Experimental investigations into pressureless microwave sintering of iron–hydroxyapatite composite for biodegradable implants

This work focusses on fabrication of biodegradable iron-hydroxyapatite (Fe-HAp) composite using rapid tooling and pressureless microwave sintering. Carbonyl iron particles and hydroxyapatite powders were mixed in a planetary ball mill in varying proportions. Molds of phosphate-based investment material were filled (under ultrasonic action) with prepared powder mixer and then sintered in a microwave furnace. Fe-HAp composite samples were successfully fabricated using the developed methodology. Based on response surface methodology, planning of experimentation was done to evaluate the effect of process parameters namely sintering temperature, soaking time, HAp percentage and heating rate on shrinkage, sintered density, and compressive yield strength. It was revealed that out of all the factors, HAp percentage was the most influencing parameter. Scanning electron microscopy of prepared samples confirmed the proper bonding of particles without any application of pressure. It was also confirmed from X-ray diffraction analysis that no oxidation and contamination of samples from mold material took place. To find the optimum processing parameters, a multi-objective optimization based on genetic algorithm (GA) was done and results were verified using confirmatory experiments.