Residual Stress of Plasma Sprayed Hydroxylapatite Coating

• Main Authors: Yang, Eric, 楊永欽
• Other Authors: Edward Chang
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/30249105814236374482

碩士 === 國立成功大學 === 材料科學(工程)學系 === 85 === Revealing excellent biocompatibility and mechanical properties, plasma-sprayed bioactive hydroxyapatite (HA) coated Ti alloy implants have raised much interest as an approach to achieving reliable implant-to-bone fixation. In the process of plasma sprayed HA coatings, residual stress induced due to the different thermal expansion coefficient between HA coatings and Ti substrates. There are many researches about residual stresses in thermal sprayed ceramic coatings on metal substrates, but only a few researches about residual stresses in plasma sprayed hydroxyapatite coatings. Consequently, the aim of this study is to measure the young's modulus and evaluate the value and distribution of residual stresses and the relation between residual stress and bonding strength of plasma sprayed HA coatings . In phase I, the three point bending test was used to measure the young's modulus of plasma sprayed HA coatings. The specimens were prepared using different plasma spraying parameters (P1, P3) and different powder feed rate. Owing to higher plasma spraying power and higher extent of coating melting, P3-HA coating shows higher young's modulus than P1-HA coating, and coating with small powder feed rate have higher young's modulus. In phase II, the residual stresses were measured by X-ray diffraction method. This method have the advantage of measuring stresses to a depth of only a few micrometers. In this study, layer-removal method was used to measure the inner residual stresses of HA coatings. Following that, through thickness residual stress distributions were difined by inferring the residual stresses distribution function. The results show that P3-HA coatings posses higher residual stress (compressive) than P1-HA coatings and the 200um- HA coatings exhibits higher value than 50um-HA coatings. It is inferred demonstrate that HA coating with denser microstructure and more thickness shows a higher residual stress. The results also show the principle stress directions of residual stresses in HA coatings are complying with the directions of plasma spraying. In phase III of this study, six HA coatings on Ti-6 Al-4V substrates were prepared using plasma spraying of different initial temperature of substrates and different cooling rate during spraying. The results show that higher temperature of substrates and slower cooling rate during plasma spraying caused higher residual stresses in the HA coatings. Results of the bonding strength test reveal that higher residual stresses show lower bonding strength at the HA/Ti-6Al-4V interface.