Explosive Consolidation Research Articles

Synthesis, characterization and mechanical behaviour of an in situ consolidated nanocrystalline FeCrNi alloy

IntroductionCurrently, nanocrystalline materials are being widelyinvestigated due to their unique properties. This interest hasspawned the development of various techniques to synthe-size materials exhibiting grain sizes (\20 nm) wherephysical properties are the most exotic. Such processesinclude: high-energy ball milling [1, 2], pulsed electrode-position [3], chemical vapour condensation [4], inert gascondensation [5] etc. However, nanocrystalline samplesproduced from these techniques are either in the formof powders or thin films. Successful consolidation to arte-fact free, fully dense material is required if structuralapplications are ever to be adopted. Many methods toconsolidate these materials (i.e., hot compaction [6],explosive consolidation [7], hot isostatic pressing [8], pre-annealing–compaction–sintering [9] etc.) have been repor-ted in the literature with partial success. In general, thesuccess of these techniques for consolidation hinges on theapplication of high temperatures and pressures, which leadto explosive grain growth in nanocrystalline materials.In situ consolidation technique as developed by Youssefet al. [10] seems promising for the synthesis of consolidatednanocrystalline materials as the step of sintering to bulkdensity is no longer a need and can be eliminated. However,this technique has not been reported widely in the literatureand has been limited to nanocrystalline Zn, Al, Al alloys,copper and copper-based alloys [10, 11]. This study showsthat in situ consolidation of a FeCrNi alloy is possible usingcombination of room temperature (RT) milling and liquidnitrogen temperature milling.Nanocrystalline materials produced by high-energy ballmilling have not been well characterized and the micro-structure of these materials is not well understood. Theprimary challenge in characterization is TEM samplepreparation from ball-milled powders. Nanocrystallinepowders as produced by ball milling are too coarse to beexamined under TEM and the sample preparation for TEManalysis on such powders is not a trivial task. In general,two methods are used for the preparation of conventionalmetallic samples for TEM analysis: electro jet polishingand dimpling followed by ion milling. Nanocrystallinematerials produced by consolidation of ball-milled pow-ders can be problematic for these preparation techniques asthe consolidated samples must first be mechanically thin-ned to \100 lm before being chemically thinned to thefinal thickness. If the material exhibits poor inter-particlebonding, the sample may not withstand the final thinning

Explosive Consolidation and its Application on Preparing of Ultra-Fine Grained Tungsten Plasma Facing Material

Nuclear fusion is a promising source of environmental friendly energy for the future, and the ultra-fine grained Tungsten (W) is a hopeful candidate material to be used as plasma-facing materials (PFMs), which are the key materials in the International Thermonuclear Experimental Reactor (ITER), for its many useful advantages. While, due to its high melting point and high sintering temperature needed, the ultra-fine grain sized tungsten is not easy to be fabricated. In this paper, the method of explosive consolidation of powders as well as its mechanism and improvements are discussed, and finally the possibility of using this method to preparing of ultra-fine grained W plasma facing material are also introduced.

Explosively Consolidated Powder-In-Tube MgB$_{2}$ Superconductor Aided by Post-Thermal Treatment

A MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> superconductor was prepared from Mg flakes or powders and B powders using the powder-in-tube technique with explosive consolidation. Compaction of Mg and B powders resulted in a two-phase alloy, due to the relatively low temperature developed during compaction as well as the very short duration of the process. Formation of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was obtained after subsequent heat treatment in argon atmosphere at a maximum temperature of 950degC.

