Zhuang Ma

Plasma boronitriding of WC(Co) substrate as an effective pretreatment process for diamond CVD

Abstract Cobalt-cemented tungsten carbide (WC–Co) is a widely used material for making cutting tools. Coating these tools with a protective diamond film should improve their lifetime and performance. However, the deposition and adhesion of diamond films on this material are hindered by the presence of the cobalt binder. To overcome this problem, we have developed a simple substrate pretreatment method with plasma boronitriding. The addition of NH 3 to B 2 O 3 –H 2 plasma can prevent cemented carbide from being etched in the plasma pretreatment and the binder phase-cobalt in the surface of the substrate was passivated during the plasma boronitriding process. Raman spectra showed that our pretreatment method efficiently reduced the catalytic effect of cobalt that leads to the formation of a non-diamond type of carbon layer between diamond coating and substrate. Indentation tests on diamond coated tungsten carbide substrate showed that the adhesion of diamond films significantly improved with plasma boronitriding the surface of cemented carbide.

First-principles calculations of crystal structure, electronic structure and optical properties of RETaO4 (RE= Y, La, Sm, Eu, Dy, Er)

It is an effective method to protect components from high power laser damage by using high reflective materials. The rare earth tantalates RETaO4 with high dielectric constant suggests that they may have very high reflectivity, according to the relationship between dielectric constant and reflectivity. In this paper, the crystal structure, electronic structure and optical properties of RETaO4 (RE=Y, La, Sm, Eu, Dy, Er) have been studied by first-principles calculation. The calculated lattice parameters are in good agreement with the previously reported values. With increasing the atomic number of RE (i.e., the number of 4f electrons), 4f electron shell moves from high energy region to low energy region, showing the tendency of moving from conduction band bottom to forbidden gap and then to valence band. The relationship between the electronic structures and optical properties is explored. The electron transitions between O 2p states, RE 4f states and Ta 5d states have a key effect on optical properties such as dielectric function, refractive index, absorption coefficient and reflectivity. For the series of RETaO4, the appearance of the 4f electronic states will obviously promote the improvement of reflectivity. When the 4f states appear at the middle of forbidden gap, the reflectivity reaches the maximum. The reflectivity of EuTaO4 at 1064nm is up to 93.47%, indicating that it has potential applications in the anti-laser radiation area.

The preparation and properties of Sm2Zr2O7 coatings by plasma spraying

Abstract Rare-earth zirconate with lower thermal conductivity compared to zirconia ceramic is very promising new thermal barrier coating material. In this article, Sm2Zr2O7 precursors were synthesised by the co-precipitation method, and the size of crystal grain was between 20 and 30u200anm. Then, the precursor and the powder calcined in 1250°C were granulated by the spray drying method. The adaptabilities of two kinds of powders for plasma spraying process were discussed. The results show that the crystal grain size of powder granulated directly by precursor was between 40 and 50u200anm, and the one granulated by precursor calcined in 1250°C was between 150 and 200u200anm. Under the same parameters of plasma spraying, the coating made by calcined powder was denser and its bond strength was higher; as the value of current dropped and secondary gas increased, the particles flied faster. To the submicron crystalline powder, the ratio of unmelted particles increased and equal-axis structures dropped, the coatings bond strength decreased. To the nano crystalline powder, the ratio of unmelted particles decreased and equal-axis structures increased, the coatings bond strength rose.

Laser ablation protection of polymer matrix composites by adhesive inorganic coatings

Further utilization of polymer matrix composites (PMCs) in the aerospace industry is threatened by the development of laser weapons, resulting from weak oxidation resistance, low operation temperature and poor anti-laser ablation performance of the PMCs. Preparing an adhesive inorganic coating on the surface of components is an effective method to improve the laser irradiation resistance. Anti-laser ablation coatings composed of ZrO2 as pigment and sodium silicate as binder with different curing agents (including SiO2 and Na2SiF6) are fabricated on the PMCs substrate with brush painting. Influence of the different curing agents on anti-laser ablation of the coatings at the laser wavelength of 1064xa0nm is investigated. The rear surface temperature of substrate with coatings, containing SiO2 and Na2SiF6, decreases from 240 to 60 and 70xa0°C, respectively, when testing at 1000xa0W for 5xa0s. After irradiation test at 1000xa0W for 10xa0s, the coating with SiO2 as curing agent shows slight molten state on the surface, while the coating with Na2SiF6 is broke down, because coating containing SiO2 possesses more compact microstructure and fewer cracks than that with Na2SiF6.

Reflectivity and laser irradiation of plasma sprayed Al coating

Its well known that Al has a very high reflectivity in the visible/near-infrared range, which makes it become a promising anti-laser material. But for a plasma sprayed coating, there are usually many defects, such as pores, cracks and interfaces among particles, which lead to properties difference with its bulk material. In this paper, the reflectivity of plasma sprayed Al coating and its laser irradiation effect were investigated. Its reflectivity, surface roughness, porosity, microstructure, and cross-section microstructure were characterized. The results show that a high reflectivity (98.1% at CO2 laser 10.6μm wavelength) of plasma sprayed Al coating, which is comparable with bulk material, could be obtained. Its optical laser damage threshold is 2×104W/cm2 that makes its reflectivity obviously decrease. Its damage mechanism is oxidation.

