Bond Layer Research Articles

Numerical investigations on energy harvesting potential of thin PZT patches adhesively bonded on RC structures

The reinforced concrete (RC) structures, such as bridges and flyovers, provide a viable platform for ambient vibration energy harvesting. Adhesively bonded thin piezoelectric ceramic (PZT) patches, operating in d31 mode, have recently been demonstrated capable of energy harvesting from ambient vibrations in RC structures in addition to structural health monitoring (SHM). Optimization of energy harvesting warrants detailed parametric investigations, which are, however, infeasible analytically or through experimentation, due to the complex piezo-structure interaction through the bond layer and the sheer large number of the parameters involved. This article investigates the effect of the adhesive bond and the related parameters on the energy harvesting capability of thin PZT patches operating in surface-bonded/embedded configurations bonded onto RC structures. Towards this end, a numerical model is generated for a real-life sized simply supported RC beam instrumented with (a) surface bonded piezo-sensor (SBPS), and (b) embedded PZT patch. Coupled field analysis is performed for both the configurations. Before employing for parametric study, the numerical model is validated with the previously developed analytical model as well as the experimental observations. The numerical model is utilized to investigate the effect of the varying load resistance, the piezo and the bond thicknesses, the patch’s plan dimensions, the shear modulus of the adhesive layer and the presence of the adhesive covering on the voltage/close circuit power generated by the patch. The results of the study show that whereas the surface bonded condition generates higher voltage, the embedded configuration is more desirable from the point of view of dependence on piezo parameters, especially larger thickness, which promises definite beneficial effects. Further, covering the surface bonded patch with an adhesive layer not only offers protection to the patch but also aids in higher voltage and higher power output from it. The results of the study are crucial for practical deployment of PZT patches on RC structures for energy harvesting in addition to SHM.

グラファイト上に成膜した金属溶射皮膜の密着強度評価

Graphite is a candidate material for heat sink, because it has extremely high thermal conductivity, and low density. On the other hand, graphite has low solderability. Therefore, it is required to improve solderability by means of a copper bond layer on the graphite surface. The conventional coating methods as represented by CVD and PVD need high vacuum environment and those deposition rates are very low. In this work, we discuss the applicability of Low-Temperature Plasma Spray (LTPS) for thin coating production onto the graphite surface. LTPS is a kind of plasma spray technique, it has high deposition rate, 10 μm/s in an atmospheric environment. The LTPS copper coating, however, does not have highly adhesion strength. However, LTPS titanium coating shows enough adhesion strength on the graphite substrates. Therefore, insertion of Ti bond layer for improvement of adhesion strength between copper coating and graphite is considered. In this study, in order to optimize coating conditions, we make some specimens in different conditions and measure particle temperature and particle velocity and flame temperature. As a result of measurements, Ti particle temperature was over 2800°C between 20 and 60mm from spray nozzle, and particle velocity was 60~100m/s. Experimental results indicate that as spray distance decrease, porosity size in a coating is smaller.

Novel self-strengthening hybrid dentin adhesive via a facile visible-light irradiation triple polymerization

