Co-reporter:W.Q. Lu, S.G. Zhang, Q.D. Hu, J.G. Li
Materials Letters 2016 Volume 182() pp:351-354
Publication Date(Web):1 November 2016
DOI:10.1016/j.matlet.2016.06.124
•The structural evolution in solidifying Al-10 wt% Bi alloy was in situ observed.•Five forces acted upon L2 droplets in front of the L1/L interface.•The droplets were dominated by the repulsive force at early stage.Using synchrotron radiography, we observed the advancing L1/L interface and its interaction with L2 droplets during directional solidification of the Al-10 wt% Bi immiscible alloy. Five forces act upon L2 droplets in front of the L1/L interface. The repulsive force that pushes the droplets away from the interface is the largest force when the droplet radius (r) is smaller than 20.5 µm, while Marangoni force is the largest one when 20.5 µm
Co-reporter:Wen-Quan Lu;Shu-Guang Zhang;Jian-Guo Li
Acta Metallurgica Sinica (English Letters) 2016 Volume 29( Issue 9) pp:800-803
Publication Date(Web):2016 September
DOI:10.1007/s40195-016-0453-7
Using synchrotron radiography, a melting process of the Al-10 wt% Bi immiscible alloy was fully observed, and Bi solute coarsening and dissolution behaviors as well as their effect on the microstructural evolution were also investigated. We found that two different steps including coarsening and dissolution processes can be used to describe the structure evolution in melting Al-10 wt% Bi immiscible alloy. And diffusion coalescence controlled the coalescence of Bi droplets at the early stage of the melting Al-10 wt% Bi immiscible alloy, while the coagulation during movement did at later stage. Also, the larger the droplet, the larger the distance of the steady-state concentration distribution around the droplet.
Co-reporter:Yan-Liang Ji;Wei Zhang;Xiao-Yang Chen
Acta Metallurgica Sinica (English Letters) 2016 Volume 29( Issue 4) pp:382-387
Publication Date(Web):2016 April
DOI:10.1007/s40195-016-0398-x
As one of the most popular used high-speed steels, M2 possesses excellent hardness and toughness as cutting tools. Networks of eutectic carbides distributing in the inter-dendritic region are academically considered to be the typical microstructure of M2, which can be refined by increasing cooling rate. In this paper, a novel casting method named fusible metal mold (FMM) is employed to refine the microstructure of M2 high-speed steel. Results show that FMM casting method can improve cooling rate by 100% without any contamination of the melts’ composition.
Co-reporter:Xiaoyang Chen, Yanliang Ji, Shuguang Zhang, Jianguo Li
Materials Letters 2015 Volume 151() pp:35-37
Publication Date(Web):15 July 2015
DOI:10.1016/j.matlet.2015.03.010
•A new method of liquid-alloy-lined Cu mold casting is introduced.•Cooling rate of the new method exceeds the upper limit of usual method by 60%.•Refined microstructure in the Fe–P–C sample is achieved by the new method.•Metallic glass surface on the Fe–P–C sample is formed by the new method.Cu mold casting is a common technique of rapid solidification, by which bulk materials (>1 mm) can be produced with a cooling rate of 1~1000 K/s. In this work, an improved Cu mold casting method with higher cooling rate is proposed. A thin layer of Ga–In–Sn liquid alloy is painted on the surface of Cu mold as a channel of heat flowing between cast sample and mold. The recorded cooling rate of the improved Cu mold exceeds the upper limit of cooling rate of Cu mold and reaches up to 1613 K/s. Accordingly, refined microstructure and even a metallic glass layer at surface are obtained in the cast sample via the new method.
