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Lee, H. S.; Han, S. Z.; Lee, H. M.; Lee, Z. H. |
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Coarsening Behavior of L1$_2$ Precipitates in Melt-Spun Al-Ti-V-Zr Alloys |
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Journal Article |
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1993 |
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Abstract |
Materials Science and Engineering A |
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Corporate Author |
Mater. Sci. Eng. A |
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163 |
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1 |
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Summary Language |
81-90 |
Series Editor |
volume fraction
high-strength
kinetics
dependence
nucleation
growth
do22 |
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Abbreviated Series Title |
Aging studies of two melt-spun Al-2at.% (Ti,V,Zr) alloys showed that the would-be metastable L1(2) Al3(Ti,V,Zr) precipitates did not transform to stable D0(23) ones, and the average radius is 5-7 nm and the interparticle spacing is 20-40 nm at 698 K up to 400 h. The coarsening rate of spherical Al3(Ti0.2V0.4Zr0.4) precipitates was observed to be five times as fast as that of Al3(Ti0.1V0.4Zr0.5) precipitates. The coarsening behavior in both alloys obeyed the Lifshitz-Slyozov-Wagner (LSW) prediction well. Owing to the low coarsening rate and the high thermal stability of the precipitated phase, Al-Ti-V-Zr systems show promise as bases for high-temperature high-strength Al alloys. |
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Times Cited: 10
Article
English
Cited References Count: 44
Lf639 |
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refbase @ user |
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1328 |
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Tewari, S.N.; Vijayakumar, M.; Lee, J.E.; Curreri, P.A. |
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Solutal partition coefficients in nickel-based superalloy PWA-1480 |
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Journal Article |
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1991 |
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Materials Science and Engineering A |
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141 |
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1 |
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97-102 |
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Solutal profiles in dendritic single-crystal specimens of PWA-1480 nickel-base superalloy, which were directionally solidified and quenched, were examined on several transverse cross-sections to obtain the partition coefficients. Similar to their nickel-base binaries, the partition coefficients of tantalum, titanium, and aluminum were found to be less than unity; those of tungsten and cobalt were greater than unity. The partition coefficients were temperature independent in the range 1584-1608 K. The contribution of solid-state diffusion to microsegregation was observed to be negligible. |
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NU @ karnesky @ |
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9820 |
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Lagow, B.W.; Robertson, I.M.; Jouiad, M.; Lassila, D.H.; Lee, T.C.; Birnbaum, H.K. |
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Observation of dislocation dynamics in the electron microscope |
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Journal Article |
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2001 |
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Materials Science And Engineering A |
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Mater. Sci. Eng. A |
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309-310 |
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445-450 |
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Deformation experiments performed in situ in the transmission electron microscope have led to an increased understanding of dislocation dynamics. To illustrate the capability of this technique two examples will be presented. In the first example, the processes of work hardening in Mo at room temperature will be presented. These studies have improved our understanding of dislocation mobility, dislocation generation, and dislocation-obstacle interactions. Zn the second example, the interaction of matrix dislocations with grain boundaries will be described. From such studies predictive criteria for slip transfer through grain boundaries have been developed. |
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0921-5093 |
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WOS:000169044600089 |
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NU @ m-krug @ |
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10533 |
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Lee, S.-W.; Yeh, J.-W. |
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Superplasticity of 5083 alloys with Zr and Mn additions produced by reciprocating extrusion |
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Journal Article |
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2007 |
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Materials Science and Engineering: A |
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460-461 |
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409-419 |
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Aluminum alloys; Extrusion; Superplasticity |
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In this study, 5083 aluminum alloys modified with grain refiner, 0.25% Zr and 0.46% Mn, were processed by reciprocating extrusion to yield high-strain-rate superplasticity above 400 [degree sign]C and superior room-temperature mechanical properties. Without any prior homogenization treatment, 10 extrusion passes could give the cast billets an equiaxed grain structure with a grain size of about 4.5 [mu]m and a subgrain size about 0.2 [mu]m, and a uniform distribution of fine inclusions and dispersoids in the matrix. The fine-grained structure was stable up to 525 [degree sign]C, giving the alloy a high-strain-rate and low-stress superplasticity over a wide operating temperature of 400-500 [degree sign]C. In the tensile test at 500 [degree sign]C, a maximum elongation of 1013% and a low flow stress of 7.7 MPa at 5 x 10-2 s-1 were achieved. The apparent and true activation energies for low temperatures (300-400 [degree sign]C) without high-strain-rate superplasticity were 220.6 and 208 kJ/mol, respectively, whereas those at high temperatures (400-500 [degree sign]C) were 88.4 and 98.7 kJ/mol, respectively. Further analysis confirms that grain boundary sliding is the dominant mechanism over the high-strain-rate region from 1 x 10-2 to 5 x 10-1 s-1 at 500 [degree sign]C, and power-law breakdown mechanism occurs over the strain rate from 5 x 10-4 to 1 x 10-2 s-1 at 300 [degree sign]C. The high-strain-rate superplasticity was more strongly enhanced by Zr addition than addition of Cr and Mn. Two enhancing mechanisms for the maximum superplastic elongation and the optimum strain rate are proposed. This study concludes that the effectiveness of Zr is caused by the fineness and the coherency of Zr-rich dispersoids in the matrix. |
