Jogender Singh

Synthesis of titanium carbide/chromium carbide multilayers by the co-evaporation of multiple ingots by electron beam physical vapor deposition

Abstract Titanium carbide and chromium carbide multilayer coatings with varying individual layer thicknesses were synthesized by the co-evaporation of titanium, chromium, and carbon (through tungsten) ingots by electron beam-physical vapor deposition. The adhesion of the multilayer coatings was found to be greater than 50 N. The hardness of the titanium carbide/chromium carbide multilayer coatings was found to increase from 1302 VHN 0.050 to 2052 VHN 0.050 by decreasing the thickness of the individual layer from 1.2 to 0.1 μm. In addition, the average grain diameter was also found to decrease from 3.315 to 0.356 μm by decreasing the thickness of the individual layers. The fracture toughness of the TiC/CrC multilayer coatings decreased from 4.179 to 1.411 MPa-m 1 2 with decreasing layer thickness. Lastly, the amount of compressive stress in both the TiC and CrC layers within the multilayer coating was found to decrease with decreasing individual layer thickness. The samples were characterized by various techniques including Vickers hardness, X-ray diffraction, scanning electron microscopy, scratch testing and fracture toughness, with the results being presented.

Synthesis and characterization of multilayered TiC/TiB2 coatings deposited by ion beam assisted, electron beam–physical vapor deposition (EB–PVD)

Abstract Polycrystalline 4 μm and 14 μm thick multilayer TiB2/TiC coatings with varying number of total layers (2–20) were deposited by ion beam assisted, electron beam–physical vapor deposition (IBA, EB–PVD) on WC–6wt.%Co–0.3wt.%TaC substrates. The average Vickers hardness numbers were found to increase with increasing total number of layers and ranged from 3215 VHN0.050 to 3726 VHN0.050 and 3294 VHN0.050 to 3991 VHN0.050 for the 4 μm and 14 μm thick multilayer TiB2/TiC coatings, respectively. The adhesion of the multilayer coatings was found to be greater than 50 N for a 4 μm thick film and less than 30 N for the thicker films. The degree of crystallographic texture was found to change with varying total number of layers, as well as the orientation of both materials within the multilayer system. The grain size and amount of residual compressive stress was found to decrease with increasing number of layers. In addition, the fracture toughness was found to decrease with increasing total number of layers. This paper discusses the effect of changing the individual layer thickness (i.e. total number of layers) for TiC/TiB2 multilayer coatings deposited on WC–6wt.%Co–0.3wt.%TaC cutting inserts on the average Vickers hardness number, adhesion, stress, fracture toughness, argon impurities, average crystallite size, crystallographic texture, surface morphology and microstructure using a variety of characterization techniques.

A novel laser-liquid-solid interaction technique for synthesis of silver, nickel and immiscible silver-nickel alloys from liquid precursors

Silver, nickel, nickel oxide and silver-nickel alloys have been produced from their inexpensive liquid precursors using CO2 and Nd-YAG lasers. Ethylene glycol, diethylene glycol and 2-ethoxyethanol were used as reductants in the synthesis reactions. Spherical and faceted silver particles of high purity were formed by laser interaction between the precursor solution and a rotating substrate, while porous dual phase nickel and nickel oxide particles were produced when nickel nitrate was used as a precursor. The composition and morphology of the alloy particles was dependent on laser parameters and chemical composition of the precursor solution. The product composition was dependent only upon the chemistry of the precursors used. The mean particle size was dependent upon the temperature generated by irradition and the duration of exposure to the laser beam. The synthesis of nano-particles and metastable alloys is proposed to occur primarily at the laser-liquid-solid interface by a nucleation and growth mechanism.

