查看更多>>摘要：In this study, different surface textures (Diamond, Cylinder, and Sin) have been designed and produced on Ti6Al4V alloys by selective laser melting technology. TiO2/Ag composite coatings were prepared on these textures by merging anodic oxidation and spray deposition methods. Tightly arranged TiO2 nanotubes (TNTs) with tube diameters of about 100 nm are found on the top and lateral sides of the textures. On the bottom of the textures, dense nanopores were found with a pore diameter of about 50 nm. Compared with the untreated titanium alloy surface, both texture and TNTs structures would endow the titanium alloy surfaces with higher in vitro bioactivity. All three textures have an enhanced antibacterial property and a complete bactericidal effect was achieved by spray deposition of Ag nanoparticles (AgNPs) on all the surfaces. The MC3T3-E1 cells can adhere to the surfaces and proliferate normally, indicating good cytocompatibility of TiO2/Ag surfaces. Besides, the deposited AgNPs have been found to promote cell proliferation.
查看更多>>摘要：Mechanical energy-induced deposition on NiTi shape memory alloys (SMAs) is difficult to accomplish due to the pseudoelasticity of NiTi SMAs. In this study, a high-frequency ball-bombardment method called ultrasonic mechanical coating and armouring (UMCA) is introduced to synthesize a hydroxyapatite (HA)-containing coating on a NiTi SMA. The effects of treatment duration, Ti addition, and ball-to-powder ratio on the HA content of the coating are investigated. Results show that the HA content of the coating largely increased during the initial 10 s and decreased with further ball-bombardment. The addition of Ti powder into the chamber assisted HA anchoring on the NiTi SMA surface. Using a ball-to-powder ratio of 1:1 induced the highest HA content on the NiTi SMA as compared to the 1:2 and 2:1 ratios. Coating consisting of 10-50 nm nanoparticles of HA and Ti formed under localized compressive forces were induced through shot collisions. The bombardment also created a local amorphous structure of the NiTi SMA near the coating/NiTi SMA interface. Laser annealing induced oxidation of the coating, which improved the coating adhesion and corrosion resistance of the NiTi SMA in Hank's balanced salt solution.
查看更多>>摘要：In order to meet the clinical demand for titanium implants, the heterogeneous structure of TiO2/SrTiO3 coating was in situ fabricated on the surface of Ti6Al4V alloy by a facile way. The well-designed Ti6Al4V/TiO2/SrTiO3 composite exhibits a strong photocatalytic antibacterial efficiency against Escherichia coli (E. coli). The suitable energy band structure, improved light absorption and enhanced carrier separation of TiO2/SrTiO3 heterojunction facilitate the generation of bactericidal reactive oxygen species (ROS) under the illumination of UV light. The biocompatible SrTiO3 component effectively favors the adhesion, proliferation and osteogenic differentiation of human bone mesenchymal stromal cells (hBMSCs) in vitro. It is worth noting that the dense oxide coating provides a reliable barrier against tribocorrosion for the titanium alloy substrate, and the wear volume loss of the Ti6Al4V/TiO2/SrTiO3 reduces to 1/8 of that of the bare Ti6Al4V alloy in simulated body fluid. In this work, a multifunctional coating system was proposed to provide inspiration for the development of novel artificial bone implant materials.
查看更多>>摘要：Refractory multi-principal element alloys (RMPEAs) have become one of the most promising candidates for hightemperature structural and hard protective coating materials due to their high strength and thermal stability. In present work, Mo-Ta-W RMPEA thin hard films were successfully fabricated via direct current (DC) multi-target magnetron co-sputtering technology. The phase structure, microstructure, surface roughness and mechanical properties of the Mo-Ta-W RMPEA thin films were investigated. The as-deposited Mo-Ta-W RMPEA thin films with a wide range of compositions presented a single body-centered cubic (BCC) solid solution structure. Nanocrystalline with average grain size of 10- 15 nm (estimated according to the Scherrer equation) was formed in these films. The surface morphology of the films exhibited the flake-like shape with small roughness value of Ra = 4- 8 nm, and cross-sectional structure revealed columnar dendrite. The Mo-Ta-W RMPEA thin films displayed superior mechanical properties with the hardness of ~20 GPa and the elastic modulus of beyond 270 GPa. The Mo-Ta-W alloy thin films had the high H/E and H3/E2 values, indicating that the alloy thin films should have excellent wear resistance. Hence, these Mo-Ta-W RMPEA thin films can be considered as candidates for hard protective coating applications.
查看更多>>摘要：In this study, the gradient structure of copper was obtained by ultrasonic surface rolling process, and its effect on the mechanical properties of copper was systematically investigated. The obtained gradient structure comprises a nanocrystalline layer (NL, 60-130 mu m in thickness) of equiaxed grains, deformed layer (DL, 40-180 mu m in thickness) of deformed grains and center layer (CL) of equiaxed grains. From CL to NL, the grain size decreases from 50 to 0.1 mu m. The yield strength of the samples with gradient structure increases by 76% (from 125.53 to 225.32 MPa) and tensile strength increases by 16% (from 240.40 to 257.24 MPa), owing to the combined strengthening effect of fine grains, dislocations, and textures of gradient structure. This study helps to guide the design and optimization of the copper microstructure to improve the comprehensive mechanical properties.
