Investigation of the effect of microwave heating on boron kinetics of biomedical 316l alloy and characterization of boride layer

AISI 316L stainless steel alloy is widely used as structural engineering material and biomaterial. In this study, boriding of AISI 316L stainless steel alloys by powder-pack boriding method using microwave heating was investigated and the characterization of the boronized surface was performed. For this purpose, AISI 316L stainless steel alloy samples were boronized in the microwave furnace (2.9 kW / 2.45 GHz) at 800, 850, 900 and 950 oC for 2, 4 and 6 hours under the Argon shielding gas. The macrostructural, microstructural, elemental, mechanical and tribological properties of the boronized AISI 316L stainless steel alloy were investigated. 6.21-63.51 µm thick boride layers were obtained in microwave borided in AISI 316L. The effect of microwave heating on boron diffusion kinetics has been also determined. Boron activation energy was determined as 244.15 kJ·mol−1 in boronized AISI 316L stainless steel alloy microwave heating. As a result of the microwave effect, the pre-exponential factor increased up to 4600 times compared to traditional heating. As a result of boiling, FeB, Fe2B, Cr5B3 and NiB borides and Fe-Ni-Si diffusion barrier formation were detected. As a result of Daimler-Benz Adhesion tests, samples boiled at 800, 850 and 900 °C showed enough adhesive strength. The best wear performances were seen in samples that were boronized at 850 °C for 6 hours and at 900 °C 4 hours. The elasticity modules of FeB, Fe2B phases and diffusion region were determined as 404.45, 367.34 and 313.11 GPa, respectively. Their hardnesses were determined as 18.86, 11.72 and 5.54 GPa, respectively. Yield strengths were calculated as 6.28, 3.90 and 1.84 GPa, respectively. As a result of the fracture toughness tests, the order of fracture toughness of the FeB and Fe2B phase was measured as 1.048 and 4.882 MPa∙m1/2. Compared to the traditional method, with microwave heating, 50% saving was achieved in boriding time and 32% increase in the thickness of the boride layer obtained.