Tribological properties of graphite-like carbon coatings coupling with different metals in ambient air and water

Tribological properties of graphite-like carbon (GLC) coatings coupling with different metals of brass, Al, GCr15 and Ti in ambient air and water were investigated. The order of friction coefficients (FCs) was GLC–brass>GLC–Al>GLC–GCr15>GLC–Ti in both of the two environments, but the FC in water was lower than that in ambient air for each tribo-pair. Wear rates (WRs) decreases of the GLC coating in water were observed when sliding against Al, GCr15 and Ti. Though the WR of GLC coating sliding against brass increased in water, it was still comparatively low.     

Corrosion resistance of novel silane-functional polybenzoxazine coating on steel

A novel silane-functional polybenzoxazine (PB-TMOS) coating, with silane groups that can bond to the substrate, was prepared through a dip-coating and thermal curing method. The coating properties were investigated by Fourier transform infrared spectroscopy, solid-state nuclear magnetic resonance spectroscopy, static contact angle measurement, electrochemical and accelerated corrosion tests. The corrosion resistant performance of PB-TMOS coated specimens was considerably enhanced by the high hydrophobicity and water resistance resulted from the dual cross-linking network of polybenzoxazine and Si–O–Si in PB-TMOS matrix.     

巯基有机硅溶胶-凝胶涂层对铜合金H90的腐蚀防护性能研究

目的 研究巯基有机硅溶胶-凝胶涂层对铜合金H90的保护性能。方法 以不同比例的巯基丙基三甲氧基硅烷（MAPMS）与正硅酸乙酯（TEOS）为前驱体,以乙酸作为催化剂,制备含巯基官能团的溶胶-凝胶,并通过浸涂法将该溶胶-凝胶涂层施加到铜合金H90上,并在120 ℃下烘干成膜。利用电化学、盐雾、接触角等一系列的手段考察巯基有机硅溶胶-凝胶涂层在铜合金H90基材上的防腐蚀、疏水性、铅笔硬度等性能。结果 当MAPMS与TEOS物质的量比达到1.5∶1时,自腐蚀电流密度为1.16×10?8 A/cm2,膜层铅笔硬度可达5H,在H90黄铜上的附着力等级达到0级,具有最佳的防腐蚀性能。中性盐雾测试中,物质的量比为1∶1的测试组在第8 d时出现了少量腐蚀斑点,但在接下来的30 d内,腐蚀并未扩大;其他测试组在30 d测试中,未出现明显腐蚀。结论 巯基有机硅溶胶-凝胶涂层具有良好的硬度以及附着力,并能显著提高铜合金H90表面防腐蚀性能。     

Synthesis,densification and oxidation study of lanthanum hexaboride

This paper presents the result of investigation carried out on the synthesis, densification and oxidation studies of LaB₆. LaB₆ was synthesized by boron carbide reduction of La₂O₃. Effect of temperature on product quality was investigated. Pure LaB₆ powder was obtained at 1500 °C, in vacuum. Pressureless sintering at 1950 °C of LaB₆ powder resulted in a density of only 85.1% of the theoretical value. Hot pressing resulted in near theoretical density at the same operating temperature. Hardness and fracture toughness of the dense LaB₆ was measured as 20 GPa and 3.02 MPa m^1/2 respectively. Oxidation study by thermogravimetry revealed that oxidation starts slowly at 500 °C and accelerates at 700 °C. Isothermal oxidation study revealed that protective oxide layer forms on LaB₆ surface on oxidation at 900 °C. The presence of protective continuous oxide layer on the surface was observed even after 64 h exposure in air atmosphere.     

Fretting-corrosion mapping of tin-plated copper alloy contacts

The fretting corrosion of tin-plated contacts is influenced by several factors including frequency, amplitude, temperature, humidity, normal load, current load, etc. The present paper aims to develop fretting-corrosion maps to assess the fretting corrosion behaviour of tin-plated copper alloy contacts under varying experimental conditions. The extent of change in contact resistance up to 20 000 fretting cycles and the nature of changes, such as, the extent of fretting wear and oxidation, assessed by surface analytical techniques, are used to develop the fretting-corrosion maps. The fretting-corrosion maps are segmented into various zones depending on the predominant processes that occur under a given set of conditions. The proposed fretting-corrosion maps are not quantitative to predict the exact life-time of the contact. However, they will be useful to draw some guidelines about the performance of the tin-plated copper alloy contacts under various conditions.     

Graphene woven fabric-reinforced polyimide films with enhanced and anisotropic thermal conductivity

Due to the growing needs of thermal management in modern electronics, polyimide-based (PI) composites are increasingly demanded in thermal interface materials (TIMs). Graphene woven fabrics (GWFs) with a mesh structure have been prepared by chemical vapor deposition and used as thermally conductive filler. With the incorporation of 10-layer GWFs laminates (approximate 12 wt%), the in-plane thermal conductivity of GWFs/PI composite films achieves 3.73 W/mK, with a thermal conductivity enhancement of 1418% compared to neat PI. However, the out-of-plane thermal conductivity of the composites is only 0.41 W/mK. The in-plane thermal conductivity exceeds its out-of plane counterpart by over 9 times, indicating a highly anisotropic thermal conduction of GWFs/PI composites. The thermal anisotropy and the enhanced in-plane thermal conductivity can be attributed to the layer-by-layer stacked GWFs network in PI matrix. Thus, the GWFs-reinforced polyimide films are promising for use as an efficient heat spreader for electronic cooling applications.     