Event Abstract Back to Event Novel self-strengthening hybrid dentin adhesive via a facile visible-light irradiation triple polymerization Qiang Ye1, Linyong Song1, Xueping Ge1, Anil Misra1, 2 and Paulette Spencer1, 3 1 University of Kansas, Bioengineering Research Center, United States 2 University of Kansas, Department of Civil Engineering, United States 3 University of Kansas, Department of Mechanical Engineering, United States Introduction: In vivo biodegradation of the bond between the composite and tooth, i.e. the composite restoration’s adhesive bond layer, is considered a major contributor to premature failure of composite restorations[1]. The structure of methacrylate-based dentin adhesives suggests a general mechanism for their chemical and enzymatic degradation in oral fluids. In our previous study[2], the crosslink density of dentin adhesives can be improved with the addition of epoxide monomers. The objective of this work was to further develop a self-strengthening methacrylate-based dentin adhesive system by introducing an epoxy cyclohexyl trimethoxysilane (TS) containing both epoxy and methoxysilyl functional groups and cured by visible-light photopolymerization. Materials and Methods: Neat methacrylate monomer mixture (Scheme 1) of HEMA/BisGMA at 45/55 wt% was used as the control (C0). Experimental formulation with HEMA/BisGMA/TS (22.5/27.5/50, wt%) was used to investigate the free radical polymerization of methacrylate, ring-opening cationic polymerization of epoxy, and photoacid-induced sol-gel reaction. The polymerization behavior was monitored in-situ using real-time Fourier transform infrared spectroscopy (FTIR). The properties of copolymers at TS concentration from 5 to 35 wt% were determined using dynamic mechanical analysis (DMA). The leachables from polymer discs were determined by HPLC using a reverse phase C18 column and UV/diode array detectors. Results and Discussion: In this triple polymIn this triple polymerization system, free radical polymerization rate was the highest and the hydrolysis-condensation reaction was the slowest. In acidic environments, the fast hydrolysis reaction and the limited condensation gave rise to the self-strengthening process, which significantly improved the mechanical properties. When the TS concentration was 10-20 wt%, the copolymers became more homogeneous and the storage modulus at 70 0C reached maximum. The cumulative amounts of leached monomers were reduced significantly (Figure 1). Conclusion: With the introduction of both epoxy and trimethoxysilyl functional groups, a self-strengthening hybrid system has been developed for application as a dentin adhesive. During visible-light irradiation, a triple polymerization mechanism was involved (Figure 2). Supported by grant NIH/NIDCR R01 DE022054. Scheme 1. Chemical structures of monomers used in the formulations. Figure 1. Cumulative release of HEMA from the dentin adhesive copolymers as a function of incubation time in ethanol at 23±2 0C Figure 2. Proposed polymethacrylate-based matrix network structure and the autonomic self-strengthening process with different TS concentrations. (A1 and A2) Polymethacrylate-based network formed by free radical polymerization, cationic ring-opening polymerization, and limited photoacid-induced sol-gel reaction in dry conditions after 40 s irradiation; (B1 and B2) photoacid-induced ring-opening polymerization and sol-gel reaction after 24 h; (C1 and C2) self-strengthening process via sol-gel reaction and ring-opening polymerization in wet environment. Supported by grant R01DE022054 (PS, JSL), from the National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20892.

Laser Direct Patterning of Dry Etch BCB Adhesive Layers for Low Temperature Permanent Wafer-to-Wafer Bonding

To enable advanced wafer level packaging approaches for devices like MEMS, image sensors or optical elements, wafer-to-wafer bonding processes using structured low temperature curable adhesives are required. A lot of Benzocyclobutene (BCB)-based wafer bonding works have been reported in the past showing a broad range of applications and good performance, but also some limitations such as long bond cycles and high cure temperature of 250 °C. In 2013 new process concepts were demonstrated [1], showing that wafer bond cycle time can be reduced to less than 10 min and a post bond batch cure at temperatures below 200 °C can be used to significantly shrink the overall cost of a BCB-based adhesive wafer bonding process. In order to create a patterned BCB bond layer, photo structuring of CYCLOTENE ® 4000 Resin is one solution. However, due to the decreased flow capability of that material after exposure, high bond forces and extended bonding times during wafer bonding as well as nearly flat surfaces with low topography are required for void-free bonding. To overcome these limitations, an increased material flow capability during wafer bonding is required. In this context non-photo sensitive CYCLOTENE ® 3000 Resin is suitable, since it has excellent flow capability in non-cured state. However, non-cured CYCLOTENE ® 3000 Resin cannot be structured with standard dry etching processes using a photo resist layer as mask. In order to enable patterned adhesive bonding based on CYCLOTENE ® 3000 Resin, alternative structuring methods have to be evaluated. One method was presented in [1] which is transfer printing of CYCLOTENE ® 3000 Resin from a help wafer to topography features of the device wafer. Although very good results were obtained, the method is restricted to applications with significant topography to enable the transfer printing. In this work we focus on a new structuring method for non-cured BCB layers formed from CYCLOTENE ® 3000 Resin. The layers were spin coated, baked and subsequently patterned using a 248 nm excimer laser stepper. The system features a 2.5× mask projection with a resulting exposure field of 6.5 × 6.5 mm2 and allows a direct ablation patterning of polymers. By using this method bond frame structures were patterned into 5 μm thick BCB layers at 200 mm silicon wafers. The wafers with the structured adhesive were bonded at 80 °C and 0.2 MPa for 5 minutes with 200 mm glass wafers. The bonded wafer stacks were subsequently post bond batch cured at 190 °C. Wafer dicing and shear tests of the bonded structures revealed excellent mechanical robustness of the BCB bond frames. The paper will review the new BCB wafer bond processes for supporting short cycle times with special focus on the new patterning approach by laser ablation. Process flow description as well as systematical analysis of pattern reproducibility of the new structuring method is part of the discussion.

