Glow discharge plasma nitriding of low alloy steel

Present study concerns with the effect of plasma nitriding on hardness of low alloy steel. Plasma nitriding had been performed at elevated temperature of 500 C which improved the hardness to 1200 Hv. The case depth was found to be 80 mm. With the variation of time the case depth also varied. The plot of the square of the case depth vs. nitriding time and the corresponding line drawn by a linear regression and extrapolation passes almost through the origin. From the plot the nitrogen diffusion co-efficient calculated to be 2.23 10 13 m2/s. The structural and morphological studies have been made by following the X-ray diffraction (XRD) and scanning electron microscopic (SEM) and EDS analyses. XRD revealed the presence of a-Fe, c0 and e phases

Parametric study of the mechanical properties of nanocrystalline TiN/CrN multilayer coatings with a special focus on the effect of coating thickness and substrate roughness

In a plot to improve the performance of steel mechanical parts subject to aggressive friction solicitations, three batches of deposits of TiN and CrN layers on steel substrates with two different roughnesses have been obtained using reactive DC magnetron sputtering. The present study was conducted to determine the effect of varying TiN/CrN multilayer coatings thickness (varying modulated period Λ and interlayer thickness), on their mechanical and tribological properties. The morphological and the structural properties were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The nanoindentation measurements displayed improvement in hardness (> 40 GPa) and Young’s modulus (> 600 GPa) for the coating with Λ ≅ 12 nm (TiN Λ/2 ≅ 7.5 nm + CrN Λ/2 ≅ 4.5 nm) thickness and the higher number (300) of interfaces, deposited on the rougher substrate. Its low coating damage under the scratch test, associated with its estimated adhesion work (Wad), indicated a good cohesive/adhesive strength and improved structural and mechanical properties

Recrystallization mechanisms and associated microstructure evolution during billet conversion of a gamma-gamma' nickel based superalloy

A partially recrystallized sample of the Ni-based superalloy AD730 was taken from an intermediate stage of the ingot to billet conversion process and isothermally forged in a single stroke compression test at a sub-solvus temperature (1080 °C). The as-received material had a heterogeneous microstructure, containing a mixture of coarse and much finer recrystallized grains as well as unrecrystallized ones, and also heterogeneous γ′ precipitation. The recrystallization mechanisms occurring dynamically in the different grain populations were investigated via electron backscatter diffraction (EBSD). It was found that local microstructure could affect the operative recrystallization mechanism, with different mechanisms seen in the deformed and recrystallized regions, owing to their different precipitate distributions. Within a single deformed grain, three apparently distinct dynamic recrystallization (DRX) mechanisms were identified. The interaction of recrystallization with precipitates plays a central role in DRX. In certain cases precipitates may stimulate discontinuous DRX by providing recrystallization nuclei, alternatively they may impede and limit the growth of recrystallized grains, or in other cases still they promote continuous recrystallization