Showing papers by "Hengzhi Fu published in 2010"
TL;DR: In this paper, the heat transfer during directional solidification by Bridgman-type directional solidization has been analyzed and a relationship has been established that reflects the effect of alloy properties, process parameters and equipment characteristics on thermal gradients.
64 citations
TL;DR: In this article, the authors measured the cellular spacing, lamellar spacing, volume fraction of Ti 5 Si 3 phases (f V ) and microhardness (H V ) of a TiAl-based alloy with a Bridgman type directional solidification furnace.
51 citations
TL;DR: In this article, the dendritic spacing, lamellar spacing, and microhardness of a TiAl-based alloy were measured by using a Bridgman type directional solidification furnace.
48 citations
TL;DR: In this article, solid-liquid interface morphologies of a nickel-base single crystal superalloy AM3 were investigated under high thermal gradient and the critical velocities of planarcellular and cellular-dendritic transition were greatly increased by high thermal gradients.
Abstract: Solid–liquid interface morphologies of a nickel-base single crystal superalloy AM3 were investigated under high thermal gradient. The critical velocities of planar–cellular and cellular–dendritic transition were greatly increased by high thermal gradients. A high thermal gradient was of great benefit to dendrite refinement. Experimental results showed that the primary and secondary dendrite arm spacings decreased with increasing cooling rate. As expected, the segregation of elements was suppressed and the size of the gamma prime (γ′) phase decreased significantly with increasing withdrawal rates. The shape of γ′ in interdendritic region kept cuboidal at higher withdrawal rate. It was found that the withdrawal rates had little influence on the crystallographic orientation in high thermal gradient directional solidification.
46 citations
TL;DR: The microstructures and phase composition of the pseudobinary ZrTi0.2V1.8 alloy were examined by scan electron microscope (SEM) and X-ray diffraction (XRD).
40 citations
TL;DR: In this paper, a single crystal superalloy AM3 oriented along and lattice directions with a deviation were produced by bottom seeding technique in a modified Bridgman directional solidification furnace.
37 citations
TL;DR: In this paper, the effect of hydrogen on hot deformation behaviors of Ti-47Al alloys was studied using a hot simulator and the optimized deformation temperature was 1150°C.
32 citations
TL;DR: In this paper, the microstructure evolution of directionally solidified DZ125 superalloy is systematically investigated by changing the melt superheating temperature, and the results show that the dendrite is refined with the melting temperature increasing from 1500°C to 1650°C.
28 citations
TL;DR: In this article, a solute diffusion transport model in a temperature gradient was proposed to describe the concentration evolution both in the mushy zone and the complete liquid melt zone during thermal stabilization.
26 citations
TL;DR: In this article, an analytical model is proposed to evaluate the Ni concentration of the melt after thermal stabilization and the effect of temperature gradient and volume fraction of liquid phase in the mushy zone on the Ni concentrations of the melted Al-Ni peritectic alloys is discussed.
25 citations
TL;DR: In this paper, the hydrogen solubility in a binary alloy melt was investigated through a theoretical analysis and the results compared subsequently with values determined experimentally, based on a modified version of Sievert's law.
TL;DR: In this paper, a comparison of the changes in Gibbs free energy of alloys deoxidized with hydrogen atoms was conducted. And the authors found that the hydrogen atoms played a major role in deoxidation.
TL;DR: In this paper, Ni59Zr16Ti13Si3Si3Sn2Nb7 amorphous material was deposited by laser cladding onto Ti-3Al-5Mo-5V-4Cr-2Zr titanium alloy.
Abstract: Ni59Zr16Ti13Si3Sn2Nb7 amorphous material was deposited by laser cladding onto Ti-3Al-5Mo-5V-4Cr-2Zr titanium alloy. Despite trials with wide range of process parameters, the present experiments were unable to retain complete amorphous surface microstructure after laser cladding. So the mixed structure with amorphous phase, intermetallic compounds and borides were obtained. XRD results showed that the amorphous phase fraction of the coatings was measured up to about50% depending on the laser cladding parameters. DSC curve showed that glass transition temperature (Tg) and crystallization temperature (Tx) was observed around 750K and 880K, respectively, which indicated that the Ni-based amorphous alloy coating had high thermal stability. The nanocrystalline grains, were about 40-100nm in size, precipitated from amorphous phase or interface between amorphous and borides. The Vickers hardness of coating depended on the amount of various phases that were present in different locations of coating.
TL;DR: In this article, a two phases separate growth microstructure is observed in directionally solidified Fe-4.2Ni alloy in diffusive regime, which consists of peritectic two solid phases, both of which grow with plane fronts in the pulling direction and occupy half width of the sample.
TL;DR: The Si-TaSi 2 eutectic in situ composite, which has highly-aligned and uniformly-distributed TaSi 2 fibers in the Si matrix, can be obtained when the solidification rate changes from 0.3 to 9.0 mm/min this article.
TL;DR: In this paper, the laser power and scanning rate necessary to carry out the ceramic melt growth is determined, and the formation condition and evolution of the particular microstructure of the composite during rapid solidification are discussed.
