Muthukannan Duraiselvam

Laser clad WC reinforced Ni-based intermetallic-matrix composites to improve cavitation erosion resistance

Nickel aluminide intermetallic coatings (IC) and nickel aluminide intermetallic matrix composite (IMC) coatings with a WC particulate reinforcement were successfully clad onto AISI 420 Martensitic stainless steel using a 4 kW Nd:yttrium-aluminum-garnet laser with rotary-disk powder feeding of Ni/Al powder and a Ni/Al+WC powder mixture, respectively. Under optimized processing with pre- and postheat treatment conditions, the nickel aluminide clad layers were free of cracks and pores. The microstructure of the IMC was mainly composed of reprecipitated and refined WC particles dispersed uniformly throughout the Ni–Al matrix with a few partially dissolved and undissolved WC particles. The average hardness of the IC was increased from 330 HV0.2 to 420 HV0.2 by the WC reinforcement. The normalized cavitation erosion resistance (Ren) of the IC and IMC were about 5.2 and 284 times that of the stainless steel substrate, respectively. The superior cavitation erosion resistance of the laser clad layers were explaine...

Tribological studies on laser surface melted Hastelloy C-276

Abstract Hastelloy C-276 was laser surface melted in a nitrogen environment in order to improve the wear resistance. The metallurgical characterisation was performed using optical microscopy, scanning electron microscopy with electron dispersive spectroscopy (EDS) and X-ray diffraction analysis. At a particular laser power and scan speed combination, significant grain refinement was achieved with finely dispersed cell-like structure which improved the hardness up to 390 HV0·3. The EDS point analysis indicated nitrogen diffusion at the cost of nickel depletion. The absence of Cr2N or CrN is a positive aspect in preserving the intrinsic corrosion characteristics of the alloy. The wear rates of the laser treated specimens were significantly lower by a factor of 2·5. Potentiodynamic polarisation corrosion test on the laser treated specimens also exhibited reduced corrosion rates compared to the base material.

Sliding wear behaviour of plasma sprayed coatings on nickel based superalloy

In this paper, the sliding wear behaviour of nickel based superalloy pin was investigated on disc with two different coatings. The plasma sprayed NiCr–Cr2O3 coating and Al2O3+40%TiO2 (A40T) coating were used on the disc for wear studies. The sliding wear tests were performed on dry conditions at room temperature for a constant sliding velocity for two different applied loads (5 and 10 N). The mass loss, wear resistance and coefficient of friction between the pin and disc were studied during investigations. The wear mechanism involved in the NiCr–Cr2O3 coatings is three-body abrasion and Cr2O3 being the third body between pin and disc. The wear rate is high due to the applied load and suppressed cracks. In A40T coating, the minute debris collected on the surface of the coatings acts as a solid lubricant and reduces friction and wear rate. The SEM and energy dispersive spectroscopy analysis were also carried out for characterisation studies on pin after wear studies. The life of nickel pin on A40T coatings is found superior than the NiCr–Cr2O3 coated disc.

Laser material processing of nickel superalloy for improved erosion resistance

ABSTRACT A nickel-based superalloy was laser surface treated, and its erosion behavior was evaluated. The laser power and scan speed were varied in different levels to impart variations in microstructure and mechanical properties. The microstructure of specimens exhibited fine equiaxed grains to columnar structure at different parameters. A high cooling rate improved the hardness of the laser-treated specimen up to 603 HV0.3 compared to the base material hardness of 430 HV0.3. The rate of erosion increased linearly from 30° to 60° impingement angle and decreased at 75° impingement angle. The accumulation of the erodent inside the crater and the consequent absorbtion of the incident kinetic energy might have caused this reduction. The laser surface treated specimens exhibited ∼1.5 factor of improvement in high temperature erosion resistance. This was attributed to the minimized energy transfer from impinging particle to the substrate achieved through laser surface melting.

Laser-treated austenitic steel and nickel alloy for human implants

ABSTRACT 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.

