氏名　TEERAWAT　LAONAPAKUL
学位の種類　博士（工学）
学位記番号　博甲第613号
学位授与の日付　平成24年3月26日
学位論文題目　Failure and Acoustic Emission Behavior of Hydroxyapatite Coating on Commercially Pure Titanium Substrate　（純チタン上のハイドロキシアパタイトコーティング破壊およびAE発生挙動）
論文審査委員
　主査　教授　武藤　睦治
　副査　教授　福澤　康
　副査　教授　井原　郁夫
　副査　准教授　宮下　幸雄
　副査　特任講師　大塚　雄市

• 論文目次
• 論文要旨
• 論文審査の結果の要旨

［平成23（2011）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

Abstract
Contents　p.i
Figures　p.v
Tables　p.ix
List of publications　p.x
Acknowledgements　p.xi

Chapter 1　Introduction　p.1
　1.1　Definitions of biomaterials and biocompatibility　p.3
　1.2　Type of Biomaterials and its properties　p.4
　1.2.1　Types of Biomaterials　p.4
　1.2.2　Properties of biomaterials　p.5
　1.3　Metallic implant materials　p.6
　1.3.1　Stainless Steels　p.7
　1.3.2　Co-Based Alloys　p.9
　1.3.3　Ti and Ti-Based Alloys　p.11
　1.4　Ceramic implant materials　p.14
　1.4.1　Type of Ceramic implant materials　p.15
　1.4.2　Calcium phosphate ceramics　p.16
　1.4.3　Resorbable calcium phosphates　p.19
　1.5　Calcium phosphatate and Hydroxyapatite coating　p.20
　1.5.1　Type of Ceramic implant materials　p.22
　1.5.2　Use of plasma-sprayed hydroxyapatite in dental and orthopedic implants　p.24
　1.6　In vitro biological testing of biomaterials　p.26
　1.7　Acoustic emission （AE）　p.29
　1.8　Motivation, Scope and Objective of the present work　p.30
　References

Chapter 2　Bending Failure Acoustic Emission Behaviour of Plasma Sprayed Hydroxyapatite Coating Layer on Commercially Pure Titanium Substrate
　Abstract　p.38
　2.1　Introduction　p.39
　2.2　Experimental Procedures　p.41
　2.2.1　Material preparation and characterization　p.41
　2.2.2　Bending strength test with acoustic emission（AE） monitoring　p.43
　2.2.2.1　Experimental setup and AE monitoring system　p.43
　2.2.2.2　Bending test　p.44
　2.3　Result and discussion　p.44
　2.3.1　Characterization of the HAp top coating before and after immersion in SBF　p.44
　2.3.2　Bendeng strength test and AE behavior　p.49
　2.3.3　Failure behavior of Ti-black and Ti/HT/HA specimen by AE signals　p.53
　2.4　Conclusion　p.55
　References　p.56

Chapter 3　Fatigue Failure and Acoustic Emission Behavior of Plasma Sprayed Hydroxyapatite Coating Layer on Commercially Pure Titanium Substate in Ambient Atmosphere
　Abstract　p.59
　3.1　Introduction　p.60
　3.2　Experimental Procedures　p.61
　3.2.1　Material preparation and characterization　p.61
　3.2.2　Fatigue test　p.62
　3.2.3　AE monitoring　p.64
　3.2.4　Fatigue damage observation　p.64
　3.3　Result and discussion　p.65
　3.3.1　Characterization of HAp top coat layer　p.65
　3.3.2　Acoustic emission behavior of Hap coating specimens　p.69
　3.3.3　In situ observation of crack nucleation and propagation in the Ti/HT/HA11 specimen　p.75
　3.3.4　Failure behavior of Ti-black and Ti/HT/HA specimen by AE signals　p.79
　3.4　Conclusion　p.81
　References　p.83

