Fantao Kong

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.

Effects of minor yttrium addition on hot deformability of lamellar Ti-45Al-5Nb alloy

Abstract The effects of 0.3%(molar fraction, the same below) yttrium addition on hot deformability of lamellar Ti-45Al-5Nb alloy were investigated by simulated isothermal forging tests. The ingots with the nominal compositions of Ti-45Al-5Nb and Ti-45Al-5Nb-0.3Y were prepared by induction skull melting. Simulated isothermal forging tests were conducted on Gleeble 1500D thermo-simulation machine using a 6 mm in diameter and 10 mm in length compressive specimen at the deformation temperatures of 1u2008100, 1u2008150, 1u2008200 °C and strain rates of 1.0, 0.1, 0.01 s −1 . The results show that yttrium addition remarkably improves hot deformability of Ti-45Al-5Nb alloy. An appropriate hot deformation processing parameter of Ti-45Al-5Nb-0.3Y alloy is determined as 1u2008200 °C, 0.01 s −1 . The flow stresses are decreased by yttrium addition under the same compressive conditions. The activation energies of deformation Q are calculated as 448.6 and 399.5 kJ/mol for Y-free and Y-containing alloys, respectively. The deformed microstructure observation under 1u2008200 °C, 0.01 s −1 condition indicates that Ti-45Al-5Nb-0.3Y alloy shows more dynamic recrystallization. The improvement of hot deformability of Ti-45Al-5Nb-0.3Y alloy induced by yttrium addition should be attributed to that the smaller the original lamellar colonies, the lower the deformation resistance and activation energy of deformation are, and the more the dynamic recrystallization is.

Ti–Nb–Sn–hydroxyapatite composites synthesized by mechanical alloying and high frequency induction heated sintering

A β-type Ti-based composite, Ti-35Nb-2.5Sn-15-hydroxyapatite (HA), has been synthesized by mechanical alloying and powder metallurgy. The effects of milling time on microstructure, mechanical properties and biocompatibility of the sintered composites were investigated by scanning electronic microscopy (SEM), X-ray diffraction (XRD), microhardness tests, compression tests and cells culture. The results revealed when milling time increased, the homogeneity and relative density of the sintered composite increased, but the finished sintering temperature decreased. The compression Youngs modulus of sintered composite from 12xa0h milled powders was about 22xa0GPa and its compression strength was 877xa0MPa. The cell culture results indicated cell viability for these sintered composites was very good. These results revealed the Ti-35Nb-2.5Sn-15HA composite could be useful for medical implants.

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.

Interfacial reactions between Ti-1100 alloy and ceramic mould during investment casting

Abstract The characteristics of the interfacial reaction between Ti-1100 melt and different primary coating materials was investigate. The effect of refractory materials and mould temperature on the reaction was analyzed by comparing the thickness, distribution of elements and microhardness of α-case layer. The α-case layer thickness of Ti-1100 casting with ZrO 2 primary coating is approximately 38 μm, which is higher than that with Y 2 O 3 primary coating (18 μm). Ti-1100 casting using ZrO 2 primary coating shows higher surface microhardness than that using Y 2 O 3 primary coating. The higher mold temperature results in more severe interfacial reaction. With the same primary coating material and mould temperature, Ti6Al4V alloy presents better stability than Ti-1100 alloy.

Constitution modeling and deformation behavior of yttrium bearing TiAl alloy

Abstract The deformation flow behaviors of Ti-45Al-5.4V-3.6Nb-0.3Y alloy at different temperatures and strain rates were studied by isothermal compressing simulation test. The apparent activation energy of deformation was calculated to be 402.096 kJ/mol and constitutive equation was established to describe the flow behavior. Microstructure and flow softening observations exhibited that Ti-45Al-5.4V-3.6Nb-0.3Y alloy had bad hot workability at low temperature (lower than 1 100 °C) and high strain rate (higher than 0.5 s −1 ) characterized by localization deformation and instability. With deformation temperature higher than 1 150 °C and strain rate lower than 0.01 s −1 , the alloy owned good hot deformability, and plenty of dynamic recrystallized grains could be observed in the deformed microstructures.

Effect of different primary coating materials and mold temperatures on fluidity of high-temperature titanium alloy

In this study, the fluidity of near-α high-temperature titanium alloy with different primary coating materials (Y2O3, ZrO2 and Al2O3) and mold temperatures were investigated. The fluidity as an index of castability was evaluated by a fluidity spiral pattern. The Y2O3 primary coating presents the best fluidity and weakest interfacial reaction compared with the ZrO2 and Al2O3 primary coating. The effect of interfacial reaction resulting from different mold materials on fluidity is determined by the stability of mold materials. The interfacial reaction becomes more and more severe with increasing mold preheating temperature. The fluidity does not increase with increasing mold preheating temperature owing to the effect of interfacial reaction. The fluidity is greatly improved at 900u2009°C, while decreases at 600u2009°C, indicating the fluidity, depends on the interaction between the interfacial reaction and chilling effect of the mold.

Fabrication of Thin-Walled High-Temperature Titanium Alloy Component by Investment Casting

In order to fabricate a thin-walled high-temperature titanium alloy component, the mold filling capacity of 600°C high-temperature titanium alloy was investigated by a mesh pattern. The results indicate that 600°C high-temperature titanium alloys present poorer mold filling capacity than Ti6Al4V alloy. The effect of different primary coating materials (Y2O3, ZrO2, and Al2O3) and mold preheating temperature on mold filling capacity were also evaluated. It is found that the Y2O3 primary coating presents the best mold filling capacity. The mold filling capacity does not continuously increase with increasing mold preheating temperature due to the influence of interfacial reaction. The proper mold temperature for 600°C high-temperature titanium alloy investment casting is about 300°C. A thin-walled high-temperature titanium alloy component was fabricated successfully.

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.