查看更多>>摘要：A diamond-like carbon (DLC) coating was deposited using a plasma-enhanced chemical vapor deposition (PECVD) method on a polydopamine (PDA) and SiO2 nanoparticle (NP) composite underlayer (PDA + SiO2) to improve its resistance to crack propagation and coating delamination, especially under cyclic loading conditions. Scratch and linear reciprocating wear tests were conducted to identify the critical loads and wear mechanisms of the coating. The PDA + SiO2/DLC coating was also compared with DLC coatings without an underlayer, with a PDA underlayer, and with a trimethylsilane [(CH3)(3)SiH] (TMS) underlayer. The PDA + SiO2/DLC coating significantly increased the critical loads for initial crack propagation, initial delamination, and global delamination. Linear reciprocating wear tests revealed that the PDA + SiO2/DLC coating had a 2.5 times reduction in the wear track cross-sectional area, and the average dimension of the cracks was 40 times smaller than those of the TMS/DLC coating. Therefore, the PDA + SiO2/DLC was superior in preventing coating crack propagation and delamination compared to the TMS/DLC coating.
Liu, HanhuiTariq, Naeem ul HaqRen, YupengLuo, Jing...
11页
查看更多>>摘要：Cold spray (CS) is an emerging deposition technique for the metallization of polymer material to improve its thermal and electrical properties. In this study, pure Al coatings were deposited on polyether ether ketone (PEEK) substrate by CS. Further, the influence of accelerating gas temperature on microstructure and properties (i.e. deposition efficiency, adhesive strength, electrical conductivity, thermal diffusivity and hardness distribution) of the prepared coatings was systematically investigated. Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), the quantitative analysis of oxygen content and Raman spectra results revealed that the prepared coatings were composed of crystalline metallic Al without obvious oxide phases. Moreover, the polymer structure of PEEK substrate remained intact after high-velocity and high-temperature impact during the CS process. The adhesive strength, electrical conductivity and thermal diffusivity of the Al coating increased with increasing accelerating gas temperature. At the accelerating gas temperature of 380 degrees C, a dense and thick Al coating with high adhesive strength was obtained in just two deposition passes. Moreover, multi-pass tests (at high nozzle traverse speed) were performed to understand the deposition mechanism of Al coating on PEEK substrate through analyzing cross-section/surface morphology of samples with different thicknesses. Finally, the deposition mechanism of cold sprayed Al coating on PEEK was proposed.
查看更多>>摘要：The advantages of the Laser Powder Bed Fusion process have led to growing interest from an industrial and academic point of view. However, the diffusion of this process has been slowed by technical challenges that have yet to be resolved, including non-optimal surface quality and low repeatability. To fix these issues and recover surface quality, several treatments are available. Our study focuses on one of them: the Directed Energy Deposition (DED) treatment, which in addition can be exploited for the repair of damaged components. In fact, the proposed study has been conducted by using AISI 316 L alloy both for producing parts throughout the L-PBF process and for coating them. Furthermore, a final Laser Scanning (LS) treatment has been carried out with the aim of maximizing the DED coating performances, in terms of surface roughness, microhardness and micro structural properties. To detect the anomalies that can emerge during the previous surface treatments, an optical monitoring system was implemented in the visible range by using a coaxial CCD camera, to monitor the geometry and morphology of the melt pool related to the DED and to the subsequent LS treatment. The results revealed many improvements in terms of surface roughness for the DED coating and even more for the LS treatment. Moreover, the latter was fundamental to improve the microhardness and the microstructural characteristics of the final coating. The data gathered and analyzed by the implemented monitoring system will allow making the treatment more stable and performing for future applications on complex geometries.
查看更多>>摘要：To improve the bonding strength of diamond-like carbon film (DLC) on Ti6Al4V alloy (TA) substrate, the effect of texturing, carburizing and their combination was investigated. The different surface treatments were carried out on the Ti6Al4V substrate surface by laser texturing and carburizing before the deposition of DLC coatings. Thus, three different DLC coated samples were prepared: 1. DLC coatings with a laser textured substrate, named TDLC; 2. DLC coatings with a laser carburized substrate, named CDLC; 3. DLC coatings with a hybrid laser textured and carburized substrate, named TCDLC. Meanwhile, the only mechanical polished DLC coatings (ODLC) were also prepared for comparison. The adhesion and tribological performance of different DLC coatings were evaluated by using variable depth nano-scratch tests and ball-on-disk wear tests. Among the four kinds of DLC coatings with different surface treatments, the bonding strength of hybrid pretreated coatings (TCDLC: 12.25 N) were highest compared with other three samples (ODLC: 5.73 N; TDLC: 8.72 N; CDLC: 9.28 N). The coupling of the mechanical-physical-chemical effects accompanying laser texturing and carburizing reaction can enhance the wettability and specific surface area of the Ti6Al4V substrate surface, thereby providing a mechanical selflocking and matching chemical property between the Ti6Al4V substrate and DLC coatings.
