Zhiguang Liu

Microstructures and properties of titanium alloys Ti-Mo for dental use

Abstract The microstructures and properties of a series of binary Ti-Mo alloys with molybdenum contents ranging from 5% to 20%(mass fraction) were investigated. The experimental results indicate that the crystal structure and morphology of the cast alloys are sensitive to their molybdenum contents. When the Mo content is 5%, the equiaxed α crystal grain is observed. When the Mo content is 10%, the equiaxed α crystal grain and fine needles β phase are observed. When the Mo contents are 15% and 20%, only the equiaxed β crystal grain is observed. When the Mo content is 10%, the synthetical properties of the Ti-Mo alloy are the best. The data of hardness (HV451), compression strength (1636 MPa), compression ratio (22.5%) and elastic modulus (29.8 GPa) were collected. The increase of molybdenum contents is propitious to crystal refinement and improvement of plasticity of Ti-Mo alloys. The dry wear resistance of Ti-Mo alloys against Gr15 ball was investigated on CJS111A ball-disk wear instrument. The results show that the dry wear resistance of Ti-Mo alloys is correlative with hardness and mechanical properties. With the ductility increasing, the dry wear resistance reduces. The friction coefficient of 10%Mo alloy is the lowest, the dry wear resistance is the best. The wear particles, wear scar depth and width of the 10%Mo alloy are smaller than that of other Ti-Mo alloys. Considering all kinds of properties of Ti-Mo alloys, 10%Mo alloy is prospective dental prostheses material.

Microstructures and mechanical properties of hot-pack rolled Ti-43Al-9V-Y alloy sheet

Abstract Ti-43Al-9V-Y alloy sheets with dimensions of 300 mm×100 mm×(1.5–2) mm were produced by hot-pack rolling. After rolling, the microstructure of Ti-43Al-9V-Y alloy sheet becomes near gamma(NG), which is comprised of γ+ B 2 phases. After heat treatment(HT) at 1 200−1 320 °C for 30 min followed by furnace cooling(FC), network shape structure of B 2 phases in as-rolled microstructure is retained on the whole. Moreover, with increasing the HT temperature, precipitation of B 2 phase lamellae in equiaxed γ grains is increased. Equiaxed γ grains transform partly to α 2 /γ/ B 2 lamellar structure after the heat treatment at 1 320 °C for 30 min. Tensile test results show that room-temperature yield strength(YS) and ultimate tensile strength(UTS) of the as-rolled material are 509 and 612 MPa, respectively. With the test temperature increasing, the YS and UTS of the as-rolled are decreased, but the elongation is improved. After HT at 1 200 °C, both yield strength and fracture strength of Ti-43Al-9V-Y alloy sheet are the lowest. With HT temperature increasing, fracture strength is increased obviously, but yield strength of the sheet after HT at 1 280 °C is the highest, about 869 MPa.

Effects of yttrium on microstructures and properties of Ti-17Al-27Nb alloy

The effects of rare earth yttrium on the microstructures and mechanical properties of Ti-17Al-27Nb alloy were studied. The as-cast microstructures of Ti-17Al-27Nb alloy with 0.85%Y(mole fraction) addition were refined and the tensile elongation also increased. Yttrium in the alloy exists as Y2Al according to the EPMA, XRD analysis and electronegativity differences. Y2Al distributes mainly on the grain boundary. Yttrium is found to improve the tensile strength of Ti-17Al-27Nb alloy due to the grain boundary strengthening. Furthermore, Y2Al distributing in the grain boundary leads to grain refinement by pinning grain growth. This fracture mode has been changed from intergranular fracture for Ti-17Al-27Nb alloy to a mixture of intergranular fracture and transgranular fracture for Ti-17Al-27Nb-0.85Y alloy. The dimples were observed distinctly. Therefore, this yttrium containing alloy shows an excellent plasticity.

Production and characterization of TiAl ribbons with Y additions

Abstract Rapid solidification method was employed to produce TiAl based alloy ribbons and finally to produce TiAl based alloys with novel microstructure and properties. TiAl based alloys with nominal compositions of Ti-46Al-2Cr-2Nb (atomic ratio) and various yttrium additions (0, 0.5%, 1.0%, 1.5%, 2.0%, atom fraction) were produced using the melt spinning method. For comparison, cast alloys with the same compositions were prepared by argon arc melting as well. It is shown that the as cast microstructure of Y free alloy is lamellar. With addition of Y up to 1.5%, the microstructure of the alloy changes from lamellae to dendrites, while more addition of Y leads to a finer dendrite structure. For the rapidly solidified TiAl based alloy ribbon, refined microstructure is produced. The increase of Y addition modifies the phase constituents from pure γ-TiAl phase of Y free alloy gradually to γ-TiAl+α2-Ti3Al and γ-TiAl+α2-Ti3Al+small amount of Al2Y phase. Though the phase constituents on the two sides of ribbons, surface contacting roll and free surface, are essentially the same, the microstructure of the former one is much finer than that of the latter one.

Effect of milling time on microstructure of Ti35Nb2.5Sn/10HA biocomposite fabricated by powder metallurgy and sintering

A new β-Ti based Ti35Nb2.5Sn/10 hydroxyapitite (HA) biocompatible composite was fabricated by mechanical milling and pulsed current activated sintering(PCAS). The microstructures of Ti35Nb2.5Sn/10HA powder particles and composites sintered from the milled powders were studied. Results indicated that α-Ti phase began to transform into β-Ti phase after the powders were mechanically milled for 8 h. After mechanical milling for 12 h, α-Ti completely transformed into β-Ti phase, and the ultra fine Ti35Nb2.5Sn/10HA composite powders were obtained. And ultra fine grain sized Ti35Nb2.5Sn/10HA sintered composites were obtained by PCAS. The hardness and relative density of the sintered composites both increased with increasing the ball milling time.

THE SOLIDIFICATION MICROSTRUCTURE OF BIOMEDICAL TITANIUM ALLOYS UNDER THE CENTRIFUGAL FORCE

Two biomedical alloys, Ti-39Nb-5.1Ta-7.1Zr (TNTZ1) and Ti-35.3Nb-5.1Ta-7.1Zr (TNTZ2) were melted using LZ5 type centrifugal equipment for casting titanium. The solidification microstructures of TNTZ1 and TNTZ2 alloys cast in graphite crucible without centrifugal force are mostly big arborescent crystal with dispersed porosity in it. After pouring into a graphite mould under centrifugal force, the lower part of ingot showed mostly arborescent crystals with few equiaxed crystals, while the upper part of ingot is basically spherical equiaxed crystals. The solidification defects, such as dispersed pores were very difficult to find. Nb is supposed to refine the arborescent crystals. X-ray diffraction (XRD) analysis showed Ti-phase and Nb-phase existing in the above two alloys. The content of Ti was found relatively low in crystal interior and relatively high in crystal boundary. The content of Nb/Zr was uniform in whole microstructure.