Printing Force Effect on Conductive Silver Tracks: Geometrical, Surface, and Electrical Properties

This study provides a quantitative contribution to the determination of the printing force effect on silver tracks properties deposited by screen-printing. A water-based silver paste containing 75% of silver particles was formulated and printed by screen-printing process. Printing force effect on line definition, thickness, width, roughness, and on electrical properties was evaluated. A minimum theoretical line width of 100 μm was aimed. A 114 μm width and 14 μm thickness was achieved with a printing load of 5 kg. It was demonstrated that higher forces were needed to enhance line definition and to print thicker and narrower lines. On the other hand, it was shown that printing pressure had no effect on line roughness and electrical conductivity of printed lines, after sintering. Electrical resistivity values varied from 18 × 10^?9 to 30 × 10^?9 Ω · m after sintering. Sheet resistance was also measured on sintered printed films. It varied from 4.5 to 5.9 m · Ω/square for thicknesses varying from 3.9 to 6.6 μm.     

Tribological Performance of Ni<Subscript>3</Subscript>Al Matrix Self-Lubricating Composites Containing Multilayer Graphene Prepared by Additive Manufacturing

In order to improve tribological performance of Ni₃Al-based alloy, Ni₃Al matrix composites containing 1.5 wt.% multilayer graphene (MLG) are prepared through additive manufacturing (AM) and spark plasma sintering (SPS), which are denoted as NMAM and NMSPS, respectively. Tribological behaviors of NMAM and NMSPS against Si₃N₄ balls are researched under constant speed (0.2 m/s) and varied loads (from 4 to 16 N) for evaluating the tribological properties of NMAM and NMSPS. The results present that NMAM exhibits the excellent tribological properties [low friction coefficients (0.26-0.40) and considerable wear resistance (2.8-4.6 × 10^?5 mm³ N^?1 m^?1)] as compared to NMSPS, which attributes to the uniform enrichment of MLG with properties of high tensile strength and being easily sheared off on the worn surfaces. Owing to the use of spherical prealloyed powder containing multilayer graphene and the characteristics of layer by layer depositing in the AM process, NMAM has a more compact and uniform substrate, which persistently provides a source of the formation of continuous and stable frictional layer. Due to the characteristics of AM rapid solidification, NMAM has the small grain size and well-compacted microstructure, which can effectively reduce the probability of spalling wear and lead to the increase in wear resistance of materials. The research can offer the reference for self-lubricating materials prepared by AM technology.     

Synthesis of Porous Silicon Nitride-Boron Nitride Composites by Gel-Casting and PIP

The Si₃N₄-BN composites were prepared by gel-casting and precursor infiltration and pyrolysis route using borazine as the precursor. The composition, mechanical, microstructural, and dielectric properties of the composites were investigated. The composites are composed of h-BN, α-Si₃N₄, and β-Si₃N₄. The typical density, porosity, flexural strength, elastic modulus, and fracture toughness of the composites are 2.21 g/cm³, 17.8%, 185.59 MPa, 69.13 GPa, and 2.47 MPa m^1/2, respectively. The dielectric constant and loss tangent of the composites are 4.507-4.635 and 1.06 × 10^?3-1.97 × 10^?3 at the frequency of 7-18 GHz. Desirable properties of the composites have been achieved.     