High electrical resistance composite magnets of Sm2Fe17N3 powders coated with ferrite layer for high frequency applications

This paper describes a novel type of high electrical resistance composite magnet. They were made by compacting or consolidating Sm–Fe–N powders coated with a continuous ferrite layer, which suppresses intergrain conductivity but sustains magnetic exchange interactions among grains. Sm–Fe–N powders (2μm in size) were coated with an “iron ferrite” (an intermediate between magnetite and maghemite) layer by ferrite plating, an aqueous process. They were compacted at 100MPa to form a ferrite/SmFeN composite magnet (note that row Sm–Fe–N powders cannot be consolidated strongly enough to form magnets), and then consolidated to 92–94vol% by the explosive consolidation technique. Coercivity and rectangularity of the compacting composite magnet decreased slightl by 2.0% and 1.4%, respectively, when compared to those of Sm–Fe–N powder compact. We also estimated the resistivity of fully dense ferrite/Sm–Fe–N magnet to be about 4000μΩcm, ten times higher than the estimated value of a fully dense Sm–Fe–N magnet. Thus, the ferrite layer in our composite magnet retains magnetic exchange coupling among Sm–Fe–N grains, and yet suppresses intergrain electrical coupling to increase resistivity. This will decrease eddy current loss and improve high frequency characteristics of composite magnets.

Preparation and characterization of superconducting MgB2 rods

AbstractSuperconducting Cu/Fe/MgB2 and Steel/Cu/MgB2 rods were prepared through the ex‐situ modified PIT technique with explosive consolidation method. The phase composition, microstructural features were investigated by X‐ray diffraction and scanning electron microscope. The AC susceptibility for a core samples was measured by the AC susceptometry. Measurements of the magnetization hysteresis loops were also carried out. It is found that no impurity phase was formed in MgB2 rods. In addition, it was found that grains in both Cu/Fe/MgB2 and Steel/Cu/MgB2 rods are densely packed. The magnetic measurements show that the critical temperature of Cu/Fe/MgB2 and Steel/Cu/MgB2 rods is 37.7 K and 37.6 K, respectively. The high critical current density of 9.22 × 105 A/cm2 (4.1 K, 0.2 T) was obtained for Steel/Cu/MgB2 rod. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Characterization of 3-phase (ternary-like) n-type and p-type thermoelectric materials fabricated by explosive (shock-wave) consolidation

Three-phase powder mixtures of Bi–Te–Se and Bi–Te–Sb were prepared by cylindrical explosive consolidation to emulate traditional, melt-grown n-type and p-type doped Bi 2Te 3 thermoelectric materials. The powder diameters ranged from 40 μm to 3 μm, with starting Bi and Te particle Vickers microindentation hardnesses of 0.18 and 0.56 GPa, respectively, in contrast to average shocked n-type and p-type monolith microindentation hardnesses of 1.15 and 1.31 GPa, respectively. The values may also be contrasted to 0.72 and 0.68 GPa hardnesses for melt-grown n-type and p-type materials, respectively. Shock consolidated monolith microstructures were characterized by optical metallography, SEM and TEM along with EDS analysis and XRD of all materials, including the melt-grown materials which had measured thermoelectric parameters considerably in excess of the shock (explosively) consolidated monoliths. Notable shock microstructures were characterized by deformation twins, while the melt-grown materials contained considerable, fine eutectic microstructures. These shock-grown microstructures do not appear to be conducive to thermoelectric figure of merit optimization.

Explosive Shock-Wave Consolidation of Aluminum Powder/Carbon Nanotube Aggregate Mixtures: Optical and Electron Metallography

The formation of conventional metal-matrix composites reinforced with carbon nanotubes (CNTs) has proven difficult because of the agglomeration and inability of CNTs to disperse. We have explored the explosive consolidation of 150-μm aluminum powder/multiwalled carbon nanotube (MWCNT) aggregates (including multiconcentric fullerenes) at volume percentages of 2 and 5 pct. These consolidated mixtures formed two-phase, monolithic systems (TPSs) with the MWCNT aggregate material spreading along the Al grains and forming carbon phases mainly at the Al particle triple points. The Al powder particle (or grain) hardness increased from HRE 22 to HRE 40 for the consolidated Al, while the two-phase system hardness dropped from HRE 40 to HRE 39 and 33, respectively, for 2 and 5 vol pct MWCNT aggregate additions. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) observations illustrate a laminate-like structure of the consolidated MWCNT aggregate material, which is easily delaminated, causing intergranular (Al) failure. The Al grains exhibited a shock-induced dislocation substructure (0.5 to 3 μm) and recrystallized subgrains, which increased the individual particle/grain Vickers hardness from 24 to 43 HV.

