Experimental Study And Spray Process Simulation Of Ceramic/Metal Gradient Wear Resistance Coating

Slurry pumps are widely used in mining , coal excavation, hydraulic engineering and so on. Because of bad work conditions and heavy loads, they fail frequently by wear problem. In order to improve their wear resistance property, a variety of wear resistance materials and special techniques are applied on the flow channels of the pumps, and effect has been made by these methods. However, most of these materials cost highly and are hard to process, thus increase the pumps' manufacture and work expense. Meanwhile, some of these materials have a low value of toughness and easy to fail under impact. So it's now technically critical and commercially significant to search for new type of wear resistance materials and new process techniques.The wear resistance property of ceramic is excellent, but its critical defect is the lack of toughness. By combining ceramic with metal, ceramic/metal gradient wear resistance coating can be prepared on the flow channels of the pumps, and their wear resistance property can be greatly improved at a reasonable cost.In this thesis, the property of the coating specimens prepared in former period has been tested again to verify the experiment result. Then, based on former work, according to choosing the kind of ceramic/metal and determining their proportions, four schemes of ceramic/metal wear resistance coating (two have gradient structures, the other two haven't) are designed and prepared on cast iron substrate by air plasma spray method. The microstructure of the specimens is observed, the microhardness, bond strength and wear resistance property are tested, and then the qualities of the four schemes are compared. A series of experiments have confirmed the merits of the gradient coating designed in this thesis; the coating with NiCrBSi as bond metal and WC as ceramic is especially satisfied, and its bond strength and wear resistance property have reach or exceed the requirement. According to the results of wear tests and the SEM photos of the wear surfaces, the wear mechanism and the principle of the coating's wearresistance property are concluded. Meanwhile, aiming at the defect of the correction method for relative resistance employed in former experiments, a new way of correction called "experiment correction method" is designed and adopted in the experiment, and the results after correction is perfect. Finally, the most satisfied coating scheme is prepared on a slurry pump, and the pump is sent to Jinshandian Iron Ore Branch, Mining of WISCO Co. Ltd for further test.It's another major work in this thesis to simulate the spray process by ANSYS. Different from the static state calculation used in former work, "birth and death method" is adopted and the transient state calculation is carried out, and the transient temperature fields are got rationally. As for the transient stress fields, attempt is made also by "birth and death method", and "plasticity deformation method" is put forward to solve the troublesome problem of phase alternation for the coating. However, the calculation of transient stress fields takes up a lot of computer resource and the hardware available in this thesis can't afford it, so the stress fields haven't been completely simulated. But in the theory, both the methods adopted here are feasible.