共查询到20条相似文献,搜索用时 15 毫秒
1.
E. V. Esquivel L. E. Murr E. A. Trillo M. Baquera 《Journal of Materials Science》2003,38(10):2223-2231
Plane-wave shock-loaded Ni exhibits {111} microtwins which increase in frequency with increasing peak shock pressure above a critical twinning pressure of 30 GPa. In contrast, microbands coincident with traces of {111} are produced below impact craters in Ni targets by stainless steel projectiles at velocities up to 3.5 km/s. The microband widths are ten times the 0.02 m twin widths and are characterized by misorientations of roughly 2°. Both shock-loaded and impacted Ni have similar dislocation cell structures which decrease in cell size with increasing pressure or equivalent stress. The exclusive formation of microbands in connection with impact craters in Ni is expected on the basis of its high SFE (130 mJ/m2), and a simple dislocation model is developed for the microtwin-microband transition based on graphical summaries which include shock (stress) geometry and SFE effects in FCC metals and alloys. 相似文献
2.
C. Berger A. Gabutti S. Janos P. Carelli M. G. Castellano R. Leoni D. Peschiaroli 《Journal of Low Temperature Physics》1993,93(3-4):509-514
The presented results are part of a feasibility study of superheated superconducting microstructure detectors. The microstructures (dots) were fabricated using thin film patterning techniques with diameters ranging from50µm up to500µm and thickness of1µm. We used arrays and single dots to study the dynamics of the superheating and supercooling phase transitions in a magnetic field parallel to the dot surface. The phase transitions were produced by either varying the applied magnetic field strength at a constant temperature or changing the bath temperature at a constant field. Preliminary results on the dynamics of the phase transitions of arrays and single indium dots will be reported. 相似文献
3.
The relatively complex microstructures developed at the interface between ferritic steel and weld metal on austenitic-ferritic transition joints have been examined by metallographic observation and by hardness tests in the as-welded condition and in the as-welded-and-tempered condition. Both austenitic stainless steel and nickel-based filler metals were used in welds. On as-welded specimens a sharp change of hardness in low-alloy steel has been measured, with increasing distance from weld metal; the hardness values have been related to the observed metallographic constituents. On post-weld heat treated specimens, the behaviour is different according to the composition of filler material, either austenitic steel or nickel-based alloy. In the case of austenitic filler material, a dark-etching narrow diffusion region of carbon toward weld metal is formed, with an adjacent markedly decarburized zone, exhibiting the minimum microhardness values in a narrow band of about 60 micrometres. Since this sharp structural variation is recorded just in the zone where often failures occur, the final post-weld heat treatment appears to be proposed with due caution. In the case of nickel-based filler material, carbon diffusion is inhibited by the precipitation of alloy carbides at the weld interface. This determines a more homogeneous heat affected zone (HAZ) in the ferritic steel and a reduced decarburization near the fusion line after a post-weld heat treatment, confirming the reasons of the preference recognized to this filler material, especially when service temperature is elevated and submitted to frequent changes, or whenever a post-welded heat treatment is required. 相似文献
4.
《Journal of Experimental Nanoscience》2013,8(1):41-51
Nickel nanoparticles have been extensively characterised by atomic force microscopy (AFM), scanning electron microscopy (SEM) and confocal micro-Raman spectroscopy. AFM underestimates the particle size compared to SEM measurements. It is shown that Raman spectroscopy can detect the nanometre-thick NiO layer on the particles having frequency shifts of the modes indicative of phonon confinement. The magnetic properties of the particles are studied by ferromagnetic resonance (FMR) of magnetic field aligned particles. The alignment is achieved by suspending the particles in the liquid crystal MBBA and freezing the liquid in a 0.4 T DC magnetic field. The in-field solidification locks the direction of maximum magnetisation of the particles parallel to the direction of the applied DC magnetic field. This removes the effects of dynamical particle fluctuations of the nanoparticles on the magnetic properties allowing a study of the intrinsic magnetic properties of the magnetic nanoparticles. The intensity of the FMR signal decreased with lowering temperature for the particles frozen in the liquid in a 0.4 T DC magnetic field. The effect is suggested to be due to a reduction of the microwave skin depth with lowering temperature. 相似文献
5.
