Kinds Of Composite Coatings Research Articles

Influence of different introduction modes of metal Ag into plasma sprayed Al2O3 coating on tribological properties

Al2O3 coating and Al2O3/Ag (10%) composite coating were prepared on the surface of GH4169 superalloy by the atmospheric plasma spraying technology. And an in-situ synthesis method was applied to introduce the Ag particles into a part of Al2O3 coatings to obtain Al2O3/Ag(synthesis) composite coating. Then, the microstructure and mechanical properties of these three Al2O3-based coatings were systematically studied in this work. In order to reveal the lubrication characteristics of Ag, their friction tests were carried out at room temperature (RT), 400 °C, 600 °C and 800 °C, respectively. The results showed that both microstructure and mechanical properties of Al2O3/Ag(synthesis) composite coating were better than that of Al2O3/Ag (10%) composite coating because many pores and cracks produced during the direct spraying. Although the friction coefficients of two kinds of composite coatings were close to that of Al2O3 coatings at RT, their wear rates were both greatly decreased due to the introduction of Ag. In addition, the lubricating performance of Ag was not enough to reduce their friction coefficients when friction temperature is lower than 600 °C. However, the friction coefficients of these composite coatings were both reduced to about 0.3 at 800 °C . At this time, the Al2O3/Ag(synthesis) composite coating also exhibited a lower wear rate because of its dense microstructure and excellent mechanical properties.

ANTICORROSION PROPERTIES OF Zn–Al–Mg–ZnO COMPOSITE COATING PREPARED BY COLD SPRAYING

Two kinds of composite coatings, Zn[Formula: see text]Al[Formula: see text]Mg5ZnO[Formula: see text] and Zn[Formula: see text]Al[Formula: see text]Mg5ZnO[Formula: see text], were prepared on steel matrix (Q235) by cold spraying. The Zn, Al, Mg, and ZnO in raw materials were calculated by percentage of mass. The morphology of the original coating was observed by scanning electron microscopy (SEM) and characterized by energy dispersive spectroscopy (EDS). It was found that the microstructures of Zn[Formula: see text]Al[Formula: see text]Mg5ZnO[Formula: see text] and Zn[Formula: see text]Al[Formula: see text]Mg5ZnO[Formula: see text] composite coatings prepared by cold spraying were compact without oxidation products, and the plastic deformation of powder particles was significant. The friction and wear test data of the two coatings showed that the Zn[Formula: see text]Al[Formula: see text]Mg5ZnO[Formula: see text] coating had longer-lasting protective properties and wear resistance under the same conditions. Neutral salt spray test (NSS) and electrochemical accelerated corrosion test were carried out on samples at different time periods. The results of samples’ corrosion microstructure and electrochemical curves showed that Zn[Formula: see text]Al[Formula: see text]Mg5ZnO[Formula: see text] and Zn[Formula: see text]Al[Formula: see text]Mg5ZnO[Formula: see text] have good electrochemical protection performance, and Zn[Formula: see text]Al[Formula: see text]Mg5ZnO[Formula: see text] coating has better protection effect.

Preparation and high temperature oxidation resistance of laser deposited Ti5Si3/MoSi2/Mo5Si3 reinforced α-Ti/NiTi composite coatings

Three kinds of composite coatings with different proportion of preplaced Ni-Mo-Si powders were fabricated on Ti6Al4V alloy by laser depositing to enhance the high temperature oxidation resistance. The microstructures of composite coatings were studied by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The microhardness of composite coatings was measured by Vickers microhardness tester. The samples of composite coatings and Ti6Al4V alloy underwent isothermal oxidation tests at 800 °C, and the oxidation mechanism was analyzed by thermodynamics and kinetics. Results indicate that composite coatings mainly include Ti5Si3, MoSi2 and Mo5Si3 as enhanced phases and α-Ti/NiTi as matrix, and have metallurgical bonding with substrate. With the increase of Ni content in composite coatings, the inter-metallic compounds α-Ti/NiTi matrix increased and the hard phase Ti5Si3 refined. The average microhardness of composite coatings is 2.6, 2.4, 2.3 times of that of Ti6Al4V alloy, respectively. Oxidation mass gain of the coatings are 5.6%, 12% and 57.9% of that of the substrate at 800 °C for 100 h, respectively, and oxide scales of the coatings are continuous and dense, showing good oxidation resistance at high temperatures.

Effects of carbon nanotubes on hardness and internal stress in Ni–P coatings

Nickel–phosphorus carbon nanotube (CNT) composite coatings were prepared via brush electroplating. The CNTs were added in amounts of 0, 0·5, 1·0 and 2·0 g L−1. Half samples of these coatings were heated at 400°C for 1 h to obtain crystalline Ni–P CNT composite coatings. The hardness and internal stress of two kinds of composite coatings were studied. The results showed that the addition of CNTs improves the microhardness of crystalline Ni–P coatings; the higher the added CNT, the greater increase in microhardness. However, the effects are completely different for amorphous coatings. Heat treatment greatly increased the microhardness of amorphous Ni–P platings, but the microhardness of Ni–P based CNT composite coatings only slightly increased. The microhardness of the crystalline Ni–P based CNT composite coatings was lower than that of the crystalline Ni–P platings and was not insensitive to the changes in the added amounts of CNTs. The addition of CNTs significantly reduced the microscopic internal pressure stress of crystalline coatings; the higher the added CNT, the lower the microscopic internal pressure stress.