The effects of adding Si3N4 as a nitrogen source on the properties of Ni-Free Co-28Cr-6Mo-xN alloy powders developed by mechanical alloying

Co-Cr-Mo alloys, which also contain Ni, are often used as materials for implants in orthopedic surgery due to their excellent mechanical properties and resistance to corrosion. However, when these alloys are implanted into the body, they can release nickel ions into the host tissues, which can pose health risks over time. To address this issue, nitrogen can be substituted for nickel. This study involves the synthesis of cobalt-based alloy powders, following the chemical composition specified by ASTM F1537, using different percentages of silicon nitride as a nitrogen source via the mechanical alloying method in an argon atmosphere. The effects of increasing silicon nitride content on the particle morphology, particle size, phase transformations, microstructure, and hardness of the synthesized powders were investigated using XRD, SEM, TEM, and microhardness tests. The results obtained from the X-ray diffraction analysis indicate that the alloying process was conducted effectively. It was observed that the silicon nitride underwent decomposition, and a portion of its nitrogen reacted with chromium to form the chromium nitride phase. Additionally, it was observed that an increase in the silicon nitride content resulted in a decrease in crystallite size and an increase in lattice strain. Adding silicon nitride in varying percentages resulted in crystal sizes within the nanometer range. The SEM results indicated that the size of powder particles decreased with an increase in the content of silicon nitride, and there was a more uniform distribution of particle sizes, with less variation in size. The TEM images showed that all percentages of silicon nitride resulted in a finegrained polycrystalline phase, where the size of the crystallites decreased with an increase in the amount of silicon nitride. The corresponding SAED patterns supported this observation. Moreover, the hardness of the material increased as the silicon nitride content increased.