Characterisation of moisture-dependent cohesive zone properties for adhesively bonded joints 总被引:1,自引:0,他引:1
Structural adhesives are being widely used in the aerospace and automobile industries. However, in many applications, aggressive environments damage the adhesive systems and degrade the structural performance of bonded members. Cohesive zone models are often employed in the numerical analysis of adhesively bonded structural joints. To accurately model these bonded joints, the characterisation of the cohesive zone properties for different environmental conditions is important. In this regard, an experimental-numerical approach was developed to characterise the environment-dependent cohesive zone properties based on a miniature cantilever peel test. As moisture is a commonly encountered aggressive environment, the current methodology was implemented to characterise the moisture-dependent cohesive zone properties for an Al 2024-T3 and FM73 system. 相似文献
6.
《Materials Science & Technology》2013,29(3):206-212
AbstractThe hot deformation behaviour of polycrystalline nickel has been characterised in the temperature range 750–1200°C and strain rate range 0·0003–100 s?1 using processing maps developed on the basis of the dynamic materials model. The efficiency of power dissipation, given by [2m/(m+1)], where m is the strain rate sensitivity, is plotted as a function of temperature and strain rate to obtain a processing map. A domain of dynamic recrystallisation has been identified, with a peak efficiency of 31% occurring at 925°C and 1 s?1. The published results are in agreement with the predictions of the processing map. The variations of efficiency of power dissipation with temperature and strain rate in the dynamic recrystallisation domain are identical to the corresponding variations of hot ductility. The stress–strain curves exhibited a single peak in the dynamic recrystallisation domain, whereas multiple peaks and ‘drooping’ stress–strain curves were observed at lower and higher strain rates, respectively. The results are explained on the basis of a simple model which considers dynamic recrystallisation in terms of rates of interface formation (nucleation) and migration (growth). It is shown that dynamic recrystallisation in nickel is controlled by the rate of nucleation, which is slower than the rate of migration. The rate of nucleation itself depends on the process of thermal recovery by climb, which in turn depends on self-diffusion.MST/1524 相似文献
7.
The solid-state diffusion bonding was carried out between commercially pure titanium and Type 304 stainless steel using nickel
as an interlayer in the temperature range of 800–900 °C for 9 ks under 3 MPa load in vacuum. The transition joints thus formed
were characterized in the optical and scanning electron microscopes. The inter-diffusion of the chemical species across the
diffusion interfaces were evaluated by electron probe microanalysis. TiNi3, TiNi and Ti2Ni are formed at the nickel–titanium (Ni–Ti) interface; however, the stainless steel–nickel (SS–Ni) diffusion interface is
free from intermetallic compounds up to 850 °C temperature. At 900 °C, the Ni–Ti interface exhibits the presence of α-β Ti
discrete islands in the matrix of Ti2Ni and λ + χ + α-Fe, λ + FeTi and λ + FeTi + β-Ti phase mixtures occur at the SS–Ni interface. The occurrence of different
intermetallics are confirmed by the x-ray diffraction technique. The maximum tensile strength of ∼276 MPa and shear strength
of ∼209 MPa along with 7.3% elongation were obtained for the diffusion couple processed at 850 °C. At the 900 °C joining temperature,
the formation of Fe–Ti base intermetallics reduces the bond strength. Evaluation of the fracture surfaces using scanning electron
microscopy and energy dispersive spectroscopy demonstrates that failure takes place through Ni–Ti interface up to 850 °C and
through the SS–Ni interface of the joint when processed at 900 °C. 相似文献
8.
An important feature of laser welded joints is the high level of strength and toughness mismatch developed between the weld and the parent plate. As a result, defects are frequently located in regions with high strength and toughness gradients. To address this issue, toughness tests have been performed on laser welded joints with strength mismatches in excess of 2. Toughness tests have been performed on high and low constraint mode I geometries and mixed-mode I/II configurations. In highly constrained geometries, the local toughness dominates the failure process causing the crack to deviate into harder and more brittle weld metal, while in low constraint configurations, the size of the plastic zone promotes crack deviation into the softer and tougher parent plate. In Charpy tests the crack also deviates into the tougher parent plate giving potentially misleading indications of the behaviour of defects in highly constrained joints. The experiments are modelled by a local approach technique for functionally graded materials in which the local yield strength and toughness are allowed to vary spatially. 相似文献
9.