Characterization of micro and nano two-phase regimes created by explosive shock-wave consolidation of powder mixtures

Mechanically mixed Al powders (150 μm in diameter) and different combinations of 21% volume fraction of SiC or Al 2O 3, (30 μm or 30 nm particle sizes) were green compacted to 70% density. The compactions were explosively consolidated in cylindrical fixtures utilizing ammonium nitrate-fuel oil (ANFO) to fabricate stacks of two-phase, cylindrical monoliths 50 mm × 32 mm (diameter), along with pure aluminum (Al-1100) monoliths (as reference). Results show that the consolidated aluminum increases from a starting powder hardness of 24 HV to 46 HV. Correspondingly, hardness for the two-phase systems exhibits an increment by ∼ 60% from the reference SWC Al-1100, while the total elongation declined by ∼ 60%. Microstructures for these systems were also observed by optical metallography and TEM to exhibit the different second phases' consolidation and its effect on the fracture mechanisms. Images presented show the different rupture mechanisms observed from the different systems' samples; the aluminum ductile-dimple fracture, the intergranular debonding caused by the micron-sized ceramic second phase and the quasicleavage and transgranular fractures caused by the nano-ceramic second phase.

Preparing tin-doped indium oxide ceramic bulk via explosive consolidation and sintering of nanopowders

The tin-doped indium oxide (ITO) ceramic ultra-dense target is the crucial material in spurting preparation of optical-electric films. The difficulty in target fabrication is due to ITO decomposing at high temperatures. In this paper, commercial ITO nanometer powders are used and are explosively shock consolidated with two different sets and different explosives. Experiment data indicate that the shock velocity should be less than 4000 m/sec, and the shock pressure should be more than 6 and even 12 GPa for obtaining good consolidation. The samples are rapidly sintered at a high temperature after shock treatment. A suitable sinter temperature of ITO nanopowders compacted via explosive consolidation (≈1000°C) is determined by a differential thermal analysis. Scanning electron microscope images show that ITO ceramic decomposes and sublimates at a high temperature. The expansion factors of the samples from our experiments and commercial targets obtained by high isostatic pressing (HIP) are measured: α l = 7.81 → 10−6 K−1 for samples sintered at 1000°C, α l = 8.8 → 10−6 K−1 for samples sintered at 900°C, and α l = 6.89 · 10−6 K−1 for HIP samples.

Explosive consolidation of Sm–Fe–N and Sm–Fe–N/(Ni, Co) magnetic powders

Explosive consolidation of Sm 2 Fe 17 N x and Sm 2 Fe 17 N x /(Ni or Co) magnetic powders were attempted to consolidate fully dense magnetic compacts. Dense Sm 2 Fe 17 N x and Sm 2 Fe 17 N x /(Ni or Co) bulk materials were obtained by cylindrical explosive consolidation technique using water as a pressure transmitting medium. The values of ( BH ) max of Sm 2 Fe 17 N x , Sm 2 Fe 17 N x –5 wt%Ni and Sm 2 Fe 17 N x –30 wt%Co magnets obtained were 23.8, 16.3 and 17.5 MGOe (190, 130 and 140 kJ / m 3 ) , respectively.

Research of Energy Deposition Caused by Pore Collapse

Mechanisms of energy deposition at the interface of particles in explosive compaction of metal powders are analyzed. A one-dimensional model of a spherically symmetric pore is proposed to reflect the collapse. The effect of heat conduction is taken into account in axisymmetric flow equations, and the temperature distribution during the sphere collapse is solved by the finite-difference method under the assumption that the material is rigid-plastic or thermoviscoplastic. The results show that the effect of heat conduction becomes more remarkable if the scale of the holes is small. During the collapse, the inner surface is converted from the elastoplastic to the fluid state, and its temperature becomes much higher than that of the remaining part of the sphere, which favors retaining of the amorphous structure in explosive consolidation of amorphous powders.

