查看更多>>摘要：Titanium boride, TiBx, thin films were grown by direct current magnetron co-sputtering from a compound TiB2 target and a Ti target at an Ar pressure of 2.2 mTorr (0.3 Pa) and substrate temperature of 450 ?degrees C. While keeping the power of the TiB2 target constant at 250 W, and by varying the power on the Ti target, P-Ti, between 0 and 100 W, the B/Ti ratio in the film could be continuously and controllably varied from 1.2 to 2.8, with close-tostoichiometric diboride films achieved for P-Ti = 50 W. This was done without altering the deposition pressure, which is otherwise the main modulator for the composition of magnetron sputtered TiBx diboride thin films. The film structure and properties of the as-deposited films were compared to those after vacuum-annealing for 2 h at 1100 ?degrees C. As-deposited films consisted of small (?50 nm) randomly oriented TiB2 crystallites, interspersed in an amorphous, sometimes porous tissue phase. Upon annealing, some of the tissue phase crystallized, but the diboride average grain size did not change noticeably. The near-stoichiometric film had the lowest resistivity, 122 mu omega cm, after annealing. Although this film had growth-induced porosity, an interconnected network of elongated crystallites provides a path for conduction. All films exhibited high hardness, in the 25-30 GPa range, where the highest value of similar to 32 GPa was obtained for the most Ti-rich film after annealing. This film had the highest density and was nano-crystalline, where dislocation propagation is interrupted by the off-stoichiometric grain boundaries.
查看更多>>摘要：To meet the needs of laser cladding remanufacturing of key parts with both corrosion and wear resistance, the "material genetic " design method was used to deduce the composition of alloy powder with the microstructure of corrosion and wear-resistant key genetic phase from the target performance of materials. The research was conducted based on the typical phase theory of traditional Fe-based alloys such as martensitic and carbide wear-resistant microstructure and austenitic and Cr-rich passivated film corrosion-resistant microstructure. A material gene design database system based on the matching design of corrosion and wear-resistant phase key genes was successfully constructed by building an atheoretical prediction model and optimizing 10,935 sets of candidate Fe-based alloy compositions using computer algorithms and thermodynamic calculations. Finally, a new 50Cr12Ni3Mo2W6Co5BSiTi3CeO(2) Fe-based alloy composition with both good wear resistance and high corrosion resistance was obtained by optimizing the design. The laser cladding formability of the designed alloy was verified and the correspondence between the key genetic microstructure and the corrosion and wear resistance was characterized with optimized process parameters. The results show that the laser cladding has good formability. The microstructure of the cladding consists of martensite and Cr23C6 carbides with the characteristics of wear-resistant key genes and austenite and Cr-rich passivation film with the characteristics of corrosion-resistant key genes. The new laser cladding of Fe-based alloy shows better corrosion and wears resistance than the 50Cr6Ni2Y alloy prepared by traditional composition design methods. We hope that this research can provide a new approach to the design of alloy compositions for laser cladding remanufacturing of Fe-based parts with both corrosion and wear resistance.
查看更多>>摘要：The boronizing treatment has been an effective way to strengthen and enhance the lubrication performance of alloys. However, the traditional power-pack boronizing method has been limited due to its time-consuming. Improving the boronizing efficiency is highly demanded for the strengthening and industry application of the high-entropy alloys (HEAs). In this study, the electrochemical boronizing strategy was applied to improve the surface hardness and self-lubrication performance of AlCoCrFeNi2.1 eutectic HEA (EHEA). The microstructure, phase formation and hardness of boronized alloys were studied. Results confirm the high efficiency of electro-chemical boronizing to form a boronized layer with a thickness of about 35 mu m in 30 min. The surface hardness of the boronized AlCoCrFeNi2.1 HEA reached to about 18 GPa due to the presence of NiB, FeB and Cr3B4 in the boronized layer. Tribological tests reveal that the self-lubrication property of AlCoCrFeNi2.1 HEA in water condition was significantly enhanced by the electrochemical boronizing treatment, e.g., the friction and wear reductions reach to about 25% and 80%, respectively. Lubrication mechanism investigation by X-ray photo-electron spectroscopy (XPS) analysis showed the formation of a H3BO3 tribofilm on the sliding surface during the friction process, which effectively reduce friction and wear. This study provided a novel and fast approach for surface hardening and self-lubrication enhancement of HEA systems using the electrochemical boronizing strategy.
