Abstract No.:
5318

 Title:
Study of the first stages of HAp coatings deposition by HVOF thermal spray

 Authors:
Juanita Hincapie-Bedoya* / Centro de Investigación y de Estudios Avanzados del Instituto Politecnico National, México
Anamelis Sanchez-Rodríguez/ CIATEQ A.C, México
Jennifer Hermann-Muñoz/ Centro de Investigación y de Estudios Avanzados del IPN, México
Astrid Lorena Giraldo-Betancur/ CONACYT - Centro de Investigación y de Estudios Avanzados del IPN, México
Jorge Corona-Castuera/ CIATEQ A.C, México
Carlos Agustin Poblano-Salas/ CIATEQ A.C, México
Juan Muñoz-Saldaña/ Centro de Investigación y de Estudios Avanzados del IPN, México
Diego Germán Espinosa/ CIDESI, México

 Abstract:
Preserving the physicochemical characteristics of hydroxyapatite (HAp) powder during thermal spray deposition allows to seek for high biocompatibility performance of the resulting coatings, which is correlated, among other variables, with the melting degree of the in-flight particles. There is however a compromise between the degree of particle melting in terms of adhesion and biocompatibility, which makes crucial the study of the first stages of coating deposition. HVOF process offers a wide processing window when looking for high quality HAp coatings. In this work, HAp coatings were deposited by HVOF on Ti6Al4V substrates. The number of variables that are involved in the HVOF process requires a detailed study of the splats in the first stages of coating deposition, therefore a design of experiments (DoE) was implemented in this work considering two inputs: a) fuel/oxygen ratio, that affects temperature and velocity of particles, and b) spraying distance, associated with the residence time of particles in the flame. The size of splats, semi-molten particles fraction, morphology and bioactivity tests in simulated body fluid (SBF) were all taken into account as responses to feed the DoE. Scanning Electron Microscopy (SEM) with image analysis and Raman spectroscopy were used to evaluate the local characteristics of the splats. Furthermore, nanoindentation measurements were employed to evaluate the mechanical properties of single splats, which were correlated with the splats constituting phases. The influence of spray conditions on the characteristics of in-flight particles was determined by using a Process Maps methodology, in order to define the most favoured spray conditions for obtaining high quality HAp coatings. The results allowed to establish the influence of the deposition parameters on the coating phase formation, where crystalline HAp, ACP, oxyapatite (OHAp) and other calcium phosphate (TTCP, a-TCP) were all identified as a function of different combination of parameters during HVOF deposition.

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