Co-reporter:Han-song Yu;Jian-guo Li
International Journal of Minerals, Metallurgy, and Materials 2015 Volume 22( Issue 11) pp:1157-1162
Publication Date(Web):2015 November
DOI:10.1007/s12613-015-1180-1
The effect of solidification cooling rate on the size and distribution of inclusions in 12%Cr stainless steel was investigated. A wide range of solidification cooling rates (from 0.05 to 106 K·s-1) was achieved using various solidification processes, including conventional casting, laser remelting, and melt spinning. The size and distribution of inclusions in the steel were observed and statistically collected. For comparison, mathematical models were used to calculate the sizes of inclusions at different solidification cooling rates. Both the statistical size determined from observations and that predicted from calculations tended to decrease with increasing cooling rate; however, the experimental and calculated results did not agree well with each other at excessively high or low cooling rate. The reasons for this discrepancy were theoretically analyzed. For the size distribution of inclusions, the effect of cooling rate on the number densities of large-sized (> 2 μm) inclusions and small-sized (≤ 2 μm) inclusions were distinct. The number density of inclusions larger than 1 µm was not affected when the cooing rate was less than or equal to 6 K·s-1 because inclusion precipitation was suppressed by the increased cooling rate.
Co-reporter:Long Zeng;Wei Zhang;Yanliang Ji
Metallurgical and Materials Transactions A 2015 Volume 46( Issue 7) pp:2819-2822
Publication Date(Web):2015 July
DOI:10.1007/s11661-015-2945-x
A new solidification process called non-interfacial-gap permanent-mold casting (NIGPMC) is proposed to improve the cooling rate by eliminating the metal–mold interfacial gap. High-Cr steel ingots were
prepared by this process and conventional permanent-mold casing (CPMC) separately. Comparing with CPMC, the primary dendrite arm spacing obtained by NIGPMC is greatly refined. It is demonstrated that the NIGPMC is a promising pathway to refine the microstructure of the large ingot.
Co-reporter:Y.J. Huang, Q.D. Hu, J.W. Hou, J.G. Li
Scripta Materialia 2014 Volume 87() pp:21-24
Publication Date(Web):15 September 2014
DOI:10.1016/j.scriptamat.2014.05.018
The isothermal internal friction (IF) behavior of dual-phase Ni52Mn32In16 magnetic shape memory alloy was investigated by dynamic mechanical analysis. The contribution of the isothermal IF to the overall IF peak is close to 90%. This high isothermal IF is obtained over a large working temperature range of 88 °C, which is broadened by the concurrence of the martensitic transformation and the intermartensitic transformation. An strong hindering effect on structural transformations is identified by microstructural observations.
Co-reporter:Y.J. Huang, Q.D. Hu, J. Liu, L. Zeng, D.F. Zhang, J.G. Li
Acta Materialia 2013 Volume 61(Issue 15) pp:5702-5712
Publication Date(Web):September 2013
DOI:10.1016/j.actamat.2013.06.012
Abstract
Two of the current challenges facing producers of Ni–Mn–In alloys are the achievement of small hysteresis and good ductility. Here, we present a dual-phase (β-Ni51.8Mn31.4In16.8 and γ-Ni62.4Mn32.5In5.1) Ni52Mn32In16 alloy prepared by the zone melting liquid metal cooling directional solidification method, which simultaneously shows small hysteresis (ΔT < 10 K) and good ductility (6.6%). In addition, and more importantly, an inter-martensitic transition with a large magnetization jump occurs in this alloy. This is expected to further broaden the working temperature range of actuators and sensors that use this magnetic shape memory alloy. The sequence of the martensitic transformation can be shown by in situ X-ray diffraction to be austenite → 10M → 14M. Additionally, the second (γ) phase dramatically enhances the entropy change of these structural transformations and shifts them to higher temperatures. During the directional solidification, a novel banded-like microstructure, consisting of two layers, one of the β single phase and the other of the two phases coupled, forms at the low growth rate. A qualitative model is presented to explain the experimental observation, taking into account both the competitive nucleation and the growth of the phases. Experimental and theoretical analysis in the present work shows a linear relationship between the maximum spacing of the β single phase layer and the growth rate.
