Yun Cai Zhao

Bio: Yun Cai Zhao is an academic researcher from Jiangxi University of Science and Technology. The author has contributed to research in topics: Materials science & Coating. The author has an hindex of 1, co-authored 3 publications receiving 6 citations.

Study on the Forming and Self-Repairing of Ni60A/MoS2 Composite Lubricating Film

Abstract: Based on the research of the tribological properties of the Ni60A/MoS2 composite coating, this paper has studied the forming and self-repairing mechanism of MoS2 lubricating film. The study shows that the forming mechanism includes four stages: the friction beginning stage, MoS2 precipitating stage, MoS2 covering stage and MoS2 forming stage. The destroying processes of the composite lubricating film includes the film thickness decreasing, the crack emerging, the crack expansion, the lubricating film flaking. Meanwhile, the hard particles piercing into the lubricating film also results in the abrasion destroying of the lubricating film and greatly shortening the lifespan of the lubricating film.

Effect of high temperature-assisted ultrasonic surface rolling on the friction and wear properties of a plasma sprayed Ni/WC coating on #45 steel substrate

Abstract: To improve the friction and wear properties of a plasma-sprayed Ni/WC coating on a #45 steel substrate and explore the influence of spindle speed on the friction and wear properties of the coating in the process of high-temperature assisted ultrasonic rolling (HT/USR), The HT/USR processing of the Ni/WC coating was conducted under various spindle speeds (173, 248, and 360 r/min). The results showed that the pores and cracks in the Ni/WC coating after HT/USR treatment were reduced, giving the coating a compact structure. The surface performance of the coating was the best when the spindle speed was 173 r/min. Compared with the untreated sample, the surface roughness of the coating treated by HT/USR-173 r/min was reduced by 49 %, and the surface hardness was increased by 38.4 %. The residual tensile stress was transformed from tensile stress to compressive stress, reaching −404.2 MPa. The wear mechanism of the coating after HT/USR treatment changed from abrasive and fatigue wear to abrasive and oxidation wear. The friction coefficient and wear amount decreased with decreasing spindle speed. The average friction coefficient and wear amount of the coating with a spindle speed of 173 r/min were the lowest, 0.03094 and 5.4 mg, respectively, which are 69.23 % and 64.23 % lower than those of the untreated sample. Therefore, HT/USR effectively improved the surface properties of the plasma-sprayed Ni/WC coatings, as well as their friction and wear properties.

Effect of friction time on heat distribution, material flow, and microstructure of friction welding of dissimilar steels

Abstract: In this paper, 1045 steel is joined to Q235 steel using continuous drive friction welding. The temperature distribution and material flow during the welding process were analyzed by numerical simulation and the flow behavior was further explained by grain distribution. The microstructure and mechanical properties of the joint were investigated experimentally. The results show that with the increase of friction time, the joint temperature first increases and remains in dynamic equilibrium. The joints were divided into a central region, a 0.5R region, and an edge region along the radial direction. The highest temperature of the joint first appears in the edge region, with a relatively low temperature in the central region. The material flow rate in the edge region is faster than that in the center and 0.5 R regions, and the maximum material flow rate increases and then decreases with increasing friction time. When the friction time is suitable, the heat distribution is uniform and sufficient, and the grains show a better refinement effect, which is beneficial to the improvement of the mechanical properties of the joint. Due to the grain refinement of the joint, the highest microhardness is obtained at the weld zone in all welding conditions. All joints fractured on the Q235 steel base material side, and the fracture form was ductile fracture.

Research on Anti-Friction Mechanism of Ni60A/MoS 2 Composite Coating

Abstract: Based on the research of the tribological properties of the Ni60A/MoS2 composite coating, this paper has studied and discussed the self-lubricating effect and mechanism of the MoS2 film in the Ni60A /MoS2 composite coating. Research shows that when self-lubricate coating rub, MoS2 solid lubricant can be precipitated, forming lubricating film on the friction surface through dragging. The Solid lubricate film of MoS2 is an important factor that lead the friction coefficient of Ni60A/MoS2 composite lubricate coating decrease. Meanwhile we analyze the formation phenomenon and friction and wear properties of self-lubricate coating, which show forming mechanism of the lubricating film contain four stages, that is, the friction beginning stage, MoS2 precipitating stage, MoS2 covering stage and MoS2 forming stage.

