Evaluation of adhesion strength and toughness of fluoridated hydroxyapatite coatings

Adhesion strength and fracture toughness are two crucial mechanical properties for bioceramic coatings on metal implants directly affecting successful implantation and long-term stability. In this study, the adhesion strength of sol-gel derived FHA coatings on Ti6Al4V substrates was measured by pull-out tensile test, and the toughness was assessed by energy release method. With increase of the degree of fluoridation, the adhesion strength increases up to about 40% and the fracture toughness increases about 200 to 300%. Contrary to the wide-spread belief, it is interesting to note that after soaking in the Tris-buffered physiological saline solution (for 21 days), the adhesion strength increases about 60% as compared with the as-deposited coating, instead of decreasing. The mechanism of the increase is discussed.     

An interfacial study of sol-gel-derived magnesium apatite coatings on Ti6Al4V substrates

Magnesium apatite coatings on Ti6Al4V substrate were synthesized by the sol-gel dip-coating method. Magnesium was incorporated in the coating according to the formula (Ca_10−xMg_x)(PO₄)₆(OH)₂, where x = 0, 0.50, 1.00, 1.50 and 2.00. Approximately 2-μm-thick apatite coatings were derived after five cycles of dip-drawing-drying-firing process. A transitional region (R_t) was formed between substrate and coating during the firing process. Adhesion tests show that the adhesion strength between substrate and apatite coating is enhanced by the incorporation of magnesium in the coating. The quantity of magnesium incorporated appeared to correspond to the Mg-Ti-O chemical bonds formed in the transitional region, which contributed to the adhesion strength of the coatings.     

Thermo-metallo-mechanical modelling of heat treatment induced residual stress in Ti–6Al–4V alloy

Residual stress fields dynamically fluctuate throughout the manufacturing process of metallic components and are caused by local misfit of a thermal, mechanical or metallurgical nature. Recent advances have been made in the area of microstructure and residual stress prediction; yet few have considered dual-phase titanium alloys. The aim of the work presented was to carry out a review of the existing state-of-the-art in residual stress modelling with an intended application to industrial heat treatment of Ti–6Al–4V alloy. Four areas were evaluated: thermal, mechanical and metallurgical sub-models, and model validation via residual stress measurement. Recommendations for future research include further investigation of transformation induced plasticity and stress relaxation behaviour in Ti–6Al–4V.

This review was submitted as part of the 2019 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged.     

电泳沉积制备羟基磷灰石/生物玻璃梯度涂层的研究

本文研究了羟基磷灰石颗粒、生物玻璃颗粒在醋酸介质中的电泳沉积规律 ,利用它们不同的沉积规律设计了羟基磷灰石 /生物玻璃梯度沉积装置。用电子探针分析了涂层横截面元素分布 ,表明所设计的装置可实现羟基磷灰石和生物玻璃的梯度涂层     

钛合金表面涂覆生物活性涂层的制备技术及进展

对于生物医用材料Ti6A14V，利用表面改性技术涂覆生物活性陶瓷羟基磷灰石（HA）涂层不仅可以保留钛合金优良的力学性能，还能提高其表面的稳定性和耐磨性，同时提高其生物活性，使新骨直接沉积于Ti6A14V表面，而无纤维结缔组织的中间隔层，从而促进缺损骨的修复，甚至引导新生骨的生长。因此该材料已成为当前人工骨种植体研究的热点之一。本文综述了该材料的制备技术及进展，并分析了各种制备方法的优缺点。     

羟基磷灰石涂层材料的制备及其性能表征

设计并采用类似搪瓷涂覆的工艺制备了羟基磷灰石－Ｔｉ６Ａｌ４Ｖ复合材料．使用ＸＲＤ、ＳＥＭ对复合材料的相组成和显微结构进行分析和表征,在模拟体液中观察了获得材料的生物相容性．结果表明;在涂层中,羟基磷灰石粒子均匀地分散在玻璃基体中,它们保持原有的晶格结构,未发生相分解等现象．烧成温度对中间层玻璃涂层的显微结构有着较为明显的影响．中间层玻璃涂层与钛合金的结合强度或不小于２９．７３ＭＰａ,远高于等离子喷涂,达到使用要求．在模拟体液中浸泡一段时间后,ＸＰＳ分析表明复合材料表面有新生羟基磷灰石粒子析出,表明复合涂层有优良的生物相容性．     

The effects of forging pressure and temperature field on residual stresses in linear friction welded Ti6Al4V joints

Linear friction welding (LFW), as a solid state joining process, has been developed to manufacture and repair blisks in aeroengines. The residual stresses after welding may greatly influence the performance of the welded components. In this paper, the distribution of residual stresses in Ti6Al4V joints after LFW was investigated with numerical simulations. The effects of applied forging pressure and temperature field at the end of the oscillating stages on the residual stresses within the joints were investigated. The results show that, the residual tensile stresses at the welded interface in the y-direction are the largest, while the largest compressive stresses being present at the flash root in the z-direction. Furthermore, the forging pressure and temperature field at the end of the oscillating stages strongly affect the magnitude of the residual stresses. The larger forging pressure produced lower residual stresses in the weld plane in all three directions (x-, y-, and z-directions). Larger variance, σ, which decides the Gaussian distribution of the temperature field, also yields lower residual stresses. There is good agreement between simulation results and experimental data.     

