Influence of surface integrity on fatigue behavior of Inconel 718 and Ti6Al4V workpieces with CBN electroplated wheel

High-speed grinding with cubic boron nitride (CBN) electroplated wheels has been widely used in the aviation manufacturing field, such as the machining of nickel-based and titanium alloys. The requirement of dimensional precision and consistency of parts can be met effectively because of the high feasibility and grinding performance of CBN electroplated wheels. Meanwhile, surface integrity has a direct and significant effect on the fatigue behavior of workpieces. Therefore, the influence of surface integrity machined by CBN electroplated wheels on fatigue behavior of Inconel 718 and Ti6Al4V specimens is investigated. Based on the experimental results of surface roughness, microhardening rate, and residual stress measured, low-cycle fatigue tests were carried out to analyze the influence mechanisms of surface integrity on low-cycle fatigue life. Under the given experimental conditions, it can be obtained that surface roughness has predominant and negative effects on the number of cycles to failure ( N f ) of Inconel 718 specimens when surface roughness is higher than R a 0.4 μm. However, when surface roughness is less than R a 0.3 μm, surface microhardening rate has predominant and positive effects on N f . Compared with polished specimens, N f of ground specimens can be increased by 47.5% utilizing the optimized parameters and conditions. As for Ti6Al4V specimens, both surface roughness and microhardening rate have negative effects on N f . Micro-recast layer and molten drops have been observed on machined surface of Ti6Al4V specimens, which have significant and negative effects on the fatigue behavior of workpieces. At the same time, N f of ground specimens with CBN electroplated wheels is less than that of milled specimens even utilizing the optimized grinding parameters. From all the comparison results, it can be achieved that the influence mechanisms of surface integrity on fatigue behavior of Inconel 718 and Ti6Al4V specimens with CBN electroplated wheels are different due to the material properties.