Showing papers on "Laves phase published in 2011"
15 Jun 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, two sets of alloys were produced: 9%Cr alloys with 0.1%C and 0.05%C (always wt) and 9%cr alloys containing ∼0.03% Ti with 0 1%C/0.5%C.
Abstract: In this work 9%Cr alloys were designed supported by computational thermodynamic methods. Two sets of alloys were produced: 9%Cr alloys with 0.1%C and 0.05%C and 9%Cr alloys containing ∼0.03% Ti with 0.1%C and 0.05%C (always wt%). Microstructure investigations showed good agreement with the predicted phases of the thermodynamic modeling. The volume fraction of precipitated M 23 C 6 carbides is directly related to the carbon content of the alloys. For Ti-containing alloys the precipitation of nano-sized Ti-rich MX carbonitrides was observed. The microstructure evolution (sub-grain and particle size) during creep at 650 °C/100 MPa was investigated by STEM-HAADF. The sub-grain size evolution and the coarsening of precipitates (MX carbonitrides, M 23 C 6 and Laves phase) were more pronounced for Ti-containing alloys. 9Cr alloys without Ti and with low carbon content presented the highest creep strength of all investigated alloys.
112 citations
15 Jul 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, two types of high chromium ferritic steels were investigated in respect to microstructure and creep in the proposed application temperature range from 700 to 800 °C.
Abstract: Two types of high chromium ferritic steels envisaged as construction materials for SOFC interconnects, were investigated in respect to microstructure and creep in the proposed application temperature range from 700 to 800 °C. The steel compositions mainly differed in the amounts of the Laves phase forming elements Nb, W and Si. The steel containing these alloying additions exhibited substantially higher creep resistance in the temperature range 700–800 °C than the high purity steel. The Laves phase formation occurred trans- as well as intragranular whereby the extent and size of grain boundary precipitates increased with increasing exposure time. Especially at 800 °C the precipitates inside the grains virtually completely vanished after longer exposure times and only intergranular precipitates remained. This change in precipitate morphology resulted especially at 800 °C in a decrease of creep resistance with increasing exposure time, although the Laves phase containing steel still exhibited higher creep strength than the high purity steel.
84 citations
TL;DR: In this paper, the structural, electronic, elastic and some thermodynamic properties of the cubic C15 structure ZrV2 compound under pressure are investigated by first-principles calculations.
Abstract: The structural, electronic, elastic and some thermodynamic properties of the cubic C15 structure ZrV2 compound under pressure are investigated by first-principles calculations. Our results for the equilibrium unit cell volume, bulk modulus and band structure are consistent with the calculated and experimental results. Cubic ZrV2 is mechanically stable according to the elastic stability criteria and shows ductile with the G/B and Cauchy pressure analysis. Moreover the pressure and temperature dependence of the bulk modulus, specific heat, Debye temperature and thermal expansion coefficient are discussed, among them our calculated Debye temperature is in good agreement with experiments.
59 citations
TL;DR: In this paper, a time and temperature dependent homogenization model of INCONEL718 superalloy was proposed to predict the elimination process of Laves phase in quantity, and the diffusion coefficients of alloying elements at 1 140 °C were obtained by fitting the linear relationship between ln d (d: residual segregation index) and time.
56 citations
25 Jan 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the TTP diagram for the Fe 2 Nb-Laves phase of stainless steel is presented, showing that at about 600°C nucleation takes place on dislocations but above 750°C, grain boundary nucleation is dominant.
Abstract: Electrolytic extraction followed by XRD analysis of precipitates after isothermal annealing of an AISI 441 ferritic stainless steel between 600 and 850 °C produced the time–temperature–precipitation (TTP) diagram for the Fe 2 Nb-Laves phase. The TTP diagram shows two classical C noses, the first one between 750 and 825 °C and the second one, estimated to be close to 650–675 °C. TEM analyses show two independent nucleation mechanisms, i.e. at about 600 °C nucleation takes place on dislocations but above 750 °C, grain boundary nucleation is dominant. The measured solvus temperature of 875 °C for Fe 2 Nb in this steel is 50 °C higher than predicted by Thermo-Calc ® . Kinetic modelling at 800 °C agreed well with the experimental results for a surface energy of 0.435 J m −2 and an initial particle center-to-center separation distance on grain boundaries of about 0.2 μm.
