Study on self-lubricating coating prepared by electrospark deposition

Abstract

It is still a matter to get thick self-lubricating coating with good tribological properties and strong bond. In the present work, Cu/BN coating was produced by electrospark deposition on mild steel. Chemical compatibility of Cu/BN/steel was analysed. The effects of the electric capacitance and deposition time on coating performance were studied, and the microscopic morphologies and structure of the coating were analysed. The results showed that there were no reactions in Cu/BN/ steel. With the increase in capacitance, the surface roughness, friction coefficient and wear mass loss all increased. With the increase in deposition time, the surface roughness increased. Scanning electron microscope images showed that the lubricating coating is smooth, and thick coating (y100 mm) was formed with metallurgical bond. IntroductionFriction is a common phenomenon in nature, and friction and wear are the main causes of high energy consumption in industrial production. 1 Friction causes a large amount of mechanical energy loss, while wear is an important reason for machinery failure. According to statistics, friction accounts for 30% of the energy consumption in industrialised countries. One important way to reduce friction coefficient and improve wear resistance is to use self-lubricating coatings on the surface of the friction pair. 2,3 Self-lubricating coatings can improve tribological performance of contacting surfaces and extend component lifetime. 4 Researchers have been studying self-lubricating coatings prepared by different methods, including chemical vapour deposition (CVD), 5 physical vapour deposition (PVD), 6-8 thermal spraying, 9,10 laser cladding, 11,12 sol-gel 13 and so on. So far, CVD and PVD are the most popular ways to prepare self-lubricating coatings. However, these coatings have small thickness of only several up to .10 mm. 5,6,14 These coatings also have low bonding strength between the coating and substrate, which causes the coatings to easily fall off. In addition, CVD can cause serious environmental pollution. On the other hand, their production cost is very high due to deposition procedure and conditions. 9 Currently, it is still challenging to obtain thick coatings with high bonding strength and good tribological performance.Electrospark deposition (ESD) is a microarc welding process. In the ESD process, a short duration plasma arc with high temperature is generated to melt the electrode surface and transfer a small amount of molten electrode material to a contacting substrate surface. 15,16 Electrospark deposition is a simple, cost effective and low energy technique, 16 which has some merits, 17-19 such as high energy density, low heat input, no environmental pollution, little heat affected zone and no deformation. What is more, metallurgical combination and thick films can be formed between coatings and substrates, 20 resulting in an improved coating adhesion compared to PVD and CVD. As an example, a TiC coating was prepared by ESD with 100 mm thickness. 21 Varieties of coatings have been prepare...

Preparation of a Self‐Lubricating Cu/h‐BN Coating on Cemented Carbide

“…Compare with our previous work [9,26], the roughness of coating prepared on the AISI 45 steel is bigger than that of coating prepared on the YT15 under the same condition. Electrical conductivity of YT15 is lower than that of AISI 45 steel.…”

“…In summary, the overall surface quality of the coating was best when prepared using the 3rd grade capacitance. However, the capacitance effect on the coating surface roughness is different than the results in our previous work [26]. Under certain test conditions, the amount of melted metal is different for different electrodes and substrate materials.…”

“…In fact, besides the three factors, there are still some other factors to affect coating thickness, such as substrate material and preparing method. In our previous work [26], the coating thickness can be 100 μm, which was prepared by another method on AISI 45 steel. e coefficient of thermal expansion of AISI 45 steel is closer to copper than YT15.…”

“…In our previous work [9,25,26], Cu/h-BN and Cu/Cu-MoS 2 self-lubricating coatings were prepared on steel and high-speed steel, respectively, by ESD. e production process, microstructure, and tribological behaviors of the self-lubricating coatings have been preliminarily investigated, with the results showing that the self-lubricating coatings could reduce the friction coefficient and wear loss.…”

Study on laser-alloyed self-lubricating anti-wear composite coating after ageing treatment

“…In this regard, surface modification techniques offer a way to solve the problem, including chemical vapour deposition, 3 physical vapour deposition, 4 electrospark deposition, 5 laser cladding, 6 sol-gel 7 and so on. In recent years, laser-alloying technology has been widely used to prepare self-lubricating anti-wear composite coating to solve the problem due to its advanced features, such as the integrity of fusion bond between the alloyed layer and substrate, high process flexibility and working efficiency 8 – 11 .…”