Enhancing Corrosion and Wear Resistance of Ti6Al4V Alloy Using CNTs Mixed Electro-Discharge Process

Blood-repellent and anti-corrosive surface by spin-coated SWCNT layer on intravascular stent materials

Despite intravascular bare metallic stents (BMS) being indispensable products in cardiovascular surgery, they face in-stent restenosis (ISR), resulting in stent failure or secondary surgical operation necessity. Accumulation or corrosion processes are key factors that promote ISR development in a vascular pathway, including an intravascular stent. The ISR can be inhibited by increasing the blood-repellency, and electrochemical corrosion resistance features using surface modification techniques on intravascular stent materials. In this study, Single-Walled Carbon Nanotube (SWCNT) structures were deposited using the spin-coating method on stent specimens made of 316L, 316LVM, CoCr-alloy, and Ti-alloy. Hydrophobicity and blood-repellency functions of coated and uncoated specimens were analysed by the Contact Angle (CA) values for distilled water (DIW), glycerol, blood plasma, and total-blood droplets using a computer-controlled goniometer system. Using a potentiostat, the electrochemical corrosion resistance features were analysed from obtained Electrochemical Impedance Spectroscopy (EIS) and Tafel curves in 37 °C Simulated Body Fluid (SBF) mimicking the human blood plasma. Due to the CA values below 90°, the repellency limit for hydrophobicity and blood-repellency, bare specimens performed hydrophilic and blood-philic features. However, SWCNT coating increased the repellency functions to 95° for DIW and 96° for total blood. The electrochemical corrosion resistance analysis showed that 1.433 kΩ cm² polarization resistance and 1.07 kΩ cm² electrochemical impedance of bare specimens increased to 142.8 kΩ cm² and 141.3 kΩ cm² by SWCNT coating. These corrosion resistance enhancements led to ratios of 78.13% inhibition in the corrosion rate and mass loss rate per year for SWCNT-coated 316LVM specimens. The maximum inhibition efficiency was observed for SWCNT-coated 316LVM specimens with a ratio of 87.92%. Obtained results indicate that SWCNT coating of the intravascular stents can inhibit the ISR risks of the BMS group.

Titanium alloy composited with dual-cytokine releasing polysaccharide hydrogel to enhance osseointegration via osteogenic and macrophage polarization signaling pathways

Titanium alloy has been widely used in orthopedic surgeries as bone defect filling. However, the regeneration of high-quality new bones is limited due to the pro-inflammatory microenvironment around implants, resulting in a high occurrence rate of implant loosening or failure in osteological therapy. In this study, extracellular matrix (ECM)-mimetic polysaccharide hydrogel co-delivering BMP-2 and IL-4 was composited with 3D printed titanium alloy to promote the osseointegration and regulate macrophage response to create a pro-healing microenvironment in bone defect. Notably, it is discovered from the bioinformatics data that IL-4 and BMP-2 could affect each other through multiple signal pathways to achieve a synergistic effect towards osteogenesis. The composite scaffold significantly promoted the osteoblast differentiation and proliferation of human bone marrow mesenchyme stem cells (hBMSCs). The repair of large-scale femur defect in rat indicated that the dual-cytokine-delivered composite scaffold could manipulate a lower inflammatory level in situ by polarizing macrophages to M2 phenotype, resulting in superior efficacy of mature new bone regeneration over the treatment of native titanium alloy or that with an individual cytokine. Collectively, this work highlights the importance of M2-type macrophages-enriched immune-environment in bone healing. The biomimetic hydrogel-metal implant composite is a versatile and advanced scaffold for accelerating in vivo bone regeneration, holding great promise in treating orthopedic diseases.

Parametric Optimization of Electric Discharge Machining of Metal Matrix Composites Using Analytic Hierarchy Process

The present study reports on the method used to obtain the reliable outcomes for different responses in electric discharge machining (EDM) of metal matrix composites (MMCs). The analytic hierarchy process (AHP), a multiple criteria decision-making technique, was used to achieve the target outcomes. The process parameters were varied to evaluate their effect on the material erosion rate (MER), surface roughness (SR), and residual stresses (σ) following Taguchi’s experimental design. The process parameters, such as the electrode material (Cu, Gr, Cu-Gr), current, pulse duration, and dielectric medium, were selected for the analysis. The residual stresses induced due to the spark pulse temperature gradient between the electrode were of primary concern during machining. The optimum process parameters that affected the responses were selected using AHP to figure out the most suitable conditions for the machining of MMCs.

Performance evaluation of graphite and titanium oxide powder mixed dielectric for electric discharge machining of Ti–6Al–4V

Ti–6Al–4V is the most commonly used titanium alloy in aerospace, marine, and biomedical applications. Due to the properties of poor machinability in conventional machining, Electrical Discharge Machining (EDM) is considered a prospective alternative for machining this strategic material. This study aims at enhancing the performance of powder mixed EDM (PMEDM) in the machining of Ti–6Al–4V with the application of two different types of powders, namely Graphite (Gr) and Titanium Oxide (TiO2) powders, with different concentrations in dielectric—kerosene. The effect of these powers and their relative quantities are studied in terms of metal removal rate (MRR), tool wear rate, Surface Roughness, and surface integrity. Machining is performed using the copper electrode and kerosene as the dielectric medium. A separate container and a submersible pump are used to limit the quantity of powder and keep the powder in suspension, respectively. Design of experiments guided by Design-Expert software is employed to minimize the number of experimental runs and develop empirical models of response parameters in terms of the variable parameters—peak current, powder type, and powder concentration. Findings indicate that TiO2 powder has a much higher effect on MRR compared to graphite powder, as the maximum MRR in the case of TiO2 powder is recorded 41.01 mm3/min against 11.98 mm3/min for graphite powder, i.e., 3.42 times higher. Similarly, the tool wear ratio for TiO2 powder is 0.0704 against 0.1219 for graphite powder at the maximum MRR, which is 1.73 times lower compared to that of graphite powder. The same ratios at the minimum MRR for TiO2 is 0.0098, and for graphite power is 0.0282, which is again 2.88 times lower compared to that of graphite powder. In terms of average surface roughness, Ra, the performance of TiO2 is far better compared to graphite powder since the maximum surface roughness attained with TiO2 powder is 3.265 μm against 9.936 μm for graphite powder at the highest MRR and the same attained at the lowest MRR are 2.228 μm and 2.411 μm for TiO2 and graphite powders respectively. The mechanism of the effects of PMEDM on surface texture has also been observed using SEM images to study the influence of powder concentration on surface morphology.

Surface Characterization and Tribological Performance Analysis of Electric Discharge Machined Duplex Stainless Steel

The present article focused on the surface characterization of electric discharge machined duplex stainless steel (DSS-2205) alloy with three variants of electrode material (Graphite, Copper-Tungsten and Tungsten electrodes). Experimentation was executed as per Taguchi L18 orthogonal array to inspect the influence of electric discharge machining (EDM) parameters on the material removal rate and surface roughness. The results revealed that the discharge current (contribution: 45.10%), dielectric medium (contribution: 18.24%) majorly affects the material removal rate, whereas electrode material (contribution: 38.72%), pulse-on-time (contribution: 26.11%) were the significant parameters affecting the surface roughness. The machined surface at high spark energy in EDM oil portrayed porosity, oxides formation, and intermetallic compounds. Moreover, a pin-on-disc wear analysis was executed and the machined surface exhibits 70% superior wear resistance compared to the un-machined sample. The surface thus produced also exhibited improved surface wettability responses. The outcomes depict that EDMed DSS alloy can be considered in the different biomedical and industrial applications.