Papers by Author: Hua Tan

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 improve the wear resistance of debris-ejecting blade of driller, cemented carbide welding coatings were prepared by arc-welding technology. The abrasive wear behavior and wear mechanisms of cemented carbide welding coatings were researched under both dry and water friction conditions. The research results show that the wear rates of the coatings increase with the increase of loads and sliding speeds. The influence of sliding speeds on wear rates of the coatings becomes intense as the increase of loads. The wear rates of the coatings under water friction conditions are bigger than those under dry friction conditions. The main wear mechanisms of the coatings are micro-cutting and multi-plastic deformation wear of matrix metal, and micro-cracking and brittle fracture as well as spalling of WC particles.

Abstract: In order to improve the grinding performance and service life of electroplating composite coatings with high percent of hard abrasives, the composite coatings of Ni-Co/SiC were prepared by occlusion electroplating technology and their microstructure and tribological properties were studied. The research results show that the cathodal electric-current density in occlusion electroplating process and the SiC abrasive size have great influence on microstructure and tribological properties of Ni-Co/SiC coatings. The optimum value of cathodal electric-current density is 1 A/dm2 and the proper SiC abrasive size is about 20 μm, in which the Ni-Co/SiC coatings have excellent wear resistance and high grinding ability. The main wear mechanisms of Ni-Co/SiC coatings are micro-cutting and adhesive wear of matrix alloy, and micro-cracking wear and spalling of SiC abrasives.

Abstract: Ni-base alloy coatings on carbon steel surface were prepared by electro-spark deposition technology and the characterization and tribological behavior of the coatings were investigated. The research results show that the microstructure of Ni-base alloy coating can be divided into three typical areas: the white alloy zone, transition zone and overheating-affected zone. The hardness across the interface of the coating and substrate, in which chemical elements transferred from the coating to substrate, gradually decreases with the depth away from the coating surface. The friction coefficient slightly decreases, while the wear loss increases with the increase of load. The main wear mechanism of the coating is micro-cutting wear at light load friction, and gradually changes into mixture of micro-cutting wear, multi-plastic deformation wear and adhesive wear at heavy load friction.