Effects of Various Polishing Techniques on the Surface Characteristics of the Ti-6Al-4V Alloy and on Bacterial Adhesion

Electrochemical Polishing of Ti and Ti6Al4V Alloy in Non-Aqueous Solution of Sulfuric Acid

This paper reports the results of our study on electrochemical polishing of titanium and a Ti-based alloy using non-aqueous electrolyte. It was shown that electropolishing ensured the removal of surface defects, thereby providing surface smoothing and decreasing surface roughness. The research was conducted using samples made of titanium and Ti6Al4V alloy, as well as implant system elements: implant analog, multiunit, and healing screw. Electropolishing was carried out under a constant voltage (10-15 V) with a specified current density. The electrolyte used contained methanol and sulfuric acid. The modified surface was subjected to a thorough analysis regarding its surface morphology, chemical composition, and physicochemical properties. Scanning electron microscope images and profilometer tests of roughness confirmed significantly smoother surfaces after electropolishing. The surface profile analysis of processed samples also yielded satisfactory results, showing less imperfections than before modification. The EDX spectra showed that electropolishing does not have significant influence on the chemical composition of the samples.

Effects of Shot Peening and Electropolishing Treatment on the Properties of Additively and Conventionally Manufactured Ti6Al4V Alloy: A Review

This literature review indicates that the basic microstructure of Ti6Al4V is bimodal, consisting of two phases, namely α + β, and it occurs after fabrication using conventional methods such as casting, plastic forming or machining processes. The fabrication of components via an additive manufacturing process significantly changes the microstructure and properties of Ti6Al4V. Due to the rapid heat exchange during heat treatment, the bimodal microstructure transforms into a lamellar microstructure, which consists of two phases: α' + β. Despite the application of optimum printing parameters, 3D printed products exhibit typical surface defects and discontinuities, and in turn, surface finishing using shot peening is recommended. A literature review signalizes that shot peening and electropolishing processes positively impact the corrosion behavior, the mechanical properties and the condition of the surface layer of conventionally manufactured titanium alloy. On the other hand, there is a lack of studies combining shot peening and electropolishing in one hybrid process for additively manufactured titanium alloys, which could synthesize the benefits of both processes. Therefore, this review paper clarifies the effects of shot peening and electropolishing treatment on the properties of both additively and conventionally manufactured Ti6Al4V alloys and shows the effect process on the microstructure and properties of Ti6Al4V titanium alloy.

Advanced Optimization of Surface Characteristics and Material Removal Rate for Biocompatible Ti6Al4V Using WEDM Process with BBD and NSGA II

Machining titanium alloy (Ti6Al4V) used in orthopedic implants via conventional metal cutting processes is challenging due to excessive cutting forces, low surface integrity, and tool wear. To overcome these difficulties and ensure high-quality products, various industries employ wire electrical discharge machining (WEDM) for precise machining of intricate shapes in titanium alloy. The objective is to make WEDM machining parameters as efficient as possible for machining the biocompatible alloy Ti6Al4Vusing Box-Behnken design (BBD) and nondominated sorting genetic algorithm II (NSGA II). A quadratic mathematical model is created to represent the productivity and the quality factor (MRR and surface roughness) in terms of varying input parameters, such as pulse active (T_on) time, pulse inactive (T_off) time, peak amplitude (A) current, and applied servo (V) voltage. The established regression models and related prediction plots provide a reliable approach for predicting how the process variables affect the two responses, namely, MRR and SR. The effects of four process variables on both the responses were examined, and the findings revealed that the pulse duration and voltage have a major influence on the rate at which material is removed (MRR), whereas the pulse duration influences quality (SR). The tradeoff between MRR and SR, when significant process factors are included, emphasizes the need for a reliable multi-objective optimization method. The intelligent metaheuristic optimization method named nondominated sorting genetic algorithm II (NSGA II) was utilized to provide pareto optimum solutions in order to achieve high material removal rate (MRR) and low surface roughness (SR).

Surface Free Energy Dominates the Biological Interactions of Postprocessed Additively Manufactured Ti-6Al-4V

Additive manufacturing (AM) has emerged as a disruptive technique within healthcare because of its ability to provide personalized devices; however, printed metal parts still present surface and microstructural defects, which may compromise mechanical and biological interactions. This has made physical and/or chemical postprocessing techniques essential for metal AM devices, although limited fundamental knowledge is available on how alterations in physicochemical properties influence AM biological outcomes. For this purpose, herein, powder bed fusion Ti-6Al-4V samples were postprocessed with three industrially relevant techniques: polishing, passivation, and vibratory finishing. These surfaces were thoroughly characterized in terms of roughness, chemistry, wettability, surface free energy, and surface ζ-potential. A significant increase in Staphylococcus epidermidis colonization was observed on both polished and passivated samples, which was linked to high surface free energy donor γ^– values in the acid–base, γ^AB component. Early osteoblast attachment and proliferation (24 h) were not influenced by these properties, although increased mineralization was observed for both these samples. In contrast, osteoblast differentiation on stainless steel was driven by a combination of roughness and chemistry. Collectively, this study highlights that surface free energy is a key driver between AM surfaces and cell interactions. In particular, while low acid–base components resulted in a desired reduction in S. epidermidis colonization, this was followed by reduced mineralization. Thus, while surface free energy can be used as a guide to AM device development, optimization of bacterial and mammalian cell interactions should be attained through a combination of different postprocessing techniques.

