Effect of hydrothermal treatment on the plasma-sprayed hydroxyapatite coatings

doi:10.3969/j.issn.2095-4344.1350

Abstract

Abstract:

BACKGROUND: Hydroxyapatite coating prepared by plasma spraying on titanium alloy surface has many advantages, such as high flame temperature, fast flight speed, little thermal effect of deposited body, good smoothness, mature technology and high automation, but there are also many problems, such as poor mechanical properties, low crystallinity and large residual stress.

OBJECTIVE: To investigate the effects of hydrothermal treatment on the characteristics and mechanical properties of hydroxyapatite coatings.

METHODS: Hydroxyapatite coatings were prepared on titanium alloys by plasma spraying. The coatings were hydrothermally treated for 2, 4, 6 and 8 hours respectively. The material characteristics of the coatings before and after hydrothermal treatment were analyzed by scanning electron microscopy, X-ray diffraction and energy dispersive spectrometry. The microhardness and elastic modulus of the coatings were also measured.

RESULTS AND DISCUSSION: Hydroxyapatite decomposition and amorphous phenomena occurred during spraying process, resulting in crystalline phases such as TCP, TTCP, CaO and a large number of amorphous phases. Hydrothermal treatment can promote the transformation of crystalline and amorphous phases into crystalline hydroxyapatite. After hydrothermal holding at 150 °C for 8 hours, the crystallinity of the coating increased from 6.9% to 93.76%. More voids and cracks were observed after spraying, which increased the specific surface area of the coating and accelerated the dissolution and recrystallization process of hydroxyapatite. Hydrothermal treatment promoted the formation and aggregation of nano-hydroxyapatite microcrystals on the crack surface, which was the fundamental cause for the phenomenon of "self-healing" of some cracks. The Young’s modulus and micro-hardness of the coating after hydrothermal treatment were better than those after spraying. The results indicate that hydrothermal treatment can effectively improve the crystallinity, elastic modulus and microhardness of hydroxyapatite coatings.

Key words: plasma spraying, hydroxyapatite, hydrothermal treatment, amorphous phases, crystallinity, self-healing phenomenon, Young’s modulus, micro-hardness

CLC Number:

Zhao Wen, Liu Feng, Wang Hongfu, Cheng Bo, Wang Junyuan . Effect of hydrothermal treatment on the plasma-sprayed hydroxyapatite coatings[J]. Chinese Journal of Tissue Engineering Research, 2019, 23(26): 4160-4164.

Figures/Tables 3

2.2 水热处理后涂层的微观结构分析图4揭示了水热处理前后羟基磷灰石涂层的显微结构特征。图4A中涂层呈现出典型的层片状和弥散球状颗粒结构，这是处于融化状态下的羟基磷灰石粉末相互叠加黏结的结果。在喷涂工艺中，大部分的羟基磷灰石粉末高速撞击基体表面形成熔融的层片状结构，少部分粉末由于融化不充分或者处于等离子射流的边缘，其相对能量较少且与外界环境接触较多，造成热量损失较大，从而在撞击过程中融化不充分，形成弥散的球状颗粒。图4B揭示了水热处理对涂层的修复作用，不同于喷涂后涂层表面“断崖式”的裂纹形貌，水热处理2 h后涂层表面的部分裂纹出现了“自愈”现象[35-37]。结合X射线衍射过程分析，水热处理使涂层中的分解相加速溶解生成羟基磷灰石微晶，这些微晶在裂纹表面不断生长、聚集，“缝合”裂纹，最终使其“自愈”。这个现象从直观上反映了涂层中新结晶相的溶解和羟基磷灰石的沉淀过程。图4C表明水热处理8 h后涂层表面生成了新的物质，这些新生成相为纳米尺度，呈卷曲直立的片状结构。与标准羟基磷灰石PDF卡片的三强线峰(211)(112)(300)相对比，此次结果中的羟基磷灰石三强线峰均发生明显的右侧偏移，表明有其他元素进入羟基磷灰石的晶格中。结合图4D中X射线能谱元素相对原子比例，新生成物为含CaCO3的钙镁磷酸盐，其化学式近似为Ca8.5Mg1.5(PO4)6(OH)2•CaCO3。 2.3 水热处理后涂层的弹性模量与微观硬度图5显示水热处理后涂层的弹性模量和微观硬度总体上得到了改善，未处理前涂层的弹性模量和微观硬度分别为4.837， 0.581 GPa；水热处理4 h后，涂层的弹性模量达到最大值8.026 GPa，水热处理6 h后涂层微观硬度达到最大值 1.478 GPa，这是因为水热处理大幅降低了涂层中由于受热产生的残余应力，起到了退火作用，同时水热处理较高的压强及加速新结晶相转变的特点，造成涂层中较大的裂纹逐步弥散化，涂层更加致密；但水热处理8 h后，涂层的弹性模量和硬度值均较之前降低，分别为7.661，0.9 GPa，这是因为0-6 h的水热处理是大裂纹裂解成小裂纹并发生裂纹弥散的过程，尽管涂层的均匀性和致密性较之前更佳，但是随着处理时间的进一步增长，裂纹的数量和应力达到阈值，发生剧烈扩散，导致涂层裂解化加剧。鉴于此结论，作者认为若对涂层进行进一步的水热处理，涂层的弹性模量和微观硬度会出现先降后升，最终趋于平稳的趋势。"

