Showing papers by "Hengzhi Fu published in 2012"
30 Jun 2012-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the precipitation behavior of grain boundary (GB) M23C6 and its effect on tensile properties at elevated temperature were investigated systematically in a Ni-Cr-W based superalloy.
Abstract: Precipitation behavior of grain boundary (GB) M23C6 and its effect on tensile properties at elevated temperature were investigated systematically in a Ni–Cr–W based superalloy. The results show that the M23C6 precipitation behavior is influenced obviously by grain boundary character (GBC) and interfacial energy. The Σ≤9 GBs and low angle GBs have low interfacial energy, and no M23C6 carbide precipitates at these GBs. Plenty of M23C6 carbide particles precipitate at the large angle GBs with high interfacial energy. The coherent orientation relationship between M23C6 and the matrix plays an important role on the precipitation morphology of M23C6. M23C6 carbides with four typical morphologies distribute at the large angle GBs, including lamellar carbide which grows into the matrix near one side or both sides of the GBs, rod-like carbide and small lamellar carbide both of which grow along GBs. Moreover, the decrease of both tensile and yield strength of the aged alloy is mainly caused by the lamellar M23C6 carbide breaking. The tensile properties vary irregularly with increasing aging time.
112 citations
TL;DR: In this article, the effect of growth rate and temperature gradient on microstructure parameters was determined and it was found that the grain size and the interlamellar spacing decreased with increasing of growing rate or temperature gradient.
61 citations
28 Feb 2012-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of M23C6 carbides on the formation of grain boundary serrations (GBSs) has been systematically investigated in a solid solution strengthened Haynes 230 alloy.
Abstract: The effect of M23C6 carbides on the formation of grain boundary serrations (GBSs) has been systematically investigated in a solid solution strengthened Haynes 230 alloy It is found that GBS occur in this alloy during the slow cooling process and are accompanied by the precipitation of intergranular planar M23C6 carbides The amplitude and proportion of GBS increase with the rise of the solution temperature and time If the specimens are cooled directly without any solution treatments, the grain boundaries remain planar and granular M23C6 carbides precipitate at them The sequential evolutions of GBS and M23C6 carbides are investigated by scanning electron microscopy (SEM) examination High-resolution transmission electron microscope (HRTEM) investigations reveal the coherent interfacial plane of M23C6 carbides formed at grain boundaries to be ( 1 1 1 ¯ ) These facts indicate that the nucleation and oriented growth of M23C6 carbides at grain boundaries play an important role in the formation of GBS Based on the interfacial energy calculations and the tensions balance relation, a semi-quantitative model about the GBS formation is proposed
51 citations
TL;DR: In this article, phase structure investigations of the as-cast and annealed Zr(V1−xFex)2 alloys indicate the annealing treatment can eliminate the minority phases originating from the non-equilibrium solidification of alloys.
43 citations
TL;DR: In this paper, a new version of secondary dendrite arm migration caused by temperature gradient zone melting during peritectic solidification, which involves both primary and per-itectic phases, was investigated.
42 citations
TL;DR: In this article, the effect of V on the primary dendritic spacing, interlamellar spacing, and microhardness of TiAl-based alloys was investigated using linear regressing analysis.
42 citations
TL;DR: In this article, Brindman type directional solidification experiments were conducted for Ti-46Al-8Nb alloy in a wide range of growth rates (1-70μm/s).
40 citations
TL;DR: In this paper, the effects of hydrogen on glass plasticity of two bulk metallic glasses were studied and it was found that hydrogen addition can increase the glass polycarbonate plasticity significantly.
38 citations
TL;DR: In this paper, the effects of growth rate on primary phase selection and solidification path as well as structure characteristics either in macro- or micro-scale were determined by varying the growth rate from 0.5 to 1.5mm/min, which implies that the brittle lamellae with orientation that is perpendicular to the crystal growth direction might be disappeared accordingly.
36 citations
TL;DR: In this article, the effect of oxygen on the microstructure of directionally solidified (DS) Ti-47Al-2Cr-2Nb alloy was investigated and the results showed that increasing the oxygen content led to a change of primary solidification β phase to α phase and finally the volume fractions of lamellae with the orientation normal to the growth orientation would then increase.
34 citations
TL;DR: In this article, X-ray photoelectron spectroscopy (XPS) was used to examine the hydrogen absorption properties of homogeneously annealed Zr 0.9 Ti 0.1 V 2 samples.
TL;DR: In this article, the microstructure and room temperature fracture toughness of pseudo-binary NiAl and Mo in situ composites were investigated, showing that uniform and well-aligned Mo fibrous structures were directionally solidified by the liquid metal cooling process at the growth rate of V = 6μm/s.
TL;DR: In this paper, the authors investigated the relationship between solidification microstructure and the properties of Ni-Ni 3 Si in situ composites and showed that the Ni−Ni 3 si hypoeutectic composites have lower micro-hardness than pure Ni 3 Si.