石墨烯对铜基制动材料的性能影响

目的为了提高铜基制动材料的力学性能和摩擦学性能,选用石墨烯作为增强填料添加到铜基制动材料中,研究石墨烯对铜基制动材料性能的影响。方法采用粉末冶金的方法制备了石墨烯含量(质量分数,后同)分别为0%、0.2%、0.4%、0.6%、0.8%的铜基复合材料,并对不同试样的力学性能和摩擦磨损性能进行比较。结果含有石墨烯的试样硬度为46.4~54.2HB,高于未添加石墨烯试样的硬度(44.5HB)。含有石墨烯的试样抗弯强度为250~418 MPa,均高于未添加石墨烯试样的抗弯强度(218 MPa),其中石墨烯含量为0.4%的试样的硬度和抗弯强度最大,分别为54.2HB和418 MPa。随着石墨烯含量的增加,材料的密度逐渐下降。当石墨烯含量为0.2%~0.4%时,材料摩擦系数的稳定性提高且磨损率降低;当石墨烯含量为0.6%~0.8%时,材料摩擦系数的稳定性下降且磨损率变大。当石墨烯含量为0.4%时,材料的摩擦系数最稳定,摩擦系数的方差为0.3×10~(-3)(未添加石墨烯的试样为1.4×10~(-3)),磨损率最低,位于0.136×10~(-6)~0.185×10~(-6) mm~3/(N·m)之间(未添加石墨烯的试样位于0.42×10~(-6)~0.82×10~(-6)mm~3/(N·m)之间)。结论少量的石墨烯(0.2%~0.4%)可以显著提高铜基制动材料的硬度和弯曲强度,其中石墨烯含量为0.4%时,制成的制动材料的机械性能最佳,同时试样的摩擦系数稳定,磨损率较低。     

Electrochemical Corrosion Behavior of Thermal-Sprayed Stainless Steel-Coated Q235 Steel in Simulated Soil Solutions

The corrosion behavior of a thermal-sprayed stainless steel (SS)-coated Q235 steel has been investigated in simulated soil solutions using electrochemical measurements, x-ray photoelectron spectroscopy analysis, and scanning electron microscope. The as-received Q235 steel and galvanized steel for grounding grids were also examined for the purpose of comparison. The effects of pH value of testing solutions have been examined. The thermal-sprayed SS-coated steel showed the best corrosion resistance among the three kinds of materials. With increasing pH value, the corrosion resistance of SS-coated Q235 steel increased. In weak alkaline solutions, the SS-coated Q235 steel showed the largest polarization resistance (3.2 × 10⁵ Ω cm²), the lowest anodic current density (1.4 × 10^?2 μA/cm²), and the largest film resistance (4.5 × 10⁶ Ω cm²), suggesting that the coated steel has the best corrosion resistance in weak alkaline environment. Related corrosion mechanisms are also discussed.     

The Sliding Wear and Friction Behavior of M50-Graphene Self-Lubricating Composites Prepared by Laser Additive Manufacturing at Elevated Temperature

M50 steel is widely applied to manufacture aircraft bearings where service lives are mainly determined by the friction and wear behaviors. The main purpose of this study is to investigate the tribological behaviors and wear mechanisms of M50-1.5 wt.% graphene composites (MGC) prepared by laser additive manufacturing (LAM) (MGC-LAM) sliding against Si₃N₄ ball from 25 to 550 °C at 18 N–0.2 m/s. XRD, EPMA, FESEM, and EDS mapping were conducted to understand the major mechanisms leading to the improvement in the sliding behavior of MGC-LAM. The results indicated that MGC-LAM showed the excellent friction and wear performance at 25-550 °C for the lower friction coefficient of 0.16-0.52 and less wear rate of 6.1-9.5 × 10^?7 mm³ N^?1 m^?1. Especially at 350 °C, MGC-LAM obtained the best tribological performance (0.16, 6.1 × 10^?7mm³ N^?1 m^?1). It was attributed to the dense coral-like microstructure, as well as the formed surface lubricating structure which is composed of the upper uniform lubricating film with massive graphene and the underneath compacted layer.     