Co-reporter:Q.H. Liu, J. Liu, Y.J. Huang, Q.D. Hu, J.G. Li
Journal of Alloys and Compounds 2013 Volume 572() pp:186-191
Publication Date(Web):25 September 2013
DOI:10.1016/j.jallcom.2013.03.278
•The microstructure and crystal orientation of directional solidified Ni-Fe-Ga-Co was studied.•Coarse columnar crystals with preferred orientation of (222) L10 martensite was obtained.•Giant martensitic single-variant set was successfully achieved by ZMMLC method.•Two types of micro-twins induced by high internal stress were discussed.Microstructure and crystal orientation of Ni52Fe17Ga27Co4 alloys during directional solidification under various conditions was investigated by zone melting liquid metal cooling (ZMLMC) method. At high temperature gradient and low growth velocity, the well-developed preferred orientation for coarse columnar crystals was identified to be (2 2 2) planes of L10 martensite. More significantly, a giant martensitic single-variant set was evident in the oriented columnar crystal. Two types of micro-twinning substructure within the martensitic lamellae, which are induced by high internal stress, were also analyzed. The magnetic domains intersecting with martensitic lamellae were observed by electron backscatter diffraction (EBSD).Graphical abstract
Co-reporter:Yongjun Zhang;Bin Huang
Metallurgical and Materials Transactions A 2013 Volume 44( Issue 4) pp:1641-1644
Publication Date(Web):2013 April
DOI:10.1007/s11661-013-1645-7
At a wide range of solidification cooling rates in various cooling effect solidification processes, the solid/liquid interface experiences planar, cellular, dendritic, and superfine-cellular morphologies, and an approximately linear correlation is shown between the logarithmic representations of dendrite arm spacing and solidification cooling rate in a Ni-based superalloy. The relationship between dendrite arm spacing and cooling rate was established by statistical analysis data in a wide range of Ni-based superalloys from the literature. It can be used comprehensively to evaluate dendritic growth at given cooling conditions in the fabrication of Ni-based superalloys.
Co-reporter:Qiaodan Hu, Peng Luo, Mengxian Zhang, Mousheng Song, Jianguo Li
International Journal of Refractory Metals and Hard Materials 2012 Volume 31() pp:89-95
Publication Date(Web):March 2012
DOI:10.1016/j.ijrmhm.2011.09.011
Hybrid ZrB2 and ZrC particles were prepared by self-propagation high temperature synthesis (SHS) using Al, Zr and B4C powders as starting reactants. As effective diluents, Al play an important role in the SHS reactions, during which the solid Al and Zr reacted in the first instance followed by melting of Al that reacted with Zr to generate ZrAl3. Meanwhile, due to the heat generated by the reactions, C and B atoms were dissolved into the Zr–Al liquid, leading to the precipitation of ZrB2 and ZrC out of the supersaturated liquid phases. In the case of samples with Al content of 30 wt.%, ZrB2 particles exhibit typical hexagonal and rectangular shapes, whilst a spherical shape was displayed with ZrC particles. The synthesized structure of the ZrB2 and ZrC can be as fine as nanoscale. Not only prevented the synthesized products from growing, the Al addition also promoted the SHS reaction.Highlights► Hybrid ZrB2 and ZrC particles were prepared by SHS from Al–Zr–B4C system. ► The formation behavior of ZrB2 and ZrC particles was discussed. ► The synthesized ZrB2 and ZrC particles were determined to be nano-scale. ► Al not only prevents the synthesized products from growing but also promotes the SHS reaction.
