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1.
Increased use of titanium alloys as biomaterials is occurring due to their lower modulus, superior biocompatibility and enhanced corrosion resistance when compared to more conventional stainless steels and cobalt-based alloys. These attractive properties were a driving force for the early introduction of alpha (cpTi) and alpha + beta (Ti-6A1-4V) alloys as well as for the more recent development of new Ti-alloy compositions and orthopaedic metastable beta titanium alloys. The later possess enhanced biocompatibility, reduced elastic modulus, and superior strain-controlled and notch fatigue resistance. However, the poor shear strength and wear resistance of titanium alloys have nevertheless limited their biomedical use. Although the wear resistance of beta-Ti alloys has shown some improvement when compared to alpha + beta alloys, the ultimate utility of orthopaedic titanium alloys as wear components will require a more complete fundamental understanding of the wear mechanisms involved. This review examines current information on the physical and mechanical characteristics of titanium alloys used in artifical joint replacement prostheses, with a special focus on those issues associated with the long-term prosthetic requirements, e.g., fatigue and wear. 相似文献
2.
Masoud Alahbakhshi Aditya Mishra Grigorii Verkhogliadov Emigdio E. Turner Ross Haroldson Austen C. Adams Qing Gu Jeffrey J. Rack Jason D. Slinker Anvar A. Zakhidov 《Advanced functional materials》2023,33(28):2214315
Perovskite light-emitting diodes (PeLEDs) are advancing because of their superior external quantum efficiencies (EQEs) and color purity. Still, additional work is needed for blue PeLEDs to achieve the same benchmarks as the other visible colors. This study demonstrates an extremely efficient blue PeLED with a 488 nm peak emission, a maximum luminance of 8600 cd m−2, and a maximum EQE of 12.2% by incorporating the double-sided ethane-1,2-diammonium bromide (EDBr2) ligand salt along with the long-chain ligand methylphenylammonium chloride (MeCl). The EDBr2 successfully improves the interaction between 2D perovskite layers by reducing the weak van der Waals interaction and creating a Dion–Jacobson (DJ) structure. Whereas the pristine sample (without EDBr2) is inhibited by small stacking number (n) 2D phases with nonradiative recombination regions that diminish the PeLED performance, adding EDBr2 successfully enables better energy transfer from small n phases to larger n phases. As evidenced by photoluminescence (PL), scanning electron microscopy (SEM), and atomic force microscopy (AFM) characterization, EDBr2 improves the morphology by reduction of pinholes and passivation of defects, subsequently improving the efficiencies and operational lifetimes of quasi-2D blue PeLEDs. 相似文献
3.
Martensitic phase transformations in the solution-treated and water-quenched binary Ti-Nb alloys in the range of 16–26 at% Nb, were examined. An ordered, base-centred orthorhombic martensite was observed for alloys containing up to 23.4 at% Nb. The substructure of this martensite was generally composed of twins and stacking faults, the presence of antiphase boundaries observed in the plates indicating that the martensite underwent ordering during quenching. Both order-disorder and M
s temperatures were observed to be affected by total interstitial content, higher contents increasing both temperatures. Increasing the niobium content to above 23.4% resulted in retention of the phase, this phase containing either athermal or diffuse depending upon niobium and total interstitial concentration. Finally, the microhardness of the Ti-Nb alloys examined was observed to decrease with increase in niobium and decrease in total interstitial content. 相似文献
4.
A series of catalysts, NiSO4/TiO2-ZrO2, for ethylene dimerization was prepared by the impregnation method using an aqueous solution of nickel sulfate. For NiSO4/TiO2 -ZrO2 sample, no diffraction line of nickel sulfate was observed up to 30 wt%, indicating good dispersion of nickel sulfate on the surface of TiO2-ZrO2. The addition of nickel sulfate to TiO2-ZrO2 shifted the phase transition of TiZrO4 from amorphous to orthorhombic to a higher temperature because of the interaction between nickel sulfate and TiO2-ZrO2. The number of acid sites of NiSO4/TiO2-ZrO2 increased in proportion to the nickel sulfate content up to 20 wt% of NiSO4. Nickel sulfate supported on TiO2-ZrO2 was found to be very active even at room temperature, giving a maximum in both activity and acidity when the catalyst containing 20% NiSO4 was calcined and evacuated at 500°C The asymmetric stretching frequency of the S=O bonds for NiSO4/TiO2-ZrO2 samples was related to the acidic properties and catalytic activity. That is, the higher the frequency, the higher both the number of acid sites and the catalytic activity for ethylene dimerization. 相似文献
5.