Abstract: In situ composite of Al2O3/GdAlO3(GAP) ceramic eutectic prepared by directional solidification is an interesting candidate for the manufacture of turbine blades because of its excellent mechanical properties. In the present paper, directionally solidified Al2O3/GAP eutectic in situ composite ceramics are manufactured by the laser zone remelting technique to investigate the rapid solidification process. The laser power and scanning rate necessary to carry out the ceramic melt growth is determined. The characteristic microstructure is investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). The as-solidified Al2O3/GAP eutectic presents an elongated colony structure consisting of only -Al2O3 and GAP phases with an oriented growth array. The eutectic spacing is strongly dependent on the laser scanning rate, rapidly decreasing to the sub-micron range for the samples grown at the highest rate. Besides, the formation condition and evolution of the particular microstructure of the composite during rapid solidification are discussed.
TL;DR: In this paper, the evolving process of column crystals of Ti46Al 0.5W0.5Si alloys that is directionally solidified by rectangular cold crucible was systematically studied.
Abstract: This paper has systematically studied the evolving process of column crystals of Ti46Al0.5W0.5Si alloys that is directionally solidified by rectangular cold crucible. The results showed that: the solid/liquid interface presented convex to the liquid metal due to the complicated influences by cold crucible. Overheating temperature and new crystal nucleus had great effects on the growth continuity and the stability of column crystals. Furthermore, the precipitation phases have been studied. As a result, the methods for controlling growing process of columnar crystals have been submitted, which are playing a critical role in optimizing experimental parameters and devising the construction-elements of cold crucible.
TL;DR: In this article, the growth characteristics of a novel binary eutectic under high temperature gradient was investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), and X-ray diffraction (XRD).
Abstract: Directionally solidified (DS) oxide eutectic in situ composites are attracting increasing attention because of their unique properties and potential applications to high temperature structural materials, optical or electronic devices. Among the alumina-based eutectic composites, DS Al2O3/Er3Al5O12(EAG) eutectic is considered to be promising candidate for use as selective emitter at high temperature. In this work, eutectic in situ composites of Al2O3/EAG rods having smooth surface and full density are successfully prepared by directional solidification using the laser zone remelting method, aiming to investigate the growth characteristic of this novel binary eutectic under high temperature gradient. The microstructure is investigated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). The Al2O3/EAG eutectic presents a very fine irregular network structure consisting of only -Al2O3 and Er3Al5O12 phases without grain boundaries and amorphous phases between interfaces. The eutectic interphase spacing is strongly dependent on the laser scanning rate, rapidly decreasing at the sub-micron levels for the samples grown at high rate. Furthermore, the microstructural formation and evolution of the composite are analyzed and discussed.
TL;DR: In this article, the effect of spraying power (arc current) on amorphous phase content and properties of the coatings was investigated and it was revealed that the coating sprayed at arc current of 150 A was nearly fully ammorphous although the spraying powders were not.
Abstract: Fe-based metallic glass coatings were prepared on Ti?3Al?5Mo?5V?4Cr?2Zr substrate by Air Plasma Spraying (APS) The effect of spraying power (arc current) on amorphous phase content and properties of the coatings was investigated It was revealed that the coating sprayed at arc current of 150 A was nearly fully amorphous although the spraying powders were not The amorphous phase content in the coatings decreased with increasing arc current Vickers microhardness and corrosion behaviour of the sprayed coatings were also studied The highest cross-section microhardness of the coatings was Hv005908, roughly three times as high as that of the substrate The coating sprayed at arc current of 300 A exhibited the best excellent corrosion resistance
TL;DR: In this paper, the authors proposed an approach that employs an abrupt growth velocity to make the in-situ composites grow stably out of the coupled zone, and the results showed that the crack distribution and extension were mainly localized in primary Ni3Nb dendrites in the non-coupled eutectics.
Abstract: At normal solidification conditions, in-situ composites of a Ni-24.8%Nb hypereutectic alloy can be produced at growth velocities below 5μm/s, with a thermal gradient of 180K/cm, and this low productivity remarkably restricts the application of this kind of in-situ composites. In this paper, we proposed an approach that employs an abrupt growth velocity to make the in-situ composites grow stably out of the coupled zone. In-situ composites of the Ni-24.8%Nb hypereutectic alloy were obtained at a growth velocity of 100μm/s and the productivity was greatly improved. This value is in the same order magnitude imposed on the single-crystal superalloys. The compression strengths were investigated on different microstructures involving the coupled eutectics and non-coupled eutectics. The results showed that the crack distribution and extension were mainly localized in primary Ni3Nb dendrites in the non-coupled eutectics, and that in-situ composites with the entirely coupled eutectics have improved mechanical properties and different deformation behaviors.
TL;DR: In this paper, the authors conducted directional solidification experiments on Pb-Bi peritectic alloys at very low velocity (V=0.5 μm/s) and high thermal gradient (G=25 K/mm) and observed complete banded and oscillatory structures in both hypoperitectic and hyperperitectic compositions over several millimeters of growth.
Abstract: Directional solidification experiments on Pb-Bi peritectic alloys have been conducted at very low velocity (V=0.5 μm/s) and high thermal gradient (G=25 K/mm). Incomplete banded and oscillatory structures have been observed in both of hypoperitectic and hyperperitectic compositions over several millimeters of growth. These structures resulted from the repeated nucleation and competition between properitectic α- and peritectic β-phases. The banded or oscillatory structures are found to be transient and the final steady-state phase was only the peritectic β-phases. With an increase in composition, β phase formed and α phase disappeared at a lower solidified distance. Composition variations in the banded structure are measured to determine the solute distribution along the growth direction.