Co-reporter:Qiaodan Hu, Mengxian Zhang, Peng Luo, Mousheng Song, Jianguo Li
International Journal of Refractory Metals and Hard Materials 2012 Volume 35() pp:251-256
Publication Date(Web):November 2012
DOI:10.1016/j.ijrmhm.2012.06.008
ZrC particles were fabricated by thermal explosion (TE) from mixture of Al, Zr and C elemental powders. Without the addition of Al, the synthesized ZrC particles had irregular shape of ~ 4.0 μm in average. Increasing Al content up to 30 wt.%, however, refined significantly them down to < 0.2 μm with regularly square morphology. The Al effect of reaction mechanism promoted the ZrC formation as diluents in the course of TE, which was clarified using differential thermal analysis and X-ray diffraction technique. The melting of Al favored the reaction with Zr to generate ZrAl3, and then the dissolution of C into the Al–Zr liquid resulted in precipitation of ZrC. Meanwhile, the exothermic effect prompted C atoms dissolving into Zr–Al liquid and eventually led to precipitation of ZrC out of the supersaturated liquid. The Al addition inhibited particle growth, but also promoted the TE reaction.Highlights► ZrC particles were prepared by TE from Al–Zr–C system. ► The formation mechanism of ZrC particles was discussed. ► The synthesized ZrC particles were determined to be ultra-fine or nano-scale with Al addition. ► Al not only prevents the synthesized products from growing but also promotes the TE reaction.
Co-reporter:Wei Zhang 张 卫;Yan Yu 于 艳;Yuan Fang 方 园
Journal of Shanghai Jiaotong University (Science) 2011 Volume 16( Issue 1) pp:65-70
Publication Date(Web):2011 February
DOI:10.1007/s12204-011-1096-5
Interfacial heat transfer is a key issue in many solidification processes. In the paper, a novel experimental apparatus has been designed and on this basis, the instantaneous interfacial heat transfer between molten steel or solidified shell and copper substrate during the first 0.2 s has been studied. The investigated parameters include melt superheat, substrate temperature and surface roughness. The results show that the peak value of the interfacial heat flux in the first stage of liquid/solid contact increases with melt superheat and changes slightly with substrate temperature and surface roughness. The interfacial heat flux in the stage of solid/solid contact has a similar trend of slow decrease in most conditions.
Co-reporter:Qiaodan Hu, Peng Luo, Youwei Yan, Jianguo Li
International Journal of Refractory Metals and Hard Materials 2011 Volume 29(Issue 4) pp:470-477
Publication Date(Web):July 2011
DOI:10.1016/j.ijrmhm.2011.02.006
Field activated sintering (FAS) was employed to fabricate dense bulk MoSi2 from Mo and Si powders. During the FAS process, Si was melted first, and then Mo was dissolved leading to a precipitation of MoSi2. A eutectic reaction of MoSi2–Mo5Si3 resulted from a combined effect of Mo–Si exothermic reactions and field induced Joule heating. With hyper-stoichiometric amount of Si (Mo/Si = 1:2.06), the FAS MoSi2 is free of Mo5Si3 phase. Subsequently, an un-lubricated sliding wear test of MoSi2 against carbon steel was conducted. Both normal load and temperature have crucial points related to a transition from mild to severe wear. Sliding speed and relative density have a negative effect on wear rate. In addition, at room temperature the wear is with a protective layer composed of oxide and transferred substance, whereas poor oxidation resistance leads to spalling of the layer and brittle fracture at an elevated temperature up to 500 °C.Research Highlights► Field activated sintering was employed to synthesize dense bulk MoSi2 in one step. ► MoSi2-Mo5Si3 eutectic was discovered in sintered MoSi2. ► With hyper-stoichiometric amount of Si, the FAS MoSi2 is free of Mo5Si3 phase. ► The dry sliding wear of MoSi2 was studied at both room temperature and 500 °C.