52 citations
TL;DR: In this article, the grain structures and precipitates in the solidification microstructure of the ultra pure 17 wt% Cr ferritic stainless steels with different Ti and/or Nb micro-alloying were investigated both experimentally and theoretically.
52 citations
TL;DR: In this paper, the shape memory thin film system was investigated with regard to its structural, phase transformation and functional fatigue properties by means of combinatorial and high-throughput methods.
52 citations
TL;DR: A review of the literature revealed that recently published phase diagrams of the Fe-Nb system show considerable discrepancies regarding phase equilibria with the melt and the homogeneity ranges of the intermetallic phases, specifically of the Laves phase Fe2Nb.
Abstract: A review of the literature revealed that recently published phase diagrams of the Fe-Nb system show considerable discrepancies regarding phase equilibria with the melt and the homogeneity ranges of the intermetallic phases, specifically of the Laves phase Fe2Nb. Therefore the system has been reinvestigated by metallography, electron probe microanalysis (EPMA), and differential thermal analysis (DTA). Temperatures of invariant reactions were determined and the homogeneity ranges of the two intermetallic phases, Fe2Nb Laves phase and Fe7Nb6 μ phase, which both exist within a wide composition range, were established.
46 citations
TL;DR: In this article, the effect of laves phase on the Cr 2 O 3 sub-layer formation and coating thickness was further discussed, and the results showed that the coating peaks shifted from mainly Co 3 O 4 with some little Mn before test to MnCo 2 O 4 after test due to Mn diffusion from substrate.
46 citations
TL;DR: In this article, the aging properties of reduced activation ferritic/martensitic steel F82H were investigated at temperature ranging from 400°C to 650°C up to 100,000h.
46 citations
TL;DR: In this article, a stable Ta(Fe,Al)2 Laves phase with hexagonal C14 structure in the Fe-Al phase at temperatures of 800, 1000 and 1150°C was established.
15 Apr 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of the Cr addition on the microstructures and mechanical properties of the Al2O3/TiAl composites was investigated, and the reinforcement mechanism of Cr addition to Al 2O3 and TiAl composite was also discussed.
Abstract: Cr-doped Al2O3/TiAl in situ composites were successfully fabricated by hot-press-assisted exothermic dispersion method with elemental powder mixtures of Ti, Al, TiO2 and Cr. The effect of the Cr addition on the microstructures and mechanical properties of the Al2O3/TiAl composites were investigated. The as-synthesized composites consisted of γ-TiAl, α2-Ti3Al, Al2O3, and a small amount of Laves phase Ti(Al,Cr)2. Microstructure analysis indicates that Al2O3 particles mainly distributed on grain boundaries of the TiAl matrix. As the Cr content increases, the Al2O3 particles are dispersed more fine and homogeneously in the TiAl matrix, which resultes in the increase of the hardness, flexural strength and fracture toughness of the composites gradually. When the Cr content was 3 wt.%, the flexural strength and fracture toughness of the Al2O3/TiAl composite reaches the top values of 820 MPa and 8.3 MPa·m1/2, respectively. The reinforcement mechanism of Cr addition to Al2O3/TiAl composites was also discussed.
TL;DR: By combining density-functional theory calculations and aberration-corrected transmission electron microscopy, dislocations in Laves phase are shown to slip in an undulating path, different from the conventional slip process in simple metals.
Abstract: By combining density-functional theory calculations and aberration-corrected transmission electron microscopy, dislocations in Laves phase (a typical complex intermetallic compound) are shown to slip in an undulating path. During the slip, the dislocation cores jump up and down between a weakly bound plane and an adjacent strongly bound plane for gliding and atomic shuffling, respectively. This is different from the conventional slip process in simple metals, which is continuous within a single plane, as described in the paradigm of the generalized stacking fault energy.
TL;DR: In this paper, a double-stage super-high-pressure metal hydride hydrogen compressor was designed to produce hydrogen with a pressure of 100 MPa from 4 MPa feed gas when hot oil was used as a heat reservoir.
25 Jun 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of nickel and cobalt addition on the microstructure of 15-mass% chromium (15Cr) steels and their mechanical properties, such as creep strength and impact toughness, was investigated.
