Laser-treated austenitic steel and nickel alloy for human implants

The recent research in biocompatible materials has been useful in replacing and supporting the fractured natural human bones/joints. Under some condition, negative reaction like release of ions from the bare metal toward the human body fluid leads to corrosion. In this proposed research paper, the biocompatibility of the laser surface-modified austenitic stainless steel (SS316L) and nickel-based superalloy (Inconel 718) was studied. The investigation on laser-modified surfaces is evaluated through electrochemical polarization analysis using simulated body fluid (SBF). The samples subjected to electrochemical polarization analysis were characterized by optical image analysis, SEM, EDS, and XRD analysis. It was inferred that laser surface-modified materials provided enhanced corrosion resistance and bare nickel alloy is more susceptible to corrosion by SBF.     

Influence of Equimolar Concentration on Structural and Optical Properties of Binary Selenides Nanoparticles

Nanoparticles of PbSe, Cu₂Se, and CdSe are prepared for two equimolar concentrations (0.05 M and 0.1 M) by precipitation method at 130°C. The obtained nanoparticles were characterized by x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and UV-visible analysis to study the structural, morphological, and optical properties and are discussed in detail.     

Application of grey-taguchi method for optimization of dry sliding wear properties of aluminum MMCs

Through a pin-on-disc type wear setup, the dry sliding wear behavior of SiC-reinforced aluminum composites produced using the molten metal mixing method was investigated in this paper. Dry sliding wear tests were carried on SiC-reinforced metal matrix composites (MMCs) and its matrix alloy sliding against a steel counter face. Different contact stresses, reinforcement percentages, sliding distances, and sliding velocities were selected as the control variables, and the responses were selected as the wear volume loss (WVL) and coefficient of friction (COF) to evaluate the dry sliding performance. An L25 orthogonal array was employed for the experimental design. Initially, the optimization of the dry sliding performance of the SiC-reinforced MMCs was performed using grey relational analysis (GRA). Based on the GRA, the optimum level parameters for overall grey relational grade in terms of WVL and COF were identified. Analysis of variance was performed to determine the effect of individual factors on the overall grey relational grade. The results indicated that the sliding velocity was the most effective factor among the control parameters on dry sliding wear, followed by the reinforcement percentage, sliding distance, and contact stress. Finally, the wear surface morphology and wear mechanism of the composites were investigated through scanning electron microscopy.     

High Temperature Tribological Characterisation of Laser Nitrided Nickel-Based Superalloy

The surface of a nickel-based superalloy used for air-borne gas turbine application was laser nitrided to improve the tribological properties. An optimal laser power and scanning speed was derived to avoid any possible variation in elemental composition of the treated surface. The metallurgical modification over the treated surfaces was studied along the cross-section through microstructural characterisation to understand the refining mechanism and possible nitriding. The coarse grains present over the base material surface reoriented to fine equiaxed grains under lower power and higher interaction time. The grains were refined with higher scanning power and lower interaction time. The higher thermal gradient and cooling rate combination attributed to the refining mechanism. Further increase in the laser power resulted in the formation of columnar grains at the treated depth. The presence of nitride species was observed over the treated surface, which improved the microhardness. All laser treated samples were subjected to wear analysis at ambient and high temperature. The treated pin surface exhibited a combination of adhesive and abrasive wear mechanism. A significant reduction in wear rate was observed for samples treated with high power and lower interaction time.     

Liquid impact erosion characteristics of martensitic stainless steel laser clad with Ni-based intermetallic composites and matrix composites

NiAl-Ni₃Al intermetallic composites (IC) and intermetallic matrix composites (IMC) with TiC and WC reinforcement were laser clad to increase the liquid impact erosion resistance of AISI 420 Martensitic stainless steel. Laser process parameter optimisation and pre- and post-heat treatment of the laser clad specimens were carried out to minimise porosity and sensitivity to crack formation. The coatings were characterised by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). The erosion resistance of the substrate material at a water droplet exit velocity of up to 150 m/s was improved from 116.9 to 838.7 min/mm³ for the nickel aluminide IC coating and from 855 to 1446 min/mm³ for the IMC coating with TiC and WC reinforcement. The pseudo-elasticity combined with the high work hardening ability was attributed to the excellent erosion resistance of nickel aluminide IC coatings. The IMC coatings with ceramic reinforcement extended significantly the initial resistance against liquid impact erosion. However, once damage occurred the erosion accelerated rapidly. No direct correlation could be established between the erosion resistance and the mechanical properties. The influence of hardness, elastic modulus, strain-hardening coefficient and the reversible penetration ratio on the erosion resistance was discussed.     

Synthesis,characterization and mechanical behavior of Al 3003 - TiO2 surface composites through friction stir processing

Aluminum 3003 alloy used in the gas turbine and aerospace applications possesses medium bearing capacity. This technical paper reports the fabrication of Al 3003 alloy/TiO₂ composites using friction stir processing. The weight fraction of reinforced TiO₂ particles is varied between 0% and 6% with the increment of 1.5% in sequence. The fabricated specimens have been characterized by optical microscopy (OM), Energy dispersive X-ray spectroscopy (EDAX), Field emission scanning electron microscopy (FESEM), X-ray Diffraction analysis (XRD) and electron backscattered diagram (EBSD). Composite weld zone has witnessed the homogeneous distribution of TiO₂ particles. The formation of such composite by reinforcement exhibits increase in the hardness and tensile strength of the weld. Corresponding strengthening mechanism is illustrated and correlated with the characterization studies. Fractography study shows brittle to ductile transformation with the addition of TiO₂ particles.