查看更多>>摘要：TiAlCrY has been used as a bonding layer for the thermal barrier coating (TBC) system on TiAl alloys, due to its excellent high temperature oxidation resistance. However, it was found that vertical cracks formed in the TiAlCrY layer during the thermal cycling tests, which would fasten the failure of TBC system. In this work, a TiAlCrNb buffer layer was introduced between TiAlCrY layer and the substrate to alleviate the nucleation and propagation of cracks in the TiAlCrY layer from the perspective of alleviating the stress concentration, aiming to improve the thermal cycling lifetime of the YSZ/TiAlCrY system. The results show that the thermal cycling lifetime of the newly designed YSZ/TiAlCrY/TiAlCrNb system was over 245 cycles by means of water-quenching, which was almost twice of the system without the buffer layer and 3-4 times of the traditional YSZ/MCrAlY system on superalloys. The influence of the TiAlCrNb buffer layer was analyzed based on the combined analysis of microstructure, residual stresses and mechanical properties. This work implies that a proper buffer layer could effectively improve the thermal cycling lifetime of TBCs on TiAl alloys.
Schuette, Waynie M.Brewer, Luke N.Perez-Andrade, Lorena I.Bhattiprolu, Venkata Satish...
10页
查看更多>>摘要：This paper studies the microstructural evolution of commercially pure titanium (CP-Ti) and Ti6Al4V powders manufactured by the Armstrong process deposited by cold spray with nitrogen and helium. The unique, coral-like morphology of the powders resulted in high density deposits sprayed with both nitrogen and helium carrier gasses. The plastic deformation of the CP-Ti and Ti6Al4V particles upon impact leads to refinement of the equiaxed grains present in the starting powder. CP-Ti deposits sprayed with nitrogen result in a grain size of 1 +/- 0.6 mu m while deposit processed with helium results in a grain size of 0.7 +/- 0.2 mu m with no clear difference between the grain size at particle interiors and at prior particles boundaries. The low levels of intragranular misorientation in the CP-Ti helium deposit indicated the presence of recrystallized grains. The higher grain refinement when using helium as carrier gas resulted in a weak basal plane (0001) fiber texture. Regions of ultrafine grains are also identified in the microstructure of Ti6Al4V analyzed by SEM. Microhardness values of the deposits made with these coral-like morphology powders were similar to CP-Ti and Ti6Al4V cold sprayed deposits produced with spherical powders.
查看更多>>摘要：During plasma spraying, interactions between successive impacting particles/droplets are critical to the interfacial bonding properties between splats and the microstructural development of the bulk coating. The transient spreading process of two successive plasma- sprayed Ni20Cr droplets with different impacting spacing was numerically studied while the interfacial features between these two solidified splats were experimentally characterized by focused ion beam (FIB) microscope and transmission electron microscope (TEM). Droplets directly impacting onto the center of a previously deposited splat solidified quickly, inducing splashed fingers and smaller solidified grains. A higher droplet impact temperature could remelt the bottom splat and promote metallurgical bonding along the splat-splat interface more readily. For droplets impacting away from the previously solidified splat, the second molten droplet could either climb over the periphery of the previous splat inducing significant finger splashing, or spread beneath the curling-up splat modifying the solidification process. The solidification behavior of the subsequent droplet at the splat-splat interaction region played an important role in influencing the formation of inter-splat pores and grain growth.
查看更多>>摘要：In this paper, an alternating current (AC) was added to filling wire in the arc deposition process. The effect of alternative current on grains size and microstructure of Ti-6Al-4V cladding layers were studied. The microstructure evolution, grain size distribution, texture, and crystal twining of cladding layers with the addition of alternative current were studied in detail using metallographic microscopy (OM), electron back scattered diffraction (EBSD), and transmission electron microscope (TEM). The results reveal that the addition of AC can effectively inhibit beta grain growth, the grains size decrease with the increase of AC value. The enhancement of microstructure uniformity and decrease of texture intensity have been realized by electromagnetic force produced by alternative current. Additionally, the {10-10}< 10-12 > compression twins system was observed in cladding layer at 45A.
查看更多>>摘要：The Si-MoSi2 ceramic coatings were prepared on TZM alloy through a hot dip silicon-plating (HDS) process. The hot dip experiments results showed that Si-MoSi2 ceramic coatings have a very dense surface morphology and low roughness (0.258 +/- 0.009 to 0.347 +/- 0.019 mu m). The Si-MoSi2 ceramic coatings presents a typical layered structure with the outermost silicon-rich MoSi2 layer, the intermediate layer is the pure MoSi2 layer, and the Mo5Si3/Mo5Si3C diffusion layer between the MoSi2 layer and the TZM substrate. The oxidation tests showed that MoSi2 ceramic coating maintained a complete appearance after high temperature oxidation at 1500 ? for 4 h. The self-healing SiO2 protective film effectively inhibits the diffusion of oxygen and reduces the consumption rate of MoSi2 layer. HDS Si-MoSi2 ceramic coating presents a very excellent oxidation resistance at high temperature, which is mainly attributed to the uniform and dense coating structure and high surface silicon concentration.
NSTL
Elsevier