Abstract: The effect of nickel and cobalt addition on the microstructure of 15 mass% chromium (15Cr) steels and their mechanical properties, such as creep strength and impact toughness, was investigated. The microstructure of 15Cr ferritic steel changes from a ferrite single phase to dual phases of ferrite and martensite by the addition of nickel, which is an austenite-stabilizing element. The creep strength and precipitation behavior of intermetallic compounds (Laves phase, χ-phase and μ-phase) during creep exposure at elevated temperature were strongly influenced by the addition of nickel and cobalt. An increase in cobalt content led to an increase in creep strength by the formation of fine particles and a homogeneous distribution of intermetallic compounds precipitated in the ferritic matrix. The creep rupture life of 15Cr steel at 923 K and 140 MPa was approximately 100 times longer than that of conventional 9Cr ferritic steels with a tempered martensitic microstructure strengthened by carbides and carbonitrides.
TL;DR: In this paper, the crystal structure, the bulk magnetization characteristics and the magnetocaloric properties of Er1−xDyxCo2 compounds were investigated and a direct correlation was pointed out between the character of the magnetic transition and the behavior of the cell parameter versus x.
TL;DR: In this paper, the role of grain boundary Laves phase in the strengthening mechanism during long-term creep was examined, and a grain boundary precipitation strengthening mechanism was proposed as "grain boundary precipitation weakening mechanism" (GBPS), which can yield up to 77% of elongation even at ρ = 89%.
Abstract: The creep behavior of a new type of austenitic heat-resistant steel Fe-20Cr-30Ni-2Nb (at.%), strengthened by intermetallic Fe2Nb Laves phase, has been examined. Particular attention has been given to the role of grain boundary Laves phase in the strengthening mechanism during long-term creep. The creep resistance increases with increasing area fraction (ρ) of grain boundary Laves phase according to equation e/e = (1−ρ), where e0 is the creep rate at ρ = 0. In addition, the creep rupture life is also extended with increasing ρ without ductility loss, which can yield up to 77% of elongation even at ρ = 89%. Microstructure analysis revealed local deformation and well-developed subgrains formation near the grain boundary free from precipitates, while dislocation pile-ups were observed near the grain boundary Laves phase. Thus, the grain boundary Laves phase is effective in suppressing the local deformation by preventing dislocation motion, and thereby increases the long-term creep rupture strength. This novel creep strengthening mechanism was proposed as “grain boundary precipitation strengthening mechanism” (GBPS).
TL;DR: Tungsten is an effective element for solid-solution strengthening and is a ferrite former in 9CrODS ferritic steel, however excessive tungsten leads to Laves phase formation.
TL;DR: In this article, the segregation of Niobium-enriched phases in a nickel-base superalloy was investigated and the degree of dendritic segregation was determined by differential thermal analysis and homogenization treatments at varied temperatures and times.
TL;DR: The pseudobinary Zr 0.9 Ti 0.1 V 2 compound was prepared by induction melting method and the microstructure and phase compositions were examined by the scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD).
TL;DR: In this paper, structural changes of the Ti0.5 alloy were studied with regard to hydrogenation and dehydrogenation cycling at 25, 40 and 60 degrees C. The maximum hydrogen capacity at 25°C is 1.71 −± −0.01
TL;DR: In this article, a comparison of different phase diagrams reveals that the coexistence of two or even three different polytypes of Laves phases coexist as equilibrium phases in binary and ternary transition-metal-based systems.
Abstract: In various binary and ternary transition-metal-based systems, two or even three different polytypes of Laves phases coexist as equilibrium phases. A comparison of different phase diagrams reveals that the coexistence is characterized by some common features. In binary systems with cubic and hexagonal Laves phases existing at the same temperature but different compositions, the cubic C15 polytype always crystallizes at and around the stoichiometric composition whereas the hexagonal C14 and C36 polytypes are observed on the A-rich (C14) and B-rich (C36) side of the stoichiometry, respectively. On replacing the B atoms of an AB2 Laves phase by ternary additions, the highest solubility is always found in the C14 Laves phase. Ternary Laves phases A(B,C)2 in systems where none of the binary boundary systems contains a Laves phase are always of the C14 type. It is discussed how these observations are related to crystallographic differences between the three polytypic structures C14, C15, and C36.
