution of the composites were analyzed utilizing scanning and transmission electron microscopy. A striking enhancement of 164% and 90% in hardness and ultimate tensile strength, respectively, were found compared with the reference 7075 aluminum alloy fabricated with the same producing history. The origins of the observed increase in hardness and strength were discussed within the strengthening mechanisms' framework.  相似文献   

6.
Two quarternary Ti-Al-Si-C powder mixtures, 55Ti-27Al-12Si-6C and 55Ti-36Al-6Si-3C, were mechanically alloyed. The as-alloyed and heated powders have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). XRD patterns showed diffuse halos of amorphous like phase for 20-40 h milled powders, but TEM examinations demonstrated that the 40 h milled powders were mainly composed of Ti solid solutions, with some amount of amorphous phase. SEM observations displayed that the lamellar structures of Ti and Al formed at the early stage of milling process subsequently led to the formation of nano- or sub-micrometer particles of homogeneous composition after prolonged milling to 40 h. It is deduced that the solid-stated reaction by inter-diffusion of components should be responsible for phase formation during mechanical alloying. DSC curves of the 40 h milled powders exhibited two sharp exothermal peaks, and the investigation on thermal stability of the 40 h milled powders indicated that Ti5Si3 was first formed at lower temperature, followed by Al2Ti4C2and TiC at intermediate temperature (820°C), and these phases were stable at elevated temperatures. These results raise the possibility of synthesizing TiAl-based composite with titanium silicides and titanium carbides as reinforcements by proper selection of powder compositions.  相似文献   

7.
Abstract

Powders with nominal composition Fe–14Cr–2W–0·4Ti were mechanically alloyed (MA) with Y2O3 in a planetary ball mill at two different rotational speeds. Consolidation of the as milled powders was performed by spark plasma sintering (SPS). As milled powders showed a highly deformed microstructure with elongated nanometre grains and, depending upon the rotational speed, different stages of the nanocluster evolution were observed to be produced. In the case of consolidated materials, grain growth occurred during the SPS process and it was possible to observe the influence of the MA parameters, with larger and more homogeneously distributed grains at the higher rotational speed. Additionally, Ti was observed to be incorporated to the nanoclusters after SPS, indicating a further step in their evolution during consolidation. The mechanical behaviour of the SPS compacts was evaluated by tensile and small punch testing also showing the influence of the MA parameters in the material behaviour.  相似文献   

8.
Elemental powder mixtures of 50Ti-50Al (at.%) were mechanically alloyed via various ball milling methods. The microstructural evolution during the milling indicates that the mechanical alloying behavior is strongly affected by milling methods, and horizontal ball milling is most effective for producing homogeneous metastable powders. The mechanically alloyed powders were consolidated by vacuum hot pressing followed by homogeneous annealing. Compression testing results showed that the annealed specimens still retain fine grains and have a good combination of fracture strength and ductility, as compared to cast specimens of the same alloy.  相似文献   

9.
Commercial crystalline AA4048 powders and mechanically alloyed amorphous Al60Nb40 (at.%) powders were used for fabrication of crystalline-amorphous composites containing 10, 20 and 30?vol% of amorphous phase. High pressure high temperature technique was used for powders compaction. The applied pressure was 7.7?GPa and temperature was in the range 600–1000?°C. The powders and bulk samples were characterized by structural investigations (X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, X-ray fluorescence spectroscopy), hardness and microhardness tests and measurements of density. The obtained sinters revealed relative density above 98.7%. The amorphous component was observed as agglomerates or as single particles surrounding the grains of crystalline AA4048 phase. The crystallization of amorphous phase was not observed. Simultaneously, up to 2.5?wt% of Fe was detected as impurity from milling media. Significant increase of hardness was observed, from 226 to 288HB, resulting from the presence of amorphous component which prevent from cracks propagation during deformation.  相似文献   

