Papers by Author: Long He

Abstract: In order to improve the anti-wear and anti-corrosion properties of mechanical parts used in high temperature friction conditions, the Ni-W alloy brush plating coatings were prepared and their tribological properties at elevated environment temperatures were investigated. The results show that the friction coefficients of Ni-W/GCr15 tribo-couples are in the range of 0.168～1.048, which take on the decreasing trend as the increase of environment temperatures. The wear losses of the coatings increase at elevated temperatures, and the critical temperature in which the coatings produce serious wear from slight wear is 250°C. The wear mechanism of the coatings are micro-cutting at room temperature, then it changes into adhesive wear accompanied by a certain of delamination when temperature is high than 250°C. When temperature is higher than 400°C, the main wear mechanism of the coatings is adhesive wear and delamination.

Abstract: Numerical simulation based on MSC.MARC was applied to predict the residual stress in double-sided double arc welding (DSDAW). The distribution of residual stress field in the welding seam was simulated and the actual situation in experiment of the residual stress was also measured. It shows that the calculated results are in good agreement with the experimental ones. The residual stress of conventional welding (CW) or a single arc welding (SAW) is calculated too. Moreover, the welding residual stress field of thick metal plates welded by DSDAW was carried out and compared with that of the CW method with back chipping. The result shows that the DSDAW technology had some excellent characteristics of smaller angular deformation, lower residual peak tensile stress, and well-proportioned stress distribution, which testifies that the welding procedures in DSDAW are reduced and the welding efficiency and quality of the welding joint are improved in great margin.

Abstract: In order to improve the wear resistance and extend service life of aluminum alloy parts, the Ni-base alloy anti-wear coatings were prepared on the surfaces of 7A05 aluminum alloy by plasma spraying technology. The microstructure and interface of the coatings were analyzed, and the friction and wear properties of Ni-base alloy coatings and aluminum alloy substrates were investigated under dry friction condition at room temperature. The research results show that the main phases of Ni-base alloy coating are γ-Ni, CrB and Cr23C6. The thicknesses of diffusion layers existing between intermediate layer and coating, intermediate layer and substrate are respectively 15μm and 20μm. The bonding types of the coating and the substrate are mechanical combination accompanied with partially metallurgical combination. When wore against GCr15 steel balls, the average friction coefficient of the Ni-base alloy coatings is 11.6% lower than that of the aluminum alloy substrates, and the average wear loss of the former is 9.3mg, which is only 1/3 of that of the latter. With the increase of loads, the wear mechanisms of the Ni-base alloy coatings change from slightly micro-cutting wear and fatigue wear to abrasive wear and micro-fracture wear, while those of the aluminum alloy substrates are mainly adhesive wear and abrasive wear as well as slight oxidation wear.

Abstract: Weldox960 steel is widely used in mechanical structure of military equipments as anti-wear parts. The tribological behavior and mechanisms of weldox960 steel were investigated under dry sliding friction conditions. The results show that friction coefficient of the steel increases from 0.268 to 0.365 with the increase of load. When the loads are smaller than 8N, the wear rates of the steel are in the range of 0.57~0.67×10^-3 mm³/m, and the wear mechanism is multi-plastic deformation wear. If the loads are bigger than 10N, the wear rates increase to the range of 1.29~1.43×10^-3 mm³/m, and the wear mechanisms change into delamination of the work-hardening layer and abrasive wear. The friction coefficients keep in a steady state of about 0.31 when the sliding speeds change from 0.05m/s to 0.2m/s. At the low speeds of 0.05m/s and 0.1 m/s, the wear rates are in the range of 1~1.3×10^-3 mm³/m and the wear mechanisms are multi-deformation wear and abrasive wear. When the sliding speed increases to a critical value of 0.15m/s, the wear rates increase to 6.2×10^-3 mm³/m and the wear mechanisms change into fatigue delamination of the work-hardening layer and multi-plastic deformation wear as well as oxidation wear.

Abstract: In order to improve the wear resistance of drill tools, stellite190 welding coatings were prepared by oxygen-acetylene flame welding technology. The abrasive wear behavior and wear mechanisms of the coatings were investigated in both dry and water friction conditions. The research results show that the wear losses of the coatings increase with the increase of loads and sliding speeds. The effects of sliding speeds on wear losses of the coatings become intense with the increase of loads. The wear losses of the coatings in water friction condition are bigger than those in dry friction condition. The main wear mechanisms of the coatings are micro-cutting and multi-plastic deformation wear in dry friction condition, and accompanied by stress corrosive wear in water friction condition.

Abstract: In order to reduce friction coefficient of the Ni-base alloy coating and further improve its wear resistance, the graphite/TiC/Ni-base alloy composite coating was prepared on the surface of 45 carbon steel by plasma spray. Effects of loads, friction counterparts and lubricants on tribological properties of the coating were investigated. The results show that friction coefficient of the composite coating is reduced by 33% than that of the Ni-base alloy coating when worn against GCr15. Wear losses of the composite coating are less than those of the Ni-base alloy coating at all loads of 6N, 8N, 10N and 12N. Worn against Si3N4, friction coefficient of the composite coating is 13% less than that worn against GCr15, but its wear loss is 2.9 times of that worn against GCr15. Wear mechanism of the composite coating is micro cutting and brittle fraction when worn against Si3N4. Under lubrication of NaCl solution, friction coefficient of the composite coating is almost the same as that under dry sliding, wear loss is increased by 1.6 times. Stress corrosion and wedging effects of the NaCl solution are main wear mechanisms of the composite coating.