Effect of particle size on microstructure of high velocity oxy-fuel (HVOF) sprayed hydroxyapatite coatings

摘要

Hydroxyapatite (HA) coatings were deposited on Ti-6Al-4V substrates using high velocity oxy-fuel (HVOF) spray process, with the aim of achieving high degree of crystallinity and limited phase decomposition of HA during coating development. The starting HA powders with particle size range, 50 ± 10μm, 40 ± 10μm, and 30 ± 10μm, were sprayed to obtain an eclectic mix of melt states in the sprayed powders. Microstructure of the coatings and sprayed powders was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Furthermore, X-ray diffraction analysis, differential scanning calorimetry (DSC), and, Fourier transform infrared spectroscopy (FTIR) were conducted to characterize the coatings and powders. Results showed that the melted portion of sprayed HA particles was responsible essentially for the HA phase transformation and decomposition. Crystalline HA coatings (>90% crystallinity) can be deposited by HVOF spraying large HA powders, >50μm. The phase composition of the as sprayed HA coatings can be controlled through controlling the melt state of the powders. It also stated that phase transformation of HA during coating formation mostly occurred within the melted portion of the particles.