Mahmood Anwar

Surface Modification Techniques for Biomedical Grade of Titanium Alloys: Oxidation, Carburization and Ion Implantation Processes

Titanium and titanium alloys are widely used in a variety of engineering applications, where the combination of mechanical and chemical properties is of crucial importance. Aerospace, chemical and automotive industries as well as the medical device manufacturers also benefited from the outstanding properties of titanium alloys. The wide spread of its uses in biomedical implants is mainly due to their well-established corrosion resistance and biocompatibility. However, not all titanium and its alloys can meet all of the clinical requirements for biomedical implants. For instance, it is reported that bare titaniumvanadium alloy has traces of vanadium ion release after long period exposure with body fluid (Lopez et al., 2010). Excessive metal ions release into the body fluid and causes toxicity problems to the host body. A new group of titanium alloy such as Ti-Nb and Ti-Zr based are recently introduced in the market to overcome the toxicity of titanium-vanadium based alloy (Gutierrez et al., 2008). Although, these alloys have a high strength to weight ratio and good corrosion resistance and biocompatible, but it suffers from poor tribological properties which limits their usefulness to a certain extent especially when they are applied to joint movements. Wear debris generated from these articulation joints can induce inflammation problem and toxic effect to the human body. In biomedical point of view, post implantation is very crucial stage where the interaction between the implanted material surface and the biological environment in human body is critically evaluated. Either in the short or long run, the toxic effect becomes an issue to host body. Hence, the implant material surface has a strong role in the responses to the biological environment. In order to improve the biological and tribological properties of implant materials, surface modification is often required (Huang et al., 2006, Kumar et al., 2010b). This chapter embarks on the commonly used implant biomaterials, followed by general overview on the surface modification techniques for treating titanium alloy. The basic principles of oxidation, carburization and ion implantation methods and their developments are discussed in the following sections.

Effect of thermal oxidation temperature on rutile structure formation of biomedical TiZrNb alloy

Wear debris and metal ion release generated during application of biomedical devices would cause adverse cellular response, inflammation and pain in the human body. Modifying of implant surface with rutile structure is one of the methods to reduce these problems. In the present study, an attempt was made to evaluate the effect of thermal oxidation temperature on surface morphology and structure of the Ti13Nb13Zr biomedical material. The substrates were heated at varied temperatures of 550°C, 700°C and 850°C for 9 hours and cooled inside muffle furnace at a constant rate of 5oC/min. Scanning electron microscopy and x-ray diffractive were employed to evaluate the surface morphology and analyze the structure of the oxidized substrates respectively. All thermally oxidized samples exhibit the presence of oxides without spallation regardless of the thermal oxidation temperatures. Surface morphology of oxidized substrates changes from smooth to nodular particles-like shape when the oxidation temperature increases from low to high. Rutile structure dominants the surface area when the substrate is thermally oxidized at 850 °C.

Effect of pretreatment process on thermal oxidation of biomedical grade cobalt based alloy

Wear on Co-Cr-Mo biomedical implants is still a major issue especially for applications in articulation joints like in total ankle, knee and hip arthroplasty. Generation of excessive wear particles can coagulate in body tissues which later cause inflammation, bone loss and necrosis. Modification of implant surfaces is a common technique for increasing the hardness and thus minimizing these effects. In this study, thermal oxidation method was carried out on the Co-Cr-Mo to investigate the effects of different pretreatment processes and surface roughness on the hardness of oxide layer formed. Prior to oxidation process, all samples were annealed and pickled to remove residual stress and oxide scales respectively. The oxidation process was done inside furnace under atmospheric condition for 3 hours at 1160 °C. The metallic compositions, surface morphology and hardness of the oxide layer formed on the substrate were verified using X-ray diffraction (XRD), scanning electron microscope and micro-Vickers hardness analysis respectively. It is found that mechanical pretreatment provides oxide/carbide layer with higher hardness than chemical pretreatment method. It is believed that remnants of polishing diamond pastes trapped in roughness valleys react with metal matrix and later transform into carbides during oxidation process. In contrast, initial surface roughness of the substrate has no significant effect on the hardness of oxide/carbide layer.

Influence of Bias Voltage on Corrosion Resistance of TiN Coated on Biomedical TiZrNb Alloy

Recently, Composite Sandwich Panel (CSP) technology considerably influenced the design and fabrication of high performance structures. Although using CSP increases the reliability of structure, the important concern is to understand the complex deformation and damage evolution process. This study is focused on the flexural and indentation behavior of CSP made of chopped strand mat glass fiber and polyester matrix as face sheets and polyurethane foam as foam core subject to flexural and indentation loading condition. A setup of three-point bending and indentation test is prepared using different strain rates of 1mm/min, 10mm/min, 100mm/min and 500mm/min to determine the effects of strain rate on flexural and indentation behavior of CSP material. The load-extension, stress-extension response and energy absorption of the panel show the relation between the flexural and indentation behavior of panels to strain rate as by increasing the strain rate, the flexural properties and the energy absorption of panel are increased.