Abstract: Ni–Ni 3 Si composites are prepared by the Bridgman directional solidification technology under different growth conditions, aiming to improve the ductility of the Ni 3 Si compound and investigate the relationship between solidification microstructure and the properties. Microstructure of the Ni–Ni 3 Si hypoeutectic in situ composites transforms from regular lamellar eutectic to cellular structure then to dendritic crystal with the increase of the solidification rate. Ni–Ni 3 Si eutectic composites display regular lamellar eutectic structure at the solidification rate R =6.0–40.0 μm/s and the lamellar spacing is decreased with the increase of the solidification rate. Moreover, the Ni–Ni 3 Si hypoeutectic composites present lower micro-hardness than pure Ni 3 Si, which indicate Ni–Ni 3 Si hypoeutectic composites have higher ductility, whereas the ductility of the Ni–Ni 3 Si eutectic composites has scarcely been improved. This is caused by the formation of the metastable Ni 31 Si 12 phase in the Ni–Ni 3 Si eutectic composites.
TL;DR: In this paper, the growth direction and lamellar orientation of the hexagonal α phase of the Ti-46Al 0.5W-0.5Si alloy were studied under different growth rates.
TL;DR: In this article, the 3D morphology and growth mechanism of primary Al6Mn intermetallic compound have been investigated in directionally solidified Al-3at.%Mn alloy at a low growth rate of 1μm/s.
TL;DR: In this paper, the dendrite morphologies of single crystal superalloy grown along were different from that of the conventional primary dendrites, showing irregular cruciforms and array in rows in a transverse section.
TL;DR: In this paper, numerical simulation and experimental investigation are utilized to analyze the casting defects of Ti-6Al-4V alloy formed under different vertical centrifugal casting conditions in graphite molds.
Abstract: Numerical simulation and experimental investigation are utilized to analyze the casting defects of Ti-6Al-4V alloy formed under different vertical centrifugal casting conditions in graphite molds. Mold rotating rates of 0, 110 and 210 rpm are considered in experimental process. Results show that centrifugal forces have significant effects on the quantity of both macropores and microdefects (micropores, microcracks and inclusions). The relative amount of all macro- and micro-scopic casting defects decreases from 62.4 % to 24.8 % with the increasing of the centrifugal force, and the macropore quantity in stepped casting decreases exponentially with the increase of the gravitation coefficient. The relative proportions of both micropores and microcracks decrease with the mold-rotating rate increase, but the relative proportion of inclusions increases significantly. Besides this, the mold-filling sequence is proved to be an important factor in casting quality control.
TL;DR: In this article, the authors studied the eutectic microstructure and growth interface morphology of directionally solidified Ni−31Al−32Cr−6Mo(at.%).
TL;DR: In this paper, the effect of peritectic reaction on dendrite coarsening was investigated in directionally solidified Ni 3.6n 2.5n 3.1%Ni alloys at different growth rates under constant temperature gradient.
Abstract: Effect of peritectic reaction on dendrite coarsening was investigated in directionally solidified Sn–36 at.%Ni peritectic alloys at different growth rates (2~200 μm/s) under constant temperature gradient. A coarsening model was used to characterize the coarsening process in terms of both the secondary dendrite arm spacing (λ
2) of the primary Ni3Sn2 phase and the specific surface area (S
V
) of dendrites. It was shown that peritectic reaction could retard the increase of λ
2 and decrease of S
V
during coarsening, which resulted from decelerating solute transport rate between adjacent dendrite arms caused by the peritectic phase enclosing the primary phase. The kinetics of the peritectic reaction that was found to be crucial to determine the coarsening process was characterized by the reaction constant (f) which not only changed with growth rates but also with solidification time in the real solidification process at a given growth rate.
TL;DR: In this article, the solute redistribution equations during planar growth of a stoichiometric intermetallic compound, Al 9 Co 2, were obtained based on the principle of solute conservation.
TL;DR: In this article, the effect of the flow driven by a travelling magnetic field (TMF) on solidification structure of Sn-1.8-wt% Cd peritectic alloy was investigated numerically and experimentally.
TL;DR: In this paper, a gradient microstructure has been observed in TC21 alloy, where the addition of hydrogen induces martensite transformation and increases the volume fraction of β. The microhardness of the upper surface drops about 45% with 14.6% H.
TL;DR: Zr55Cu30Ni5Al10 alloys with different amounts of hydrogen have been prepared by arc melting under the gaseous mixture of hydrogen and argon, and the positive effect of hydrogen on glass-forming ability has been interpreted from the thermodynamic and structural points of view.
