Papers by Keyword: Structural Evolution

Abstract: In this article, a novel Al–6Y–2P master alloy with YP particles was successfully synthesized. By means of the fracture surface observation, it was found that YP particles with an average size of 21.5 μm exhibit the cubic morphologies. With the addition of Al–6Y–2P master alloy, primary Mg₂Si particles in Al–Mg₂Si composites can be significantly refined to 21.2 μm and 20.3 μm after holding for 30 min and 120 min respectively. Meanwhile, the morphologies of eutectic Mg₂Si alter from a flake-like to fine fibrous shape. The reason for the excellent refining performance of this master alloy was discussed based on the chemical kinetics theory. During the solidification process, P atoms distribute homogeneously in the Al melt and precipitate in the form of AlP, providing heterogeneous nucleation sites for primary Mg₂Si.

Abstract: The effect of temperature on the structural evolution and physical properties of nanocrystalline BiFeO₃ compound has been studied systematically. The results show that the compound crystallizes in the hexagonal LiNbO₃ type-structure (space group R3c) and the structural characterization was a=b=5.5979 Å, c=13.9163 Å and V=387.43 Å3. The average crystallite size was about 32.5 nm. The Neel temperature was the same in the vacuum and air conditions, but the decomposition temperature in the air condition was higher 190°C than that of the vacuum condition.

Abstract: In the present study, Fe-50at%Al/WC intermetallic matrix composite powder was produced through mechanical alloying (MA) followed by annealing treatment. The phase transformations, grain size, microstructure and thermal stability of the composite powder during milling and annealing treatment were studied. The results showed that a bcc Fe(Al) solid solution reinforced with nanoscale WC particles was formed through high-energy ball milling The grain size of Fe(Al) decreased and the lattice strain of Fe(Al) increased with increasing milling time. The as-milled Fe(Al)/WC composite powder had lamellar structure. The oxygen content of Fe(Al)/WC composite powder increased with increasing milling time. The phase transformation from Fe(Al) to Fe-Al intermetallic phases was related to the milling time of composite powder and could occure at temperature of 400°C.

Abstract: The East China Sea shelf basin, which is a fault subsidence during the Cenozoic Era, locates in the East China Sea continental shelf. In this paper, balanced section technique has been applied to analyzing the differential evolution in the East China Sea shelf basin south of Cenozoic tectonic and summarizing the control factors of tectonic activities on the petroleum accumulation. Our study results will provide essential data and basis for the distribution of the Cenozoic oil and gas and promote the development of the petroleum exploration in the East China Sea shelf basin.

Abstract: North Uskyurt Basin, located on Turan Plain, northwestern Central Asian, is continental polycyclic cratonic. The structural evolution of the basin underwent six phases: basement formulation, passive edge, rifting, post-rifting, compression, early Neogene depression. Regional structural evolution takes control of complicated transition of North Uskyurt sedimentary structure. In general, basin sedimentary environment underwent basement (granite, metamorphic rocks) passive edge, late Devonian epoch carboniferous period (marine facies) rifting, late Permian epoch-triassic period (continental facies) post-rifting, Jurassic period-Cretaceous period (Marine-continental Transition Facies, marine facies) compression, late Eocene-Miocene epoch (marine-continental facies coexistence) Neogene depression, Pliocene-Holocene (continental facies). Consequently, sedimentary formation in which various sedimentary environment, such as marine facies, continental facies, are coexisted with various rock types, such as clastic rocks, carbonate rocks, is generated.

Abstract: FeCoNi system equimolar alloys were fabricated by a vacuum arc melting. The phase constitution of FeCoNi system alloys was determined by XRD analysis and the microstructure was observed by OM. The comprehensive atomic radius δ, the mixing enthalpy ΔH_mix and the mixing entropy ΔS_mix of alloys were also calculated according to relevant equations. The results show that the addition of Ti, Al and Cu has an obvious influence on the microstructure and phase constitution of FeCoNi system equimolar alloys. Single Ti addition resulted in almost entire solid solution with a typical dendrite growth character and a little unknown phase. However, further addition of Al, Cu or Al+Cu into the FeCoNiTi equimolar alloys led to the occurrence of an entire solution phase with dendrite, coarse dendrite, and rosette dendrite respectively. Such a phenomena suggested that the mixing entropy caused by the increase of components number rather than the comprehensive atomic radius between the elements or the mixing enthalpy of the alloy systems might be responsible for the formation of almost entire solid solution in FeCoNi system equimolar alloys.

Abstract: For the study of soft subgrade pavement cracking process, it establishes the pavement structure tension crack model by elastic layered theory. Based on the finite element method, it studies the tension crack evolution process. It establishes the tension crack stress criterion to the roadbed. Analysis shows that the distresses of asphalt pavement of the real highway results from the damage by asymmetric sedimentation which is under excessively axle loading on pavement structure, rather than the fatigue damage by axle loading repetitions in the condition of asymmetric intensity in the same layer. The results show that the soft degree of the subgrade is proportional to the tensile stress, the more localized soft, the easier to crack the road. The soft roadbed does not have a homogeneous structure of the road surface, the tension stress rupture occurred in the discontinuous surface. The road structure has a set of tensile stress under the circulation wheel load, it formats a new fracture surface, and the structure form corresponding evolves, and causes stress state change. At last most of the road sub-base crack, and surface cracking occurres, so the pavement failure.

Abstract: The superplastic tensile deformation behavior and structural evolution of two kinds of α+β titanium alloys were investigated in this paper, one is a new high strength high toughness Ti alloy with damage tolerance called TC21, and the other is a new superplastic Ti alloy so called Ti-SP2500. The results indicated that TC21 alloy has good superplasticity at the temperature from 720
to 960
and with the strain rate of 5.510-5s-1∼1.110-2s-1. On the optimal superplastic condition, the maximum elongation is over 1300%. During the superplastic tensile deformation, the dynamic recrystallization occurs in deformation zone of the specimens and the superplasticity is improved. Ti-SP2500 alloy has good superplasticity at the temperature from 720°C to 800°C and with the strain rate of 6.67 10-4s-1∼1.1110-2s-1. The maximum elongation for Ti-SP2500 alloy will exceed 2200% at 780°C with the strain rate of 5.5610-3s-1. Its superplastic deformation mechanism is controlled by grain boundary sliding, and the grain deformation and dislocation creep has the coordinating action.

Abstract: The present communication is concerned with the interdiffusion kinetics and the interface breakdown that take place in the Nb/NbC multilayer system as the result of thermal annealing in the 400-800oC temperature range. Within this temperature range carbon is the diffusing species. Carbon diffuses from the carbide layer into the adjacent Nb layer, depleting its concentration within the carbide, causing the nucleation and subsequent growth of an intermediate Nb2C layer and decreasing the width of the original Nb layer. TEM examination of the cross-sections of the multilayer specimens provides data regarding the evolution of the microstructure and, in particular, regarding the initial nucleation stage of the newly formed Nb2C layer.