Research on Lubrication and Wear-Resistant Mechanism of Ni60A/MoS2 Composite Coating

Abstract: The influence of MoS2 lubrication phase on the tribological properties of the Ni60A/MoS2 composite coating was conducted on UMT-2 micro-wear testing machine (USA), discussing the self-lubricating effect and mechanism. The result shows that with the increasing content of MoS2, the friction coefficient of the coating which changed with the increasing content of the MoS2 presents firstly decreases then increases, and the value reach the minimum when the quality percent of MoS2 wrapped with Nickel is 35%. Low-friction property of the Ni60A/MoS2 composite coating is due to the forming of MoS2 lubricating film in friction surface. The decreasing of the friction coefficient of the coating is in proportion to the coverage area of MoS2 lubricating film.

Solid-State Rotary Friction-Welded Tungsten and Mild Steel Joints

Abstract: This paper is a study of the microstructure and other selected properties of solid-state, high-speed, rotary friction-welded tungsten and mild steel (S355) joints. Due to the high affinity of tungsten for oxygen, the welding process was carried out in a chamber with an argon protective atmosphere. Joints of suitable quality were obtained without any macroscopic defects and discontinuities. Scanning electron microscopy (SEM) was used to investigate the phase transformations taking place during the friction welding process. Chemical compositions in the interfaces of the welded joints were determined by using energy dispersive spectroscopy (EDS). The microstructure of friction welds consisted of a few zones, fine equiaxed grains (formed due to dynamic recrystallization) and ultrafine grains in the region on the steel side. A plastic deformation in the direction of the flash was visible mainly on the steel side. EDS-SEM scan line analyses across the interface did not confirm the diffusion of tungsten to iron. The nature of the friction welding dissimilar joint is non-equilibrium based on deep plastic deformation without visible diffusive processes in the interface zone. The absence of intermetallic phases was found in the weld interface during SEM observations. Mechanical properties of the friction-welded joint were defined using the Vickers hardness test and the instrumented indentation test (IIT). The results are presented in the form of a distribution in the longitudinal plane of the welded joint. The fracture during strength tests occurred mainly through the cleavage planes at the interface of the tungsten grain close to the friction surface.

Preparation, Corrosion Resistance and Mechanical Properties of Electroless Ni-W-P-eGO Composite Coatings

Abstract: In this paper, highly dispersed edge graphene oxides (hereinafter referred to as eGO) were successfully applied in the Ni-W-P bath system, and high-performance Ni-W-P-eGO coating was prepared on the surface of N80 carbon steel by an electroless deposition method. By investigating concentration of eGO in solution in the solution, and using XPS, XRD, EDS, and SEM to analyze the crystal properties, electroless composition, micromorphology, and microstructure of the coating in detail,and the hardness, corrosion resistance and wear resistance of the coatings were investigated by microhardness tests, electrochemical corrosion and friction and wear tests. The niversal electrochemical methods determined the corrosion resistance of the coating, and the abrasion resistance of the coating was determined by ageneralduty reciprocating test. The experimental characterization results show that the addition of eGO nanomaterials to the Ni-W-P composite coating significantly improves the corrosion resistance of the coating in 3.5 wt% NaCl solution, improve the mechanical properties of the coating. When eGO content reaches 0.1 g/l, Ni-W-P-eGO coating demonstrated the most excellent corrosion resistance with a corrosion current of 0.9476 μA/cm 2 , and mechanical properties (the average friction coefficient is 0.173, and the microhardness value is 744.58 HV). In this paper, nanometers were added to the Ni-W-P composite coating, and a series of tests were carried out. The surface morphology, crystal structure and elemental composition of the coatings were characterized, and the corrosion resistance, wear resistance and hardness of the coatings were tested. The results show that the addition of eGO improves the hardness, corrosion resistance and wear resistance of the coatings. • For the first time, the two-dimensional hierarchical nanomaterial eGO was applied to the field of electroless Ni-W-P coating. • We used various characterization methods. • Ni-W-P-eGO (0.1 g/L) coating exhibits the best corrison resistance (R ct = 29815 Ω·cm 2 ), and the best hardness (744.58 HV). • Provides a new idea for the preparation of high-performance Ni-W-P composite coatings.

