Effects of Sand Blasting on Surface Integrity and High Cycle Fatigue Properties of DD6 Single Crystal Superalloy

DD6 is a second generation single crystal superalloy independently developed in China, which offers advantages such as high-temperature strength, stable structure, and satisfactory casting process performance. Currently, it is being widely used in development of aviation engine turbine blades. Sand blasting can be performed for surface cleaning and adjusting surface roughness of single crystal turbine blades and is an essential process in manufacturing of single crystal blades. Although sand blasting has been widely used in the manufacturing process of DD6 alloy turbine blades, only few reports studied the impact of sand blasting on the surface integrity and fatigue performance of DD6 alloy. Therefore, research is required to provide a theoretical basis for the safe service of DD6 alloy turbine blades. In this work, several specimens after a standard heat treatment are blasted with white corundum sand with 150, 124, and 100 mu m diameters at 0.5 MPa to study the effect of sand blasting on the surface integrity of DD6 alloy; the rotary bending high cycle fatigue properties of the specimens without and with sand blasting (blasting with white corundum sand with 150 mu m diameter) were tested at 760 and 980 degrees C, respectively, to study the effect of sand blasting on the alloy's fatigue property. The results show that sand blasting destroys the surface integrity of the single crystal superalloy, resulting in irregular pits on the surface caused by the cutting by sand particles while changing the surface morphology as well; the surface roughness and microhardness increase with sand particle size increase; after sand blasting, many dislocations slip in the gamma phase, and the dislocation density near the surface is high. Additionally, many dislocations shear the gamma' phase, forming antiphase domain boundaries and stacking faults; sand blasting results in deformation strengthening and residual stress; blasting with 150 mu m diameter sand at 0.5 MPa has a small effect on the rotary bending high cycle fatigue properties of DD6 alloy at 760 degrees C, but it considerably reduces the alloy' s fatigue properties at 980 degrees C in the low stress amplitude region, decreasing the fatigue strength of the alloy by 7.3%. The combined action of the notch effect, oxidation damage, deformation strengthening, and residual compressive stress leads to the changes in fatigue life without and with sand blasting.