References

[1]殷亚康.钛合金表面等离子喷涂钛/羟基磷灰石复合涂层及其细胞相容性研究[D].乌鲁木齐:新疆大学,2015.

[2]吴永智.等离子喷涂羟基磷灰石/纳米氧化锆梯度涂层的研究[D].北京:北京工业大学,2008.

[3]郑学斌,陈益凯,梁莹,等.等离子体喷涂新型生物活性涂层研究[J].热喷涂技术,2009,1(1):59-62.

[4]El-hadad AS.An approach to design new coatings for biomedical applications.Universidad Carlos III de Madrid, 2012.

[5]Piccinini M.Porous calcium phosphate granules for biomedical applications.University of Trento, 2012.

[6]Ibrahim MZ,Sarhan AAD,Yusuf F,et al.Biomedical materials and techniques to improve the tribological, mechanical and biomedical properties of orthopedic implants- A review article.J Alloy Compound. 2017;714:636-667.

[7]Zhou H,Lee J.Nanoscale hydroxyapatite particles for bone tissue engineering.Acta Biomater. 2011;7(7):2769-2781.

[8]高淑春.NiTi形状记忆合金和TA2钛合金生物材料的表面改性及生物学性能研究[D].沈阳:东北大学,2013.

[9]于振涛,韩建业,麻西群,等.生物医用钛合金材料的生物及力学相容性[J].中国组织工程研究,2013, 17(25):4707-4714.

[10]Geetha M,Singh AK,Sokamani RA,et al. Ti based biomaterials, the ultimate choice for orthopaedic implants-A review.Prog Mater Sci. 2009;54(3):397-425.

[11]Rokosz K, Hryniewicz T, Raaen S. Development of plasma electrolytic oxidation for improved Ti6Al4V biomaterial surface properties.Int J Adv Manuf Technol.2016;85(9):1-13.

[12]张文毓.生物医用钛合金的研究进展[J].化学与粘合,2014,36(5): 369-373.

[13]张玉梅,王勤涛,赵铱民,等.新型医用Ti75,TiZr合金的生物腐蚀行为研究[J].稀有金属材料与工程, 2016,33(1):19-22.

[14]Fomin A,Fomina M,Koshuro V,et al.Structure and mechanical properties of hydroxyapatite coatings produced on titanium using plasma spraying with induction preheating.Ceram Int. 2017;43(14): 11189-11196.

[15]高亚丽,熊党生.医用镁合金等离子喷涂羟基磷灰石涂层研究[J].材料热处理学报,2011,32(1):109-113.

[16]Wang Y,Liu X,Fan T,et al.In vitro evaluation of hydroxyapatite coatings with (002) crystallographic texture deposited by micro-plasma spraying. Mater Sci Eng C-Mater.2017;75:596-601.

