Surface Integrity of Powder Metallurgy Superalloy FGH96 Affected by Grinding with Electroplated CBN Wheel

Powder metallurgy superalloy FGH96 is a key material for manufacturing aero-engine high temperature parts due to its excellent high-temperature mechanical performances. Machined surface integrity has a directly influence on the fatigue behavior. Unique properties of FGH96, like high-temperature strength and poor machinability, make it extremely difficult to control the machined surface integrity. Grinding technology utilizing super abrasive wheel is widely used in finish machining of powder metallurgy superalloy. Therefore, improving the fatigue property of parts by controlling grinding surface integrity is significantly important. Experimental results of grinding FGH96 with CBN electroplated wheel show that the grits size of wheel is the main factor influencing on surface roughness. With the decreases of the grits size, the surface roughness decreases gradually. Surface roughness of workpieces machined with 400#CBN wheel is Ra=0.76 μm, while that with 600#CBN wheel is Ra=0.56 μm. In the experimental conditions, feed speed and grinding depth have little influence on surface roughness. Grinding speed has hardly any influence on surface roughness. Meanwhile, the surface microhardness of workpieces is maintained at 460 HV to 500 HV and the surface residual stress is -700 MPa to -620 MPa. There is almost no plastic deformation in the microstructure of machined surface. Therefore, grits size of grinding wheel has a tremendous influence on surface integrity of powder metallurgy superalloy FGH96 in the range of experimental parameters, and controlling the surface roughness is a crucial method to improve the fatigue behavior of FGH96 parts.