The effects that adsorbed precursor surface diffusion has on electron beam induced deposition are explored via a three-dimensional Monte Carlo simulation. Initially the growth rate and resolution are compared for a common set of deposition conditions with a variable surface diffusion coefficient ranging from 0 to 1 × 10(-8)?cm(2)?s(-1). The growth rate and resolution are shown to both be enhanced as the growth changes from a mass transport limited regime to a reaction rate limited regime. The complex interplay between the vertical growth rate, the lateral growth rate, the interaction volume and the adsorbed and diffused precursor species are discussed. A second scenario is also simulated in which only gas diffused from a constant source at the perimeter of the simulation boundary is assumed (no gas phase adsorption). At low diffusion coefficients, the diffusing gas is consumed by secondary and backscattered electrons and experimentally observed ring-like structures are generated. At higher diffusion coefficients, the diffusion length is sufficient for the precursor atoms to diffuse to the center (and up the pillar sidewalls) to generate nanowires. 相似文献
6.
Hydrogenated amorphous silicon films were grown on to thermally oxidized silicon wafers by Radio Frequency magnetron sputtering, and SiNx and Al2O3 capping layers were used to control the residual thermal stress. After annealing, a comparison of the silicon films with and without capping layers indicates that tensile stress induced by the capping layer enhances the crystallinity of the annealed amorphous silicon film. The stress is due to the mismatch between the coefficients of thermal expansion for the capping layer and amorphous silicon film. These results highlight the potential of thermal stress as a means to alter the crystallization in thin film architectures and suggest that even larger effects can be obtained with suitable choices of capping layer chemistry. 相似文献
7.
The influence of microstructure on the strength and fracture toughness of 18 Ni (350) maraging steel was examined. Changes
in microstructure were followed by X-ray and neutron diffraction and by optical and electron microscopy. These observations
have been correlated with the fracture morphology established by scanning electron microscopy. Air cooling this alloy from
the austenitizing temperature results in a dislocated martensite. During the initial stage of age hardening, molybdenum atoms
tend to cluster (forming preprecipitates) and the cobalt assumes short range ordered positions. Subsequent aging results in
Ni3Mo and σ-FeTi with overaging being associated with the formation of equilibrium reverted austenite and Fe2Mo. The fracture behavior is examined in terms of elementary dislocation precipitate interactions. It is suggested that the
development of coplanar slip in the underaged conditions leads to its increased stress corrosion susceptibility and decreased
fracture toughness. The optimum aged condition is then associated with cross-slip deformation. The fracture behavior of the
overaged condition is a dynamic balance between a brittle matrix and the ductile (crack blunting) reverted austenite. 相似文献
8.
Phase transformations in solution treated and quenched Ti-(13-26) Nb-(22-38) Ta (wt.%) and Ti-(13-35.5) Nb-(5-22) Ta-(4-7.2) Zr alloys have been studied. It has been observed that phase transformations in these alloys are sensitive to both composition and cooling rate. In ternary alloys, water and oil quenching resulted in the formation of orthorhombic martensite () in a retained + athermal matrix, whereas slower cooling showed evidence of fine and isothermal formation within the matrix. Increase of Nb + Ta content decreases the volume percentage of martensite. Moreover, addition of Zr stabilized the phase, lowered the martensite start temperature and suppressed formation. Finally, dynamic moduli of air cooled quaternary alloys showed that the modulus was sensitive to the composition, a minima at Nb/Ta ratio of 12.0 and 5 at% Zr being observed, this minimum in dynamic modulus being consistent with phase suppression. 相似文献
9.
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