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Xu T.W.,Northwestern Polytechnical University | Kou H.C.,Northwestern Polytechnical University | Li J.S.,Northwestern Polytechnical University | Zhang F.S.,Western Superconducting Technology Co. | Feng Y.,Western Superconducting Technology Co.
Journal of Materials Engineering and Performance | Year: 2015

The influence of phase transformation conditions (α/β solution treatment plus aging, β solution treatment plus aging, and β solution treatment plus duplex aging) on the microstructure and tensile properties of Ti-3Al-15Mo-3Nb-0.2Si alloy was studied. Microstructure observation indicates that the primary α phase, which formed during α/β solution treatment, can effectively limit the growth of the β grains. The alloy was heat treated in the α/β solution, which together with aging, formed smaller grains and finer precipitates in the sample and showed good tensile ductility with a 15% elongation. Aging temperatures from 450 to 600 °C were used to study the effects of aging treatment on the alloy’s microstructure and tensile properties. Precipitation phases appeared in particular positions (αGB, αWGB, and αWM) during the aging process which depended on phase transformation conditions and caused variations in the alloy’s tensile properties. The alloy treated by duplex aging after β solution had a higher ultimate tensile strength at 1370 MPa than that of other samples, resulting from the finer α precipitates transformed from the ω phases. The relationship of tensile properties and phase transformation was investigated by observing the material fracture, and small and dense dimples were seen in the tensile specimen treated by α/β solution plus aging treatment which led to excellent ductility. Deep dimples in the duplex aging specimen resulted in beneficial high strength. © 2015 ASM International Source


Xu G.,Northwest University, China | Xu G.,Western Superconducting Technology Co. | Kou H.,Northwest University, China | Liu X.,Western Superconducting Technology Co. | And 3 more authors.
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2014

The porous titanium (PT) with porosity of 45% was fabricated by a stacked-forced-sintering method. The specimen was treated by three solution media, which were a mixture acid (HF: HNO3:H2O=5:15:80) medium (ACT), alkali medium (5 mol/L NaOH, 24 h) and heat treatment (630℃/1 h) abbreviated as AKT, as well as simulated body fluids treatment (SBF). The microstructure and mechanical properties of the treated and untreated (UT) specimen were investigated by scanning electron microscope (SEM), elements analysis (EDS), X-ray diffraction analysis (XRD) and universal testing machine. The Young's modulus and yield stress (σ0.2) were calculated from the stress-strain curve. The results show that the surface of porous titanium treated by ACT is smooth and lamellar, while the surface treated by AKT is porous with nano/mirco-pore. And the uniformly hydroxyapatite have been observed on the surface of the specimen treated by SBF. Young's modulus of PT treated by ACT and AKT are dramatically declined, but Young's modulus of of PT treated by SBF increases on the contrary. The yield stress has the same tendency, but it is not changed so sharply as Young's modulus. ©, 2015, Science Press. All right reserved. Source


Xu G.,Northwest University, China | Xu G.,Western Superconducting Technology Co. | Kou H.,Northwest University, China | Liu X.,Western Superconducting Technology Co. | And 3 more authors.
Xiyou Jinshu Cailiao Yu Gongcheng/Rare Metal Materials and Engineering | Year: 2014

Porous titanium with two different topology structures was designed and fabricated by a titanium mesh-stacking-sintering method. The microstructure and mechanical properties of the porous titanium specimens were investigated by scanning electron microscope (SEM) and electrical universal testing machine, respectively. The Young's modulus and yield stress (σ0.2) were calculated from the stress-strain curves. The results show that the square pore distribution such as the staggered pore in the regular pore model can reduce the elastic modulus and yield stress as much as 74% and 10% at the same porosity, respectively. On the basic analysis from the analytical model, it is suggested that the bending and stress concentration are the main reasons of the elastic modulus and yield stress reduction. Copyright © 2014, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved. Source


Guangsheng X.,Northwest University, China | Guangsheng X.,Western Superconducting Technology Co. | Hongchao K.,Northwest University, China | Ruolin L.,Northwest University, China | And 4 more authors.
Advanced Materials Research | Year: 2013

Three methods have been used to modify the porous titanium surface, which is the alkali heat treatment, alkali heat treatment + SBF solution soak and alkali heat treatment + precalcidied + SBF solution soak. The morphology of different surfaces was observed by scanning electron microscopy (SEM). The MC3T3-E1 osteoblast cell was cultured on the modified and unmodified surface of porous titanium with 3days and 7days, the morphology of osteoblast adhesion and growth on different surface was observed. The results showed that osteoblast adhere on the modified and unmodified surface of the porous titanium. Osteoblast on AHS and HA modified surface can grow and spread, but it cannot grow and spread on unmodified and AH modified surface of the porous titanium. Osteoblast can grow across the different titanium fibers of on HA modified surface of porous titanium. Osteoblast on the HA surface has the very good biological suitability, which is beneficial to the combination of bone tissue and porous titanium. © (2013) Trans Tech Publications, Switzerland. Source


Xu T.W.,Northwestern Polytechnical University | Xu T.W.,Western Superconducting Technology Co. | Li J.S.,Northwestern Polytechnical University | Zhang S.S.,Western Superconducting Technology Co. | And 2 more authors.
Journal of Alloys and Compounds | Year: 2016

The microstructure and texture were investigated in cold-rolled Ti-15Mo-3Al-2.7Nb-0.2Si alloy with differing degrees of reduction. The texture of the alloy was prone to rotate to <110> orientation and more sub-boundaries were produced with the increase of the cold-deformation. Precipitation during aging was influenced by the dislocations, sub-boundaries and other defects formed in cold rolling, for they would provide assisted-nucleation sites and decrease the duration of β→α transformation. The α precipitates with the scale of 100-400 nm in the cold-rolled 20% plus aging sample, brought about the high-strength of 1612 MPa and the elongation of 6.5%. The highest strength of 1770 MPa was obtained in the cold-rolled 50% plus aging sample, which has little plastic deformation, due to the coarse α phase precipitated in sub-boundaries. The role of dislocations and sub-boundaries in influencing α precipitation and the tensile properties of Ti-15Mo-3Al-2.7Nb-0.2Si alloy are described in this paper. © 2016 Elsevier B.V. Source

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