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The study is devoted to pack-powder boriding of ASTM A709 steel in a powder mixture containing boron carbide, potassium fluoroborate and silicon carbide. This surface hardening process is conducted between 1123 and 1273 K for from 2 to 8 h. The formed diiron boride layers are studied by different techniques (scanning electron microscopy, x-ray diffraction (XRD) analysis, glow discharge optical emission spectroscopy (GDOES), Vickers microhardness testing, surface profilometry, Rockwell-C indentation cohesion and pin-on-disc tests). Kinetically, an integral-method-based approach is applied to calculate the boron diffusivities in Fe2B. The activation energy of the process is deduced and compared to reported data. The same model is ultimately verified by comparing the empirical values of the thickness of the Fe2B layers obtained at 1223 K and 1273 K for 9 h and the predicted values. [ABSTRACT FROM AUTHOR]

Abstract: In this study, new data about the growth kinetics and indentation properties of cobalt boride layers formed on the surface of the ASTM F-75 biomedical alloy were estimated. The boron diffusion at the surface of the biomedical alloy was conducted using a powder-pack boriding process at temperatures of 1223–1273K with different exposure times for each temperature. Two mathematical approaches were proposed to determine the boron diffusion coefficients of the CoB and Co2B layers in the range of boriding temperatures, in which the experimental results of the kinetics of the cobalt boride layers were compared with those estimated using diffusion models. Finally, the mechanical characterization of the cobalt boride layers was evaluated by indentation techniques with applied loads of 0.98N and 50mN, respectively. According to the nanoindentation tests, a maximum hardness value (30GPa) and a maximum Young's modulus (380GPa) were obtained near the surface region (5μm) of the borided cobalt alloy. [Copyright &y& Elsevier]