Synthesis of metastable silver-nickel alloys by a novel laser-liquid-solid interaction technique

Metastable silver-nickel alloys have been synthesized by chemical wetness and laser-liquid-solid interaction techniques from nitrate and acetate precursors of silver and nickel. Ethylene glycol and 2-ethoxyethanol were used as reductants in the synthesis reactions. Rotating niobium substrates immersed in the liquid precursor were irradiated by a continuos wave CO2 and Nd-YAG laser (λ = 1064 nm). The powders were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and high-resolution transmission electron microscopy (HRTEM). Two-phase alloys containing silver, nickel, and oxygen were fabricated, and the shape of the particles was found to be dependent on laser parameters and the chemical composition of the precursor solution. The synthesis mechanism of non-equilibrium Ag-Ni alloy nanoparticles has been proposed to occur primarily at the laser-liquid-solid interface by a nucleation and growth mechanism.

Functionally gradient ceramic/metallic coatings for gas turbine components by high-energy beams for high-temperature applications

Failure of turbine blades generally results from high-temperature oxidation, corrosion, erosion, or combinations of these procedures at the tip, and the leading and trailing edges of a turbine blade. To overcome these limitations, functionally gradient ceramic/metallic coatings have been produced by high-energy beams for high-temperature applications in the aerospace and turbine industries to increase the life of turbine components. Thermal spray processes have long been used to apply high-temperature thermal barrier coatings to improve the life of turbine components. However, these processes have not met the increased demand by the aerospace and turbine industries to obtain higher engine temperatures and increased life enhancement as a result of the inhomogeneous microstructure, unmelted particles, voids, and poor bonding with the substrate. High-energy beams, i.e. electron beam-physical vapour deposition (EB-PVD), laser glazing, laser surface alloying, and laser surface cladding, have been explored to enhance the life of turbine components and overcome the limitations of the thermal spray processes. EB-PVD has overcome some of the disadvantages of the thermal spray processes and has increased the life of turbine components by a factor of two as a result of the columnar microstructure in the thermal barrier coating (TBC). Laser glazing has been used to produce metastable phases, amorphous material, and a fine-grained microstructure, resulting in improved surface properties such as fatigue, wear, and corrosion resistance at elevated temperatures without changing the composition of the surface material. Laser surface alloying and laser surface cladding have shown promising results in improving the chemical, physical, and mechanical properties of the substrates surface. Metal-matrix composite coatings have also been produced by a laser technique which resulted in increased wear and oxidation-resistant properties. The advantages and disadvantages of thermal spray processes, EB-PVD, laser glazing, laser surface alloying, and laser surface cladding will be discussed. Microstructural evolution of thermal barrier coatings, recent advancements in functionally gradient coatings, laser grooving, and multilayered textured coatings will also be discussed.

Laser-beam and photon-assisted processed materials and their microstructures

Laser processing is a relatively new technique for modifying the near-surface region of materials without altering the in-bulk characteristics. A single laser can perform several functions by manipulating processing conditions such as laser power, beam diameter, and traverse speed. Lasers have shown attractive applications, such as cutting, welding, glazing, alloying, and cladding. A laser glazing process has demonstrated an improvement in the microstructure of vacuum plasma-coated copper-based alloys containing cavities, unmelted particles, and segregation. Laser glazing has also been shown to restore the degraded microstructure of components and make them equivalent to, or better than, the original wrought alloy. The laser cladding concept was used to develop nickel-based alloys for high-temperature applications that exhibited higher thermal stability than the nickel-based Rene-95 alloy. Rapid melting and quenching occurred during the laser glazing, alloying, and cladding processes resulting in a fine-grained microstructure, metastable phases and extended solid solubility of alloying additions in the matrix.Photon-assisted processing of material is a relatively new technique being explored to synthesize new materials from various substrates (solid, liquid, and gas). This process is successfully used to fabricate high-quality thin films for electronic industries. Thin films of multicomponents can be deposited with stoichiometric composition. Diamond thin films have been synthesized from liquid hydrocarbon (Benzene, C6H6) by laser-liquid hydrocarbon-substrate interaction. A laser-assisted physical vapour deposition process was found to be very successful in depositing stoichiometric compositions of multilayered thin films such as superconducting YBa2Cu3O7, ferroelectric Pb0.52Zr0.48TiO3 and other coatings such as TiN and CoSi2. This review reports some of the major advances in the understanding and engineering of new materials for electronic industries and high-temperature applications in the auto, aerospace, and turbine industries.