Co-reporter:M.S. Song, B. Huang, M.X. Zhang, J.G. Li
Powder Technology 2009 Volume 191(1–2) pp:34-38
Publication Date(Web):4 April 2009
DOI:10.1016/j.powtec.2008.09.005
ZrC particles were fabricated via self-propagating high-temperature synthesis (SHS) from 0 to 40 mass% Al–Zr–C elemental powder mixtures. The typical layered structures of the reaction products were observed due to the non-steady-state oscillatory motion of the combustion wave. With the Al content increasing, the reaction temperature decreased and the ZrC particle sizes evidently reduced from ~ 8 µm in Al free to ~ 50 nm in 40 mass% Al. The microstructures and formation mechanism of ZrC have been analyzed using XRD, SEM and quenched experiment. For Al free, including the low Al content, the formation of ZrC was controlled by the dissolution of C into a Zr melt or a solid ZrC layer. While for the high Al content, the formation of ZrC was controlled by the dissolution of C into a Zr–Al melt and the precipitation of ZrC, in which Al serves not only as a diluent to inhibit the ZrC particles from coarsening, but also as an intermediate reactant to participate in the reaction process.Graphical abstractFormation path of ZrC particles was investigated by the SHS-quenched experiment from 30 mass% Al–Zr–C compact. The macrograph and XRD results of water-quenched sample show the reaction evolution and formation path of ZrC, namely: Zr(s) + 3Al(s) = ZrAl3(s) → Al(s) = Al(l) → Zr(s) + 3Al(l) = ZrAl3(s) → ZrAl3(s) = ZrAl3(l) → ZrAl3(l) + C(s) = ZrC(s) + Al(l).
Co-reporter:Changjiang Song, Zhenming Xu, Jianguo Li
Materials & Design (1980-2015) 2007 Volume 28(Issue 3) pp:1012-1015
Publication Date(Web):2007
DOI:10.1016/j.matdes.2005.11.007
The aim of this paper is to investigate the structure of in situ Al/Si functionally graded materials by electromagnetic separation method. The research shows that the structure of Al/Si (hypereutectic) sample produced by this method changes from Al–Si hypereutectic structure with a great number of primary Si particles to Al–Si eutectic structure to Al–Si hypoeutectic structure with a great number of primary Al dendrites from one side of the sample to the other. Moreover, the hardness of the sample and the volume fraction of primary Si particles have gradient character in the sample.
Co-reporter:Chang-Jiang Song, Zhen-Ming Xu, Jian-Guo Li
Materials Science and Engineering: A 2007 Volumes 445–446() pp:148-154
Publication Date(Web):15 February 2007
DOI:10.1016/j.msea.2006.09.009
The aim of this paper is to investigate primary Al3Ni phase distributions in in-situ Al/Al3Ni functionally graded materials (FGMs) by electromagnetic separation method. Investigation results show that volume fraction and size of primary Al3Ni particles are of gradient distribution in Al/Al3Ni samples by electromagnetic separation method. Particle volume fraction gradient of Al–17 wt.%Ni sample is greatest in Al–12 wt.%Ni, Al–17 wt.%Ni, and Al–23 wt.%Ni samples. In the part with higher particle volume fraction, major axis of Al3Ni primary particles tends to be perpendicular to direction of the electromagnetic Archimedes force. In addition, compared with the sample solidified without the electromagnetic field, size of primary Al3Ni particles becomes smaller in the sample solidified with the electromagnetic field.
Co-reporter:Peiran Deng, Jianguo Li
Scripta Materialia 2006 Volume 55(Issue 8) pp:747-750
Publication Date(Web):October 2006
DOI:10.1016/j.scriptamat.2006.04.030
Solidification of giant magnetostrictive materials TbFe1.9, DyFe1.9, and Tb0.3Dy0.7Fe1.9 in a magnetic field has been investigated. Suppressing the turbulence in the melt is a key factor in texturing the magnetic materials. Those factors which influence convective flow during the course of solidification are discussed, and a critical Rayleigh number Rac can be used to reflect the state of turbulence at various cooling rates. Once the value of Rac in a magnetic field is larger than that of the practical Rayleigh number Ra in the melt, the temperature oscillations will be restrained, and the texture along the easy magnetic axis for those ferromagnetic materials will be dominant in the sample.