Chemical compatibility and oxygen-ion conductivity of Ba2DyAlO5 ceramic for thermal barrier coatings

Abstract Owing to its low thermal conductivity, and high thermal expansion coefficient at high-temperature, a novel ceramic Ba2RAlO5 (R represents rare-earth element) will be one of the candidate materials used for the thermal barrier coatings (TBCs). The chemical compatibility is critical to the durability of the TBCs system. Ba2DyAlO5 powder and ceramic were prepared by traditional solid state reaction and pressure-less sintering. The chemical compatibility of Ba2DyAlO5 with Al2O3 was investigated by annealing approximate diffusion couples and mixed powder at 1300, 1400, and 1500°C for 8u200ah, respectively. The microstructures of the interface between the Ba2DyAlO5/Al2O3 approximate diffusion couples were observed, and the phase compositions of sintered mixed powder were characterised. The oxygen-ion conductivity of the material was studied using the ac impedance spectroscopy technique over a wide temperature (400–600°C) and frequency (1u200aHz–1u200aMHz) ranges. The results show that Ba2DyAlO5 and Al2O3 keep good chemical compatibility on the whole after heating at 1300°C for 8u200ah. Only a few Ba element diffuses into Al2O3 lattice. As the temperature increases to 1400 and 1500°C, the obvious chemical reaction occurs producing Ba2Al2O4, AlDyO3 and BaO. The highest oxygen-ion conductivity of Ba2DyAlO5 is 1·95u2009×u200910−u20096u2009Su2009cm−u20091 at 600°C, which is much lower than that of Y2O3 stabilized ZrO2 (YSZ) (4·59u2009×u200910−u20093 at 600°C). It indicates that the material Ba2DyAlO5 has excellent oxygen obstruction capability.

Damage characteristic of interpenetrating phase composites under dynamic loading

In order to investigate the damage characteristic of ceramic-metal interpenetrating phase composite (IPC) under dynamic loading, uniaxial dynamic compression was performed to characterize the failure of SiC/Al composite with 15% porosity using a modified Split Hopkinson Pressure Bar (SHPB). High speed photography was used to capture the failure procedure and set up the relationship between deformation and real stress. The deformation control technology was used to obtain collected samples in different deformations under dynamic loading. Micro CT technology was utilized to acquire real damage distribution of these specimens. Moreover, SEM was employed in comparing the damage characteristics in IPC. A summary of the available experimental results showed that IPC without lateral confinement formed double cones. The different features compared with ceramic materials without restraint was shown to be the result of the lateral restraint effect provided by metal phase to ceramics skeleton.

Full-Scale Numerical Simulation of Plasma-Sprayed Functionally Gradient Materials

To develop novel and advanced thermal barrier coatings, full-scale numerical simulation of plasma-sprayed functionally gradient materials is conducted in this paper, including the prediction of basic parameters at the nozzle exit, simulation of three dimensional simulation of the plasma jet, modeling of the interaction between the plasma jet and the particles, calculation of flight trajectories and temperature history of flying metal and ceramic particles, the interaction between the molten particles and the substrate, as well as the deposition process of the coatings. Various complex phenomena, such as turbulent effects with chemical reactions in the plasma jet, dispersion status of the particles onto the substrate, and the composition distribution of the functionally gradient materials, are fully taken into account. The numerical simulation results are found to be in good agreement with experimental evidence.

First-principle calculations of crystal structures, electronic structures, and optical properties of RETaO4 (RE = Y, La, Sm, Eu, Dy, Er)

Abstract. It is an effective method to protect components from high power laser damage using high reflective materials. The rare earth tantalates RETaO4 with high dielectric constant suggests that they may have very high reflectivity, according to the relationship between dielectric constant and reflectivity. The crystal structures, electronic structures, and optical properties of RETaO4 (RE=Y, La, Sm, Eu, Dy, Er) have been studied by first-principle calculations. With the increasing atomic number of RE (i.e., the number of 4f electrons), a 4f electron shell moves from the bottom of conduction band to the forbidden gap and then to the valence band. The relationship between the electronic structures and optical properties is explored. The electron transitions among O 2p states, RE 4f states, and Ta 5d states have a key effect on optical properties such as dielectric function, absorption coefficient, and reflectivity. For the series of RETaO4, the appearance of the 4f electronic states will obviously promote the improvement of reflectivity. When the 4f states appear at the middle of the forbidden gap, the reflectivity reaches the maximum. The reflectivity of EuTaO4 at 1064 nm is up to 93.47%, indicating that it has potential applications in the antilaser radiation area.

First-principles calculations of crystal structure, electronic structure and optical properties of Ba 2 RETaO 6 (RE = Y, La, Pr, Sm, Gd)

AbstractThe crystal structure, electronic structure and optical properties of Ba2RETaO6 (REu2009=u2009Y, La, Pr, Sm, Gd) have been studied by first-principles calculation. The calculated lattice parameters are in good agreement with the previously reported values. With increasing the atomic number of RE (i.e., the number of 4f electrons), the energy level of RE 4f bands becomes lower continuously. The relationship between the electronic structure and optical properties is explored based on first-principles calculation. The electron transitions between O 2p states, RE 4f states and Ta 5d states have a key effect on optical properties such as dielectric function, refractive index, absorption coefficient and reflectivity. The phase structures have great influence on the optical properties of Ba2SmTaO6 and Ba2GdTaO6, and the big variation of reflectivity induced from phase transition makes them have potential applications in the infrared radiation protection area.n