Chapter 4　Fatigue Failure and Acoustic Emission Behavior of Plasma Sprayed Hydroxyapatite Coating Layer on Commercially Pure Titanium Substate in Simulated Body Field
　Abstract　p.85
　4.1　Introduction　p.86
　4.2　Experimental Procedures　p.87
　4.2.1　Material preparation and characterization　p.87
　4.2.2　Bend Fatigue test with acoustic emission （AE） monitoring　p.88
　4.2.2.1　Experimental setup and AE monitoring system　p.88
　4.2.2.2　Fatigue test method under SBF environment　p.88
　4.2.2.3　Fatigue tests of the Ti/HT/HA specimen　p.90
　4.2.2.4　Fatigue damage observation　p.91
　4.3　Result and discussion　p.91
　4.3.1　Characterization of the Hap top coating before and after immersion in SBf　p.91
　4.3.2　Fatigue behavior of Ti/HT/HA specimen under ambient and aimulated body fluid （SBF） environment　p.98
　4.3.2.1　S-N curve　p.98
　4.3.2.2　Fatigue life of Ti/HT/HA specimen under SBF environment　p.100
　4.3.3　Acoustic Emission and Fatigue Mechanism for the Ti/HT/HA specimen　p.102
　4.4　Conclusion　p.107
　References　p.108

Chapter 5　Conclusion
　5.1　General conclusion　p.111
　5.2　Recommendation for further work　p.113

Appendix A　Recipe for preparing simulated body fuild （SBF）　p.115

Plasma sprayed hydroxyapatite （HAp） coating on Titanium （Ti） substrate widely used as implant materials can provide a good biocompatibility with excellent mechanical properties. For improving the bonding strength of the plasma sprayed HAp coating on commercially pure Ti substrate, surface modification of Ti substrate and bond coating technologies have to be developed. Furthermore, reliability of this coated material under an in vitro needs to be evaluated for safely use of this coating material as an implant material. In this study, the monotonic bending failure and fatigue failure behavior of the HAp coating under ambient and simulated body fluids （SBF） environments has been investigated. Acoustic emission （AE） signals during entire the tests were monitored to discuss the failure behavior of the HAp coated specimen in detail. The effects of HAp/Ti bond coat and apatite precipitation by immersing in SBF on failure behavior of the HAp coating were also investigated.

Chapter 1 Introduction: Basics of biomaterials as well as basic properties and requirements of the materials which are used as implant materials have been introduced. General properties of metallic and ceramic implant materials including the plasma spray hydroxyapatite coating have been described. Problem statements encouraging the present study have also been presented.

Chapter 2 Bending Failure and Acoustic Emission Behavior of Plasma Sprayed Hydroxyapatite Coating Layer on Commercially Pure Titanium Substrate: Relationship between AE peak amplitudes and stress-strain behavior was obtained to discuss how the damage of coating layer was developed under four point bending test. After a week immersion in SBF, the AE patterns obtained from four point bending test of HAp top coating specimens with and without bond coat clearly showed earlier stage of failure of the coating compared to those without SBF immersion. It was also found that the bond coating improved the failure resistance of the HAp top coating layer compared to that without the bond coat for both ambient and SBF environments. The delamination and spallation of the coating layer were occurred at the final stage of loading, while micro-cracks in the coating layer might be nucleated at the early stage of loading.

Chapter 3 Fatigue Failure and Acoustic Emission Behavior of Plasma Sprayed Hydroxyapatite Coating Layer on Commercially Pure Titanium Substrate in Ambient Atmosphere: Relationship between peak amplitudes of detected AE signal and number of cycles was obtained to discuss the fatigue damage processes under the four point bend fatigue test. The coated specimens tested under ambient environment could survive up to 107 cycles without spallation of HAp coating layers at the stress amplitude of 120 MPa. The HAp coated specimens without HAp/Ti bond coat layer showed shorter fatigue life and earlier crack nucleation compared to the HAp coated specimens with HAp/Ti bond coat layer. Therefore, HAp/Ti bond coat layer was found to significantly improve fatigue damage resistance of HAp coating layer. Three stages of the fatigue failure behavior of HAp top coat with HAp/Ti bond coat on cp-Ti substrate could be clearly identified by the AE monitoring technique. These stages were: （1） crack nucleation and propagation in coating layer, （2） the crack propagation in the substrate and （3） the unstable crack propagation to final fracture.