Co-reporter:Peiran Deng, Jianguo Li, Zhenming Xu
Materials Science and Engineering: A 2006 Volume 419(1–2) pp:39-44
Publication Date(Web):15 March 2006
DOI:10.1016/j.msea.2005.11.058
The melt-textured technique in a magnetic field for giant magnetostrictive materials TbFex and Tb0.3Dy0.7Fex (1.9 ⩽ x ⩽ 2) alloy was investigated. The cooling rate, melt temperature, and the chemical composition were found to influence the texture formation along the easy magnetic axis during crystallization in a field. The experiments showed that the 〈1 1 1〉 orientation of Tb0.3Dy0.7Fe1.9 and TbFe1.9 alloy was dominant in the samples when those alloys were solidified at a cooling rate of less than 0.8 °C/min from a temperature slightly above their melting point, respectively, while in a magnetic field of above 100 mT. However, with the Fe concentration increasing from x = 1.93, excessive RFe3 phases precipitate in the melt and degrade the orientation degree of the sample during the slow solidification. Therefore the chemical composition of Tb0.3Dy0.7Fex and TbFex alloy should be controlled within 1.90 ⩽ x ⩽ 1.93 for better orientation and comprehensive performance.
Co-reporter:Chang-Jiang Song, Zhen-Ming Xu, Gaofei Liang, Jian-Guo Li
Materials Science and Engineering: A 2006 Volume 424(1–2) pp:6-16
Publication Date(Web):25 May 2006
DOI:10.1016/j.msea.2005.12.011
The aim of this paper is to investigate effects of the process parameters on the particle volume fraction distributions of in-situ Al/Mg2Si functionally graded materials (FGMs) by the electromagnetic separation method. Experimental results show that the electromagnetic force, the melt solidification rate, and the alloy compositions have great effects on the distributions of the particle volume fraction. Analysis suggests that the effects of these process parameters attribute to their effects on the movement velocity, the movement time and the total volume fraction of primary Mg2Si particles. Increasing of the movement velocity, the movement time, and the total volume fraction of primary Mg2Si particles make the particle volume fraction of the particle packed regions and the distribution gradient of the particle volume fraction increase, and vice versa.
Co-reporter:YingChun Wang, YanMin Li, HaiLiang Yu, Jianjun Ding, XinHua Tang, JianGuo Li, YaoHe Zhou
Surface and Coatings Technology 2005 Volume 200(Issue 7) pp:2080-2084
Publication Date(Web):21 December 2005
DOI:10.1016/j.surfcoat.2005.07.076
A bioceramic composite coating was fabricated onto AISI 316L stainless steel in situ by laser cladding with mixed powders of CaHPO4•2H2O and CaCO3 without a bonding agent. The microstructures of the mixed powders and cladding layer were investigated by scanning electron microscopy, and the compositions/phases were analyzed by electron diffraction spectroscopy and X-ray diffraction. The major phases in the coating are β-Ca2P2O7 and Ca10 (PO4)6(OH)2. The coating consists of the granular HAP that is distributed among the overlapped club-shaped β-Ca2P2O7. It is shown that there is a bonded structure of the epitaxial planar growth between the substrate and cladding layer, and there is evidently a typical cellular microstructure in the middle and an equiaxed microstructure at the top of the cladding layer. The microstructure evolution in the cladding layer was analyzed based on the ratio of temperature gradient to solidification rate (G / R) produced in laser cladding.
Co-reporter:Hongxing Zheng, Weizeng Ma, Chunsheng Zheng, Xuefeng Guo, Jianguo Li
Materials Science and Engineering: A 2003 Volume 355(1–2) pp:7-13
Publication Date(Web):25 August 2003
DOI:10.1016/S0921-5093(03)00060-1
Structural evolution of bulk undercooled Ni–11.56 at.% Pb monotectic alloy was investigated systematically by using molten glass denucleating combined with superheating cycling. Within the achieved undercooling range 10–286 K, the solidification structures were classified into three categories. When the undercooling was less than 50 K, the structures consisted of coarse dendrites and interdendritic lead phase. With the undercooling increasing into the range of 70–232 K, the dendrite clusters were refined and fine lead particles separated out from the supersaturated primary dendrite arms because of solute trapping. When the undercooling exceeded 242 K, the granular grains formed and fine lead particles homogeneously distributed in the whole sample. The phase selection of high temperature melts was analyzed by adopting steady state nucleation theory. The calculated results shown that undercooled Ni–11.56 at.% Pb monotectic alloy melts solidified in the form of α(Ni) dendrites essentially during the stage of rapid solidification and after recalescence, the interdendritic residual melts solidified in the equilibrium mode. Based on the observation of the solidification structures and the calculated results with BCT dendritic growth model, it was confirmed that the granulation mechanism of the granular grains was owing to the primary dendritic disintegration and subsequent recrystallization.
