稀有金属材料与工程最新文献

CrN films were deposited on 304 stainless steel by DC reactive magnetron sputtering. The effects of nitrogen flow on the microstructure, mechanical and tribological properties were characterized by X-ray diffraction, scanning electron microscopy, atom force microscope, microhardness, wear tester and Nanomap 500LS profile. The results show that with the increase of nitrogen flow, the CrN films exhibit a preferential orientation in the (200) direction. The deposition rate of CrN films decreases with the increase of nitrogen flow. Besides, the surface roughness decreases first and then increases with further increase of nitrogen flow. As nitrogen flow increases from 15 cm³/min to 30 cm³/min, microhardness HV is improved from 5273 MPa to 10422 MPa, and then decreases to 9180 MPa when the nitrogen flow further increases to 35 cm³/min. Wear test results show that the CrN films deposited at nitrogen flow of 30 cm³/min achieve minimum friction coefficient value of 0.93 and wear rate 2.02×10⁻¹⁵ m³·(N·m)⁻¹, which present best wear resistance performance.

Graphene nanoplatelets (GNPs)/Ti composites were fabricated by spark plasma sintering (SPS) and hot-rolling. This work was focused on the effects of rolling reduction on microstructure and mechanical properties of GNPs/Ti composites. The SEM microstructure results show that matrix grains are gradually elongated and the amount of GNPs along the rolling direction rises with the increase of rolling reduction. The tensile test results indicate that the ultimate tensile strength and fracture elongation of the GNPs/Ti composites increase with the increase of rolling reduction. The ultimate tensile strength of the composites at 60% rolling reduction is 680 MPa, which is increased by 33% compared with pure Ti. Hot-rolling process can relieve defects and lead to GNPs aligned along the rolling direction, which improves the tensile property.

Biodegradable magnesium (Mg)-based biomaterials have draw extensively attention, due to the high strength-to-weight ratio, low elastic modulus and good biocompatibility. However, the high corrosion rate is still a major obstacle for the potential clinical applications. Therefore, the highly biocompatible hydroxyapatite (HA) coatings are usually introduced to restrain the interactions between Mg-based substrate and the body fluid environment. In the present paper, HA and strontium (Sr)-doped HA coatings were prepared on Mg-4Zn substrates by electrochemical deposition. The surface properties of the samples were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), three-dimensional laser scanning microscopy (3D LSM) and a contact angle video system. The dynamic ion release, protein adsorption, cell adhesion, proliferation and differentiation behavior of the samples were also evaluated. The results reveal that the incorporation of Sr in the HA coatings leads to lattice distortion and decreased crystallinity. The smaller amount of Mg ion release of the Sr-doped HA coated samples suggests a better corrosion resistance. The improved protein adsorption and initial adhesion of mesenchymal stem cells (MSCs) of the Sr-doped samples should be due to their higher surface roughness and wettability. The introduction of Sr leads to comparable cell proliferation behavior, but significantly improved osteogenic differentiation. It is concluded that the Sr-doped HA coatings are promising candidates for the protective biocompatible coating on Mg-based implants.

With continuously growing oil and gas demand, exploitation of highly sour reservoirs brings large corrosion risks due to the coupling effects of corrosive factors including elemental sulfur, CO₂, and formation water. In the present work, corrosion behavior of P110 tubing steel in simulated oilfield formation water containing elemental sulfur and CO₂ was investigated by immersion tests and electrochemical measurements. The results indicate that increasing temperature accelerates the corrosion rate of P110 tubing steel, promotes the formation of iron sulfide, and causes serious pitting corrosion. However, influence of temperature varies in different temperature range mainly due to the different corrosion-controlling species like CO₂ at low temperatures and elemental sulfur at high temperatures. Based on the results, the coupling effects of elemental sulfur and carbon dioxide were discussed.

Layered Ti-clad diamond/Cu composites used in electronic packaging were prepared by spark plasma sintering (SPS) and hot pressing (HP) separately. The structure was determined by Scanning Electron Microscopy (SEM) and the thermal properties, including the thermal conductivity (TC) and the coefficient of thermal expansion (CTE) were analyzed. The theoretical TC of the layered composites 446.66 W·(m·K)⁻¹ was calculated by the modified Hasselman and Johnson (HJ) model considering the influence of the TiC interface and the CTE was determined by dilatometer. The results show that the sample of SPS has fewer defects than that of HP and the interfacial bonding affects the TC of the composites significantly. A schematic graph of the interface influences is proposed and the TC decreases with the increase of carbide layer thickness and the appearance of pores. In this regard, the composites with a thin carbide layer and no pores should be processed to achieve a high TC.

WC-6Co nanocrystalline composite powders without excess C and decarburization phases were synthesized via a facile route including spraying conversion, calcination and in situ reduction-carbonization processes. The phase constituents obtained by XRD show that the as-prepared powders after each step of the preparation are amorphous, WO₃ and Co₃O₄ phases, WC and Co phases, respectively. Pure WC-Co composite powders could be obtained by a reduction-carbonization process heat treated at 900 °C for 1 h under a hydrogen atmosphere due to the catalytic effect of Co on the carbonation reaction. The effects of heat treatment temperature on phase constituents of powders were investigated in a range of 700∼900 °C. Morphology and microstructure of powders were observed by SEM and HRTEM. The results indicate that the morphology of powder is spherical. The grain size of WC is about 0.36 μm, and the crystalline size of WC is about 56 nm, which indicates that the WC grain is polycrystalline and composed of many crystallites. It is also found that the individual particles of WC are bonded together under the action of Co. Furthermore, a few sintering necks could be observed in the composite powders due to the contacts between WC particles. The stoichiometry of WC-Co composite powders could be adjusted easily. Moreover, the formation process and mechanism of the sphere structure were also discussed in this paper.