Chapter 4 Fatigue Failure and Acoustic Emission Behavior of Plasma Sprayed Hydroxyapatite Coating Layer on Commercially Pure Titanium Substrate in Simulated Body Fluid （SBF）: In order to investigate the influence of SBF environment on the fatigue failure behavior of HAp top coat with HAp/Ti bond coat on cp-Ti, the four point bend fatigue test under SBF environment was conducted with AE monitoring during the entire fatigue test. The coated specimen tested under ambient and SBF environments could survive up to 107 cycles without spallation of HAp coating layers at the stress amplitude of 120 MPa. The specimens tested under SBF environment and those immersed in SBF before fatigue test under ambient environment showed shorter fatigue life compared to those tested under ambient environment without SBF immersion. Micro-cracks were nucleated in the coating layers at the initial stage of fatigue test and then propagated into the cp-Ti substrate in the intermediate stage, which unstably propagated to failure at the final stage. Significant AE signals were detected during the entire fatigue loading for the coated specimens tested under SBF environment. The degradation of coating strength and fatigue life of the specimens tested under SBF environment would result from disappearance of the co-existing phases from the coating layer during immersion in SBF.

Chapter 5 Conclusion: The general conclusions with the new findings of the current work and recommendation for future work were summarized and discussed.

本論文は、「Failure and Acoustic Emission Behavior of Hydroxyapatite Coating on Commercially Pure Titanium Substrate （純チタン上のハイドロキシアパタイトコーティングの破壊およびAE発生挙動）」と題し、5章より構成されている。
第1章「Introduction」では、本研究に関わる研究動向を概説するとともに、本研究の目的と範囲を述べている。
　第2章「Bending Failure and Acoustic Emission Behavior of Plasma Sprayed Hydroxyapatite Coating Layer on Commercially Pure Titanium Substrate」では、ハイドロキシアパタイト（HAp）プラズマ溶射皮膜にはHAp相に加え、テトラカルシウムフォスフェイト（TetCP）などの相が混在しているが、擬似体液（SBF）中に浸漬すると混在相は溶出し、HAp相として析出し、溶射相はHAp単層となること、曲げ強度はSBF浸漬後のHAp単層となると低下することなどを明らかにしている。
　第3章「Fatigue Failure and Acoustic Emission Behavior of Plasma Sprayed Hydroxyapatite Caoting Layer on Commercially Pure Titanium Substrate in Ambient Atmosphere」では、大気中でのHApコーティング材の曲げ疲労試験を行い、疲労の初期にコーティング相にき裂が生じ、それがTi基材に進展し、最終破断に至ることを明らかにするとともに、AEによりき裂がコーティング層から基材へと進展する時点を検出することができること、Ti/HAp混合ボンドコート層は疲労き裂の発生を抑え、疲労強度の改善に有効であることなどを示している。
　第4章「Fatigue Failure and Acoustic Emission Behavior of Plasma Sprayed Hydroxyapatite Coating Layer on Commercially Pure Titanium Substrate in Simulated Body Fluid （SBF）」では、Ti/HAp混合ボンド層を導入したHApコーティング試験片を用い、時前にSBFに浸漬した後の疲労試験、およびSBF中に浸漬しながらの疲労試験を行い、いずれもHAp溶射層はTetCP相などの混在相は消失し、HAp単層となること、疲労強度は両者ともほぼ同等であること、SBFに浸漬しながら疲労負荷を加えると、AE信号の発生が浸漬後に負荷を加えた場合にくらべ顕著であるが、これは疲労負荷と混在相の溶出が同時に行われ、疲労強度には影響を与えない界面き裂の発生を生じるためであることなどを明らかにしている。
　第5章「Conclusion」では、以上の研究の結果を総括的にまとめるとともに、将来の展望について述べている。
よって、本論文は工学上及び工業上貢献するところが大きく、博士（工学）の学位論文として十分な価値を有するものと認める。