Shock Consolidation of Sm-Fe-N Magnetic Powders and Magnetic Properties

Sm2Fe17Nx compound is a prospective candidate as a material for high performance permanent magnets because of its good intrinsic magnetic properties with a Curie temperature of 747K, a room-temperature anisotropy field of 14T and a room-temperature saturation magnetization of 1.5T. However, Sm2Fe17Nx compound decomposes to -Fe and Sm nitride above 873K and conventional powder metallurgy processing techniques fail to meet the processing requirements. Shock consolidation is a viable alternative to process this compound. Fully dense Sm2Fe17Nx bulk materials were fabricated by cylindrical explosive consolidation technique using water as a pressure transmitting medium. Explosive consolidation is performed under cold state and fully dense materials can be obtained without any degradation of the characteristics of the powder states. Sound compacts were obtained without any cracks or teas, and the value of (BH)max of Sm2Fe17Nx compact is 23.8 MGOe.

Numerical Simulation of Explosive Consolidation of Superconducting Bulk Components

The explosive compaction technique has been used for manufacturing bulk superconducting components, e.g. three dimensional plates and axisymmetric billets, rods, discs and tubes, with high density and good electrical and magnetic characteristics. The high pressures and temperatures developed in a very short time result in sintering and in fracturing of the original grains, inducing primarily line defects that would provide flux pinning centers in Type II superconductors. Densified superconducting ceramic YBCO bulk components of various geometries were produced by this dynamic technique and the whole process was simulated by the explicit finite element code LS-DYNA3D. In this paper, experimental and numerical results of the fabricated superconducting bulks are reported and discussed. Applications are also briefly outlined.

Explosive consolidation and jacketing of tungsten base materials in hot conditions

The process of consolidation of nanocrystalline W and clad W-(15-50%)Cu composition powders, as well as jacketing of conventional heavy alloys by steel in hot conditions under shock wave loading, was studied. The temperature of loading was in the range 20-1200°C and intensity of loading was up to 10 GPa. As investigation showed, the application of high temperatures and consolidation of W and W-Cu composition powders in two stages (first at room temperatures and second, in hot conditions) enables the powders to be compacted to near theoretical densities with high value of hardness. The value of densityand hardness depends on treatment temperature and the content of Cu in composition. The investigation of joining processes and jacketing of W-Ni-Feheavy alloys (WHA) by steel showed that, depending on the loading temperature, it is possible to achieve the jacketing by steel with the formation of an intermediate layer upon the whole length of the WHA. The structure of the intermediate layer, as well its properties, depend on the value of the loading temperature.

On appearance of "cold" layer in explosive consolidation of powders

Abstract. Numerical modeling of explosive consolidation of powders under two-dimensional conditions has been performed. Various regimes of flow depending on detonation velocity have been considered. The appearance of “cold” layer during explosive consolidation of powders has been studied by calculations.

Metallic/CerMet laminates from explosively consolidated powders

The technique this study focuses on is the use of explosive consolidation to create distinct interfacial systems from metallic and metallic-cermet powder mixtures. One of the advantages of this technique is that undesired intermetallic formation between the constituents (which can happen with other techniques such as hot-pressing) is usually avoided due to the relatively low temperatures involved. In addition, interfacial strengths actually higher than the surrounding bulk material are achieved. Finally, since extremely high dislocation densities are created by the passage of the shock wave, the strength contribution from dislocation pile-ups is maximized.