10.
Formation of Magnesium Silicide by Mechanical Alloying   总被引:3,自引:0,他引:3  
Elemental Mg and Si powders were mechanically alloyed in a planetary ball mill. The formation of magnesium silicide as well as the formation of magnesium oxide and hydride in the milled powders was studied in detail by X-ray diffraction and scanning differential calorimetry. It was found that direct formation of the magnesium silicide, Mg2Si, occurred after 10 hours of milling and the content of Mg2Si increased with increasing the milling duration. The activation energy for the formation of Mg2Si was calculated by the Kissinger approach to be 215 kJ/mol. Besides oxidizing and hydrizing of Mg by decomposed organic additives during mechanical alloying, an increased contamination of powders from steel and alumina milling tools with increasing milling duration was detected. A short milling duration followed by a thermal treatment was thus suggested to synthesize magnesium silicide.  相似文献   

11.
In the present investigation we have made an attempt to synthesize T-Mg32(Al,Zn)49 Frank Kasper phase and investigate the mechanical properties of the T-Phase in micro and nano scale. Single T-Phase (bcc, a = 1.42 nm) has been prepared by conventional casting with a proper combination of flux in order to avoid the loss of magnesium from the melt. Chemical analysis by energy dispersive X-ray microanalysis system attached to scanning electron microscope has confirmed the desired composition for T-phase. The as-cast material was then rapidly solidified by melt spinning and mechanically milled using a high-energy ball mill. The samples were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction techniques. The rapidly solidified foils showed the presence of mostly nanoquasicrystalline phases coexisting with a minute amount of crystalline phases in the thin region where the cooling rate is expected to be high. The dark field imaging in electron microscopy clearly confirms the existence of nano phases. Mechanically milled powder exhibited the evolution of nanophases at higher milling time. Microhardness measurement at low load was carried out in both the as-cast and nanophase materials in order to understand the influence of nanophases on the mode of deformation and cracking at low load.  相似文献   

12.
High-energy ball milling process has been applied to gadolinia-doped ceria system. The sinterability of gadolinia-doped ceria was significantly enhanced by the high-energy ball milling process. A comparison was also made of the sintering behavior of milled powders doped with gallia as a sintering aid. Dense Ce0.8Gd0.2O1.9 ceramics with 97% of the theoretical density could be obtained by sintering the milled mixture with 0.5 mol% Ga2O3 addition at 1,250 °C for 5 h.  相似文献   

13.
Two methods were used to obtain amorphous aluminium alloy powder: gas atomization and melt spinning. The sprayed powder contained only a small amount of the amorphous phase and therefore bulk composites were prepared by hot pressing of aluminium powder with the 10% addition of ball milled melt spun ribbons of the Al84Ni6V5Zr5 alloy (numbers indicate at.%). The properties were compared with those of a composite containing a 10% addition of Al2O3 ceramic particles. Additionally, a composite based on 2618A Al alloy was prepared with the addition of the Al84Ni6V5Zr5 powder from the ribbons used as the strengthening phase. X-ray studies confirmed the presence of the amorphous phase with a small amount of aluminium solid solution in the melt spun ribbons. Differential Scanning Calorimetry (DSC) studies showed the start of the crystallization process of the amorphous ribbons at 437 °C. The composite samples were obtained in the process of uniaxial hot pressing in a vacuum at 380 °C, below the crystallization temperature of the amorphous phase. A uniform distribution of both metallic and ceramic strengthening phases was observed in the composites. The hardness of all the prepared composites was comparable and amounted to approximately 50 HV for those with the Al matrix and 120 HV for the ones with the 2618A alloy matrix. The composites showed a higher yield stress than the hot pressed aluminium or 2618A alloy. Scanning Electron Microscopy (SEM) studies after compression tests revealed that the propagation of cracks in the composites strengthened with the amorphous phase shows a different character than these with ceramic particles. In the composite strengthened with the Al2O3 particles cracks have the tendency to propagate at the interfaces of Al/ceramic particles more often than at the amorphous/Al interfaces.  相似文献   

