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Wang Y.,Central South University | Liu Y.,Central South University | Yang G.Y.,Northwestern Institute for Nonferrous Metal Research | Li J.B.,Central South University | And 3 more authors.
Materials Science and Engineering A | Year: 2013

Flow behaviors and microstructures during hot compression of a Ti-43Al-4Nb-1.4W-based alloy containing β phase at various deformation conditions were investigated by physical simulations, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The dependence of the peak stress on the deformation temperature and the strain rate can be expressed by a hyperbolic-sine type equation. The activation energy for hot deformation of the alloy is determined to be 601.7kJ/mol, which is closely related to microstructure and alloy composition. Microstructure analysis shows that both the fraction of dynamically recrystallized grains and the average size of spherical β phases increase with the decrease of Zener-Hollomon (Z) parameter. The dynamic phase transformation of β phases is apparently accelerated due to hot deformation, leading to the spheroidizing of irregular β phases. It is found that different deformation mechanisms are operated on hot deformation of the alloy, which is related to the value of Z parameter. At low Z, the dynamic softening mechanisms involve the main dynamic recrystallization (DRX) and twinning. At high Z, the DRX accompanied by the bending of lamellar colonies, γ grains and β phases would occur during hot deformation of the alloy. The existence of Y2O3 can also provide additional particle stimulated nucleation of DRX. Besides, the evolution of β phase during hot deformation plays an important role in the dynamic softening of the alloy. © 2013 Elsevier B.V. Source


Sun L.-L.,Northwestern Polytechnical University | Wang J.,Northwestern Polytechnical University | Kou H.-C.,Northwestern Polytechnical University | Tang B.,Northwestern Polytechnical University | And 3 more authors.
Transactions of Nonferrous Metals Society of China (English Edition) | Year: 2015

Abstract Diffusion behavior of Ni in Zr48Cu36Ag8Al8 metallic glass was investigated in the temperature range of 683-723 K by secondary ion mass spectrum (SIMS) and transmission electron microscope (TEM). The diffusivity of Ni in Zr48Cu36Ag8Al8 is reasonably fitted by a single Arrhenius relation with small effective activation energy. The diffusivity of Ni in Zr48Cu36Ag8Al8 is an instantaneous function of annealing time in the supercooled liquid region. In addition, a large number of nano-crystals are detected near the interface of Ni-Zr48Cu36Ag8Al8 diffusion couple, and its width is broader than the Ni diffusion depth determined by SIMS. The results indicate that atomic inter-diffusion is an important factor to promote the formation of nano-crystals within the diffusion zone. © 2015 The Nonferrous Metals Society of China. Source


Wang J.,Northwestern Institute for Nonferrous Metal Research | Tang H.,Northwestern Institute for Nonferrous Metal Research
Materials Technology | Year: 2016

Selective electron beam melting (SEBM) is a typical powder bed fusion based additive manufacturing (AM) technology. Compared with other AM technologies for metals, SEBM offers two distinct advantages: high vacuum environment and low residual stresses. Since the appearance of the technique in 1992, anumber of strong improvements have been madetoSEBM, and awide variety of metallic materials have been processed and evaluated. Todate, SEBM has proved to be competent in the manufacturing of complex metallic parts with excellent mechanical properties. As a result, it is being increasingly adopted by industry. However, from the point of research and industrial applications, the fundamental research of the technique is not enough and theoretical study of the metallurgical process is of particular importance. Meanwhile, developing advanced systems, new structures and alloys special for SEBM should be important for the future development. © 2015 W. S. Maney & Son Ltd. Source


Jia W.,Northwestern Polytechnical University | Jia W.,Northwestern Institute for Nonferrous Metal Research | Zeng W.,Northwestern Polytechnical University | Yu H.,Northwestern Polytechnical University
Materials and Design | Year: 2014

The effect of aging temperature between 650°C and 750°C for different aging times on the tensile properties and microstructures of Ti60 alloy were studied. The results show that the strength of the alloy increases first and then decreases with the aging temperature increases from 650°C to 750°C. The reduction of area of the alloy is more sensitive to the aging time than elongation. With increasing aging temperature and time, the volume fracture and grain size of silicides and α2 phase increase gradually. The silicides have the strengthen effect on the Ti60 alloy, but the effect weakens when the silicides grow up. The loss of ductility is mainly attributed to the precipitation of α2 phase after aging treatment. © 2014 Elsevier Ltd. Source


Tang H.P.,Northwestern Institute for Nonferrous Metal Research | Qian M.,Northwestern Institute for Nonferrous Metal Research | Qian M.,RMIT University | Liu N.,Northwestern Institute for Nonferrous Metal Research | And 4 more authors.
JOM | Year: 2015

An advantage of the powder-bed-based metal additive manufacturing (AM) processes is that the powder can be reused. The powder reuse or recycling times directly affect the affordability of the additively manufactured parts, especially for the AM of titanium parts. This study examines the influence of powder reuse times on the characteristics of Ti-6Al-4V powder, including powder composition, particle size distribution (PSD), apparent density, tap density, flowability, and particle morphology. In addition, tensile samples were manufactured and evaluated with respect to powder reuse times and sample locations in the powder bed. The following findings were made from reusing the same batch of powder 21 times for AM by selective electron beam melting: (i) the oxygen (O) content increased progressively with increasing reuse times but both the Al content and the V content remained generally stable (a small decrease only); (ii) the powder became less spherical with increasing reuse times and some particles showed noticeable distortion and rough surfaces after being reused 16 times; (iii) the PSD became narrower and few satellite particles were observed after 11 times of reuse; (iv) reused powder showed improved flowability; and (v) reused powder showed no measurable undesired influence on the AM process and the samples exhibited highly consistent tensile properties, irrespective of their locations in the powder bed. The implications of these findings were discussed. © 2015, The Minerals, Metals & Materials Society. Source

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