查看更多>>摘要：This paper presents an experimental and modelling study on the beta-phase depletion behaviour in a vacuum plasma sprayed (VPS) CoNiCrAlY coating during isothermal oxidation. The microstructure of the as-deposited CoNiCrAlY coating before and after oxidation exposure was characterised by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It was shown that the as-deposited CoNiCrAlY coating retained the gamma + beta two phase structure from the feedstock powders. A dual oxide layer, consisting of an outer spinel oxides and an inner alumina scale, was formed in the as-deposited VPS CoNiCrAlY coating during isothermal oxidation. The beta-phase depletion behaviour under the growth of spinel oxide and alumina scale was modelled using Thermo-Calc and DICTRA software. Both Ni and Al fluxes were considered at the boundary to reflect the loss of Ni and Al to form the spinel oxides and alumina scale at the coating surface. Good agreement between the experimental and modelled beta-phase depletion was obtained. The small discrepancy between the experimental measurements and calculated results is likely due to the infinite boundary flux at the beginning of the diffusion calculation and the overestimated Al flux from the experimentally determined oxide growth kinetics.
查看更多>>摘要：This work compares silicide layers grown on Ti-46Al-8Ta (at.%) substrates in pack cementation and in diffusion couple experiments at elevated temperatures. Based on preliminary experiments showing Kirkendall porosity at the coating/substrate interface, a micrometric Ti-10%Si interlayer was deposited by magnetron sputtering prior to siliconizing treatments to prevent excessive Ti diffusion from the substrate. In both types of experiments, the diffusion zone was multi-layered and consisted of Ti/Ta silicides in the outer part and Ti/Ta aluminides in the inner part next to the interface with the alloy. Significant differences were found in the overall thickness and thicknesses of the individual layers. Kinetics of layer growth was followed by thickness measurements. Although inward diffusion of silicon was the dominant mechanism of coating formation, other concurrent processes evidently contributed to the development of the characteristic microstructural features and to the observed differences in thickness.
查看更多>>摘要：ABSTR A C T In order to improve the thickness uniformity of thin film deposited on inner surface, an auxiliary magnetic field was set inside the arc ion plating device and applied during thin film deposition. Effect of magnetic field on the film thickness uniformity was studied through simulation and experiments. Simulation results revealed that magnetic field significantly increased the amount of ions deposited in the pipe. Along the axis of the pipe, the number of deposited ions first decreased and then increased. Experiment results proved that magnetic field changed the trend of the film thickness along the axis of the pipe and raised the ratio of the minimum to the maximum of the film thickness, thereby improving the film thickness uniformity. When magnetic field was applied together with bias, both the film thickness and thickness uniformity increased with the magnetic field intensity.
查看更多>>摘要：The Al-doped Ti-12Si(3)N(4) (wt%) coatings were fabricated on Ti-6Al-4V alloys by laser cladding to enhance their tribological and elevated-temperature anti-oxidation properties. The effects of Al addition on the phase constituents, microstructure characteristics, and performance of the coatings were investigated. The phase constituents in the coatings were the matrix phases of alpha-Ti and Ti3Al and the in-situ reinforcing phases of Ti5Si3 and TiNx. Replacement of Al for Ti refined the coating microstructures, led to the matrix transition from alpha-Ti to Ti3Al, and promoted the dispersed distribution of TiNx and Ti5Si3 reinforcements. Coupled with the dissolved-Al providing solid strengthening, the hardness and wear resistance of the coatings increased with an increase of Al content, and the wear mechanism was mainly abrasive wear. Introducing Al into the coatings effectively enhanced the oxidation resistance of the coatings at 700 degrees C, which was ascribed to the formation of the external Al2O3 protective oxide layer and the densification of the internal TiO2 oxide layer. The Ti-20Al-12Si(3)N(4) coating exhibited the optimal tribological and anti-oxidation performance, and its wear loss and oxidation weight gain were approximately 3.9% and 32.3% of those of the Ti-6Al-4V substrate respectively.
NSTL
Elsevier