A Study on the Passivation Behavior and Semiconducting Properties of Gamma Titanium Aluminide in 0.1 N H2SO4, HNO3, and HClO4 Acidic Solutions

The study focuses on the passivation behavior of single-gamma-phase titanium aluminide in acidic solutions with a particular emphasis on the role of oxidizing strength in characteristics of passive layer. The report includes potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies along with Mott-Schottky analysis in order to determine the corrosion behavior of the alloy and the semiconducting properties of the scale formed during exposure to acidic environment. Passive current density measured from potentiodynamic polarization curve, polarization resistance (R _p) estimated by EIS, defect density, and flatband potential drawn from Mott-Schottky analysis are mainly used in estimating the ability of passive film formed on alloy in protecting it against high corrosion rates in Sulfuric acid (a non-oxidizing acid), perchloric acid, and nitric acid (oxidizing acid with different oxidizing strength). The results show that passive current density (i _pass) in Sulfuric acid is 2.67 × 10^?5 A cm^?2, which is 2.5 and 3 times greater than the values obtained in perchloric acid (i _pass = 9.91 × 10^?6) and nitric acid (i _pass = 7.98 × 10^?6), respectively. EIS data reveal that the value of R _p in sulfuric acid (20 kΩ cm²) is about three and five times smaller than that its value in perchloric acid and Nitric acid, respectively. Mott-Schottky analysis shows that the passive layer exhibits an n-type semiconducting characteristics irrespective of acidic environment. The greatest and the smallest values of donor density (N _D) are obtained for the passive scale formed in sulfuric acid (N _{D, H2SO4} = 18.36 × 10¹⁹) and nitric acid (N _{D, HNO3} = 13.13 × 10¹⁹), respectively. The report concludes that characteristics of the passive scale are directly affected by reduction potential of the acid, which is the criterion of its oxidizing strength. An increase in the oxidizing strength of the acidic solution results in formation of more protective and less conductive layer on γ phase titanium aluminide.     

Compressive Characterization of Single Porous SiC Hollow Particles

Silicon carbide hollow spheres are compression tested to understand their energy absorption characteristics. Two types of particles having tap densities of 440 kg/m³ and 790 kg/m³ (referred to as S1 and S2, respectively) were tested in the present study. The process used to fabricate the hollow spheres leads to porosity in the walls, which affects the mechanical properties of the hollow spheres. The porosity in the walls helps in obtaining mechanical bonding between the matrix material and the particle when such particles are used as fillers in composites. The single-particle compression test results show that the S1 and S2 particles had fracture energies of 0.38 × 10^?3 J and 3.18 × 10^?3 J, respectively. The modulus and fracture energy of the particles were found to increase with increasing diameter. However, the increasing trend shows variations because the wall thickness can vary as an independent parameter. Hollow particle fillers are used in polymer and metal matrices to develop porous composites called syntactic foams. The experimentally measured properties of these particles can be used in theoretical models to design syntactic foams with the desired set of properties for a given application.     

Copper-Filled Electrically Conductive Adhesives with Enhanced Shear Strength

In this study, the effects of diethyl carbitol (diluent) and tertiary amines on the electrical, mechanical, and rheological properties of the Cu-filled polyurethane-based electrically conductive adhesives (ECAs) were investigated. Significant difference could be observed in the electrical resistivity and shear strength of ECA prepared with different amount of diethyl carbitol. Reduced electrical resistivity was found in ECAs prepared with addition of tertiary amines, but no obvious change was observed in the shear strength of the ECA joint. Rheological property of the ECA paste was investigated in order to understand the correlation of the viscosity of ECA paste and electrical resistivity and shear strength of ECA joint. Results revealed that decrease in viscosity of the ECA paste reduced electrical resistivity and enhanced shear strength of ECA joint. A Cu-filled polyurethane-based ECA with considerably low electrical resistivity at the magnitude order range of 10^?3 Ω cm, and significantly high shear strength (above 17 MPa) could be achieved.     

