Effect of microplasma spraying working gas on crystallinity of HA coatings

Hydroxyapatite(HA) coatings were prepared on Ti-6Al-4V substrate by using the method of microplasma spraying.Commercially pure argon gas and helium/argon(50% in volume) mixed gas were used as working gas in the spraying processing respectively.The surface morphology, phase compositions and degree of crystallinity of the coatings were examined by scanning electron microscope(SEM) and X-ray diffraction(XRD).Results show that less impurity phases and no TTCP and CaO phases were found in the coatings.The crystallinity of coatings is higher than 70%, which is beneficial for implantation materials stability in vitro and vivo.The enthalpy of microplasma arc in which helium/argon mixed is used as working gas is higher than that in which commercially pure argon gas is used.The crystalline phases in the former coatings mainly consist of recrystallization grains while the latter coatings were mainly made up of lots of unmelted HA particles.