Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

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This paper discusses the results of laser peening without coating on low carbon austenitic stainless steel 316L. Unlike typical experiments on laser peening without coating (LPwC) performed with frequency doubled (green) laser and underwater irradiation, the present study reports LPwC with infrared radiation using thin layer of water as confinement medium. The dependence of laser pulse density on properties such as surface roughness, surface residual stress, microhardness, and corrosion behavior of LPwC specimen were investigated. The magnitude of surface compressive residual stress on laser peened specimen showed appreciable improvement compared to unpeened base material. Microhardness of the specimen improved by 3040% after LPwC. However, the potentiodynamic polarization study indicated that though there is an enhancement of corrosion potential (E corr), the corrosion current density (I corr) increased with increase in laser pulse density. © 2012 Elsevier Ltd.

Department of Physics

School of Advanced Sciences

Vellore Campus

VIT Unitversity

Optics and Lasers in Engineering

Effect of laser shot peening without coating on the surface properties and corrosion behavior of 316L steel

Laser Shot Peening without protective Coating (LPPC) was performed on SS304 austenitic stainless steel using a 300 mJ, 10 ns pulse, 1064 nm wavelength Nd:YAG laser with three different pulse densities. A thin layer of water was used as a confinement layer. The peened specimen was characterised with XRD, AFM and a Profilometer. The stress evaluated at the surface of the laser peened sample shows a maximum compressive stress of 1.6 GPa. The surface roughness and depth profile of microhardness before and after LPPC were investigated.The LPPC region indicate substantial improvement in microhardness and compressive residual stress, with marginal increase of surface roughness.

Materials Science Forum

Laser Shot Peening of 304 Austenitic Stainless Steel without Protective Coating

Grain boundary sliding during high temperature deformation can lead to stress concentrations and an enhancement of diffusion in mobile boundaries. Experiments were conducted on a fine grained 3. mol% yttria stabilized tetragonal zirconia, under conditions associated with superplastic flow involving grain boundary sliding. Tracer diffusion studies under creep conditions and without load indicate that there is no enhancement in either the lattice or grain boundary diffusivities. The experimental creep data are consistent with an interface controlled diffusion creep mechanism. © 2011 Elsevier Ltd.

World University root node

Journal of the European Ceramic Society

Influence of grain boundary sliding on diffusion in yttria doped zirconia

Pure and cerium dioxide doped bismuth sodium potassium titanate (CeO2 doped BNKT) ceramics were synthesized by conventional method. CeO2 doped BNKT was prepared according to the composition Bi0.5(Na0.8K0.2)0.5TiO3x CeO2 where x = 0.1,0.2, 0.4, 0.6, 0.8 and 1.0 wt %. The heat treated powders were calcined from 800 to 900°C for 2 h. The samples were sintered from 1000 to 1100°C for 1 hr. The phase formation was confirmed by X-ray diffraction (XRD). The microstructures of the samples were analyzed by scanning electron microscope (SEM). It was observed that the there was a decrease in grain size with the increase in CeO2. Further, square pillar morphology was observed in the microstructures. The fourier transform infrared spectroscopy (FTIR) was used to investigate the phase evolution of compounds. The particle size measurement done for the sample (1 wt % CeO2 doped BNKT) using laser scattering particle size distribution analyzer revealed a particle size around 592 μm. © 2011, Sphinx Knowledge House. All rights reserved.

International Journal of ChemTech Research

Synthesis and characterization of CeO2 doped bismuth sodium potassium titanate ceramics

Oxygen uptake and oxygen diffusion in Mayenite (Ca12Al 14O33) were investigated using the stable tracer 18O2. Mayenite contains one intrinsic, highly mobile oxygen anion. It was shown that for high temperatures (above 700 °C), the diffusion goes through a interstitialcy mechanism, where the interstitial oxygen anion knocks out a lattice oxygen anion. The activation enthalpy for this process is around 0.9 eV, suggesting that the ionic migration is very fast. © (2009) Trans Tech Publications.

Defect and Diffusion Forum

Oxygen uptake and diffusion in Mayenite

Dense CeO2 layers of 350 nm thickness, with columnar grains of size 25 nm, were RF-sputtered on silicon. 18O isotope exchange in the temperature range from 200 to 575 °C showed surface exchange at CeO2 as the rate-determining step, while diffusion through the polycrystalline thin layer was fast. The surface exchange coefficients controlled by surface or grain boundary processes were found to be ks = 2.7 × 10- 8 exp (frac(- 0.3 eV, k T)) cm s- 1 or kgb = 1 × 10- 9 exp (frac(- 0.3 eV, k T)) cm s- 1. Comparison with literature data on doped ceria revealed that surface exchange could be dominated by grain boundary processes. A lower limit for the diffusion coefficient was determined as 10- 15 cm2 s- 1 at 575 °C. © 2007 Elsevier B.V. All rights reserved.

Solid State Ionics

Fast ion transport in nanoscaled thin film cerium oxide

Hafnium oxide and ytterbium oxide were deposited on the surface of 3 mol.% yttria stabilized tetragonal zirconia (3YTZ) samples with an initial grain size of 0.8 μm, and diffusion annealed at temperatures from 1673 to 1873 K in type-B kinetics regime. Secondary ion mass spectrometry was used to measure the lattice and grain boundary diffusion coefficients for the two species. The diffusivities did not have significant dependences on the mass of the diffusing species, and it was concluded that Hf4+ and Yb3+ acted as tracers for Zr4+ and Y3+, respectively. The experimental results for the cation lattice (Dl) and grain boundary diffusion coefficients (Dgb) are as follows: DlZr=5×10-4exp(-515,000/RT) m2s-1,DgbZr=1×10-3exp(-370,000/RT)m2s-1,DlY=4×10-3exp(-500,000/RT) m2s-1 and DgbY=1×10-2exp(-390,000/RT)m2s-1, where the superscripts Zr and Y refer to the diffusing species. Calculations suggest that Zr diffusion along grain boundaries is rate controlling during high temperature creep and superplasticity. The slower grain growth kinetics may also be related to slower grain boundary diffusion in 3YTZ compared to cubic zirconia. Examination of experimental data on self-diffusion in oxides indicates that the activation energy for grain boundary diffusion is ∼0.8 times that for lattice diffusion. © 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Acta Materialia

Lattice and grain boundary diffusion of cations in 3YTZ analyzed using SIMS

Small levels of various dopants have a significant effect on creep in polycrystalline alumina. While most previous studies have examined the effect of ionic size, the influence of valency of dopants on creep has not yet been completely characterized. The present detailed experimental study, utilizing magnesia and zirconia with a similar ionic size, demonstrates that the ionic valency of dopants also plays a crucial role in creep since magnesia does not significantly alter creep whereas zirconia retards creep substantially. Magnesia doped alumina deforms by Coble diffusion creep whereas zirconia doped alumina deforms by an interface controlled diffusion creep process. © Indian Academy of Sciences.

Fulltext

Bulletin of Materials Science

Role of small amount of MgO and ZrO2 on creep behaviour of high purity Al2O3

The phenomenon of superplasticity has been demonstrated in several zirconia-alumina composites. However, the rate controlling mechanism has not yet been unambiguously identified, due to the limited data available on these materials in comparison with 3 mol% yttria stabilized tetragonal zirconia (3YTZ). The limited data on a zirconia-20 wt% alumina (3Y20A) composite suggest that the mechanical characteristics are similar to those of 3YTZ. The present experimental study on 3Y20A reveals the occurrence of diffusion creep. The experimental results are examined critically in terms of dislocation activity and diffusion creep, and their relevance to superplastic deformation.