《Materials Science & Technology》2013,29(3):313-321
AbstractInert gas atomised Inconel 718 superalloy powder was characterised for various important properties and subsequently consolidated by hot isostatic pressing (hipping) at 1200° C and 120 MPa for 3 h. The density of the as compacted material was nearly the same as its theoretical density. Optical microscopy of as hipped material showed a fine grained structure with no porosity but having annealing twins and prior particle boundaries (PPBs). Electron probe microanalysis (EPMA) studies revealed that the PPBs were decorated with Al, Ti oxides, and MC type carbides enriched with Nb and Ti. In addition to these phases, the presence of very fine γ"-Ni3Nb and γ'-Ni3(Al,Ti) precipitates in the matrix were revealed by TEM analysis, which indicates that the compacted material was partially aged during the slow cooling stage of hipping. Tensile tests conducted on the as hipped material showed that the ultimate tensile strength (UTS) and ductility values were comparable to those obtained in the (solution treated and two step aged) wrought alloy 718, although its yield strength was marginally lower at room temperature. 相似文献
10.
《Materials at High Temperatures》2013,30(1):7-12
AbstractImpedance spectroscopy has been used to measure the electrical properties of oxide scales formed from oxidation of IN738LC superalloy at high temperature. Electrical resistance and capacitance of the oxide scales were obtained from the simulation of the measured impedance diagrams based on the equivalent circuit model, which represents the features of the oxide scales. For oxidation of IN738LC superalloy, the electrical resistance of oxide scales increased with increasing oxidation time for the specimens exposed to air at 900°C. However, for the specimens oxidised at 1,200°C, the oxide scales showed very low electrical resistance, which indicated that cracking and spallation in oxide scales occurred continuously. By using scanning electron microscopy and X-ray diffraction techniques, the composition and microstructure of the oxide scales were examined. It was found that electrical properties were determined, not only by the microstructure of oxide scales, but also by the composition of the oxide scales. By determining the relationship between electrical properties, microstructure and composition of oxide scales, impedance spectroscopy could be used as a non-destructive technique for monitoring the oxidation of metallic alloys at high temperature. 相似文献
11.
12.
《Materials Science & Technology》2013,29(3):336-342
AbstractSheet joints of carbon steel fabricated by two different clinching methods, namely TOX and Eckold, have been investigated. The holding force of the joints was determined by shear tension tests and the deformation microstructure was characterised using optical microscopy. The surface residual stress and mean residual stress distributions as a function of increasing distance from the outer diameter of the interlock button were mapped by X-ray and neutron diffractometry, respectively. The Eckold joints showed more severe joint distortion in the form of global sheet bending, but nevertheless possessed higher shear tension strength than the TOX joints. Characteristic residual stress distributions depending on the clinching method were found in both the TOX and Eckold joints. The observed residual stress distributions have been attributed to the different die construction employed by the two methods, which permitted different degrees of plastic deformation during clinching. 相似文献
13.
《Materials Science & Technology》2013,29(2):170-175
AbstractSessile drop spreading tests have been carried out to evaluate the influence of braze and substrate chromium content on the wetting and flow of Ni–Cr–Si–B and Ni–Cr–P brazes on nickel and Ni–Cr substrates. The effect of filler metal chromium additions is examined in terms of fluidity processes, while the role of base metal chromium content is discussed in the context of oxide reduction and alloying phenomena.MST/1056 相似文献
14.
Aluminum brazed joints are used extensively in the automotive and aircraft industries. In order to insure the integrity of the bond, the effects of processing variables on the quality of the bond must be understood. The effects of brazing period and joint thickness on the microstructure, tensile properties, microhardness and micromechanisms of failure of two aluminum alloy 3003 plates connected by a layer of 4047 aluminum filler material were investigated. It was found that the amount of aluminum-silicon eutectic microstructure in the reaction zone decreased with increasing brazing period and decreasing joint thickness. This was attributed to silicon diffusion from the joint material and dissolution of base metal and its entrance into the liquid joint. The amount of shrinkage porosity in the reaction zone was found to increase with increasing brazing period due to base material solutioning. The ultimate tensile strength of joints decreased with increasing brazing period and decreasing joint thickness. This was attributed to the joint microstructure and shrinkage porosity formed in the joint. Shrinkage porosity was found to be the primary cause of decreased joint strength. Joints with 10 minutes brazing period failed within the base material, while for brazing periods greater than 10 minutes, joints failed within the aluminum-silicon eutectic microstructure of the reaction zone. This indicated that the joint strength was greater than the base material for joint with brazing period of 10 minutes. Finite element analysis was performed to determine the effect of joint material yield strength and joint thickness on the stress and strain field in the brazed joint. Finite element analysis results supported experimental observations. 相似文献
15.