查看更多>>摘要：The pre-oxidation treatment was conducted for NiAlHf coatings in a sealed glass tube with low oxygen atmosphere at 900 degrees C. The microstructure evolution and oxidation resistance of the NiAlHf coatings with and without pre-oxidation treatment were systematically investigated via isothermal oxidation at 1200 degrees C for up to 200 h in laboratory air. The results revealed that a dense Al2O3 scale was formed on the NiAlHf coating surface after pre oxidation treatment, which could effectively reduce oxygen pressure and Al consumption on the NiAlHf coating surface. Furthermore, the NiAlHf coating microstructure evolution was effectively delayed from beta-NiAl to the gamma-Ni3Al phase due to Al2O3 scale formation by pre-oxidation treatment. Oxidation resistance of the NiAlHf coating with pre-oxidation treatment was improved after 200 h of oxidation, of which the oxidation rate constant was enhanced by 40% compared to the NiAlHf coating without pre-oxidation treatment. The mechanism of oxygen diffusion inhibition by pre-oxidation was also discussed. This research was beneficial to understand the effect of pre-treatment on the NiAHf coating microstructure evolution and could further guide the improvement of the oxidation resistance of NiAlHf coatings for long-term oxidation.
查看更多>>摘要：In this study, multilayered AlTiN/ZrN and AlTiN/CrN/ZrN coatings with CrN layer addition were prepared by cathodic arc evaporation (CAE) system using AlTi target, Cr target and Zr targets. According to the XRD and TEM experimental results, the coatings are all B1 NaCl structure, and the columnar structure continues from the bottom CrN to the top multilayered coating and the growth of the columns is not interrupted. After CrN addition, the AlTiN/CrN/ZrN coating consisted of ZrN, AlTiN and CrN multilayers. By increasing the cathode current of Cr, thicker CrN layers were obtained. The nanoindentation results showed that the AlTiZrN had the highest hardness of 30.4 GPa and residual stress of -3.1 GPa, mainly due to the contribution of ZrN into AlTiN. The multilayered Al12Ti7Cr12Zr22N and Al8Ti5Cr21Zr17N coatings with different CrN layer thicknesses had lower hardness values. Compared to the low hardness of CrN (~18 GPa), the multilayered AlTiN/CrN/ZrN coating still possessed high hardness enough. In addition, after CrN addition, the multilayered Al12Ti7Cr12Zr22N and Al8Ti5Cr21Zr17N coatings had lower residual stresses (-1.6-2.6 GPa). The low residual stress of the hard coating is beneficial for tribological applications. For the ball-on-disc tribological tests, although the AlTiN/ZrN coating had the highest hardness but it had the highest wear rate (4.96 x 10(-6) mm(3)/Nm). The multilayered Al12Ti7Cr12Zr22N coatings with thin CrN layer addition and small Cr content had the best wear performance with the lowest wear rate of 4.21 x 10(-7) mm(3)/Nm. The results showed that the special multilayered AlTiN/CrN/ZrN hard coating possessed better wear performance than that of AlTiN/ZrN coating, which was due to the fact that the multilayer architecture with CrN addition effectively released the internal stress to resist abrasion wear.