Preparation and characterization of ZnO/Cu/ZnO transparent conductive films

ZnO/Cu/ZnO transparent conductive thin films were prepared by RF sputtering deposition of ZnO target and DC sputtering deposition of Cu target on n-type (001) Si and glass substrates at room temperature. The morphology, structure, optical, and electrical properties of the multilayer films were characterized by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), UV/Vis spectrophotometer, and Hall effect measurement system. The influence of Cu layer thickness and the oxygen pressure in sputtering atmosphere on the film properties were studied. ZnO/Cu/ZnO transparent conductive film fabricated in pure Ar atmosphere with 10 nm Cu layer thickness has the best performance: resistivity of 2.3×10-4 Ω·cm, carrier concentration of 6.44×1016cm-2 , mobility of 4.51cm2·(V·s)-1 , and acceptable average transmittance of 80 % in the visible range. The transmittance and conductivity of the films fabricated with oxygen are lower than those of the films fabricated without oxygen, which indicates that oxygen atmosphere does not improve the optical and electrical properties of ZnO/Cu/ ZnO films.     

Behavior of Dental/Implant Alloys in Commercial Mouthwash Solution Studied by Electrochemical Techniques

This study investigates the electrochemical behavior of the various dental materials: Paliag (Ag-Pd based), Wiron 99 (Ni-Cr based), Cp-Ti (commercial pure titanium), and experimental Ti12Mo5Ta alloy in commercial mouthwash solution with 500 ppm F^? (Oral B^®) and compares it with the behavior of the same dental materials in artificial saliva. Linear potentiodynamic polarization (LPP) and electrochemical impedance spectroscopy (EIS) are the electrochemical procedures of investigation. The passivation of all dental samples in artificial saliva and mouthwash solution occurred spontaneously at open circuit potential. The corrosion current density of all tested dental materials in mouthwash solution were low (1-2 μA/cm²). The results suggest a non-predominant fluoride effect on the passive layer formed on all samples at open circuit potential. No passivation could be established with Paliag alloy when polarized in mouthwash solution. The EIS results confirm that all dental sample exhibit passivity in mouthwash solution at open circuit potential (polarization resistance was around 5 × 10⁵ Ω cm²). For Paliag alloy after LPP in mouthwash solution the protectiveness passive layer was no more present. The corrosion resistances of four dental materials in mouthwash solution are in the following order: Ti12Mo5Ta > Cp-Ti > Wiron 99 > Paliag.     

Friction and wear behaviours of in situ reduced graphene oxide reinforced zirconia ceramic

The tribological behaviour of zirconia composites reinforced by in situ reduced graphene oxide (IrGO) was investigated by a rotating ball-on-plate configuration at room temperature, and was followed by a comparison with composites reinforced by pre-reduced graphene oxide(rGO). The results indicate that both the friction and wear resistance of ceramics increase with the incorporation of graphene oxide (GO). IrGO is better for enhancing the tribological performance of zirconia than rGO. The wear rate decreases by up to one order of magnitude (from 2.33 × 10⁻⁵ mm³·N⁻¹·m⁻¹ to 4.66 × 10⁻⁶ mm³·N⁻¹·m⁻¹) with 0.5 wt% GO. A protective tribofilm containing reduced graphene oxide forms at wear surfaces of ceramics, and the protruding-out of rGO is more pronounced. The main wear mechanism changes from severe delamination to plastic deformation and micro-cracking with increasing GO content. The analysis of wear tracks for ceramics with GO additives by Raman mapping reveals a decrease in the tetragonal-monoclinic phase transformation after sliding wear, which is regarded as the intrinsic reason for the improved wear resistance.     

Effect of Strain Rate on Tensile Properties of Carbon Fiber Epoxy-Impregnated Bundle Composite

The tensile tests for high tensile strength polyacrylonitrile (PAN)-based (T1000GB) carbon fiber epoxy-impregnated bundle composite at various strain rates ranging from 3.33 × 10^?5 to 6.0 × 10² s^?1 (various crosshead speeds ranging from 8.33 × 10^?7 to 1.5 × 10¹ m/s) were investigated. The statistical distributions of the tensile strength were also evaluated. The results clearly demonstrated that the tensile strength of bundle composite slightly increased with an increase in the strain rate (crosshead speed) and the Weibull modulus of tensile strength for the bundle composite decreased with an increase in the strain rate (crosshead speed), there is a linear relation between the Weibull modulus and the average tensile strength on log-log scale.     