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NU @ karnesky @ |
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9637 |
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Lee, Z.; Witkin, D.B.; Radmilovic, V.; Lavernia, E.J.; Nutt, S.R. |
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Bimodal microstructure and deformation of cryomilled bulk nanocrystalline Al-7.5Mg alloy |
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Journal Article |
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2005 |
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Materials Science and Engineering: A |
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The Langdon Symposium: Flow and forming of Crystalline Materials |
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410-411 |
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462-467 |
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Nanocrystalline; Bimodal; Cryomilling; Aluminum; Deformation |
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The microstructure, mechanical properties and deformation response of bimodal structured nanocrystalline Al-7.5Mg alloy were investigated. Grain refinement was achieved by cryomilling of atomized Al-7.5Mg powders, and then cryomilled nanocrystalline powders blended with 15 and 30% unmilled coarse-grained powders were consolidated by hot isostatic pressing followed by extrusion to produce bulk nanocrystalline alloys. Bimodal bulk nanocrystalline Al-7.5Mg alloys, which were comprised of nanocrystalline grains separated by coarse-grain regions, show balanced mechanical properties of enhanced yield and ultimate strength and reasonable ductility and toughness compared to comparable conventional alloys and nanocrystalline metals. The investigation of tensile and hardness test suggests unusual deformation mechanisms and interactions between ductile coarse-grain bands and nanocrystalline regions. |
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NU @ karnesky @ |
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10321 |
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Darling, K.A.; VanLeeuwen, B.K.; Semones, J.E.; Koch, C.C.; Scattergood, R.O.; Kecskes, L.J.; Mathaudhu, S.N. |
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Stabilized Nanocrystalline Iron-based Alloys: Guiding Efforts in Alloy Selection |
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Journal Article |
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2011 |
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Materials Science and Engineering: A |
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In Press |
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Accepted Manuscript |
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Mechanical Alloying; Grain Growth; Interfaces; Recrystallization and Nanostructured Materials |
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Using a modified regular solution model for grain boundary solute segregation, the relative thermal stability of a number of Fe-based nanocrystalline binary alloys was predicted with considerable accuracy. It was found that nanocrystalline iron was strongly stabilized by zirconium, moderately stabilized by tantalum, and not significantly stabilized by nickel or chromium. These findings are fully in line with the aforementioned predictions. This success with iron based alloys highlights the utility of this practical approach to selecting stabilizing solutes for nanocrystalline alloys. |
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0921-5093 |
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NU @ karnesky @ |
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11038 |
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Lee, W.S.; Chen, T.H. |
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Effects of strain rate and temperature on dynamic mechanical behaviour and microstructural evolution in aluminium-scandium (Al-Sc) alloy |
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Journal Article |
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2008 |
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Materials Science and Technology |
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24 |
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10 |
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1271-1282 |
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AL-SC ALLOY; STRAIN RATE SENSITIVITY; ACTIVATION ENERGY; ADIABATIC SHEARING; DISLOCATION; AL3SC PRECIPITATES |
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The present study applies a compressive split Hopkinson bar to investigate the mechanical response, microstructural evolution and fracture characteristics of an aluminium-scandium (Al-Sc) alloy at temperatures ranging from − 100 to 300°C and strain rates of 1·2 × 103, 3·2×103 and 5·8 × 103 s−1. The relationship between the dynamic mechanical behaviour of the Al-Sc alloy and its microstructural characteristics is explored. The fracture features and microstructural evolution are observed using scanning and transmission electron microscopy techniques. The stress-strain relationships indicate that the flow stress, work hardening rate and strain rate sensitivity increase with increasing strain rate, but decrease with increasing temperature. Conversely, the activation volume and activation energy increase as the temperature increases or the strain rate decreases. Additionally, the fracture strain reduces with increasing strain rate and decreasing temperature. The Zerilli-Armstrong fcc constitutive model is used to describe the plastic deformation behaviour of the Al-Sc alloy, and the error between the predicted flow stress and the measured stress is found to be less than 5%. The fracture analysis results reveal that cracks initiate and propagate in the shear bands of the Al-Sc alloy specimens and are responsible for their ultimate failure. However, at room temperature, under a low strain rate of 1·2 × 103 s−1 and at a high experimental temperature of 300°C under all three tested strain rates, the specimens do not fracture, even under large strain deformations. Scanning electron microscopy observations show that the surfaces of the fractured specimens are characterised by transgranular dimpled features, which are indicative of ductile fracture. The depth and density of these dimples are significantly influenced by the strain rate and temperature. The transmission electron microscopy structural observations show the precipitation of Al3Sc particles in the matrix and at the grain boundaries. These particles suppress dislocation motion and result in a strengthening effect. The transmission electron microscopy analysis also reveals that the dislocation density increases, but the dislocation cell size decreases, with increasing strain rate for a constant level of strain. However, a higher temperature causes the dislocation density to decrease, thereby increasing the dislocation cell size. |
