AFM machining of cold work tool steel coated by thermochemical method

In this thesis study, boronizing and TiVC coating was applied to AISI D2 steel, which is widely used as cold work steel, using thermoreactive diffusion methods. Then, 5, 10, and 15 cycles of abrasive flow machining (AFM) with Al₂O₃ were applied to uncoated, boronized, and TiVC-coated samples. The samples were then thoroughly examined for surface roughness, microstructure, hardness, corrosion, friction, and wear behavior. The analyses revealed that FeB–Fe₂B phases formed in the boronized samples and TiC–VC phases in the TiVC-coated samples, a diffusion layer forming between the coating and substrate to ensure adhesion, and the matrix structure of the AISI D2 steel remaining intact beneath the coating layer. The coating layer thicknesses of boronizing and TiVC coatings were measured as 15.08±0.58 μm and 7.48±0.46 μm, respectively, and the microhardness values were measured as 1820±63 HV₀.₀₅ and 3142±96 HV₀.₀₂₅, respectively. An increase in surface roughness was observed after boronizing and TiVC coating. Following the coating process, the AFM procedure significantly reduced surface roughness in both uncoated and coated samples. Surface roughness was reduced at 5, 10, and 15 cycles, but thinning and structural damage occurred in the coating layer at 15 cycles. In corrosion tests, the best corrosion resistance was obtained in the uncoated sample at 5 cycles, while in the boronized and TiVC-coated samples, the best corrosion resistance was obtained in the samples exposed to 15 cycles of AFM. In wear and friction tests, the application of AFM resulted in a 2–4-fold increase in wear resistance, and decreases in friction coefficient values were observed, particularly in the first 50–100 m of the wear tests. In conclusion, it was determined that the optimized AFM process is an effective method for improving the surface properties and service performance of AISI D2 steel in both uncoated and boronized and TiVC-coated conditions.