Superlubricity of nanodiamonds glycerol colloidal solution between steel surfaces

Abstract In this paper, nanodiamonds glycerol colloidal solution is investigated as a lubricant between steel ball and disk, and it is compared with glycerol solution. Although stable superlubricity (coefficient of friction ≈ 0.006) can be achieved with both solutions after a running-in period, the colloidal solution causes much less wear than the glycerol solution. With the content of the nanodiamonds at only 0.01 wt%, the colloidal solution can lead to a reduction of 32.5% in the diameter of the wear scar on the ball, resulting in an increase of 119.3% in the contact pressure between the rubbing surfaces during the superlubricity period. Therefore, a novel superlubricity system based on nanodiamonds glycerol colloidal solution is discovered. Through theoretic calculations, the novel superlubricity system is determined to be in the mixed lubrication regime, but not far from the hydrodynamic lubrication regime. It is believed that the ultralow COF is attributed to the hydrodynamic effect and the hydrogen bond layer. And the reduced wear derives from the rolling effect of the nanodiamonds. This work enriches the field of water-based superlubricity by firstly introducing nanoparticles into this area and has prosperous potential applications.

Fabrication and thermal shock resistance of multilayer γ-Y2Si2O7 environmental barrier coating on porous Si3N4 ceramic

A dense multilayer γ-Y2Si2O7 environmental barrier coating was in-situ fabricated by the liquid infiltration and filling method on porous Si3N4 ceramic for water resistance. When the sintering temperature was 1350°C, as-prepared coating consisted of the top glass layer, the γ-Y2Si2O7 interlayer and the bottom bond layer. With increasing sintering temperature from 1350 to 1450°C, the microstructure of the coating transformed from three layers into two layers including the γ-Y2Si2O7 layer and the bond layer. The γ-Y2Si2O7 layer in the coating consisted of γ-Y2Si2O7 and Y–Si–Al–O glass, and the γ-Y2Si2O7 content increased with the increase of sintering temperature. Thermal shock resistance of the coatings was tested. The results showed that the coating prepared at 1450°C displayed the better thermal shock resistance. After thermal shock for 15 times from 1000°C to room temperature, the microstructure of the coating showed little change, and water absorption increased slightly from 4.8% to 5.3%.