Abstract: Zr55Cu30Ni5Al10 alloys with different amounts of hydrogen have been prepared by arc melting under the gaseous mixture of hydrogen and argon. Proper additions of hydrogen have been proved to effectively increase the glass-forming ability (GFA) of this alloy. Positive effect of hydrogen on GFA has been interpreted from the thermodynamic and structural points of view. Proper additions of hydrogen can decrease the liquidus temperature, which leads to more stable glass-forming liquid. Structure analysis by positron annihilation lifetime spectroscopy shows that proper additions of hydrogen can increase the concentration of shortest open volume and decrease the concentration of intermediate and largest open volumes. This leads to formation of a denser random packed structure, and thus increases the GFA of Zr55Cu30Ni5Al10 alloys.
Patent•
06 Jun 2012
TL;DR: In this article, a method for the plastification of massive amorphous alloy with plasticity at room temperature was proposed, which can be applied in fields of aerospace, weapon industry, precision machines, information technology and the like.
Abstract: The invention relates to a method for preparing zirconium-base amorphous alloy with plasticity at room temperature, and relates to a method for preparing amorphous alloy, which solves the problem of poor plasticity at room temperature of the amorphous alloy in the prior art The method comprises the following steps of: filling a zirconium-base amorphous alloy raw material into a water-cooling copper crucible of an arc furnace, vacuumizing a smelting chamber, introducing hydrogen and argon into the smelting chamber according to a certain ratio, smelting the raw material of the zirconium-base amorphous alloy in a mixed atmosphere, and preparing by a copper mold suction casting method to obtain the zirconium-base amorphous alloy with the plasticity at room temperature The zirconium-base amorphous alloy has excellent plasticity at room temperature, and the plasticity is improved by 7 times The method can be widely applied to the plastification of massive amorphous alloy, so that the amorphous alloy can be applied in fields of aerospace, weapon industry, precision machines, information technology and the like
TL;DR: In this paper, three technologies were proposed to solve the difficulty in the explosive welding of corrosion-resistant aluminum and stainless steel tubes, and a 3D finite element model was established for systematic simulations in the parameter determination.
Abstract: To solve the difficulty in the explosive welding of corrosion-resistant aluminum and stainless steel tubes, three technologies were proposed after investigating the forming mechanism through experiments. Then, a 3D finite element model was established for systematic simulations in the parameter determination. The results show that the transition-layer approach, the coaxial initial assembly of tubes with the top-center-point the detonation, and the systematic study by numerical modeling are the key technologies to make the explosive welding of LF6 aluminum alloy and 1Cr18Ni9Ti stainless steel tubes feasible. Numerical simulation shows that radial contraction and slope collision through continuous local plastic deformation are necessary for the good bonding of tubes. Stand-off distances between tubes (D
1 and D
2) and explosives amount (R) have effect on the plastic deformation, moving velocity, and bonding of tubes. D
1 of 1 mm, D
2 of 2 mm, and R of 2/3 are suitable for the explosive welding of LF6-L2-1Cr18Ni9Ti three-layer tubes. The plastic strain and moving velocity of the flyer tubes increase with the increase of stand-off distance. More explosives (R>2/3) result in the asymmetrical distribution of plastic strain and non-bonding at the end of detonation on the tubes.
TL;DR: In this article, a multicrystalline silicon ingot with 60mm×60mm in cross section was continuously and directionally solidified by a novel technology that combines the advantages of electromagnetic cold crucible and continuous casting.
TL;DR: In this paper, the deoxidization effects of hydrogen arc melting (HAM) on Zr-based alloys were investigated, and the effect of the hydrogen percentage and melting duration on the oxygen content and glass-forming ability of Zr 55 Cu 30 Ni 5 Al 10 alloys was studied.
TL;DR: In this article, a huge triple phase region of the non-isothermal peritectic reaction within a large temperature region (around 8 K) was obtained in directionally solidified Cu-Ge alloys, which provides a convincing experimental evidence for studying the morphology of peritectical reaction trijunction region.
TL;DR: In this paper, a previously proposed numerical model for binary alloy solidification, and the corresponding algorithm for solving the strong coupling among the solidification temperature, solid fraction, and liquid composition (T − f S − C L ), are extended to ternary alloys.
Abstract: In this paper, a previously proposed numerical model for binary alloy solidification, and the corresponding algorithm for solving the strong coupling among the solidification temperature, solid fraction, and liquid composition ( T – f S – C L ), are extended to ternary alloys. The feasibility of the extended numerical method is demonstrated by sample simulations for the directional solidification of blade-like castings of Al–Cu–Si alloys using three different thermodynamic data-acquisition methods: direct coupling with the CALPHAD software Thermo-Calc via the TQ6-Interface, using the “mapping technique” and regression functions. The computational efficiency and the accuracy of the calculation results of the three different methods are compared. The present numerical simulations confirm that thermodynamic data-acquisition method of using regression functions and the “mapping technique” are much more efficient than that of direct coupling with Thermo-Calc.