Development of carbide intermetallic layer by electric discharge alloying on AISI-D2 tool steel and its wear resistance

Abstract Electrical discharge alloying was performed on AISI-D2 steel using Ni–W powder mixed dielectric in order to improve the hardness and to reduce the specific wear rate. The alloyed layer was characterized using optical microscopy, scanning electron microscopy, X-ray diffraction analysis and energy-dispersive spectroscopy. Wear tests were conducted based on L9 orthogonal array in a pin-on-disc tribometer and the alloying parameters were optimized using Taguchis technique. Hard intermetallics based on Fe7C3, Cr3C2 and Ni2W4C were formed by electric discharge alloying, which primarily contributed to the improvement in hardness up to 600 HV0.5. The specific wear rate of the alloyed layer was subsequently reduced by around a factor of eight compared to that of the base material. The pulse off-time was found to be predominant in obtaining higher hardness and lower specific wear rate among the alloying parameters, peak current, pulse on-time and off-time.

NUMERICAL MODELING OF WC-12% Co LASER ALLOYED CAST IRON IN HIGH TEMPERATURE SLIDING WEAR CONDITION USING RESPONSE SURFACE METHODOLOGY

The wear behavior of untreated and WC-12% Co laser alloyed nodular cast iron samples were analyzed using a high temperature pin-on-disc tribometer. Response surface methodology (RSM) based Box–Behnken technique was employed to minimize the sum of trials and to develop a mathematical model for the input process parameters namely sliding velocity, temperature and load. The interaction effects of the process parameters were investigated using the developed model. Further, the developed model was analyzed using analysis of variance. Scanning electron microscopy and energy dispersive spectrum were used for characterization. Laser alloyed samples showed a minimum wear rate (0.3379×10−3 to 0.9537×10−3mm3/m) and friction coefficient (0.10 to 0.39) compared to untreated samples. The results of the validation test showed that the experimental results agreed well with predicted results of the developed mathematical model.

Effect of laser glazing on the thermo-mechanical properties of plasma-sprayed LaTi2Al9O19 thermal barrier coatings

ABSTRACT Conventional duplex (DL) and functionally graded (FG) LaTi2Al9O19 (LTA) coatings were deposited over C263 nickel alloy by air plasma spray (APS) and compared with subsequent laser glazing processes. The effect of laser glazing on adhesion strength and thermal barrier performance was investigated. The thermal barrier effect was measured using the temperature difference technique involving infrared (IR) rapid heater and the adhesion strength was measured using the scratch tester. The surface morphology and microstructure were analyzed by optical microscopy (OM), Scanning Electron Microscope (SEM) and 3D profilometer. Based on the experimental results, the laser glazing showed a remarkable temperature drop after IR rapid heating. The changes in porosity and grain refinement make more contributions to the temperature drop of the laser-glazed coatings than that of as-sprayed coatings. The temperature drop is about 110°C for laser-glazed LTA FG coating after 100 s of IR flash, while the drop in DL as-sprayed coating is 60°C compared to the base material.

High-temperature tribological characterisation of laser surface melted Ni-based superalloy

Laser surface treatment was performed on nickel-based superalloy to improve their high temperature tribological properties for enhanced service life specifically in gas turbine applications. The laser power and scan speed were strategically controlled to optimally refine the microstructure. The metallurgical and mechanical modifications in the treated area were studied to understand the refining mechanism. The coarser grains in the base material re-orient to fine dendrites during laser surface melting. The equiaxed grains are refined with increased laser power and reduced interaction time under the influence of higher cooling rate. The finely refined grains improve the microhardness of the treated surface. The tribological performance and its mechanism of the treated surfaces were evaluated at room temperature and at 500°C. A significant reduction in the wear rate was observed for the laser treated surface, where abrasion and adhesion found to be the dominant wear mechanisms.

Multi-response optimization of tribological characteristics of aluminum MMCs using PCA

Purpose – Since, wear is the one of the most commonly encountered industrial problems leading to frequent replacement of components there is a need to develop metal matrix composites (MMCs) for achieving better wear properties. The purpose of this paper is to fabricate aluminum MMCs to improve the dry sliding wear characteristics. An effective multi-response optimization approach called the principal component analysis (PCA) was used to identify the sets of optimal parameters in dry sliding wear process. Design/methodology/approach – The present work investigates the dry sliding wear behavior of graphite reinforced aluminum composites produced by the molten metal mixing method by means of a pin-on-disc type wear set up. Dry sliding wear tests were carried on graphite reinforced MMCs and its matrix alloy sliding against a steel counter face. Different contact stress, reinforcement percentage, sliding distance and sliding velocity were selected as the control variables and the response selected was wear vol...