Recent Advances in the Control of Clinically Important Biofilms

Biofilms are complex structures formed by bacteria, fungi, or even viruses on biotic and abiotic surfaces, and they can be found in almost any part of the human body. The prevalence of biofilm-associated diseases has increased in recent years, mainly because of the frequent use of indwelling medical devices that create opportunities for clinically important bacteria and fungi to form biofilms either on the device or on the neighboring tissues. As a result of their resistance to antibiotics and host immunity factors, biofilms have been associated with the development or persistence of several clinically important diseases. The inability to completely eradicate biofilms drastically increases the burden of disease on both the patient and the healthcare system. Therefore, it is crucial to develop innovative ways to tackle the growth and development of biofilms. This review focuses on dental- and implant-associated biofilm infections, their prevalence in humans, and potential therapeutic intervention strategies, including the recent advances in pharmacology and biomedical engineering. It lists current strategies used to control the formation of clinically important biofilms, including novel antibiotics and their carriers, antiseptics and disinfectants, small molecule anti-biofilm agents, surface treatment strategies, and nanostructure functionalization, as well as multifunctional coatings particularly suitable for providing antibacterial effects to the surface of implants, to treat either dental- or implant-related bacterial infections.

Material Removal and Surface Integrity Analysis of Ti6Al4V Alloy after Polishing by Flexible Tools with Different Rigidity

Ti6Al4V alloy has been widely used in many fields, such as aerospace and medicine, due to its excellent biocompatibility and mechanical properties. Most high-performance components made of Ti6Al4V alloy usually need to be polished to produce their specific functional requirements. However, due to the material properties of Ti6Al4V, its polishing process still requires significant development. Therefore, this study aimed to investigate the performance of polishing Ti6Al4V by using tools with different rigidities. Two kinds of bonnet tool were used, namely a pure rubber (PR) bonnet and a semirigid (SR) bonnet. The characterization of material removal and surface integrity after polishing was conducted through a series of experiments on a 6-DOF robotic polishing device. The results demonstrate that both bonnet tools successfully produce nanometric level surface roughness. Moreover, the material removal rate of the SR bonnet tool is significantly higher than that of the PR bonnet, which is consistent with the material removal characteristics of glass polishing in previous research. In addition, the presented analysis on key polishing parameters and surface integrity lays the theoretical foundation for the polishing process of titanium alloy in different application fields.

Development of an ultraprecision metal mirror on additively manufactured Ti-6Al-4V

Metal mirrors for precise optical applications are commonly fabricated by coating of a metal base substrate with a nickel-phosphorus alloy (NiP). The NiP layer is then processed by precision diamond turning and polishing to obtain a high-quality mirror surface. In this work, Ti-6Al-4V samples that were made by additive manufacturing, also called 3D printing, were used as a base for the development of metal mirrors. The additively manufactured samples were electroplated with a NiP coating and machined using single-point diamond turning (SPDT) to obtain a flat mirror with optical quality and low form error surface. The periodic structure of the SPDT toolmark was then removed by polishing postprocessing. Polishing optimization was first performed on NiP-coated aluminum test samples to find an optimal polishing setup. Based on this optimization, postprocessing of titanium samples was carried out by pitch polishing in combination with 1, 0.25, and 0.1µm diamond slurries. Using this polishing processing, a scratch-free surface was attained with surface microroughness below 0.5 nm.

Experimental Study on Ultra-Precision Polishing of Ti-6Al-4V by Ultraviolet-Induced Nanoparticle Colloid Jet Machining

Ti-6Al-4V is widely used in various fields of modern industry, but it is difficult to obtain an ultra-smooth surface of Ti-6Al-4V due to its poor machinability. In this article, ultraviolet-induced (UV-induced) nanoparticle colloid jet machining was utilized to carry out ultra-precision polishing of Ti-6Al-4V to improve the surface quality. The results of infrared differential spectroscopy before and after polishing show that new chemical bonds such as Ti-O-Ti (Al-O-Ti and V-O-Ti) appear on the Ti-6Al-4V workpiece surface, which indicates that the material of Ti-6Al-4V workpiece is removed through the chemical interaction between TiO₂ nanoparticles and workpiece surface in the process of UV-induced nanoparticle colloid jet machining. The comparison of metallographic structure of Ti-6Al-4V before and after polishing shows that the chemical activity and material removal rate of the primary α phase in Ti-6Al-4V is higher than that of the remnant β phase in UV-induced nanoparticle colloid jet machining, which lead to the well-distributed nano-scale surface peaks and valleys at regular intervals on the polished Ti-6Al-4V workpiece surface. After polishing, the longitudinal residual stress on the surface of Ti-6Al-4V workpiece decreases from 75 MPa to 67 MPa and the transverse stress decreases from 13 MPa to 3 MPa. The surface roughness of Ti-6Al-4V workpiece is reduced from Sa 76.7 nm to Sa 2.87 nm by UV-induced nanoparticle colloid jet machining.