Metallurgical bond between magnesium AZ91 alloy and aluminium plasma sprayed coatings

We report on creation of metallurgic bond between AZ91 magnesium alloy and aluminium plasma sprayed coatings which has been so far observed only after additional surface treatments. High-enthalpy plasma spray process employing water-stabilized plasma torch was used to spray commercially pure aluminium and AlCr6Fe2 alloy and, thus, creating around 200 and 450μm thick coatings, respectively, with presence of aluminium oxides. For both coatings, metallurgical bond layers with thickness of around 100μm and notable for their eutectic morphology were obtained. Analyses of microstructure, elemental and phase compositions revealed that the bond layer with the commercially pure aluminium coating is dominantly Al12Mg17 while the bonding with AlCr6Fe2 alloy comprises both Al12Mg17 and Al3Mg2. Despite the presence of porosity, the coatings' polarization resistance measurements showed increased values as compared with the bare substrate. Results of adhesion tests did not confirm the deterioration of adhesion strength due to the presence of intermetallics in the bond, and more important factor was the phase composition and microstructure of the coatings. The thickness of the metallurgic bond can be thermally controlled via the substrate preheating and/or its thickness.

Effects of Bonding Conditions on Bondability Using Zn/Al/Zn Clad Solder

Three-layer Zn/Al/Zn clad solders have been developed for high-temperature die attachment. The clad structure is used to improve the wettability and bondability of Zn-Al eutectic solder by preventing Al oxidation. The effects of the bonding conditions on the bondability with Zn/Al/Zn clad solder were investigated. Bonding was achieved in the temperature range from 385°C to 420°C under N2 atmosphere with oxygen concentration below 100 ppm. However, the bonding strength of the joint formed under N2 + 4% H2 atmosphere was almost 0 MPa, and stripe defects and air gaps remained in the bond layer. To improve the bondability under N2 + 4% H2 and expand the application range, a five-layer Cu/Zn/Al/Zn/Cu clad solder was developed in an attempt to prevent the Zn layers from being oxidized by the outer Cu layers. Cross-sectional observation of the Cu/Zn/Al/Zn/Cu clad solder revealed that the surface was covered by a Cu layer, and that Cu5Zn8 layers grew between the Cu and Zn layers. This clad solder exhibited high shear strength of over 80 MPa when formed under N2 + 4% H2 atmosphere, and no stripe defects or air gaps were observed in the bond layer.

Nondestructive characterization of thermal barrier coating by noncontact laser ultrasonic technique

We present the application of a laser ultrasonic technique in nondestructive characterization of the bonding layer (BL) in a thermal barrier coating (TBC). A physical mode of a multilayered medium is established to describe the propagation of a longitudinal wave generated by a laser in a TBC system. Furthermore, the theoretical analysis on the ultrasonic transmission in TBC is carried out in order to derive the expression of the BL transmission coefficient spectrum (TCS) which is used to determine the velocity of the longitudinal wave in the BL. We employ the inversion method combined with TCS to ascertain the attenuation coefficient of the BL. The experimental validations are performed with TBC specimens produced by an electron-beam physical vapor deposition method. In those experiments, a pulsed laser with a width of 10 ns is used to generate an ultrasonic signal while a two-wave mixing interferometer is created to receive the ultrasonic signals. By introducing the wavelet soft-threshold method that improves the signal-to-noise ratio, the laser ultrasonic testing results of TBC with an oxidation of 1 cycle, 10 cycles, and 100 cycles show that the attenuation coefficients of the BL become larger with an increase in the oxidation time, which is evident for the scanning electron microscopy observations, in which the thickness of the thermally grown oxide increases with oxidation time.

The Laser Interlaminar Reinforcement of Continuous Glass Fiber Composites

Interlaminar crack initiation and propagation are a major mode of failure in laminate fiber reinforced composites. A laser reinforcement process is developed to bond layers of glass fabric prior to the vacuum-assisted transfer molding of laminate composites. Glass fabric layers are bonded by fusing a dense glass bead to fibers within the laser focal volume, forming a 3D reinforcement architecture. Coupled heat transfer and viscous flow modeling is used to capture the temperature and morphology evolution of glass during the reinforcement process under experimentally observed conditions. Mode I double cantilever beam (DCB) testing is performed to quantify the effects of laser interlaminar reinforcements on composite delamination resistance. Postmortem high-resolution imaging of the fracture surface is used to characterize the toughening mechanism of the interlaminar reinforcements. Improved delamination resistance of laser reinforced composites derives from crack arrest and deflection mechanisms, showing a positive correlation to the reinforcement thickness.