《Materials Science & Technology》2013,29(7):686-692
AbstractThree superheater transition joints, between 2·25Cr–1 Mo and 316 stainless steel, welded with nickel–base weld metal, removed from service after 72337 h, have been examined using optical and scanning electron microscopy. In addition, microhardness measurements have been made and local chemical compositions have been analysed using the energy dispersive X-ray attachment on a scanning electron microscope. Temperature accelerated creep rupture tests have been carried out between 590 and 625°C at stresses of 31–62 MN m?2 on cross–weld tensile specimens machined longitudinally from the walls of the joints. Detailed metallographic examinations showed the same failure mode as that found in long–term service failures. Therefore, the use of post-exposure temperature accelerated testing of uniaxial cross-weld specimens appears to be a viable method of assessing the remanent life of nickel-base transition joints operating at elevated temperatures. The applicability of various multiaxial stress rupture equations to transition joint failures is considered. The present rupture data are compared with previous data generated from initially as-welded specimens to provide upper and lower estimates of the long-term failure lives.MST/403 相似文献
16.
The Hall effect and resistivity have been measured on single crystals of hexagonal NiS above and below the transition temperature, and magnetic susceptibility measurements have been made on powders and ground-up single crystals in the same temperature region. It is found that the material behaves as an extrinsic semiconductor in the low temperature region, with the charge carriers arising from the nickel vacancies. 相似文献
17.
The mechanical properties and microstructures ofcopper and brass soldered with eutectic tin-bismuth solder have been determined and the joints examined using metallographic techniques. Joints made with copper were stronger than those made with brass. At the copper/solder interface a uniform layer 2m thick of Cu5.2Sn5 was formed and at the brass/solder interface a uniform layer 2 m thick of (Cu, Zn)2.9Sn and an irregular layer 2 to 5m thick of (Cu, Zn)5.7Sn5 were formed. Copper joints fractured etthocopper/solder interface and brass joints fractured in the internmetalic layer. Copper joints soldered with eutectic Sn-Bi were stronger than copper joints soldered with eutectic Sn-Pb and the reverse was true for brass joints. Results are also given for the effect of thermal shock on copper and brass joints soldered with Sn-Bi and Sn-Pb solders, and also for We fatigue and creep behaviour of joints soldered with eutectic Sn-Bi solder. 相似文献
18.
T. Z. Blazynski 《Materialwissenschaft und Werkstofftechnik》1989,20(8):262-271
Using high energy-rate implosive techniques, multi-layered foil and foil mesh reinforced cylinders were manufactured in a range of ordinary engineering alloys based on aluminium, copper and variety of steels. Mechanical Properties of the welded interfaces and of the composites are discussed. Explosive welding of tubular bimetallic transition joints in four different welding systems is discussed together with the effect of the chosen technique on the mechanical properties of the joints. 相似文献
19.
《Materials Science & Technology》2013,29(12):1605-1614
AbstractThe microstructure and texture of friction stir welded joints of hot mill stock 5754 and 5182 aluminium alloy sheets were examined after a commercial joining process. The as received sheet was cut into two pieces, one piece was cold rolled with 20 reduction in thickness, whereas the other was subsequently aged at 230C for 100 h after the 20 prestrain. These two pieces with different thermal pretreatments were joined by friction stir welding FSW. On FSW, a uniform fine grained microstructure in the through thickness of the sheet having a width corresponding to the diameter of tool shoulder was observed in both the 5754 and 5182 joints. Moreover, the microhardness profile did not reveal a softened heat affected zone between the weld and the base metal. An X-ray pole figure study showed that the 5754 and 5182 weld zones were not highly textured and both comprised of similar texture components. The calculated average sheet formability of the weld zones predicts a more isotropic behaviour than that for the start materials. Orientation image mapping of the weld zone in 5182 and semi-automatic electron backscatter pattern linescan analysis of the 5754 weld zone showed that most of the grain boundaries were high angle ones. This determination affirms that the weld zones in AA 5754 and AA 5182 joints undergo homogeneous dynamic recrystallisation throughout the thickness resulting in uniform mechanical properties. 相似文献