Showing papers on "Microstructure published in 2002"
TL;DR: A thermomechanical treatment of Cu is described that results in a bimodal grain size distribution, with micrometre-sized grains embedded inside a matrix of nanocrystalline and ultrafine (<300 nm) grains, which impart high strength, as expected from an extrapolation of the Hall–Petch relationship.
Abstract: Nanocrystalline metals--with grain sizes of less than 100 nm--have strengths exceeding those of coarse-grained and even alloyed metals, and are thus expected to have many applications. For example, pure nanocrystalline Cu (refs 1-7) has a yield strength in excess of 400 MPa, which is six times higher than that of coarse-grained Cu. But nanocrystalline materials often exhibit low tensile ductility at room temperature, which limits their practical utility. The elongation to failure is typically less than a few per cent; the regime of uniform deformation is even smaller. Here we describe a thermomechanical treatment of Cu that results in a bimodal grain size distribution, with micrometre-sized grains embedded inside a matrix of nanocrystalline and ultrafine (<300 nm) grains. The matrix grains impart high strength, as expected from an extrapolation of the Hall-Petch relationship. Meanwhile, the inhomogeneous microstructure induces strain hardening mechanisms that stabilize the tensile deformation, leading to a high tensile ductility--65% elongation to failure, and 30% uniform elongation. We expect that these results will have implications in the development of tough nanostructured metals for forming operations and high-performance structural applications including microelectromechanical and biomedical systems.
2,531 citations
TL;DR: In this paper, the current status of research and development on laser shock processing of metals, also known as laser peening, using Q-switched high power lasers is reviewed and the influence of processing parameters on the laser-induced shock waves in metal components are discussed and analyzed.
933 citations
TL;DR: A grain refinement mechanism induced by plastic deformation during the SMA treatment in Fe was proposed in this article, which involves formation of dense dislocation walls (DDWs) and dislocation tangles (DTs) in original grains and in the refined cells under further straining.
889 citations
TL;DR: Combustion synthesis has emerged as a facile and economically viable technique for the preparation of advanced ceramics, catalysts and nanomaterials as discussed by the authors, and recent innovations in the combustion and processing parameters have resulted in a better understanding of combustion phenomena and control of microstructure and property of the products.
Abstract: Combustion synthesis has emerged as a facile and economically viable technique for the preparation of advanced ceramics, catalysts and nanomaterials. Recent innovations in the combustion and processing parameters have resulted in a better understanding of combustion phenomena and control of microstructure and property of the products.
767 citations
TL;DR: In this article, a systematic study of various spark plasma sintering (SPS) parameters, namely temperature, holding time, heating rate, pressure, and pulse sequence, was conducted to investigate their effect on the densification, grain-growth kinetics, hardness, and fracture toughness of a commercially available submicrometer-sized Al 2 O 3 powder.
Abstract: A systematic study of various spark plasma sintering (SPS) parameters, namely temperature, holding time, heating rate, pressure, and pulse sequence, was conducted to investigate their effect on the densification, grain-growth kinetics, hardness, and fracture toughness of a commercially available submicrometer-sized Al 2 O 3 powder. The obtained experimental data clearly show that the SPS process enhances both densification and grain growth. Thus, Al 2 O 3 could be fully densified at a much lower temperature (1150°C), within a much shorter time (minutes), than in more conventional sintering processes. It is suggested that the densification is enhanced in the initial part of the sintering cycle by a local spark-discharge process in the vicinity of contacting particles, and that both grain-boundary diffusion and grain-boundary migration are enhanced by the electrical field originating from the pulsed direct current used for heating the sample. Both the diffusion and the migration that promote the grain growth were found to be strongly dependent on temperature, implying that it is possible to retain the original fine-grained structure in fully densified bodies by avoiding a too high sintering temperature. Hardness values in the range 21-22 GPa and fracture toughness values of 3.5 ± 0.5 MPa.m 1/2 were found for the compacts containing submicrometer-sized Al 2 O 3 grains.
729 citations
TL;DR: In this article, the microstructure of a nanocrystalline Mg97Zn1Y2 bulk alloy prepared by warm extrusion of rapidly solidified powders has been investigated by a combination of techniques, such as conventional high-resolution transmission electron microscopy (HRTEM), atomic-resolution high-angle annular dark field scanning-TEM (HAADF-STEM) with Z-contrast and energy-dispersive X-ray spectroscopy (EDS) with a sub-nanometer electron probe.
605 citations
TL;DR: There are more than 200 different methods for measuring thin film adhesion, suggesting it to be material, geometry and even industry specific as discussed by the authors, suggesting that the major extrinsic variables are film stress, extent of delamination, thickness and temperature while the major intrinsic ones are modulus, yield strength, the thermodynamic work of adhesion and one or more length scales.