Titanium and hydroxyapatite coating of polyetheretherketone and carbon fiber-reinforced polyetheretherketone: A pilot study in sheep.

The purpose of this study was to evaluate the bone formation capability of polyetheretherketone (PEEK) and carbon fiber-reinforced PEEK (CFR-PEEK) implants coated with different titanium and hydroxyapatite plasma-sprayed layers after 2 and 12 weeks. In six sheep 108 implants were placed in the pelvis. Altogether six different surface modifications were tested. After 2 and 12 weeks, n = 3 implants per group were examined histologically and n = 6 implants per group were tested by a pull-out test. Biomechanically (p = 0.001) as well as histologically (p > 0.05) surface coating of PEEK/CFR-PEEK led to an increase of osseointegration from 2 to 12 weeks. After 12 weeks, coated implants demonstrated significant (p < 0.001) higher pull-out values in comparison to uncoated implants. Overall, the double coating (titanium bond layer and hydroxyapatite top layer) showed the most favorable results after 2 and 12 weeks. Plasma-sprayed titanium and hydroxyapatite coatings on PEEK or CFR-PEEK demonstrated a significant improvement of osseointegration. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1182-1191, 2016.

The measurement and analysis of micro bonding force for electroplated CBN grinding wheels based on response surface methodology

The superabrasive (e.g. CBN or diamond) grain dislodgement occurrence on the wheel surface due to insufficient bonding force is the major failure phenomena in the grinding process with electroplated grinding tools. This failure leads to the abrupt increase of load on the immediate grains, accelerating more grain dislodgement on wheel surface. Ultimately, the aggregated grain dislodgement causes the workpiece profile accuracy degradation and catastrophic wheel sharpness loss. Therefore, the provision of sufficient and uniform micro bonding force all through the wheel surface is the critical task in electroplated superabrasive grinding wheel design. Considering the complexity in the micro bonding force enabling factors, e.g. the grain shape, dimensional size, spatial orientation, and bond layer thickness, it is vital to establish the quantitative and comprehensive relationship between these factors with the micro bonding force for optimal electroplated grinding wheel design. In this paper, an inclined micro-thread turning test is developed to measure the single grain micro bonding force. In addition, the finite element model of single CBN grain bonding force is established and validated to simulate the grain dislodgement. Finally, the response surface methodology (RSM) is applied to build the comprehensive correlation of the bonding force with its dimensional size, spatial orientation, and bond layer thickness. Therefore, the optimal bonding condition through regressed prediction model is identified to provide the quantitative basis for the electroplated CBN grinding wheels design, which indicates that the bonding force can be predicted for specific wheel manufacturing parameters and improved by related variable adjustment.

Three-dimensional temperature effect modelling of piezoceramic transducers used for Lamb wave based damage detection

The paper presents a three-dimensional temperature-dependent model of surface-bonded, low-profile piezoceramic transducers (PZT) used for Lamb wave propagation. The effect of temperature on Lamb wave actuation, propagation and sensing is investigated. The major focus is on the study of actuation and sensing properties of PZT for various temperature levels. These properties are investigated through the electric field analysis of transducers. The temperature effect on transducer bond layers is also investigated. Numerically simulated amplitude responses are analysed for various temperatures and excitation frequencies. Numerical simulations are validated experimentally. The results demonstrate that temperature-dependent physical properties of PZT, bond layers and particularly host structures significantly affect the amplitude and phase of Lamb wave responses.

