Research On The Shot Blasting Of TC4 Heavy Gas Tuebin Blade And The Effectson Fatigue Properties

In order to meet the requirement of the fatigue property of the TC4 gas turbine compressor blade, the optimization of the shot peening process on the blade was studied in this work. The shot peening process on the mechanical properties of the forged material was firstly studied, then the shot peening process of the blade was investigated. Finally, the effects of the spot penning process and surface polishing process on the fatigue properties of the blade were investigated. The main conclusions of the following were drawn.The samples obtained from the forged TC4 rod were studied. After the investigations on the microstructure and mechanical properties, the influence of pellet type, shot penning pressure, substrate-to-target distance and coverage percentage on the properties of the forged alloy was analyzed. The results indicated that the surface residual stress of the ceramic pellets possesses had weak penning strength dependence, which is in favor of the process control. In addition, a better residual stress distribution state might be created by ceramic pellets than the cast steel pellets. The spot penning pressure had the most intense influence and showed a linear relationship on the penning strength, surface roughness and surface microhardness. However, the substrate-to-target distance and the angle showed weak influence on the penning strength, surface roughness and surface microhardness. The spot penning strength increased with increasing penning pressure, while firstly increased and then decreased with increasing substrate-to-target distance and increased with increasing penning angle. The changes of surface roughness and microhardness are also similar to that of the penning strength. The surface roughness of 0.8μm and penning strength of 0.16 mm A were obtained at penning pressure 0.15 MPa and substrate-to-target distance 150 mm.Based on previous penning processes, nine shot peening processes were determined. Fatigue properties of the samples were measured using Rotary Bending Fatigue Tests(RBFT). The results indicated that the shot peening process with ceramic pellets of diameter 0.15 mm, shot penning strength of 0.1mm A~0.2mm A and surface coverage of 100%~300% showed the best result, which resulted in an average fatigue life of 5×106 times under 600 MPa pressure. This average fatigue life is almost 20 times higher than that of the samples before shot peening tested under the pressure of 560 MPa. So the parameters of ceramic pellets of diameter 0.15 mm, shot penning strength of 0.1mm A~0.2mm A and surface coverage of 100%~300% were chosen as the preliminary optimization penning process. The residual stress analysis after high temperature holding at 500℃/1h or 200℃/1h with surface coverage of 100% showed that the obtained residual stress state and microstructure benefitted for the fatigue property.Because the surface condition of the blade may influence the spot penning effect, the influence of combined surface polishing process and spot penning process on the spot penning were investigated. When the penning strength is 0.2mm A, the effect of surface polishing may be overlapped by the penning process. However, the effect of surface polishing at 0.1mm A cannot be completely eliminated by penning process. The spot penning of the blade was carried out using the optimized process and the resonant amplitude monitoring method was used to evaluate the effect of the spot penning process. The results demonstrated that the optimized penning process may meet the requirement of the <Gas turbine compressor motor frequency measurement and fatigue strength check specifications> and can be used as a guide for manufacturing of the blade.