14.
We employed a high-energy ball mill for the synthesis of nanograined Ti55C45 powders starting from elemental Ti and C powders. The mechanically induced self-propagating reaction that occurred between the reactant materials was monitored via a gas atmosphere gas-temperature-monitoring system. A single phase of NaCl-type TiC was obtained after 5 h of ball milling. To decrease the powder and grain sizes, the material was subjected to further ball milling time. The powders obtained after 200 h of milling possessed spherical-like morphology with average particle and grain sizes of 45 μm and 4.2 nm, respectively. The end-products obtained after 200 h of ball milling time, were then consolidated into full dense compacts, using hot pressing and spark plasma sintering at 1500 and 34.5 MPa, with heating rates of 20 °C/min and 500 °C/min, respectively. Whereas hot pressing of the powders led to severe grain growth (~ 436 nm in diameter), the as-spark plasma sintered powders maintained their nanograined characteristics (~ 28 nm in diameter). The as-synthesized and as-consolidated powders were characterized, using X-ray diffraction, high-resolution electron microscopy, and scanning electron microscopy. The mechanical properties of the consolidated samples obtained via the hot pressing and spark plasma sintering techniques were characterized, using Vickers microhardness and non-destructive testing techniques. The Vickers hardness, Young's modulus, shear modulus and fracture toughness of as-spark plasma sintered samples were 32 GPa, 358 GPa, 151 GPa and 6.4 MPa·m1/2, respectively. The effects of the consolidation approach on the grain size and mechanical properties were investigated and are discussed.  相似文献   

15.
We report the preparation and characterization of amorphous/non-equilibrium solid solution Fe100 − xZrx (x = 20–35) alloys by mechanical alloying process. The microstructure and magnetic properties of milled powders have been studied as a function of Zr substitution. The effective magnetic moment of as-milled powders decreases as concentration of Zr is increased. Thermomagnetization measurements confirmed that the Fe80Zr20 sample exhibits two clear magnetic phase transitions due to the co-existence of an amorphous phase and a Fe rich non-equilibrium solid solution. All the other samples exhibiting an amorphous structure showed a single magnetic phase transition with Curie temperature of ~ 570 °C,which did not vary much with different composition. The Curie temperature of the mechanically alloyed powders is noticeably higher than those of melt-spun amorphous ribbons.  相似文献   

16.
In this study, LaB6–Al2O3 nanocomposite powders were synthesized via ball milling-assisted annealing process starting from La2O3–B2O3–Al powder blends. High-energy ball milling was conducted at various durations (0, 3, 6 and 9 h). Then, the milled powders were annealed at 1200 °C for 3 h under Ar atmosphere in order to obtain LaB6 and Al2O3 phases as reaction products. X-ray diffractometry (XRD), scanning electron microscopy/energy-dispersive spectrometry (SEM/EDS) and transmission electron microscopy (TEM) techniques were utilized to carry out microstructural characterization of the powders. No reaction between the reactants was observed in the XRD patterns of the milled powders, indicating that high-energy ball milling did not trigger any chemical reactions even after milling for 9 h. LaAlO3 and LaBO3 phases existed in the annealed powders which were milled for 0, 3 and 6 h. LaBO3 phase was removed after HCl leaching. 9-h milled and annealed powders did not exhibit any undesired phases such as LaAlO3 and LaBO3 after leaching step, and pure nanocrystalline LaB6–Al2O3 composite powders were successfully obtained. TEM analyses revealed that very fine LaB6 particles (~?100 nm) were embedded in coarse Al2O3 (~?500 nm) particles.  相似文献   