TL;DR: In this article, the structural similarities between the precipitates of the Mg-Zn-Y alloy system have been investigated via electron microscopy, showing that icosahedrally coordinated zinc atoms arranged as a series of broad rhombohedral units.
Abstract: Intermetallic precipitates formed in heat-treated and aged Mg-Zn and Mg-Zn-Y alloys have been investigated via electron microscopy. Coarse spheroidal precipitates formed on deformation twin boundaries contained domains belonging to either the MgZn2 hexagonal Laves phase or the monoclinic Mg4Zn7 phase. Both phases are structurally related to the quasi-crystalline phase formed in Mg-Zn-Y alloys, containing icosahedrally coordinated zinc atoms arranged as a series of broad rhombohedral units. This rhombohedral arrangement was also visible in intragranular precipitates where local regions with the structures of hexagonal MgZn2 and Mg4Zn7 were found. The orientation adopted by the MgZn2 and Mg4Zn7 phases in twin-boundary and intragranular precipitates was such that the icosahedral clusters were aligned similarly. These results highlight the close structural similarities between the precipitates of the Mg-Zn-Y alloy system.
TL;DR: In this article, pressure-composition-temperature (PCT) curves were obtained for both structures at temperatures of 348, 373, 398 and 423 K, and H-pressures from 10 1 to 10 6 ǫPa, showing that the cubic phase is less stable than the hexagonal ones.
TL;DR: In this paper, a laser treatment of Inconel 718 alloy surface is carried out and the microstrutural and morphological changes in the laser treated region are examined using optical and scanning electron microscopes, energy dispersive spectroscopy, and X-ray diffraction.
TL;DR: In this paper, phase equilibria and diffusion processes for an Fe-Cr-Nb model alloy using Thermo-Calc and DICTRA revealed that this combined enrichment/depletion process can be explained by the influence of alloy chromium concentration on the Nb activity.
Abstract: During oxidation of a Laves-phase strengthened ferritic steel at 800 C in Ar/H2/H2O a precipitate-depleted zone occurs as a result of subscale chromium depletion. In parallel, an enrichment of Laves-phase is found in the immediate vicinity of the scale/alloy interface. Modeling the phase equilibria and diffusion processes for an Fe-Cr-Nb model alloy using Thermo-Calc and DICTRA revealed that this combined enrichment/depletion process can be explained by the influence of alloy chromium concentration on the Nb activity. VC 2011 The Electrochemical Society. [DOI: 10.1149/1.3590258] All rights reserved.
TL;DR: In this article, annealing and homogenization of homogenized Fe-Ni-Mn-Mo-Ti-Cr maraging steels resulted in the formation of submicrocrystalline Fe{sub 2}(Mo,Ti) Laves phase particles.
TL;DR: In this article, it was shown that the deuterium short-range order in cubic Laves phase deuteride YFe{sub 2}D{sub 4.2} cannot be explained only by applying the Switendick rule.
TL;DR: In this article, a phase map for the Laves-phase part of the Hf-Cr system has been constructed, which is based on X-ray powder diffraction (XRPD) and high-resolution transmission electron microscopy (HRTEM).
TL;DR: In this article, the Gibbs energy of Laves phases in the Ta-V periodic system has been modelled using two-and three-sublattice models to revise the thermodynamic description of the system.
Abstract: The Ta-V system is an interesting system exhibiting the existence of Laves phases among elements of the same group in the periodic system, and with an unusual order of stability of Laves phase structures at 0 K. Whereas the hexagonal C14 Laves phase is stable at 0 K and at high temperatures, the C15 structure is the most stable Laves phase at intermediate temperatures. The ab initio calculations of the total energies of formation for both C14 and C15 Laves phases employed two- and three-sublattice models to revise the thermodynamic description of the system published recently. The remodeled Gibbs energies of Laves phases require less fitting parameters than those obtained in previous treatments and the corresponding phase diagrams provide an excellent agreement with the experimental data on the phase stability and phase boundaries found in the literature. The new fitting procedure proposed involves a temperature dependent heat capacity for the C15 structure and allows us to compare the optimized heat capacity differences between the Laves phase and Standard Element Reference structure with those determined experimentally and theoretically. (C) 2010 Elsevier Ltd. All rights reserved.