Co-reporter:Wenquan Lu, Shuguang Zhang, Wei Zhang, Jianguo Li
Journal of Materials Science & Technology (December 2016) Volume 32(Issue 12) pp:
Publication Date(Web):1 December 2016
DOI:10.1016/j.jmst.2016.09.020
Using synchrotron X-ray imaging technique, the segregation evolution in solidifying Al–10 wt% Bi immiscible alloys was investigated at different cooling rates. Irrespective of the cooling rate, most of the Bi solute appeared at the upper part of the sample after solidification. The reason for this Bi enrichment phenomenon is different for different cooling rates. Besides Marangoni motion, positive segregation, which has rarely been noticed before, can also make Bi solute transfer to the hot top zone. It is also found that, bubbles (or pores) appear in solidifying Al–10 wt% Bi alloys, and the number of bubbles (or pores) increases with the increase of the cooling rate, while the size of the bubbles (or pores) decreases.
Co-reporter:J.Z. Li, B. Huang, J.G. Li
Journal of Crystal Growth (15 February 2011) Volume 317(Issue 1) pp:110-114
Publication Date(Web):15 February 2011
DOI:10.1016/j.jcrysgro.2011.01.007
Large crystallites of Co37Ni34Al29 ferromagnetic shape memory alloys were prepared by zone melting liquid metal cooling (ZMLMC) directional solidification; the effect of solidification rate and temperature gradient on the crystal microstructure and orientation was studied. Results show that at the solidification rate of 15 μm/s the alloy morphology exhibits coarse columnar crystal that is several millimeters in size and with worm-like γ′ precipitate, while at 150 μm/s it presents coarse dendrite surrounded by β+γ interdendritic eutectic. At the temperature gradient of 800 K/cm, a strong 〈1 1 0〉 oriented austenite crystal can be obtained at 15 μm/s and the preferred orientation turns into 〈1 0 0〉 direction as the solidification rate increases to 150 μm/s. The change of preferred orientation with solidification rate becomes more remarkable when the temperature gradient reaches 1200 K/cm.
Co-reporter:M.S. Song, B. Huang, Y.Q. Huo, S.G. Zhang, M.X. Zhang, Q.D. Hu, J.G. Li
Journal of Crystal Growth (1 January 2009) Volume 311(Issue 2) pp:378-382
Publication Date(Web):1 January 2009
DOI:10.1016/j.jcrysgro.2008.10.065
A large amount of titanium carbide (TiC) octahedra were synthesized in situ by self-propagating high-temperature synthesis using Al, Ti, C elemental powders as source materials. The phase constituents and microstructure morphologies of as-product were characterized by X-ray powder diffraction, field emission scanning electron microscopy and transmission electron microscopy. Due to the strong faceting tendency of the growing TiC crystal, the TiC grain grew as an octahedral morphology. If V[1 0 0]/V[1 1 1]=1.5, the TiC grain will grow as a perfect octahedral morphology. While if V[1 0 0]/V[1 1 1]>1.5, the TiC grain will grow as an imperfect octahedral morphology. According to the experimental results, the detailed microstructure and growth mechanism of TiC octahedron have been observed and analyzed. The models have been proposed to understand the formation and growth mode of TiC octahedron.