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NU @ m-krug @ |
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10531 |
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Lee, Woei-Shyan; Chen, Tao-Hsing; Lin, Chi-Feng; Lu, Ging-Ting |
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Adiabatic Shearing Localisation in High Strain Rate Deformation of Al-Sc Alloy |
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Journal Article |
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2010 |
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Materials Transactions |
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51 |
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7 |
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1216-1221 |
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aluminium-scandium alloy, strain rate sensitivity, adiabatic shearing, precipitates |
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Aluminium-scandium (Al-Sc) alloy is subjected to shear deformation at high strain rates ranging from 3.0×105 s−1 to 6.2×105 s−1 using a compressive-type split-Hopkinson pressure bar (SHPB). The effects of the strain rate on the shear stress, adiabatic shear band characteristics, and fracture features of the Al-Sc alloy are systematically examined. The results show that both the shear stress and the strain rate sensitivity increase with an increasing strain rate. In addition, it is shown that an adiabatic shear band is formed within the deformed specimens for all values of the strain rate. As the strain rate is increased, the width of the shear band decreases, but the microhardness increases. Moreover, the distortion angle and the magnitude of the local shear strain near the shear band both increase with an increasing strain rate. At a strain rate of 3.0×105 s−1, the fracture surface is characterised by multiple transgranular clearage fractures. However, for strain rates greater than 4.4×105 s−1, the fracture surface has a transgranular dimple-like characteristic, and thus it is inferred that the ductility of the Al-Sc alloy improves with an increasing strain rate. |
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NU @ karnesky @ |
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10917 |
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Han, S. Z.; Chung, S. C.; Lee, H. M. |
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Alloy Design and Coarsening Phenomenon of L1$_2$ Precipitates in High-Temperature Al-2at.%(Ti,V,Zr) Systems |
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Journal Article |
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1995 |
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Metallurgical and Materials Transactions A |
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20 |
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7 |
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1633-1639 |
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v-zr alloys
ti
behavior
elements
phase
do22
l12 |
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Aging works of two melt-spun Al-2 at pet (Ti,V,Zr) alloys showed that metastable Ll(2)Al(3)(Ti,V,Zr) precipitates were dominant and did not transform to stable DO23 ones: the average radius was 3 to 4 nm and the interparticle spacing was 10 to 30 nm at 698 K up to 400 hours. Coarsening kinetics was found to be very sluggish and was coincident with the low lattice mismatch. Due to the low coarsening rate and the high thermal. stability of the precipitated phase, rapidly solidified Al-Ti-V-Zr systems show promise as base of high-strength Al alloys for high-temperature applications. |
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Times Cited: 7
Article
English
Cited References Count: 26
Rj768 |
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refbase @ user |
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1169 |
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Lee, W.-B.; Hong, S.-G.; Park, C.-G.; Park, S.-H. |
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Carbide precipitation and high-temperature strength of hot-rolled high-strength, low-alloy steels containing Nb and Mo |
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Journal Article |
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2002 |
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Metallurgical and Materials Transactions A |
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33 |
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6 |
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1689-1698 |
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Abstract The effects of a Mo addition on both the precipitation kinetics and high-temperature strength of a Nb carbide have been investigated in the hot-rolled high-strength, low-alloy (HSLA) steels containing both Nb and Mo. These steels were fabricated by four-pass hot rolling and coiling at 650C, 600C, and 550C. Microstructural analysis of the carbides has been performed using field-emission gun transmission electron microscopy (TEM) employing energy-dispersive X-ray spectroscopy (EDS). The steels containing both Nb and Mo exhibited a higher strength at high temperatures (∼600 C) in comparison to the steel containing only Nb. The addition of Mo increased the hardenability and led to the refinement of the bainitic microstructure. The proportion of the bainitic phase increased with the increase of Mo content. The TEM observations revealed that the steels containing both Nb and Mo exhibited fine (<10 nm) and uniformly distributed metal carbide (MC)-type carbides, while the carbides were coarse and sparsely distributed in the steels containing Nb only. The EDS analysis also indicated that the fine MC carbides contain both Nb and Mo, and the ratio of Mo/Nb was higher in the finer carbides. In addition, electron diffraction analysis revealed that most of the MC carbides had one variant of the B-N relationship ((100)MC//(100)ferrite, [011]MC//[010]ferrite) with the matrix, suggesting that they were formed in the ferrite region. That is, the addition of Mo increased the nucleation sites of MC carbides in addition to the bainitic transformation, which resulted in finer and denser MC carbides. It is, thus, believed that the enhanced high-temperature strength of the steels containing both Nb and Mo was attributed to both bainitic transformation hardening and the precipitation hardening caused by uniform distribution of fine MC particles. |
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NU @ p-kolli @ |
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9838 |
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