Assessment of Selected Structural Properties of High-Speed Friction Welded Joints Made of Unalloyed Structural Steel

Abstract: Commonly used S235JR structural steel, generally associated with good weldability, was joined by high-speed friction welding (HSFW). The friction welding tests were performed with a rotational speed of n = 8000 rpm and four different values of the unit pressure in the friction phase (pf) in the range of 64–255 MPa. The obtained joints were subjected to metallographic observations using an optical microscope; in selected zones of friction joints the average grain size was specified in accordance with the EN ISO 643:2012 standard; the hardness of friction joints was measured using the Vickers method. The friction-welded joint with the highest pf was EBSD-investigated. The obtained friction-welded joints resembled an hourglass, and the microstructure of individual zones of the joints differed depending on the height (axis, radius) of the observations. The generated joining conditions resulted in a significant refinement of the microstructure in the friction weld—the average grain size is about 1 µm2 (for base material it was 21 µm2). The highest increase in hardness above 340 HV0.1 was recorded in the friction weld of the welded joint with the lowest used value pressure in the friction phase. Such a sharp increase in hardness can make the resulting friction-welded joint become sensitive to dynamic or fatigue loads. The electron backscatter diffraction (EBSD) investigation confirmed the strong refinement of the microstructure in the friction-welded joint and the occurrence of the phenomenon of dynamic recrystallization (DRX). The friction weld was also characterized by a large share of high-angle boundaries (HAGBs) >80%. These results may indicate that during high-speed friction welding it is possible to create conditions like those obtained during the High-Pressure Torsion (the method used to produce UFG materials) process.

Study of Orthogonal Test of the Tribological Properties of the Surface Texturing Coating

Abstract: In order to research tribological properties of texturing coating and get the best formulation and moulding of preparing surface textured lubricant anti-wearing coating, in this paper, the tribological orthogonal test which is about lubrication phase and surface micro moulding of coating is carried out, under different temperatures, analysis of variance is also carried out for friction coefficient and wear rate, getting a better level combination of every factor, then by synthetically analyzing the tribological properties, the level combination of the better friction coefficient is formulation 1(lubricant WS 2 : content of 30%) and its moulding(surface texture: pit trench). The level combination of the better wear rate is formulation 2(lubricant WS 2 : content of 20%) and its moulding(surface texture: diamond texture). To the two formulations and their mouldings, according to the test and analysis, the abrasion loss is low, so it isn’t considered for different components’ influence on wear, but it is mainly considered different components have an effect on friction coefficient. The best formulation and moulding are got: formulation 1(lubricant WS 2 : content of 30%) and its moulding(surface texture: pit trench).

Preparation, corrosion resistance and mechanical properties of electroless Ni-B/α-ZrP composite coatings

Abstract: Ni-B/α-ZrP composite coatings were successfully prepared on the surface of N80 carbon steel by electroless plating. The effects of the two-dimensional hierarchical material α-ZrP on the surface morphology, corrosion resistance and mechanical behavior of the coatings were investigated. Compared with Ni-B alloy coatings, the corrosion resistance and mechanical behavior of Ni-B/α-ZrP composite coatings are significantly enhanced. When the content of α-ZrP is 1.5 g/L, the coating exhibits the highest hardness (1000.92 HV) and the lowest friction coefficient (COF = 0.302). Its wear volume is 86% lower than that of Ni-B alloy. At this time, the coating also has the maximum impedance (Rct = 24,870 Ω·cm2) and the lowest corrosion current, showing the best corrosion resistance.