Feasibility study on preparation of coatings on Ti–6Al–4V by combined ultrasonic impact treatment and electrospark deposition

A novel method combining ultrasonic impact treatment (UIT) with electrospark deposition was developed to prepare coatings on Ti–6Al–4V substrates. The microstructure, phase composition, residual stress, microhardness, and wear performance of the coating were studied, and new amorphous and nanocrystalline phases (titanium carbide nitride and iron titanium oxide) were found. In addition, the residual stress in the coating and in the substrate near the coating is compressive stress. The maximum compressive residual stress is about −717 MPa, and its depth is about 470 μm. Because of contributions from multiple factors, the wear volume loss of the sample subjected to combined UIT and electrospark processing was reduced by four orders of magnitude compared with that of the base material.     

A simple chemical method for preparation of hydroxyapatite coatings on Ti6Al4V substrate

A novel, simple and economical chemical bath method for deposition of calcium hydroxyapatite coating has been developed. The coatings were prepared from EDTA solutions in alkaline media on Ti6Al4V substrates. The method is based on thermal dissociation of the Ca(EDTA)^2- complex at 65–95 °C. Two chemical baths with and without presence of Na⁺ and Cl^- were used for the deposition. The Rutherford back scattering study shows that the coating material from bath which contained sodium and chlorine ions have their presence in the coated material. The bath which has been prepared with potassium substituting sodium and nitrate substituting chlorine produced coatings with better stoichiometry, with Ca/P=1,67. The X-ray analysis revealed that the calcium hydroxyapatite coatings have preferred crystal orientation in the 002 direction. © 2001 Kluwer Academic Publishers     

Evaluation of residual stress in stainless steel 316L and Ti6Al4V samples produced by selective laser melting

Selective laser melting (SLM) has great potential in additive manufacturing because it enables the production of full-density complex parts with the desired inner structure and surface morphology. High temperature gradients as a result of the locally concentrated energy input lead to residual stresses, crack formation and part deformation during processing or after separation from the supports and the substrate. In this study, an X-ray diffraction technique and numerical simulation were used for investigating the residual stress in SLM samples fabricated from stainless steel 316L and Ti6Al4V alloy. Conclusions regarding directions and values of stresses in SLM objects are given.     

Ti6Al4V表面HAP/TiO2生物活性复合涂层的表征及结合强度分析

采用溶胶一凝胶法在Ti6Al4V基体上制备了HAP／TiO2纳米复合涂层,并引入TiO2作为缓冲层。使用XRD、FT-IR和FE-SEM协同EDS研究了450、550和650℃温度下煅烧后涂层的组成和结构特征。实验结果表明,HAP／TiO2涂层均具有较好的结晶态,涂层厚度均匀、致密,与金属基体结合紧密。由亚微米级HAP晶体颗粒(100～200nm)镶嵌在分布均匀的纳米TiO2胶质之中,TiO2凝胶颗粒大小随煅烧温度的变化在10～30nm变动。力学测试结果表明这些复合涂层具有较高的结合强度,随着煅烧温度的升高,涂层的抗拉强度呈现上升的趋势。体外生物活性的测试证实了它们的生物活性。     

Biocompatible and mechanical properties of low temperature deposited quaternary (Ti, Al, V) N coatings on Ti6Al4V titanium alloy substrates

A series of quaternary (Ti, Al, V) N coating layers were obtained by low temperature reactive plasma sputtering in differing deposition conditions to improve the wear resistance and the biocompatibility of a titanium surgical alloy, specifically Ti-6Al-4V. Characterization of the mechanical properties, structure and the chemical composition of the coating layer was explored by microhardness test, ball against flat wear test, scanning electron microscopy and X-ray diffraction. The biocompatibility of the optimum coating layer (as determined by mechanical performance) was examined by a modified MTT toxicity test and by monitoring cell growth assessed by quantitative stereological analysis. The experimental results are encouraging, indicating that this low temperature deposited, dense, quaternary (Ti, Al, V) N coating layer exhibits improved mechanical properties such as high hardness and excellent adhesion to a Ti alloy substrate and is highly biocompatible.     

Fabrication,characterization, and biocompatibility of ethyl cellulose/carbonated hydroxyapatite composite coatings on Ti6Al4V

In order to improve the biocompatibility of metallic implants, bioactive components are often used as coatings so that a real bond with the surrounding bone tissue can be formed. We prepared ethyl cellulose/carbonated hydroxyapatite composite coatings (ECHCs) on Ti6Al4V substrates with carbonated hydroxyapatite coatings (CHACs) without ethyl cellulose as controls. The inorganic constituent on the CHACs and ECHCs is calcium-deficient carbonated hydroxyapatite with a flaky texture and a low degree of crystallinity. The flaky carbonated hydroxyapatite plates aggregate to form macropores with an aperture size of around 0.5–2.0 μm. The presence of ethyl cellulose provides superior morphology, contact angle, and biocompatibility characteristics. In comparison to CHACs, ECHCs exhibit a smoother, crack-free surface because the cracks are filled by ethyl cellulose. Moreover, the contact angle of ECHCs is 37.3°, greater than that of CHACs (13.0°). Surface biocompatibility was investigated by using human bone mesenchymal stem cells (hBMSCs). The attachment, spreadability, viability and proliferation of hBMSCs on ECHCs are superior to those on CHACs. Thus, the crack-free ECHCs have excellent biocompatibility and are appropriate for use as biological implants.     