Improvement of Adhesion Strength of High Temperature Plasma Coated Aluminum Substrate with Aluminum-Alumina Powder Mixture

High temperature plasma coating technology has been applied to recover damaged aluminum dies from wear by spraying pure aluminum and alumina powder. However, the coated mixed powder layer composed of aluminum and alumina often undergoes a detachment from the substrate, making the coated substrate die unable to maintain its expected life span. In this study, in order to increase the bonding strength between the substrate and the coating layer, a pure aluminum layer was applied as an intermediate bond layer. In order to prepare the specimen with variable bond coating conditions, the bond coat layers with a various gun speed from 10 cm/sec to 30 cm/sec were prepared with coating cycle variations ranging from three to nine cycles. The specimen with a bond coat layer coated with a gun speed of 20 cm/sec and three coating cycles exhibited ~13MPa of adhesion strength, while the specimen without a bond coat layer showed ~6 MPa of adhesion strength. The adhesion strength with a variation of bond coat layer thickness is discussed in terms of coating parameters.

The behavior of ZrO2/20%Y2O3 and Al2O3 coatings deposited on aluminum alloys at high temperature regime

Aluminum alloy present numerous advantages like lightness, high specific strength and diversity which recommend them to a high number of applications from different fields. In extreme environments the protection of aluminum alloys is difficult and requires a high number of requirements like high temperature resistance, thermal fatigue resistance, corrosion fatigue resistance and galvanic corrosion resistance. To obtain these characteristics coatings can be applied to the surfaces so they can enhance the mechanical and chemical properties of the parts. In this paper two coatings were considered for deposition on an AA2024 aluminum alloy, ZrO2/20%Y2O3 and Al2O3. To obtain a better adherence of the coating to the base material an additional bond layer of NiCr is used. Both the coatings and bond layer were deposited by atmospheric plasma spraying on the samples. The samples were subjected to a temperature of 500°C and after that slowly cooled to room temperature. The samples were analyzed by electron microscopy and X-ray diffraction to determine the morphological and phase changes that occurred during the temperature exposure. To determine the stress level in the parts due to thermal expansion a finite element analysis was performed in the same conditions as the tests.

Static tensile strength characteristics of fillet welding lap joints assisted with bonding

A series of tensile tests were carried out on fillet welded lap joints assisted with bonding for investigating the static tensile strength characteristics of the joints from the viewpoints of stress reduction effect around the welded part due to bonding. It was confirmed that the mechanical properties of epoxy resin bonding used in this study were not deteriorated by heating to less than 150°C. When the fillet welded lap joints with bonding were assembled, the bond layer 20 mm from the weld toe was subjected to heating to over 150°C. In other words, the mechanical properties in that region deteriorated. The strengths of the elastic limits of specimens with welding and bonding were higher than those of specimens with only welding by from 60 to 100 MPa. The ultimate tensile strengths of them were almost the same because they were broken at the base plate. The strains around the weld toe and the root of specimens with welding and bonding were smaller than those of specimens with welding by around 13% in the elastic region. The strengths of specimens with only bonding were 170 MPa, which could be explained by a theory of elastic stress distribution. Even if the bond layer 20 mm from weld toe of the specimens with welding and bonding was thermally damaged, the possibility was confirmed that the residual bond layer had around 100 MPa in strength. It could be concluded that the strength of the residual bonding assisted to decrease the stress around the welded part of the specimens with welding and bonding.

Ultra thermal stability of LED die-attach achieved by pressureless Ag stress-migration bonding at low temperature

Using recently-developed Ag stress-migration bonding (SMB), a light-emitting diode (LED) die can be bonded on a glass substrate above 200°C in air without pressure, where both the die and substrate surfaces are coated with a few-microns-thick Ag layer. We investigate this emerging die-attach method and reveal the detailed bonding processes. The thermal residual stress in the Ag coating layer causes hillock formation on both the surfaces, and the extruded Ag grains grow to fill the gap between the contacted surfaces. A sound contact over the large bonded area can be achieved without applying any pressure. However, the LED dies exposed to a high working temperature may increase the risk of void formation in the bonding interface structure, leading to a crack or interface failure due to the bond strength degradation. In this study, we insert a barrier layer of a high melting-point metal like Pt or Ru under the Ag bond layer to prevent void diffusion from the Ag layer. The high bond strength achieved by Ag SMB is then unaffected by the heat exposure tests even at 440°C for 2h, assuring sufficiently long lifetime for the LED die-attach. Our pressureless Ag SMB method thus achieves excellent thermal stability, in addition to the ideal reflectivity and electric/heat conductivities of Ag, perfectly suitable for LED applications, as well as various other power devices of high-temperature wide-bandgap power semiconductors like GaN and SiC.