600 citations
TL;DR: In this paper, the microstructure of a Ni-rich NiTi shape memory alloy and its influence on the thermal characteristics of martensitic transformations were studied. But the authors did not consider the effect of stress on the precipitation process of Ni4Ti3-precipitates.
585 citations
TL;DR: In this article, the microstructure of commercially available nanocrystalline (nc) electroplated Ni foils is studied by means of Xray diffraction and transmission electron microscopy.
501 citations
15 Dec 2002-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the growth mechanism, morphology and mechanical properties of Fe-Al intermetallic compound layers on the surface of carbon steel were systematically evaluated for specimens diffused at temperatures ranging from 873 to 1323 K after hot dip aluminizing.
Abstract: The toughening of Fe–Al intermetallic compound coating formed by aluminizing of carbon steel was investigated. The growth mechanism, morphology and mechanical properties of Fe–Al intermetallic compound layers on the surface of carbon steel were systematically evaluated for specimens diffused at temperatures ranging from 873 to 1323 K after hot dip aluminizing. Fe2Al5 was mainly formed on the specimen surfaces at the usual diffusion temperatures from 873 to 923 K. However, FeAl and Fe3Al layers having relatively high fracture resistance and oxidation resistance properties were preferentially formed in the specimens diffused at temperatures greater than 1273 K. The activation energies required for the growth of the FeAl and Fe3Al layers were QFeAl=180 and QFe3Al=260 kJ mol−1, respectively. It was identified that the formation and growth of Fe–Al intermetallic compound layers is controlled by the diffusion of Fe atoms into the intermetallic compound layers.
497 citations
TL;DR: In this paper, metallographic details are reported of the very fine bainitic microstructure associated with the incredibly low transformation temperature, where during the time scale of the experiments, an iron atom cannot diffuse over a distance greater than ~ 10-17 m.
Abstract: Bainite has been obtained by heat treatment at temperatures as low as 125°C in a high carbon, high silicon steel. This has had the effect of greatly refining the microstructure, which is found to have a strength in excess of 2.5 GPa together with an ability to flow plastically before fracture. Such properties have never before been achieved with bainite. In this paper metallographic details are reported of the very fine bainitic microstructure associated with the incredibly low transformation temperature, where during the time scale of the experiments, an iron atom cannot diffuse over a distance greater than ~ 10-17 m. Yet, the microstructure has a scale in the micrometre range, consistent only with a displacive mechanism of transformation.
TL;DR: The very fast (within minutes) in situ formation of a tough interlocking microstructure in Si3N4-based ceramics is reported, which is uniform and reproducible in terms of grain size distribution and mechanical properties, and are easily tailored by manipulating the kinetics.
Abstract: Ceramics based on Si3N4 have been comprehensively studied and are widely used in structural applications1, 2. The development of an interlocking microstructure of elongated grains is vital to ensur ...
TL;DR: In this paper, the aluminum alloys 6063-T5 and T4 were friction-stir welded at different tool rotation speeds (R), and then distributions of the microstructure and hardness were examined in these welds.
Abstract: The aluminum (Al) alloys 6063-T5 and T4 were friction-stir welded at different tool rotation speeds (R), and then distributions of the microstructure and hardness were examined in these welds. The maximum temperature of the welding thermal cycle rose with increasing R values. The recrystallized grain size of the weld increased exponentially with increasing maximum temperature. The relationship between the grain size and the maximum temperature satisfied the static grain-growth equation. In the as-welded condition, 6063-T5 Al was softened around the weld center, whereas 6063-T4 Al showed homogeneous hardness profiles. Different R values did not result in significant differences in the hardness profile in these welds, except for the width of the softened region in the weld of 6063-T5 Al. Postweld aging raised the hardness in most parts of the welds, but the increase in hardness was small in the stir zone produced at the lower R values. Transmission electron microscope (TEM) observations detected a similar distribution of the strengthening precipitates in the grain interiors and the presence of a precipitation-free zone (PFZ) adjacent to the grain boundaries in all the welds. Microstructural analyses suggested that the small increase in hardness in the stir zone produced at the lower R values was caused by an increase in the volume fraction of PFZs.
TL;DR: In this article, the kinetics and topology of grain growth in 3D are simulated using a phase-field model of an ideal polycrystal with uniform grain-boundary mobilities and energies.
01 Aug 2002-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the microstructures and tensile properties of three typical Sn-Ag-Cu alloys, Sn-30wt%Ag-05wt%Cu and Sn-39Ag-06Cu, were evaluated after casting under three different cooling conditions.
