Surface property modifications of silicon carbide ceramic following laser shock peening

This paper is focused on Laser shock peening (LSP) of silicon carbide (SiC) advanced ceramic. A comprehensive study was undertaken using a pulsed Nd:YAG laser. Surface modifications were investigated, particularly: the roughness, hardness, fracture toughness, microstructure, phase transformation and residual stress induced before and after the LSP surface treatment. The findings showed increase in the surface roughness, changes to the surface morphology, improved hardness, and a reduction in the fracture lengths. The LSP surface treatment also improved the surface fracture toughness from an average of 2.32 MPa m1/2 to an average of 3.29 MPa m1/2. This was attributed to the surface integrity and the induced compressive residual stress as a maximum of −92 MPa was measured compared to an average of +101 MPa on the as-received SiC. A slight change in the surface chemistry was also observed from the XPS spectra, however, no real phase transformation was seen from the X-ray diffraction analysis. Laser energy density of around 1.057 J/cm2, 8.5 mm spot size, 10 Hz pulse repetition rate (PRR) at 6ns pulse duration, and 1064 nm wavelength resulted to obtaining a crack-free surface treatment and demonstrated that the technique is also beneficial to enhance some of the properties to strengthen brittle ceramics such as Si

Development and characterization of yttria stabilized zirconia and Al2O3 thin films by pulsed laser deposition:Special Issue

The present study concerns development of yttria stabilized zirconia (YSZ), Al2O3 and a multilayer of Al2O3-YSZ thin film deposition by pulsed laser deposition (PLD) technique for its application as thermal barrier coating (TBC). The detailed study included characterization (microstructure, composition, phase and surface topography) of the thin film. The phase analysis of the YSZ films deposited at room temperature showed amorphous feature, while the film deposited at high temperature showed the formation of tetragonal phase. Residual stress analysis of the coating showed the presence of compressive stress and was maximum at 573 K (sigma(11) = -8.1 GPa and sigma(22) = -6.4 GPa). Residual stress was found to decease with increase in substrate temperature and was found to be lowest at 973 K (sigma(11) = -3.0 GPa and sigma(22) = -1.7 GPa). The cross-sectional morphology of the YSZ and Al2O3 thin films deposited at room temperature showed presence of inter-columnar porosities which changed to a dense structure with increase in substrate temperature

Study of Reduction Kinetics of Iron Ore Pellets by Noncokingcoal

Demand of sponge iron and pre-reduced pellets for the manufacture of different varieties of steel is increasing day by day and new solid reductant based sponge iron plants are being commissioned. In the existing blast furnace an increase in production by at least 25 to 35% can be achieved by using pre reduced iron ore. Pre-reduced iron ore pellets have been established as a good substitute for steel scrap in an electric arc furnace which enhances the productivity of the arc furnace. Also majority of fines which are generated during the course of handling, mining, transportation etc are exported at a through away price which need to be utilized by making iron ore pellets for sponge iron making. A lot of investigations have been carried out on direct reduction process of iron oxides by carbonaceous materials, but little work has been done on the characterization of properties and reduction behavior of iron ore of some mines of Orissa. In the present project work, an attempt has been made to study the reduction behavior and kinetics of fired iron ore pellets. The effect of different reduction parameters such as temperature (850-10000C), time (15-120 min.), reductant quality, pellets Vs lump, mixing of particles of different sizes at different ratios for pellet preparation etc. on the reduction behavior of iron ore pellets. These form the subject matter of the thesis. First chapter gives the introduction of the subject. It speaks about the need of DRI industry, scope, present status and future planning of DRI industry in India, world wise DRI production, etc. It also presents the mechanism of direct reduction process. The second chapter shows the literature review. The third chapter deals with planning of experiments, selection of raw materials, preparation of samples, preparation of iron ore pellets, experimental procedure for characterization of different chemical and strength properties of the selected iron ore lump, proximate analysis of selected noncoking coals, evaluation of reduction and activation energies, study of swelling behavior, evaluation of strength properties of pellets, etc. The results obtained and the discussions made from these observations have been outlined in chapter four. The result for fired iron ore pellets indicated an increase in degree of reduction with increase in reduction temperature (850-10000C). Fired iron ore pellets showed higher degree of reduction of iron ore pellets than iron ore lump. The reduction behavior of iron ore was identical in all the selected coals.. Abnormal swelling was observed at temperature 8500C and 9000C; whereas shrinkage in the pellets was observed at 9500C and 10000C. The reduction kinetics of Zenith iron ore pellets were studied in the temperature range of 850-10000C. None of the data were found to fit to the kinetic models. So the activation energies of all the iron ore – coal combinations were calculated using Integration method. Pellets made from fines of (-100#) 100% + (-18+25#)10% + (-10+16#)% were showing reduction in activation energy as compared to the pellets made from fines of -100#. In all the studied coal size, least activation energy was observed with coal of -6+16# size. Results obtained from chapter four have been summarized in chapter five. Lastly, these conclusions have been followed by the list of references. a) The degree of reduction increased with increase in reduction temperature from 850-10000C b) There was no effect of type of coal on the degree of reduction of iron ore pellets c) Iron ore lumps were less reducible than their corresponding iron ore pellets. d) The reduction behavior of iron ore pellets made from fines of different sizes were comparable with pellets made from fines of -100#. e) At 8500C and 9000C, the iron ore pellets were showing abnormal swelling after reduction, whereas at 9500C and 10000C, shrinkage was observed in the reduced iron ore pellet

Thermophysical behavior of thermal sprayed yttria stabilized zirconia based composite coatings

The effective thermal conductivity of a composite coating depends on intrinsic thermal conductivity of the constituent phases, its characteristics (size, shape) and area fraction of porosities. The present study concerns studying the effect of CoNiCrAlY and Al2O3 content on the coefficient of thermal expansion and thermal conductivity of the YSZ (YSZ-CoNiCrAlY and YSZ- Al2O3) based composite coatings developed by thermal spray deposition technique. The coefficient of thermal expansion and thermal conductivity of the composite coatings were measured by push rod dilatometer and laser flash techniques, respectively, from room temperature to 1000 °C. Variation in density, porosity, coefficient of thermal expansion, and thermal conductivity was observed in the composite coatings with the addition of different volume fraction of CoNiCrAlY and Al2O3 powders in YSZ-CoNiCrAlY and YSZ-Al2O3 composites, respectively. Comparison between the theoretical and experimental thermal conductivities showed a mismatch varying from 4% to 58% for YSZ-CoNiCrAlY composite coatings and from 58% to 80% for YSZ- Al2O3 composite coatings. Model based analyses were used to understand the mechanism of thermal conductivity reduction in the composite coatings. It was concluded that the morphology of porosities varied with composition. Publisher Statement - NOTICE: this is the author’s version of a work that was accepted for publication in Ceramics International. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Ceramics International, [(in press), (2017)] DOI: 10.1016/j.ceramint.2017.05.170© 2017, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0