Adhesion and residual stress of plasma sprayed Alumina–titania coatings

Plasma-sprayed coatings are formed by the impacting of particles onto a fixed substrate layer-by-layer. Residual stresses inside the coatings are essential for their influencing on the coatings’ performance and durability during service life. In the present work, heat transfer and elastic–plastic residual stresses generation during plasma spraying in Al2O3–13wt.%TiO2/NiCrAl (AT13) coating system were analyzed by finite element analysis (FEA). The sophisticated spraying process was simulated and the laminated structure of the coating was modeled under three-dimension. In this simulation, radial and axial compressive stresses were concentrated at the interfaces and inside the bond layer. Besides, at the specimen corner of the free edge, there were high tensile radial and axial stress concentrations. Such remarkable stresses, no matter tensile or compressive, may lead to the delamination and failure of coatings. Comparing with the numerical results, X-ray diffraction measurement was conducted on the AT13 coatings. As a result, the tested values matched well with the FEA simulated results.

Effect of powder reactivity on fabrication and properties of NiAl/Al2O3 composite coated on cast iron using spark plasma sintering

Powder mixtures of Ni, NiO and Al are ball milled for 1 and 10h. X-ray diffractometry and differential thermal analysis show that while ball milling for 1h produced mechanically activated powder; 10h ball milling produced NiAl and Al2O3 phases. Dense NiAl/Al2O3 composite coatings are formed on gray cast iron substrate by spark plasma sintering (SPS) technique. The effect of powder reactivity on microstructure, hardness and scratch hardness of NiAl/Al2O3 coatings after SPS is discussed. Results show that in the coating sample made of mechanically activated powder in situ synthesis of NiAl/Al2O3 composite coating is fulfilled and a thicker well-formed diffusion bond layer at the interface between coating and substrate is observed. The diffusion of elements across the bond layers and phase evolution in the bond layers were investigated. No pores or cracks were observed at the interface between coating layer and substrate in any of samples. Higher Vickers hardness and scratch hardness values in coating made of 10h ball milled powder than in coating fabricated from 1h ball milled powder are attributed to better dispersion of Al2O3 reinforcement particles in NiAl matrix and nano-crystalline structure of NiAl matrix. Scratched surface of coatings did not reveal any cracking or spallation at coating-substrate interface indicating their good adherence at test conditions.

Significant contribution of As4porbitals to the low-lying electronic structure of the 112-type iron-based superconductorCa0.9La0.1FeAs2

We report a systematic polarization-dependent angle-resolved photoemission spectroscopy study of the three-dimensional electronic structure of the recently discovered 112-type iron-based superconductor Ca1-xLaxFeAs2 (x = 0.1). Besides the commonly reported three hole-like and two electron-like bands in iron-based superconductors, we resolve one additional hole-like band around the zone center and one more fast-dispersing band near the X point in the vicinity of Fermi level. By tuning the polarization and the energy of incident photons,we are able to identify the specific orbital characters and the kz dependence of all bands. Combining with band calculations, we find As 4pz and 4px (4py) orbitals contribute significantly to the additional three-dimensional hole-like band and the narrow band, respectively. Also, there are considerable hybridization between the As 4p zand Fe 3d orbitals in the additional hole-like band, which suggests the strong coupling between the unique arsenic zigzag bond layers and the FeAs layers therein. Our findings provide a comprehensive picture of the orbital characters of the low-lying band structure of 112-type iron-based superconductors, which can be a starting point for the further understanding of their unconventional superconductivity.