N-rich Zr3N4 nanolayers-dependent superhard effect and fracture behavior in TiAlN/Zr3N4 nanomultilayer films

The TiAlN/Zr₃N₄ nanomultilayer films were successfully fabricated by alternatively inserting nitrogen-rich orthorhombic o-Zr₃N₄ monolayers onto TiAlN nanolayers via magnetron sputtering, and then the Zr₃N₄ layer thicknesses (l_Zr3N4)-dependent microstructure, hardness and deformation behavior was further explored. At a thin l_Zr3N4 of =1.1 nm, Zr₃N₄ nanolayers were forced to crystallize with a metastable cubic c-Zr₃N₄ pseudocrystal structure and form (111)-oriented c-TiAlN/c-Zr₃N₄ coherent interfaces with c-TiAlN sublayers, thereby achieving maximum H of 34.7 GPa yet superior toughness. For a thicker l_Zr3N4, Zr₃N₄ nanolayers gradually transformed from the pseudocrystal c-Zr₃N₄ to bulk-energy-stabilized o-Zr₃N₄; it destroyed the coherent growth and yielded fast drop in both H and fracture toughness. Furthermore, the indenter induced deformation behavior of the nanomultilayer with l_Zr3N4 = 4.2 nm was observed by transmission electron microscopy (TEM), thus indicating that severe plastic deformation in the nanomultilayer is primarily accommodated via the bending of nanolayers and formation of nanoscale longitudinal and lateral cracks rather than the formation of large-scale cracks because of crack deflections that can be attributed to layer interfaces.     

Preparation and mechanical properties of β-Zr2O(PO4)2: A soft and damage tolerant ceramic with machinability and good thermal shock resistance

Damage tolerant and easily machinable ceramics play important roles in the field of thermal sealing and insulation. Herein, a soft and machinable β-Zr₂O(PO₄)₂ ceramic with excellent thermal shock resistance is reported through detailed investigation on its mechanical properties. β-Zr₂O(PO₄)₂ exhibits low hardness (5.9 GPa), low Pugh’s ratio (G/B = 0.36) and good thermal shock resistance. It also can be machined by WC tools and tolerant to damage. The damage tolerance is demonstrated by the residual strength versus indentation load curve as well as the load-displacement curve during compression strength test. From the crystal structure point of view, the mechanism that underpins the damage tolerance of β-Zr₂O(PO₄)₂ is the anisotropic chemical bonding within the crystal structure, which results in low and anisotropic shear deformation resistance. The possible slip systems of β-Zr₂O(PO₄)₂ are (010)[100] and (100)[010].     

Diffusion and electrotransport of some transition elements in (b.c.c.) thorium

Diffusion and electrotransport parameters of the transition elements molybdenum, rhenium, tungsten and zirconium in β thorium were measured, for the temperature range 1660–1945 K. For each solute element, except zirconium, the measurement was made at four different temperatures, where as for zirconium, studies were performed for only two temperatures 1770 and 1870K. Our results indicate that all four solute elements migrate to the anode in b.c.c. thorium with mean Z¹ values of −6.6 for Mo, −4.6 for Re, −8.2 for W and about −2.5 for Zr. The results also indicate that molybdenum, rhenium and tungsten diffuse much faster in β thorium than zirconium which suggests a correlation between solute atom electric mobility and diffusivity with the atomic sizes of both the solute and matrix atom. Results of the diffusion studies yield the following equations of diffusion for Molybdenum: D_Mo = 15.1 exp(−51,500/RT) Renium: D_Re = 4.04 × 10⁻³ exp(−20,100/RT) Tungsten: D_W = 0.103 exp(−38,100/RT) Zirconium: D_Zr = 1.70 × 10⁴ exp(−91,700/RT).     

纤维增强环氧树脂复合材料抗固体颗粒流冲蚀磨损研究进展

在生产生活中,固体颗粒流冲蚀磨损会造成经济损失,并且存在安全隐患。环氧树脂复合材料具有较好的强度和耐冲蚀性能,被广泛地应用于颗粒流冲蚀磨损工况下。为进一步提升环氧树脂的耐冲蚀性能,通常通过填料来改性环氧树脂,其中纤维增强环氧树脂表现出优异的耐固体颗粒流冲蚀性能,使得环氧树脂复合材料的应用更加广阔。根据纤维的种类可以将其分为无机纤维(玻璃纤维或碳纤维)、自然纤维及混和纤维增强环氧树脂复合材料。综述了纤维增强环氧树脂复合材料抗固体颗粒流冲蚀性能的研究现状,讨论了不同的纤维增强复合材料表现出的冲蚀行为(塑性、脆性、半塑性、半脆性),重点分析和对比了不同纤维填料特性(纤维类型、纤维含量、纤维取向)增强环氧树脂复合材料在不同工况条件(冲蚀角度、冲蚀速度、磨粒特性)下的耐冲蚀磨损性能,阐明了不同纤维增强环氧复合材料的冲蚀模式和抗冲蚀机理,指出其现存的问题并展望其发展方向和前景。