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A first-principles study of site occupancy and interfacial energetics of an H-doped TiAl-Ti_3 Al alloy

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Science China(Physics,Mechanics & Astronomy) 2012年第2期55卷 228-234页

作者： WEI Ye ZHANG Ying LU GuangHong XU HuiBin School of Materials Science and Engineering Beihang UniversityBeijing 100191China Deparment of Physics Beihang UniversityBeijing 100191China

We investigate the site occupancy and the interfacial energetics of TiAl-Ti3Al binary-phase system with H using a first-principles method. H energetically prefers to occupy the Ti-rich octahedral interstitial site because H prefers to bond with Ti rather than with Al. The occupancy tendency of H in the binary phase TiAl-Ti3Al alloy from high to low is α2-Ti3Al to γ/α2 interface and 7-TiAl, because the decrease of the Ti local concentration is in the same order. We demonstrate that H can largely affect the mechanical properties of the TiAl-Ti3Al system. On the one hand, H at the interface reduces the interface energy with the H2 molecule as a reference, implying the TiAl/Ti3Al interface is stabilized. On the other hand, the ratio between the cleavage energy and the unstable stacking fault energy decreases after H-doping, indicating H will reduce the ductility of the TiAl/Ti3Al interface. Consequently, the mechanical property variation of TiA1 alloy due to the presence of H not only depends on the amount of TiAl/Ti3Al interfaces but also is related to the H concentration in the alloy.

关键词： tiai alloy hydrogen site occupancy shear deformation interfacial energetics first-principles mechanical property

A MICROMECHANICAL MODEL FOR γ-TiAl BASE PST CRYSTALS

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Acta Metallurgica Sinica(English Letters) 2005年第6期18卷 686-694页

作者： J.L. Su G.K. Hu School of Mechanics-Electrics Engineering Fujian Agriculture and Forestry University Fuzhou 350002 China Department of Applied Mechanics Beijing Institute of Technology Beijing 100081 China

An analytical micromechanical method is proposed to examine the dependence of plastic deformation on the microstructure for a PST crystal. The sub-domain microstructure of the γ phase and the effect of the α2 phase are taken into account by a proper micromechanical formulation, the dislocation slip and twinning deformation mechanisms are considered in the context of crystal plasticity. The model can well predict the dependence of stress-strain relations on loading angle with respect to the microstructure. The influence of the twinning and lamellar spacing on the deformation behavior and biaxial yield surfaces for PST crystals are also examined.

关键词： tiai alloy crystal plasticity micromechanical model yield surface

Dual-Material Electron Beam Selective Melting:Hardware Development and Validation Studies

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Engineering 2015年第1期1卷 124-130页

作者： Chao Guo Wenjun Ge Feng Lin Department of Mechanical Engineering Tsinghua University Key Laboratory for Advanced Materials Processing Technology (Ministry of Education of China) Tsinghua University Biomanufacturing and Rapid Forming Technology Key Laboratory of Beijing Tsinghua University

Electron beam selective melting （EBSM） is an additive manufacturing technique that directly fabricates three-dimensional parts in a layerwise fashion by using an electron beam to scan and melt metal powder. In recent years, EBSM has been successfully used in the additive manufacturing of a variety of materials. Previous research focused on the EBSM process of a single material. In this study, a novel EBSM process capable of building a gradient structure with dual metal materials was developed, and a powder-supplying method based on vibration was put forward. Two different powders can be supplied individually and then mixed. Two materials were used in this study： Ti6AI4V powder and Ti47AI2Cr2Nb powder. Ti6AI4V has excellent strength and plasticity at room temperature, while Ti47AI2Cr2Nb has excellent performance at high temperature, but is very brittle. A Ti6AI4V/Ti47AI2Cr2Nb gradient material was successfully fabricated by the developed system. The microstructures and chemical compositions were characterized by optical microscopy, scanning microscopy, and electron microprobe analysis. Results showed that the interface thickness was about 300 μm. The interface was free of cracks, and the chemical compositions exhibited a staircase-like change within the interface.

关键词： additive manufacturing electron beam selectivemelting gradient materials titanium alloy tiai alloy

Numerical study of crucial parameters in tilt casting for titanium aluminides

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China Foundry 2011年第3期8卷 274-281页

作者： Hong Wang G. Djambazov K. A. Pericleous School of Petroleum Engineering University of Changzhou Changzhou 213164 China Centre for Numerical Modeling and Process Analysis Universi~ of Greenwich London SEIO 9LS UK

Numerical modeling of the tilt casting process for tiai alloys was investigated to achieve a tranquil mould filling and tiai castings free of defects. Titanium alloys are very reactive in molten state, so they are widely melted in cold crucible, e.g. the Induction Skull Melting （ISM） furnace. Then the crucible holding the molten metal together with the mould is rotated to transfer the metal into the mould -- ISM＋ tilt casting. This paper emphasizes the effect of crucial parameters on mould filling and solidification of the castings during tilt casting. All crucial parameters, such as rotation rate, rotation profile, venting, initial mould temperature, casting orientation, feeder design, change of radius in ＇T＇ junction and mould insulation have been discussed using numerical modeling data. Simulations were performed using a 3D CFD code PHYSICA implemented with front tracking, heat transfer algorithms and a turbulence model （which accounts for an advancing solid front）.

关键词： crucial parameters numerical modeling tilt casting tiai alloy

Microstructure and Mechanical Properties of TiAl-based alloy

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Journal of Materials Science & Technology 1993年第6期9卷 449-457页

作者： Zhongjie PU Jiandong SHI Dunxu ZOU Zengyong ZHONG Central Iron and Steel Research Institute,Beijing,100081,China

Two phases gamma titanium aluminide alloy,*** investigated to characterize microstructures and to define the microstructure/mechanical property *** kinds of microstructure of gamma and α_2 phases were obtained by heat treatments in the α+γ,α_2+γ and α *** effects of microstructure on tensile properties,fracture toughness and J-R resistance curve at room temperature,were systematically *** experimental results showed that the microstructure had a strong effect on mechanical properties,The duplex microstructure produced by heat treatment at 1250℃×4 h with controlled cooling resulted in the highest ductility of 4.8% tensile elongation,low fracture toughness and crack growth *** fully lamellar microstructure produced by heat treatment in the α field having large grain sizes resulted in the highest fracture toughness but the lowest ductility.

关键词： microstructure mechanical property tiai alloy