Iron-based alloys, due to their favorable mechanical properties, biocompatibility, and biodegradability in the body, have emerged as promising candidates for the development of biodegradable implants. These alloys gradually degrade after fulfilling their mechanical functions, eliminating the need for secondary surgeries to remove the implants. However, a major challenge is their low corrosion rate in the body, which can affect their long-term performance. This study investigated the improvement of corrosion rate by adding silicon nitride (Si₃N₄) using the spark plasma sintering (SPS) method. Temperatures of 800, 900, and 1000°C, along with Si₃N₄ concentrations of 1%, 3%, and 5%, were selected as process parameters. The samples were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical tests, including potentiodynamic polarization and electrochemical impedance spectroscopy. The results showed that increasing the Si₃N₄ content led to higher porosity and, consequently, a higher corrosion rate. The sample with the highest Si₃N₄ content and the lowest temperature exhibited the best corrosion rate. It was also observed that porosity increased significantly, and despite this, a severe decrease in hardness was not observed due to the inherent hardness of silicon nitride. The fracture surfaces revealed elongated and flow-like regions. Additionally, the samples were immersed for 28 days in simulated body fluid (SBF) and for 3 months in phosphate-buffered saline (PBS) to eva‎luate their degradation and biological behavior in vitro. Silicon nitride not only improved the hydrophilicity of the samples but also enhanced their bioactivity. Samples with higher Si₃N₄ content formed more hydroxyapatite, indicating better compatibility with bone tissue. Microscopic observations showed that Si₃N₄ particles aggregated at the boundaries, aiding in the formation of a hydroxyapatite layer. The degradation test, performed by immersing the samples in PBS, showed no significant weight change by the end of the test, indicating that a longer time is required for the onset of degradation in these alloys. This study demonstrated that the addition of Si₃N₄ can control the corrosion rate while also improving the mechanical and biological properties of iron-based alloys. Data analysis using the Taguchi and response surface methodology (RSM) was performed to optimize the process parameters, helping to identify the optimal composition and conditions to achieve the desired mechanical and biological properties.

عباس بهرامي , ابوذر طاهري زاده

بهزاد صادقيان

مهدي رفيعائي , محمد خدائي