[17]冷喷涂技术在生物医学领域中的应用及展望[J].表面技术, 2016,45(9):25-31.

[18]陈枭,白小波,纪岗昌,等.微米羟基磷灰石/钛复合粒子冷喷沉积行为[J].金属热处理,2018,43(11):89-95.

[19]智伟,匙峰,李金雨,等.羟基磷灰石球形颗粒表面微形貌构建及其对干细胞生物学行为的调控[J].无机材料学报, 2017,32(3):319-325.

[20]Asri RI,Harun WS,Hassan MA,et al.A review of hydroxyapatite-based coating techniques: Sol-gel and electrochemical depositions on biocompatible metals.J Mech Behav Biomed Mater.2016;57:95-108.

[21]李素敏,张芹,赵玉涛,等.HAF/YSZ梯度复合涂层的制备及结构和性能[J].中国组织工程研究,2011, 15(47):8805-8808.

[22]Jansen JA,Wolke JGC,Swann S,et al.Application of magnetron sputtering for producing ceramic coatings on implant materials.Clin Oral Implants Res.2010;4(1):28-34.

[23]Boccaccini AR,Keim S,Ma R,et al.Electrophoretic deposition of biomaterials. J R Soc Interface. 2010;7 Suppl 5(51): S581-S613.

[24]鞠昊.微弧氧化处理Ti6Al4V的体外生物相容性研究[D].长春:吉林大学, 2017.

[25]Yang YC.Influence of residual stress on bonding strength of the plasma-sprayed hydroxyapatite coating after the vacuum heat treatment.Surf Coat Technol. 2007;201(16-17):7187-7193.

[26]Im KH,Lee SB,Kim KM,et al. Improvement of bonding strength to titanium surface by sol–gel derived hybrid coating of hydroxyapatite and titania by sol–gel process.Surf Coat Technol.2007;202(4-7):1135-1138.

[27]Zheng X, Huang M, Ding C. Bond strength of plasma-sprayed hydroxyapatite/Ti composite coatings. Biomaterials. 2000;21(8): 841-849.

[28]Fan X,Chen J,Zou JP,et al.Bone-like apatite formation on HA/316L stainless steel composite surface in simulated body fluid.Trans Nonferrous Met Soc China.2009;19(2):347-352.

[29]Oliver WC,Pharr GM.Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology.J Mater Res. 2004;19(1):3-20.

[30]Shamray VF,Sirotinkin VP,Smirnov TV.Structure of the hydroxyapatite plasma-sprayed coatings deposited on pre-heated titanium substrates. Ceram Int. 2017;43(12):9105-9109.

[31]Sun L,Berndt CC,Gross KA,et al. Material fundamentals and clinical performance of plasma‐sprayed hydroxyapatite coatings: A review. J Biomed Mater Res.2010;58(5):570-592.

[32]Leylavergne M,Vardelle A,Dussoubs B,et al.Comparison of plasma-sprayed coatings produced in argon or nitrogen atmosphere. J Therm Spray Technol.2018;(4):527-536.

[33]Sadikov KG,Sofronitskiy AO,Dautov TG.Functional plasma sprayed coatings on magnesium ceramic substrates. JPCS. 2017:012043.

[34]Sargin Y,Kiziyalli M,Telli C,et al.A new method for the solid-state synthesis of tetracalcium phosphate, a dental cement: X-ray powder diffraction and IR studies.J Eur Ceram Soc.1997;17:963-970.

[35]Yang CW,Lui TS. Microstructural self-healing effect of hydrothermal crystallization on bonding strength and failure mechanism of hydroxyapatite coatings.J Eur Ceram Soc. 2008;28(11):2151-2159.

[36]Yang CW,Lee TM,Lui TS,et al.A comparison of the microstructural feature and bonding strength of plasma-sprayed hydroxyapatite coatings with hydrothermal and vacuum post-heat treatment.Mater Trans. 2005;46(3):709-715.

[37]Yang CY,Lee TM,Yang CW,et al.The in vitro and in vivo biological responses of plasma-sprayed hydroxyapatite coatings with post- hydrothermal treatment.J Biomed Mater Res.2007; 83A:263-271.