Abstract: The microstructures and tensile properties of three typical Sn–Ag–Cu alloys, Sn–30wt%Ag–05wt%Cu, Sn–35wt%Ag–07wt%Cu and Sn–39wt%Ag–06wt%Cu, prepared under three different cooling conditions were evaluated after casting The microstructures of all rapidly cooled specimens consisted of the eutectic phase of β-Sn with fine fibrous Ag3Sn dispersion surrounding primary β-Sn grains The slowly cooled Sn–35Ag–07Cu and Sn–39Ag–06Cu alloys exhibited additional large primary Ag3Sn platelets, while the Sn–30Ag–05Cu did not For all alloys, both ultimate tensile strength and 02% proof stress increased with increasing strain-rates in tensile tests Lowering cooling speed decreased tensile strength Elongation increased with an increasing strain rate from 10−5 to 10−2 s−1, and decreased slightly at 10−1 s−1 for the rapidly cooled specimens Elongation remarkably decreased for the slowly cooled Sn–35Ag–07Cu and Sn–39Ag–06Cu alloys, a degradation attributable to the formation of large primary Ag3Sn platelets
TL;DR: The high bioactivity of the PDLLA foam/Bioglass composites indicates the potential of the materials for use as bioactive, resorbable scaffolds in bone tissue engineering.
TL;DR: In this paper, the authors discuss the critical issues of improved magnetic performance, environmental stability, net-shape formability and magnetization behavior for the main categories of NdFeB magnets.
31 Jan 2002-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a banded microstructure consisting of alternating hard particle rich and hard particle poor regions is developed for friction stir welds in 7 mm thick, 2024-T351 aluminum rolled sheet material.
Abstract: Friction stir welds in 7 mm thick, 2024-T351 aluminum rolled sheet material have been completed. Metallurgical, hardness and quantitative energy dispersive X-ray measurements have been performed which demonstrate that a segregated, banded, microstructure consisting of alternating hard particle rich and hard particle poor regions is developed. Mixed-mode I/II monotonic fracture experiments confirm that the observed banded microstructure affects the macroscopic fracture process. Since the band spacing is directly correlated with the welding tool advance per revolution, our results indicated that the opportunity exists to manipulate the friction stir weld process parameters in order to modify the weld microstructure and improve a range of material properties, including fracture resistance.
TL;DR: In this paper, the thermal stability of Ti1−xAlxN films deposited by arc evaporation from Ti-Al cathodes with 67 and 75% aluminum, respectively, has been investigated.
Abstract: The thermal stability of Ti1−xAlxN films deposited by arc evaporation from Ti–Al cathodes with 67 and 75 at. % aluminum, respectively, has been investigated. The microstructure of as-deposited and ...
TL;DR: In this article, two zirconium diboride base composites were produced and characterised, which were compared to those of a monolithic ZrB2+4 wt% Ni material.
Abstract: Two zirconium diboride-base composites were produced and characterised The chosen starting compositions were: 55 wt% ZrB2+41 wt%TiB2+4 wt% Ni and 83 wt% ZrB2+13 wt% B4C+4 wt% Ni The microstructure and properties of these composites were compared to those of a monolithic ZrB2+4 wt% Ni material In all cases, metallic Ni as the sintering aid promoted the formation of the liquid phase which improved mass transfer mechanisms during sintering From the powder mixture ZrB2+TiB2, two solid solutions of Zr–Ti–B were obtained In the case of the other mixture, B4C particles were dispersed in the ZrB2 matrix The composite materials have better mechanical properties than those of the monolithic ZrB2 ceramic; in particular the fracture toughness and the flexural strength were almost doubled at room temperature Long term oxidation tests indicated that the ZrB2-based composites, particularly the composite containing B4C as the second phase, were more resistant to oxidation than the monolithic ZrB2 due to the formation of surface oxide products which were protective against the complete degradation by oxidation observed for the ZrB2 matrix material
TL;DR: It seems quite promising that a dense and adhesive apatite coating can be achieved through water-based sol gel technology after short-term annealing at around 400 degrees C in air.
TL;DR: Experiments were conducted to evaluate the grain refinement introduced by equal-channel angular pressing (ECAP) in three different Al-3% Mg alloys containing either 2% Sc, 2% Zr or a combination of 2%Sc and Zr as mentioned in this paper, but superplasticity was not achieved in the Al-Mg-Zr alloy due to the onset of rapid grain growth at 573 K.
TL;DR: In this article, the micellar shape transitions from bilayers to cylinders to spheres with increasing PEO composition were determined with direct cryogenic transmission electron microscopic (cryo-TEM) imaging of the microstructures in the form of thin vitreous hydrated specimens.
Abstract: We investigated the micellar polymorphism of poly(ethylene oxide)(PEO)-based block copolymers to illustrate the possibility of a rational control of the aggregation structure through synthetic manipulation of the molecular characteristics. Boundaries for the micellar shape transitions from bilayers to cylinders to spheres with increasing PEO composition were determined with direct cryogenic transmission electron microscopic (cryo-TEM) imaging of the microstructures in the form of thin vitreous hydrated specimens. Analyses of cryo-TEM images lead to determination of the packing properties of the hydrophobic block in terms of the interfacial area per chain and the degree of chain stretching. Also, the micellar phases of the block copolymers are characterized by anomalous structural behaviors such as coexistence of different structures and formation of exotic compound structures, which are discussed in terms of metastability inherent in the system comprising polymeric materials.
