Effect of Vacuum Heating Temperature on the Bonding Strength of Plasma-Sprayed HA Coating Layer

• Main Authors: Hung-Bin Jeng, 鄭弘彬
• Other Authors: Chuan-Sheng Liu
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/70196074937273431922

碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 92 === Abstract 　　Hydroxyapatite (HA) is a bioactive ceramic with calcium to phosphorous ratio similar to that of nature bone and good biocompatibility. In this study, plasma-sprayed HA coatings (HACs) on Ti6Al4V substrate with post heat treatment in vacuum were employed to improve the properties of HACs. The heating temperatures are 300ºC, 400ºC, 500ºC, 600ºC, 700ºC and 800ºC. After heat treatment, the HACs were analyzed by XRD, SEM, coefficient of thermal expansion and bonding strength measurement with reliability analysis. 　　XRD analysis indicates that the crystallinity of heat-treated HACs increases with increasing temperature and it rises to 85% at 700ºC heat treatment. The heat-treated HACs contains the least impurity phases at 600ºC heating temperature, but it starts to decompose into tetra-calcium phosphate (TP) and CaO phase at 700ºC and 800ºC. 　　From the cross-sectional microstructure, HACs with some spraying defect including pores and microcracks. The change in spraying defect content of heat-treated HACs is not evident at lower heating temperature, but it increases with increasing temperature above 500ºC heat treatment. Especially higher than 600ºC heat treatment, some microcracks become large, concentric and perpendicular to substrate as a result of volume contraction of HA coatings. 　　The coefficient of thermal expansion(CTE) of HACs has a minimum value about 13.6×10-6/ºC with 600ºC heat treatment. At 800ºC, the CTE value increases to 14.3×10-6/ºC. This small difference of CTE in temperature interval 600-800ºC will not affect the thermal stress within HACs significantly, but it indicated that the phase decomposition of HA phase and the induction of large cracks when heating temperature higher than 600ºC. 　　Post vacuum-heat treatment could improve the average bonding strength to 32.1MPa and the minimum life of HACs. By the reliability analysis of bonding strength, the Weibull’s modulus of bonding strength distributes between 2~4. It means that the failure modes of HACs during 300-800ºC heat treatments belong to “Increasing failure rate (IFR)” mode and the failure will increase with loading or increasing using time.