Effect of WS2 particle size on mechanical properties and tribological behaviors of Cu-WS2 composites sintered by SPS

The mechanical properties and tribological behaviors of Cu-WS₂ composites fabricated by spark plasma sintering (SPS) using two different WS₂ particle sizes of 0.6 and 5.0 µm and Cu powders as raw materials were investigated. The results indicate that the bending strength and tribological behavior of Cu-WS₂ composites are greatly affected by the size of WS₂ particles. The bending strength of Cu-WS₂ composites with the WS₂ particle size of 5.0 μm is 292.2 MPa. As the size of WS₂ particle decreases to 0.6 µm, the bending strength also decreases to 181.5 MPa. Moreover, as the WS₂ particle size decreases from 5.0 to 0.6 µm, the wear rate of Cu-WS₂ composite sharply increases from 2.99×10^?14 to 6.13×10^?14 m³/(N·m) and its friction coefficient increases from 0.158 to 0.172. The size of WS₂ particle (5.0 μm) plays an important role in forming transfer film formed on the counter-face. The sample with 5.0 μm WS₂ particle forms smoother and more continuous transfer film, which results in a low wear rate and friction coefficient of the Cu-WS₂ composites.     

Temperature-Dependent Properties of Spray-Deposited ITO Thin Films

Sprayed indium tin oxide (ITO) thin films are synthesized by mixing adequate quantities of ethanolic solutions of indium trichloride and stannic chloride at different substrate temperatures. The pyrolytic decomposition temperature affects the properties and morphology of ITO samples. X-ray diffraction results showed that the films are polycrystalline with cubic structure and exhibit preferential orientation along (222) plane. The SEM and AFM studies indicated that the surface morphology of the samples increases with substrate temperature. The typical I₅₀₀ sample is composed of cubic grains and has carrier concentration of 3.26 × 10²⁰ cm^?3 and mobility of 9.77 cm²/V s. The electrical resistivity of ITO films decreased with increasing deposition temperature. The highest figure of merit of film is 4.4 × 10^?3 Ω^?1. Optical absorption studies reveal that films are highly transparent in the visible region and band gap increases with substrate temperature owing to Moss-Burstein effect.     

Electrically Insulative Performances of Ceramic and Clay Films Deposited via Supersonic Spraying

Supersonic spray coating techniques were applied to deposit ceramic and clay particles as films for use in electrical insulation. TiO₂ and Al₂O₃ ceramics were aerosol-deposited under vacuum while kaolinite, montmorillonite, and bentonite clays were deposited by cold spraying in open air. The electrical resistivity of Al₂O₃ and TiO₂ were ~10⁹ and ~10⁸ Ω cm, respectively. The resistivity of kaolinite and montmorillonite were ~10¹² Ω cm. Bentonite showed the lowest electrical resistivity of ~10⁹ Ω cm among the clays because of the high cation exchange capacity of the material. The film surface morphologies and mechanical properties in the form of hardness and scratchability were also investigated.     

Additive Manufacturing of Syntactic Foams: Part 1: Development,Properties, and Recycling Potential of Filaments

This work focuses on developing filaments of high-density polyethylene (HDPE) and their hollow particle-filled syntactic foams for commercial three-dimensional (3D) printers based on fused filament fabrication technology. Hollow fly-ash cenospheres were blended by 40 wt.% in a HDPE matrix to produce syntactic foam (HDPE40) filaments. Further, the recycling potential was studied by pelletizing the filaments again to extrude twice (2×) and three times (3×). The filaments were tensile tested at 10^?4 s^?1, 10^?3 s^?1, and 10^?2 s^?1 strain rates. HDPE40 filaments show an increasing trend in modulus and strength with the strain rate. Higher density and modulus were noticed for 2× filaments compared to 1× filaments because of the crushing of some cenospheres in the extrusion cycle. However, 2× and 3× filament densities are nearly the same, showing potential for recycling them. The filaments show better properties than the same materials processed by conventional injection molding. Micro-CT scans show a uniform dispersion of cenospheres in all filaments.     

