Ye Fa Tan

Research on Friction and Wear Properties of Plasma Spraying Ni-Base Alloy Coatings on Aluminum Alloy Surfaces

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.

Tribological properties of laser surface cladding Ni-base alloy coatings under dry friction and seawater conditions

Ni-base alloy coatings were prepared on aluminium alloy 7005 by laser surface cladding (LSC). The tribological properties of the coatings under dry friction and seawater conditions were investigated. Results showed that the coatings contained the phases of NiAl, NiAl3, Al3Ni2 and a few Cr23C6 and CrB. Compared with atmosphere plasma spraying (APS) Ni-base alloy coatings, LSC Ni-base alloy coatings exhibited higher microhardness, interfacial adhesion and cohesion force, and smaller friction coefficients and wear losses. The wear mechanisms of LSC Ni-base alloy coatings changed from micro-cutting wear into multi-plastic deformation wear, adhesive wear and oxidative wear as loads increased in dry friction. In seawater environment, LSC Ni-base coatings experienced micro-cutting wear and pitting corrosion wear at the loads of 3∼6 N, and multi-plastic deformation wear and local fracture wear at the loads higher than 9 N.

Tribological Behavior and Mechanisms of the Deloro60 Alloy Coatings by Electro Spark Deposition under Dry Sliding Friction Conditions

The Ni-base alloy coatings of Derolo60 were prepared on the surface of carbon steel by electro spark deposition. The tribological properties of the coatings were investigated in a tribometer under dry sliding friction conditions. The results show that the coatings exhibit excellent properties of wear resistance because of their unique microstructure with a rational combination of hard phases and tough matrix. With the increase of the normal loads and sliding speeds, the friction coefficients of the coatings decrease, while the wear losses increase. The main wear mechanisms of the coatings are micro-cutting wear and multi-plastic deformation wear at low speed and light load conditions, and then gradually change into micro-cutting wear and adhesive wear as well as fatigue fracture accompanied by some oxidation wear at high speed and heavy load conditions.

Microstructure and Mechanical Properties of Cobalt Alloy Coating Deposited by Electro-Spark

Stellite190 cobalt alloy coating was deposited on 45 carbon steel by electro-spark deposition. Formation mechanism, microstructure, phase composition and mechanical properties of the coating were researched, fracture mechanism of the coating was analyzed. The results indicate that, the coating has dense and well distributed microstructure, mainly composed of Co, (CoCrW)6C, Cr7C3. The coating presents excellent mechanical properties with a tensile strength of 731.83 MPa, a bonding strength of 213.01 MPa and good peeling resistance. The mechanism for tensile fracture of the coating is dimple fracture, and for shear fracture is cleavage fracture.

Microstructure and Tribological Properties of Stellite21 Coating by Electro-Spark Deposition

Setellite21 cobalt-based alloy coating was deposited on 45 steel by electro-spark deposition. Microstructure and phase composition of the coating were analyzed. Wear resistance and wear mechanism of the coating were researched. The results indicate that the coating with compact structure is mainly composed of Co, Co6W6C, CoCx and CoCr. Average microhardness of the coating is 445.34 HV0.5, which is about 2 times to that of the substrate. The coating presents excellent wear resistance with no obvious peelings and scratches. Wear resistance of the coating is about 2.3~2.7 times to that of the substrate. Wear mechanism of the coating mainly contains abrasive wear and fatigue wear, and along with oxidization wear.

Effects of Tribo-Couple and Environmental Medium on the Tribological Properties of the Graphite/CaF2/TiC/Ni-Base Alloy Composite Coating

The graphite/CaF2/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 the tribological properties of the composite coating were investigated. The results show that the wear rate of the GCTN composite coating against Si3N4 is 0.67×10-3mm3/m, which is about 2 times that against GCr15 steel, because Si3N4 induces micro-cutting wear of the composite coating. Water and NaCl solution may induce increasing of friction coefficients and wear rates. Especially, wear rate of the GCTN composite coating in NaCl solution is increased by 3.1 times compared with those under dry sliding and water. The GCTN composite coating presents better anti-wear property than Ni-base alloy coating in different environmental mediums.

Effects of Thixotropic Agent and Storage Time on the Rheological Properties of Epoxy Resin

In order to modify the rheological properties of epoxy resin adhesive in casting moulding technology and improve its bonding quality, the effects of thixotropic agents of hydrophilic nano-silica, organic bentonite and the composite agent of the two thixotropic ones on the rheological properties of epoxy resin (E-44) were studied by the evaluation parameters of viscosity and thixotropic index in this paper. The variation regulation of rheological properties of epoxy resin (E-44) with different thixotropic agents as the storage time was also investigated. The results show that the two thixotropic agents play a significant role in thickening the density and modifying the thixotropy of the epoxy resin (E-44). Especially, the thickening and thixotropic effects of the composite agent of 3phr hydrophilic nano-silica with 6phr organic bentonite are the most remarkable and the storage stability is also excellent.

Research on the Tribological Properties of Ni-W Alloy Electric Brush Plating Coatings at Elevated Temperatures

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.

Research on Key Technology of Knowledge-Based Intelligent Fault Diagnosis of Hydraulic System

A general framework of hydraulic fault diagnosis system was studied. It consisted of equipment knowledge bases, databases, fusion reasoning, knowledge acquisition and so on. The tree-structure model of the fault knowledge was established based on fault hierarchy and logicality. Fault nodes knowledge was encapsulated by object-oriented technique. Complete knowledge bases were made including fault bases and diagnosis bases. It could describe the fault positions, system structure, cause-symptom relationships, diagnosis principles and other knowledge. The results show that the methods are effective.

Numerical Simulation of Double-Sided Double Arc Welding without Back Chipping Based on MSC.MARC

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.