Selective laser melting of a stainless steel and hydroxyapatite composite for load-bearing implant development

Selective laser melting (SLM) is emerged as a new manufacturing technique to directly fabricate customised implants using metallic materials. This technique is also capable of processing powder mixtures to generate advanced composites offering desirable properties. In this research, the SLM technique was used to directly fabricate hydroxyapatite (HA) and 316L stainless steel (SS) powders mixture with an objective to develop load-bearing and bioactive implants. SLM processing parameters were identified to fabricate pure SS and SS/HA composite specimens. The visual inspections, density measurements, tensile and hardness tests, and microstructural examinations was conducted to illustrate the effect of SLM parameters and HA particles on the properties of SS/HA composites. It was found that the incorporation of HA particles influenced SLM processing parameters including laser power, scanning speed and scanning procedure. A duplication of scanning procedure was necessary to avoid the balling effects and to form well joined SS/HA composite layer. The highest tensile strength of SS/HA parts produced at optimum processing parameters was close to human bone tensile strength and adequate for load-bearing bone implants. Moreover, the SS/HA part had a finer grain size than that of the SS attributed to the HA particles as nuclei to assist heterogeneous nucleation. These finer grains enhanced the hardness of the SS/HA part.