17.
《Advanced Powder Technology》2020,31(10):4319-4335
In this study, the Al59Cu25.5Fe12.5B3 nanoquasicrystalline alloy and related crystalline phases were synthesized through mechanical alloying using a high-energy ball milling and consolidated by a cold isostatic pressing apparatus. This paper focuses on the synthesis, structural and microstructural evolutions, thermal stability, microhardness, and electrical and optical properties of the Al59Cu25.5Fe12.5B3 nanoquasicrystalline alloy for solar selective absorber usages. The structural evolutions of the mechanically alloyed and heat-treated AlCuFeB powders were investigated by X-ray diffractometry. Accordingly, the effect of milling time and heat treatment on the formation of quasicrystalline and related crystalline phases were studied in the AlCuFeB alloy system. The microstructure, morphology, and chemical microanalysis of the un-milled and as-milled powders were examined by field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. The composition of the as-milled AlCuFeB powders was estimated employing inductively coupled plasma-atomic emission spectroscopy. The thermal stability of the AlCuFeB powders was recorded by differential thermal analysis, and the weight gain of the particles during annealing was investigated through thermogravimetric analysis. The nanostructured Al59Cu25.5Fe12.5B3 stable quasicrystalline phase and crystalline Al(Cu,Fe) solid-solution were synthesized by the ultrafast milling procedure in 1 h. The rationale behind using the term ultrafast synthesis is to synthesize the QC i-phase only by the high-energy ball milling procedure in short-term ball milling without subsequent annealing treatment. However, the single quasicrystalline phase could not be obtained even after the annealing treatment. The quasicrystalline size was calculated by the Williamson–Hall method and optimized by the Rietveld refinement procedure, and it was found that the size is varied between 53 and 61 nm. Furthermore, the particle size distribution of the as-milled AlCuFeB powders was measured using laser static light scattering, which ranges from 0.1 to 50 μm. The microhardness of the consolidated as-milled and heat-treated samples was estimated utilizing the Vickers microhardness indenter. At the same time, their electrical resistivity was assessed by the four-point probe method at room temperature. The spectral analyses of absorption on the consolidated as-milled samples were carried out in the ultraviolet, visible, and near-infrared regions. It was found that the presence of the quasicrystalline phase in the AlCuFeB alloy prominently improves the microhardness, electrical resistivity, and particularly sunlight absorptance.  相似文献   

18.
Mechanically alloyed Mg2Ni/Ni nano-composite and Zr55Cu30Ni5Al10 amorphous powders were hydrogen charged at constant pressure under ball milling. While the Mg-based samples were able to absorb large amount of hydrogen under static conditions, and from the very onset of the mechanical treatment, an incubation milling period was needed for the hydrogen activation in the case of the amorphous sample. A progressively decreasing rate characterizes the process kinetics in the case of Mg2Ni/Ni, whereas a self increasing sigmoid trend was observed for the multicomponent Zr alloy, which showed structural demixing phenomena in the absorption course. Irrespective of the system, the maximum absorption rate was strongly dependent on the milling intensity (Watt·g-1). The hydriding rate (mole·g-1s-1) and the mechanochemical yield (mole·Joule-1) were used to compare the processes on an absolute scale. In the case of Mg-based alloy, comparison was also made between mechanically induced and thermally (static) activated hydriding processes. Attempt was also made to work out the hydrogen atoms absorbed at the ball-hit event.  相似文献   

19.
In order to investigate the effect of the preparation technique on quasicrystal formation, amorphous (Zr0.585Ti0.082Cu0.142Ni0.114Al0.077)100?x Nb x alloys with x = 2.5 and 5 at.% were produced by melt spinning and by ball milling of crystalline intermetallic compounds. The calorimetric and microstructure investigations revealed striking similarities between the differently synthesized samples. All the samples are characterized by a two-step crystallization process in which the first crystallization product does not depend on the way of preparation. In fact, the same metastable nanoscale quasicrystalline phase has been obtained by partial devitrification of ball-milled powders as well as of melt-spun ribbons. This demonstrates that ball milling is an alternative processing route to rapid solidification techniques for the preparation of quasicrystal-forming Zr-based alloys.  相似文献   

20.
Mechanically alloyed Al-4.9Ni-4.9Ti powders were prepared by milling mixed aluminium, titanium and nickel powders, and then consolidated by hot hydrostatic extrusion. The microstructures of milled powders and extruded bars were characterized by X-ray diffraction and transmission eIectron microscopy observation. The results show that mechanical alloying and consolidating processes have great effects on the microstructures and mechanical properties of extruded materials. Polycrystalline materials having an ultrafine grain size may be prepared by mechanical alloying. The strength and thermal stability are improved with the increasing of processing time of mechanical alloying, since grain size decreases and volume fraction of dispersoids increases as milling time increased  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号