Synthesis of aluminum infiltrated boron suboxide drag cutters and drill bits

Synthesis of boron suboxide (B6O) was made by reactive sintering of crystalline boron and zinc oxide powders at 1450 °C, in argon, for 12 h. After sintering, Vickers microhardness testing was performed on the material synthesized and an average hardness value of 34 GPa was obtained. Sintered suboxide (in crushed and ground powder form) was then analyzed through optical and scanning electron microscopies and X-ray diffraction. Following the completion of the analyses, consolidation of the powder was performed. Two different routes were carried out: (1) “explosive consolidation” which was performed in double tube (with a density value of 2.22 g/cm3) and single tube (with a density value of 2.12 g/cm3) canister design arrangements and (2) “hot pressing” which was performed in a graphite die assembly, at 1600 °C, in vacuum, for 2 and 4 h (with density values of 2.15 and 2.18 g/cm3 respectively). Consolidated samples of both routes showed different levels of mechanical attachment, agglomeration, porosity, fracture toughness and fracture strength values, whereas microhardness values and X-ray diffraction plots (as shown in Table I and Figs 6 and 8 respectively) were determined to be similar. Following characterizations, compacts of both routes were then given a high temperature sintering treatment (pressureless sintering) at 1800 °C, in vacuum, for full densification. Both in the “as consolidated” and “densification sintered” stages test results revealed the most desirable and well-established properties for the “explosively consolidated double tube design” compacts (with densification sintered density, microhardness and fracture toughness values of 2.46 g/cm3, 38 GPa and 7.05 MPa m1/2 respectively). Consolidation and desification sintering steps were then followed by a pressureless infiltration step. Aluminum was infiltrated into densification sintered “double tube design consolidated” and “4 h of pressed” samples (better-compacted and better-sintered compacts) in the temperature range 1100–1250 °C, in argon, for 10 h. During infiltrations, the optimum temperature of the infiltration process was determined to be 1200 °C. Characterization results revealed the most uniform and well established properties once more for the double tube design explosively consolidated compact (with aluminum infiltrated density, microhardness and fracture toughness values of 2.55 g/cm3, 41 GPa and 8.70 MPa m1/2 respectively).

Hot Explosive Consolidation of Mo-Ti and W-Ti Alloys

A novel hot explosive compaction (HEC) technique has been applied to molybdenum (Mo) and tungsten (W)-based titanium (Ti) alloys. The precursor powders of the alloy billet were surrounded by an exothermic mixture, which, when ignited, released a large amount of heat via a self-propagating high-temperature synthesis (SHS) reaction. Heat from the SHS reaction diffused into the precursor powder bed, causing the interior temperature to rise above 1,500°C. When the powder bed became isothermal, it was consolidated to high density by pressure waves generated by the detonation of an explosive. The amount of explosive charge and the molar ratio of exothermic mixture to sample were adjusted to produce full-density Mo-Ti and W-Ti alloys. The billets were sectioned and examined with scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), x-ray diffraction analysis (XRD), and microhardness measurements. In context of the fabrication process the similarities and differences of the resultant product microstructures are discussed.

Explosive consolidation of amorphous cobalt-based alloys

This paper addresses the explosive consolidation of amorphous cobalt-based alloys. Using the experimental setup introduced in the present paper, specimens with high compact density, excellent magnetic properties and great wearability have been made. In comparison with permalloy and ferrite, the present specimens exhibit superior magnetic properties. Therefore, the compact is deemed as being a promising material for magnetic recording heads.

Explosive consolidation of mechanically alloyed Ti-Al alloys

Ti-Al intermetallics are of great interest because of their attractive mechanical properties, but they require advanced processing methods, due to their low ductility at room temperature. In this work, the following processes were employed in order to obtain bulk TiAl and Ti 3Al intermetallics: (1) mechanical alloying: ball milling of elemental Ti and Al powders caused formation of supersaturated solid solutions; (2) explosive consolidation: in this operation no phase transitions were observed and sample densities after consolidation reached over 90% of theoretical values; (3) annealing: resulted in additional increase of material density and caused phase transitions leading to formation of TiAl and Ti 3Al compounds.