热处理对羟基磷灰石涂层相组成、表面形貌与结合强度的影响

羟基磷灰石(HA)涂层的喷涂及其后处理工艺对其组织结构和结合强度具有重要影响.比较了热处理对不同粒度HA涂层相组成、表面形貌与结合强度的影响,为该类涂层制备工艺的优化提供实验依据.采用等离子喷涂法在纯钛表面制备了不同粒度的HA涂层,对其进行650℃不同保温时间的后热处理.利用X射线衍射仪、扫描电子显微镜和电子拉伸机检测了涂层的相组成、表面与断口形貌及剪切结合强度等.结果表明,涂层经650℃保温0.5h热处理后,非晶相和分解相基本全部转变为结晶HA.经热处理晶化后,涂层表面生成300nm以下的微粒子,双重涂层BC表面更易形成.粗粉末涂层CC和BC热处理后的剪切强度提高,而细粉末涂层FC则相反;HA涂层的剪切断裂主要是发生在涂层与基体间的界面上.     

Ti6Al4V表面生物陶瓷涂层设计与生物活性研究

设计并制备了适用于Ti6Al4V表面涂覆层的生物陶瓷材料,将烧结后的陶瓷浸入模拟体液中,借助SEM、ICP、FTIR等分析技术研究其生物活性机理,结果表明所研制的陶瓷材料不仅具有和Ti6Al4V相匹配的热膨胀系数,且表面可沉积生成碳酸羟基磷灰石(HCA)具有良好的生物活性.     

Numerical simulation of residual stresses in diamond coating on Ti-6Al-4V substrate

In this paper, we present numerical simulations of the residual stresses developed between diamond coatings and Ti-6Al-4V substrates when using chemical vapour deposition technique. The large difference in thermal expansion coefficients of diamond and titanium alloys results in high residual stresses in the diamond film. This could lead to interfacial cracking and material failure. The finite element method was used to simulate the cooling process of diamond films at various thicknesses and deposited at temperatures ranging from 600 °C to 900 °C. The influence of different parameters such as temperature, film thickness, material characteristics, geometry and edge effects are investigated for different case geometries. The film debonding and cracking is discussed and numerical results are compared with existing experimental and numerical results. Finally, some propositions are made to enhance the experimental process in order to reduce the residual stress intensities and the possible material degradation.     

Development and characterization of laser clad high temperature self-lubricating wear resistant composite coatings on Ti–6Al–4V alloy

To enhance the wear resistance and friction-reducing capability of titanium alloy, a process of laser cladding γ-NiCrAlTi/TiC + TiWC₂/CrS + Ti₂CS coatings on Ti–6Al–4V alloy substrate with preplaced NiCr/Cr₃C₂–WS₂ mixed powders was studied. A novel coating without cracks and few pores was obtained in a proper laser processing. The composition and microstructure of the fabricated coating were examined by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) techniques, and tribological properties were evaluated using a ball-on-disc tribometer under dry sliding wear test conditions at 20 °C (room-temperature), 300 °C, 600 °C, respectively. The results show that the coating has unique microstructure consisting of α-Ti, TiC, TiWC₂, γ-NiCrAlTi, Ti₂CS and CrS phases. Average microhardness of the composite coating is 1005 HV_0.2, which is about 3-factor higher than that of Ti–6Al–4V substrate (360 HV_0.2). The friction coefficient and wear rate of the coating are greatly decreased due to the combined effects of the dominating anti-wear capabilities of reinforced TiC and TiWC₂ carbides and the CrS and Ti₂CS sulfides which have excellent self-lubricating property.     

Rapidly cured epoxy/anhydride composites: Effect of residual stress on laminate shear strength

The drive towards rapid cure thermosetting composites requires a better understanding of the residual stresses that develop during curing. This study investigates the impact of residual stresses on the interlaminar shear strength of resin-infused epoxy/anhydride carbon-fibre laminates. The magnitude of the residual stress was varied by changing the initial injection cure temperature between 75 °C and 145 °C. The corresponding cycle times and the final glass transition temperature of the resin were also measured. The experimentally measured chemical shrinkage and thermal expansion properties of the resin after vitrification were used as inputs to a finite element analysis to calculate the peak residual stresses in the composite. An increase in the initial cure temperature from 85 to 135 °C resulted in an increase of 25% in the residual stress, which led to an experimentally measured reduction in the composite’s short beam shear strength of approximately 16% (8 MPa), in good agreement with model prediction.