Mechanical, biocorrosion, and antibacterial properties of nanocrystalline TiN coating for orthopedic applications

The solution and aging treatments (SAT) were adopted to improve the microstructure and the corrosion resistance ability of laser solid formed (LSFed) Ti-6Al-4 V titanium alloy. The effect of the SAT on the electrochemical properties of the LSFed Ti-6Al-4 V in a 3.5 wt. % NaCl solution was studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The microstructure changes after SAT, resulting in the transition from the columnar grains in the LSFed Ti-6Al-4 V to the basket-weave grains. After SAT, the microhardness of material is significantly reduced. The corrosion resistance of solution and aging treated (SATed) Ti-6Al-4 V is slightly better than that of the as-deposited Ti-6Al-4 V, which is manifested by the decrease of icorr value, the increase of impedance modulus and the reduction of the number of surface pits after electrochemical corrosion.

Effect of solution and aging treatments on corrosion performance of laser solid formed Ti-6Al-4V alloy in a 3.5 wt. % NaCl solution

Hastelloy C-276 superalloy has a wide range of applications including petroleum and petrochemical industries. Since welding forms an essential fabrication method for joining different structures in these industries, selection of suitable welding parameters is a prime concern that is yet to be addressed for Hastelloy C-276. In the present study, optimization of process parameters for electron beam welding of 2.6-mm-thick Hastelloy C-276 sheet has been carried out to obtain weld bead having through-penetration and minimum weld (or melt) zone cross-sectional area. A simple optimization technique is employed in the present study to solve the multi-objective minimization problem. After carrying out the full factorial experiment using selected process parameters, various geometric elements of the weld bead are identified as the output responses. The regression equation is developed for each geometric element from the experimental data. The desired value of a geometric element is specified as a constraint for the corresponding regression equation. A number of regression equations (considering all the geometric elements) are solved in parallel to obtain an optimized set of process parameters, followed by a confirmation test. Further, the optimized melt zone is subjected to cyclic potentiodynamic polarization test to study its susceptibility to localized corrosion. It is observed that polarization curve characteristics of base metal and optimized melt zone are not significantly different; however, the repassivation potential of the melt zone is less than that of the base metal. A flowchart showing the layout of the employed optimization technique followed by corrosion test is attached.

Optimization of Melt Zone Area for Electron Beam Welded Hastelloy C-276 Sheet and Study of Corrosion Resistance of the Optimized Melt Zone in 3.5 wt% NaCl Aqueous Solution

In this study, surface hardening of Ti-5Al-2.5Sn alloy was performed using a pulsed Nd:YAG laser. The effect of laser parameters including laser frequency, laser pulse width, laser speed, and focal point position was investigated on the microstructure, geometrical dimensions of hardened zone (hardened width, hardened depth, and entry angle of hardened zone), and micro-hardness. In the specimens with higher cooling rate, martensitic phase (ά) is formed in the hardened zone, while in the specimens with lower cooling rate, combination of equaxied and acicular alpha phase is formed in the hardened zone. The laser speed has a significant effect on the overlapping factor compared to other laser variables. By increasing the laser speed, the cooling rate increase and the pulse overlapping decreases in the hardened zone. High cooling rate leads to the refinement of prior beta grain size in this zone. Combination of equiaxed and acicular alpha phase, as well as acicular martensitic phase, is observed in the transition zone. The martensitic phase is a dominant phase in location near the hardened zone. A laser power of 165 W, lase frequency of 14 Hz, pulse width of 22 ms, laser speed of 105 mm/min, and focal point position of + 3.5 mm are optimum parameters for obtaining the best laser surface hardening results. The presence of martensitic phase in the optimum sample causes an increase in the hardness about 36% as compare to the base metal.

Surface transformation hardening of Ti-5Al-2.5Sn alloy by pulsed Nd:YAG laser: an experimental study

Pulsed laser welding is a joining process, which takes advantage of the laser energy quality with precise control equipment. Its characteristics allow joining thinner materials with reduced thermal distortion without filler material, fulfilling the industrial interest in this process. In the present work, AISI 1005 steel sheets of 1.7 mm thickness were subjected to different pulse Nd:YAG laser treatments to obtain one side bead-on-plate weld samples and double sided butt welds. Since the quality of the joints is strongly influenced by the process parameters, an experimental design methodology was adopted to define a suitable combination of the laser beam power, pulse duration and spot diameter. The Box-Behnken technique and response surface methodology associated with analyses of defects allowed the determination of the appropriate welding parameters. The microstructure characterisation revealed the melted fusion zones originated from the thermal effect of the overlapped pulses. Additionally, microhardness measurements at fusion zone exhibited higher values than the base material and heat affected zone, due to the hard microconstituents developed. The tensile test performed at samples extracted from double sided laser welds showed good resistance results, fracturing at the base material of joints. The present work demonstrates that pulsed laser welding methodology is suitable to obtain high quality joints of steel thin plates.

Pulsed laser butt welding of AISI 1005 steel thin plates

Corrosion behavior of TIG and laser welded Ti–5Al–2.5Sn alloy was compared using different electrochemical techniques. Bead on plate (BoP) configuration was used for welding of 1.6 mm thick Ti–5Al–2.5Sn plates which led to the formation of complete α′ martensitic structure in laser welds and acicular α along with α′ martensite within coarse prior β grains was observed in TIG welds. Potentiodynamic and cyclic polarization were carried out in 5, 7 and 9 M HNO3 to study the effect of concentration on the galvanic corrosion of laser and TIG welded Ti–5Al–2.5Sn. The oxide layer developed after 192 h of immersion in fuming HNO3 was studied using electrochemical impedance spectroscopy (EIS) and SEM. All the samples showed good passivity but different oxidation behavior was observed mainly because of the surface modification after the welding operation.

Muhammad Shamir

Papers

A comparative study of electrochemical corrosion behavior in Laser and TIG welded Ti–5Al–2.5Sn alloy