TL;DR: In this paper, the state of the art of current research on the electron field emission properties of carbon nanotube films and present recent results outlining their potential as field emitters as well as illustrating some current concerns in the research field.
TL;DR: In this paper, the deformation mechanisms of the grains inside the shear bands, the origin of the inhomogeneous deformation, and the propensity for shear localization in nanostructures are explained based on microstructural information acquired using transmission electron microscopy.
Abstract: Shear band development in consolidated nanocrystalline and ultrafine-grained Fe has been monitored as a function of overall strain from the onset of plastic deformation. The deformation mechanisms of the grains inside the shear bands, the origin of the inhomogeneous deformation, and the propensity for shear localization in nanostructures are explained based on microstructural information acquired using transmission electron microscopy.
TL;DR: In this article, the authors investigated the metallurgical transformations that occur during heat treatment of Nd-based magnets and showed that thin and smooth RE-rich film is associated with the highest coercivity.
TL;DR: In this article, the nano-structure of hydroxyapatite/chitosan composite will have the best biomedical properties in the biomaterials applications in order to have good biocompatibility, high bioactivity and great bonding properties.
TL;DR: Large-scale 3D simulations of dislocation dynamics were performed yielding access for the first time to statistically averaged quantities, providing a parameter-free estimate of the dislocation microstructure strength and of its scaling law.
Abstract: The mechanisms of dislocation intersection and strain hardening in fcc crystals are examined with emphasis on the process of junction formation and destruction. Large-scale 3D simulations of dislocation dynamics were performed yielding access for the first time to statistically averaged quantities. These simulations provide a parameter-free estimate of the dislocation microstructure strength and of its scaling law. It is shown that forest hardening is dominated by short-range elastic processes and is insensitive to the detail of the dislocation core structure.
TL;DR: The origin of the formation of this core microstructure can be explained by Marangoni motion on the basis of the temperature dependence of the interfacial energy, which shows that this type of powder can be formed even if the cooling rate is very high.
Abstract: The egg-type core microstructure where one alloy encases another has previously been obtained during experiments in space. Working with copper-iron base alloys prepared by conventional gas atomization, we were able to obtain this microstructure under gravity conditions. The minor liquid phase always formed the core of the egg, and it sometimes also formed a shell layer. The origin of the formation of this core microstructure can be explained by Marangoni motion on the basis of the temperature dependence of the interfacial energy, which shows that this type of powder can be formed even if the cooling rate is very high.
TL;DR: In this article, the authors examined how the overall resistance to high-cycle fatigue in Ti-6Al-4V compares between the bimodal microstructure and a coarser lamellar (β-annealed) micro-structure.
Abstract: The high-cycle fatigue (HCF) of titanium alloy turbine engine components remains a principal cause of failures in military aircraft engines. A recent initiative sponsored by the United States Air Force has focused on the major drivers for such failures in Ti-6Al-4V, a commonly used turbine blade alloy, specifically for fan and compressor blades. However, as most of this research has been directed toward a single processing/heat-treated condition, the bimodal (solution-treated and overaged (STOA)) microstructure, there have been few studies to examine the role of microstructure. Accordingly, the present work examines how the overall resistance to high-cycle fatigue in Ti-6Al-4V compares between the bimodal microstructure and a coarser lamellar (β-annealed) microstructure. Several aspects of the HCF problem are examined. These include the question of fatigue thresholds for through-thickness large and short cracks; microstructurally small, semi-elliptical surface cracks; and cracks subjected to pure tensile (mode I) and mixed-mode (mode I+II) loading over a range of load ratios (ratio of minimum to maximum load) from 0.1 to 0.98, together with the role of prior damage due to sub-ballistic impacts (foreign-object damage (FOD)). Although differences are not large, it appears that the coarse lamellar microstructure has improved smooth-bar stress-life (S-N) properties in the HCF regime and superior resistance to fatigue-crack propagation (in pure mode I loading) in the presence of cracks that are large compared to the scale of the microstructure; however, this increased resistance to crack growth compared to the bimodal structure is eliminated at extremely high load ratios. Similarly, under mixed-mode loading, the lamellar microstructure is generally superior. In contrast, in the presence of microstructurally small cracks, there is little difference in the HCF properties of the two microstructures. Similarly, resistance to HCF failure following FOD is comparable in the two microstructures, although a higher proportion of FOD-induced microcracks are formed in the lamellar structure following high-velocity impact damage.