查看更多>>摘要：Maraging steel grade18Ni300 produced by powder bed fusion (PBF) in its as built condition was plasma nitrided at three different temperatures. The aim of the work was to investigate the impact of the nitriding temperature on the microstructural changes as well as on the surface properties such as hardness, wear and corrosion resistance. The microstructural features in the bulk as well as in the nitride layer were investigated using electron-backscatter diffraction (EBSD), transmission electron microscopy (TEM) and X-Ray diffraction (XRD) analysis. The bulk microstructure consists of martensite with a small amount of retained austenite, the amount of which increases with a higher nitriding temperature. The nitriding process also causes the formation of precipitates and can therefore also act as an aging treatment. A specific lamellar structure occurs on the surface during the nitriding process, which in the majority of cases consists of the Fe4N phase. The retained austenite also transforms during nitriding to the nitride phase Fe4N. It was found that nitriding at higher temperatures leads to the formation of cracks in the nitride layer. The crack formation is related to nano and micro segregation during the LPBF. These segregations lead to austenite formation, which also takes place along the grain boundaries and transforms during nitriding to Fe4N. Higher nitriding temperatures lead to a thicker nitride compound layer and to better wear resistance. The impact of the cracks on the static mechanical properties is negligible. However, the corrosion resistance is governed by the formation of cracks at higher nitriding temperatures.
查看更多>>摘要：Peri-implant angiogenesis plays important roles in osseointegration of implants. Unfulfilling neovascularization will lead to delayed union or non-union after prosthetic implanted. In this paper, a nanostructured surface composed of TiO2, CuO and Cu2O was fabricated on Ti-Cu alloy using an alkali-heat treatment. The nano structure strengthened anticorrosion but accelerated Cu ions release. Meanwhile, in vitro cells experiments proved both Cu ions release and nanostructure on the surface of Ti-Cu alloy improved the functionality of human umbilical vein endothelial cells (HUVECs) resulting in excellent pro-angiogenesis potential indicated by promoted initial adhesion and spreading, satisfied cytocompatibility, enhanced migration, improved tube formation, upregulated angiogenesis-related genes and increased VEGF protein secretion. It was suggested that the modified Ti-Cu alloy with desired angiogenesis might be a promising strategy to improve osseointegration.
查看更多>>摘要：In this article we show the optical, mechanical and surface properties change depending on the Hf-Zr-Ce-Y-O thin film composition. Hf4Zr4CeY2O21 shows up to three times higher hardness compared to binary HfZrO4 oxide and up to 50% higher hardness compared to cubic ZrO2 and HfO2 due to the solid solution hardening effect. Equimolar film exhibit a high transmittance > 85% and high hydrophobicity with the water contact angle asymptotic to 106?degrees. Variation of the elemental composition in Hf-Zr-Ce-Y-O is allows to simultaneously tune mechanical and wetting properties for the optimum configuration depending on the application.
查看更多>>摘要：Corrosion protection of magnesium alloys is a challenge in industrial applications because of the high chemical reactivity of Mg. In this work, a coating is prepared by plasma electrolytic oxidation (PEO) on the AZ31B Mg alloy and then modified by insoluble zinc phosphate to improve the corrosion resistance. To avoid the influence of the weak acidic Zn-containing electrolyte on the formation of the passivation layer on the magnesium alloy, a two-step process is designed to first produce a passivation layer before introduction of zinc phosphate. Zinc phosphate is mainly distributed on the surface and the sidewalls of the holes in the porous coating and blocks the interactions between the corrosive solution and Mg substrate. The corrosion potential of the optimal coating (Zn-15) increase while the passive current density at the terminal potential decreases, suggesting the significantly improved corrosion resistance compared to the pristine AZ31B. The life time demonstrated by neutral salt spraying is 4200 h that is about 3 times longer than that observed from the Mg alloy with the undoped coating.
Sidelev, D. V.Ruchkin, S. E.Syrtanov, M. S.Kashkarov, E. B....
11页
查看更多>>摘要：Cr coatings with CrN/Cr multilayers with a layer thickness of 100, 250 and 750 nm were deposited by a multi cathode magnetron sputtering on E110 zirconium alloy in Ar and Ar + N-2 atmosphere. The mechanical properties of the as-deposited coatings were measured by scratch testing and tribometry. A comparative study of crack and oxidation resistance of the Cr-coated E110 alloy was performed under thermal cycling (1000 degrees C) and high-temperature (1200-1400 degrees C) steam oxidation conditions. The influence of the CrN/Cr multilayers and their thickness on the mechanical properties and oxidation resistance of the coated E110 alloy is discussed. It is found that the CrN/Cr multilayers can limit interdiffusion between the coating and E110 alloy at high temperatures only for a short period.
NSTL
Elsevier