A novel technique for synthesis of silver nanoparticles by laser-liquid interaction

Ultrafine particles of many materials have received much attention over the last few years by researchers because of their unique physical and mechanical properties due to increased surface area to volume ratio. A novel laser–liquid interaction technique has been developed to synthesize silver nanoparticles from inexpensive silver nitrate solution in distilled water. The shape, size distribution, microchemistry and crystal structure of the silver nanoparticles were studied using X-ray diffraction, scanning electron microscopy and electron probe X-ray microanalysis.

Mechanical properties and microstructural stability of wrought, laser, and electron beam glazed NARloy-Z alloy at elevated temperatures

Microstructure of wrought, laser and electron beam processed NARloy-Z (Cu-3 wt % Ag–0.5 wt% Zr) was investigated for thermal stability at elevated temperatures 539–760 °C (1100 to 1400°F) up to 94 h. Optical and scanning electron microscopy and electron probe microanalysis were employed for studying microstructural evolution and kinetics of precipitation. Grain boundary precipitation and precipitate free zones (PFZs) were observed in the wrought alloy after exposing to temperatures above 605 °C (1120 °F). Fine-grained microstructure observed in the laser and electron beam (EB) processed NARloy-Z was much more stable at elevated temperatures. Tensile properties of laser and EB glazed NARloy-Z can be tailored by giving suitable heat treatments and maintaining the same strength with increased ductility. Microstructural changes correlated well with hardness measurements and mechanical properties.

Laser glazing of vacuum plasma spray coated NARloy-Z

Abstract A CO 2 laser was used to modify the surface layer of vacuum plasma sprayed NARloy-Z (Cu-3 wt.%Ag-0.5 wt.%Zr). The laser glazing dramatically reduced voids and cavities originally present in the alloy matrix. In addition, grain boundary precipitates were eliminated. A highly refined microstructure was obtained with extended solid solubility of solute atoms (Ag and Zr) into the matrix. A theoretical model was developed to predict the melt pool depth that occurred during laser glazing.

Nanostructured component fabrication by electron beam-physical vapor deposition

Fabrication of cost-effective, nano-grained net-shaped components has brought considerable interest to Department of Defense, National Aeronautics and Space Administration, and Department of Energy. The objective of this paper is to demonstrate the versatility of electron beam-physical vapor deposition (EB-PVD) technology in engineering new nanostructured materials with controlled microstructure and microchemistry in the form of coatings and net-shaped components for many applications including the space, turbine, optical, biomedical, and auto industries. Coatings are often applied on components to extent their performance and life under severe environmental conditions including thermal, corrosion, wear, and oxidation. Performance and properties of the coatings depend upon their composition, microstructure, and deposition condition. Simultaneous co-evaporation of multiple ingots of different compositions in the high energy EB-PVD chamber has brought considerable interest in the architecture of functional graded coatings, nano-laminated coatings, and design of new structural materials that could not be produced economically by conventional methods. In addition, high evaporation and condensate rates allowed fabricating precision net-shaped components with nanograined microstructure for various applications. Using EB-PVD, nano-grained rhenium (Re) coatings and net-shaped components with tailored microstructure and properties were fabricated in the form of tubes, plates, and Re-coated spherical graphite cores. This paper will also present the results of various metallic and ceramic coatings including chromium, titanium carbide (TiC), titanium diboride (TiB2), hafnium nitride (HfN), titanium-boron-carbonitride (TiBCN), and partially yttria stabilized zirconia (YSZ) TBC coatings deposited by EB-PVD for various applications.