Ultrafine eutectic Ti x Sn y /TiNi composites with high damping capacity

Three kinds of bulk-type ultrafine Ti _x Sn _y /TiNi (Ti _x Sn _y represents Ti₃Sn, Ti₂Sn, and Ti₅Sn₃ or Ti₆Sn₅) composites with homogeneous eutectic microstructure were prepared by arc melting. The composites exhibit high damping capacity (tanδ greater than 1 × 10^?2) and enhanced mechanical strength (the highest fracture strength is 2.15 GPa). The damping capacity originates from TiNi and Ti₃Sn, while the eutectic contributes to the mechanical strength.     

Structural,Microstructure, Mechanical and Electrical Properties of Porous Zr4+-Cordierite Ceramic Composites

Zirconium-cordierite ceramic composites have been synthesized by a co-precipitation method using MgCl₂·6H₂O, NaAlO₂, Na₂SiO₃·5H₂O, and ZrOCl₂·8H₂O as starting materials. XRD, FT-IR, and SEM techniques were employed to study the effect of zirconium on the crystal structure and microstructure of the samples. XRD results revealed that spinel MgAl₂O₄ and t-ZrO₂ phases were predominant in the samples with low Zr⁴⁺ content (10 wt.%), whereas zircon ZrSiO₄ was predominant with high Zr⁴⁺ content (≥15 wt.%). The densification behavior was improved from 30.4 to 44.6% of the theoretical density (2.6 g/cm³) at 15 wt.% of Zr⁴⁺. However, microhardness of the sintered samples was enhanced from 7.1 to 7.5 GPa with increasing the Zr⁴⁺ dose from 0 to 25 wt.%. On the other hand, the gradual increase in Zr⁴⁺ content from 0 to 25 wt.% led to suppression in the electrical resistivity (ρ) from 16.6 to 2.8 × 10⁹ Ω/cm, respectively. In addition, the dielectric permittivity (ε) of the pure cordierite was decreased with Zr⁴⁺ ion addition. The maximum dielectric permittivity (ε) at low frequencies (10 MHz) was 18.7 at 10 wt.% Zr⁴⁺ content, whereas at high frequencies (1 GHz) it was 38.8 at 15 wt.% Zr⁴⁺ content.     

Thermomechanical properties of TiC particle-reinforced tungsten composites for high temperature applications

Tungsten and tungsten alloys are widely used in high temperature environments where arc ablation or mechanical deformation and damage are the main sources of materials failure. For high temperature critical applications in thermomechanical environments, however, the low strength limits the use of tungsten and tungsten alloys. Hence, new tungsten based materials with good high temperature thermomechanical properties need to be developed in order to extend the use of tungsten. TiC particle-reinforced tungsten based composites (TiC_p/W) were fabricated by hot pressing at 2000 °C, 20 MPa in a vacuum of 1.3×10⁻³ Pa. The composites were examined with respect to their thermophysical and mechanical properties at room temperature and at elevated temperature. Vickers hardness and elastic modulus increased with increasing TiC content from 0 to 40 vol.%. The highest flexural strength, 843 MPa, and the highest toughness, 10.1 MPa m^1/2, of the composites at room temperature were all obtained when 20 vol.% TiC particle were added. As the test temperature rose, the flexural strength of the TiC_p/W composites firstly increased and then decreased, except in the monolithic tungsten. The highest strength of 1155 MPa was measured at 1000 °C in the composite containing 30 vol.% TiC particles. The strengthening effect of TiC particles on the tungsten matrix is more significant at high temperatures. With the addition of TiC particles, the thermal conduction of tungsten composites was drastically decreased from 153 W m⁻¹ K⁻¹ for monolithic W to 27.9 W m⁻¹ K⁻¹ for 40 vol.% TiC_p/W composites, and the thermal expansion was also increased. The new composites are successfully used to make high temperature grips and moulds.