Effect of pickling and mechanical surface treatment methods on adhesion strength of Ti oxide layer formed on Titanium alloy substrate

Titanium alloys are commonly used in biomedical application in hard tissues replacement especially for knee and hip implants but facing huge wear debris due to continuous cyclic contact within the joints of the implants. Diamond coating is a potential solution for improving the tribological and wear properties of the implants made from this alloy. Diamond is known for having high wear resistance property and chemical vapour deposition (CVD) is one of the most promising methods for diamond coating. However, the major concern for CVD process is the poor adhesion of the diamond to the substrate material due to the large mismatch of coefficient of thermal expansion (CTE) properties between the two. A suitable interlayer material can be introduced to reduce the gap of CTE differences by oxidation process. In this study, the effect of pickling temperature and mechanical surface treatment methods on the adhesion strength of Ti oxide interlayer prior to diamond coating were investigated. Besides, the thickness of oxide layer and surface morphology were also evaluated. Experiments were carried out on Ti6Al4V substrate by varying the surface treatment pickling temperature from 25°C to 50°C. In mechanical surface treatment, all samples were ground using #220 to #1200 grits and followed with polishing using alumina paste. After the surface treatment process, all the substrates underwent thermal oxidation for 25 hours at 900°C. The results showed that the adhesion strength of oxide layer increases with the increasing of pickling temperature. Mechanical surface pretreatment provides better adhesion of oxide layer than chemical pretreatment (pickling process). However, the adhesion strength decreases with the increases of oxide layer thickness.

Effect of Carburization Process on Adhesion Strength of Ti Carbide Layer on Titanium Alloy Substrate

Titanium alloys are commonly used in biomedical application in hard tissues replacement especially for knee and hip implants. Surface modifications are required prior to diamond coating process for improving tribological and wear properties of the titanium alloy. In this study, experiments were carried out to investigate the effects of different carburizing times on the adhesion strength of carbide layer formed on the Ti-6Al-7Nb. Prior to carburization process, all samples were treated to remove residual stress and oxide scales by annealing and pickling processes respectively. Hard wood charcoal powder was used as a medium. The carburizing process was carried out for 6, 12 and 24 hours at 950 °C under normal atmospheric condition. Surface morphology, carbide layer thickness and adhesion strength were evaluated using SEM, XRD, 3D Surface Profilometer and Blast Wear Tester (BWT). It is found that a mixture of oxide and carbide layers formed on the substrate and the thickness of these layers increases with carburizing time. It is also revealed that the 24 hr carburizing time provides the strongest adhesion strength among the three and TiC as the dominant layer.

Effect of pickling process on adhesion strength of Ti oxide layer on titanium alloy substrate

Titanium alloys are commonly used in biomedical application in hard tissues replacement especially for knee and hip implants. Surface modifications are required prior to diamond coating process for improving the tribological and wear properties of the titanium alloy. In this study, experiments were carried out to investigate the effects of different pickling times as well as temperature on the adhesion strength of oxide layer formed on the Titanium alloy after oxidation process. The aqueous acid solution of HF and HNO3 was used as a pickling solution. The chemical pretreatment was carried out at 4 levels by varying the pickling time as well as temperature. All treated samples were thermally oxidized in a fixed parameters at 900 °C for 25 hours. Surface morphology, oxide layer thickness and adhesion strength were measured after each step using FESEM and Blast Wear Tester (BWT). It was revealed that the thickness of oxide layer increases with pickling time but the adhesion strengths become weaker. It was also found that the adhesion strength of oxide layer formed on Ti substrate surface increases with the increase of temperature while the thickness of the oxide layer decreased within 40oC pickling temperature.

Counter‐Top Thermoacoustic Refrigerator‐ An Experimental Investigation

Thermoacoustic phenomenon is a new alternative refrigeration technology. Though design and fabrication is complex for getting the desired effect, it is environmentally friendly and successful system showed that it is relatively easy to run compared to the traditional vapor compression refrigeration system. Currently, theories supporting the thermoacoustic refrigeration systems are yet to be comprehensive to make them commercially viable. Theoretical, experimental, and numerical studies are being done to address the thermodynamics‐acoustics interactions. In this study, experimental investigations were completed to test the feasibility of the practical use of a thermoacoustic refrigerator in its counter‐top form for future specific application. The system was designed and fabricated based on linear acoustic theory. Acoustic power was given by a loud speaker and thermoacoustic effects were measured in terms of the cooling effects produced at resonanance. Investigations showed that discrepancies between desig...

Thermal Optimization of Electronic Equipment: Form Factor Improvement

The need to have equipments with a low form factor, defined as depth divided by the width multiplied by the height, is very essential for a particular product to be marketable. Thus, when an old product needs to be customized to a new form factor, while maintaining the standardized components, there will be distorted thermal distribution. In this study, original product was tested and the temperature distribution was measured. Temperature for critical components were numerically modeled and experimentally measured. The usage of ducting inside the prototype was introduced along with variable fan speed to ensure heat load meets the requirements. Numerical and experimental approach was used to verify the temperature distribution in the new prototype. The results show that, increase in duct size reduce the Nusselt number for the flow, which is detrimental to the overall heat distribution. Consequently, the fan speed needs to be increased to ensure optimum flow velocity that will conform to the accepted noise level. Final prototype was completed with form factor transform from 9m-1 to 1m-1 with more than eighty percent components maintained. The reduction in form factor shows the usage of ducting aids significantly in achieving good heat distribution. Numerical and experimental data show good agreement at all critical points measured.