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Item The effect of strain induced phase transformation on the thermal expansion compatibility of plasma sprayed spinel coating on SOFC metallic interconnect – A study using in-situ high temperature X-ray diffraction(Elsevier Ltd, 2023) N, M.; Santhy, K.; Rajasekaran, R.A new and novel approach has been adopted in this study to evaluate thermal mismatch induced by thermal expansion in substrate-coating contact pairs using in-situ high-temperature X-ray diffraction (HT-XRD). Atmospheric plasma sprayed (APS) Mn1.0Co1.9Fe0.1O4 (MCF) coating on Crofer 22 APU steel interconnect was investigated. In-situ HT-XRD was performed individually for substrate and coating from 25 °C to 900 °C. Diffraction data were recorded for different temperatures to obtain lattice parameters and strain as a function of temperature. The coefficient of thermal expansion (CTE) of MCF coating was slightly higher than steel substrate and showed no significant thermal expansion mismatch till 700 °C. The increasing lattice strain measured by Scherrer and Williamson-Hall methods indicates strain-induced phase transformation of MCF coating with temperature, supporting the phase transformation-induced self-healing phenomenon of MCF coating. The merit of in-situ HT-XRD as a tool for optimizing operating temperature and measuring thermal mismatch of solid oxide fuel cell (SOFC) stacks has been discussed. © 2023 Hydrogen Energy Publications LLCItem In Situ High-Temperature X-ray Diffraction Study on Atmospheric Plasma and Detonation Sprayed Ni-5 wt.%Al Coatings(Springer, 2023) Purushotham, N.; Santhy, K.; Suresh Babu, P.; Govindarajan, G.; Rajasekaran, R.In situ high-temperature x-ray diffraction (HT-XRD) was used in the present study to assess the coefficient of thermal expansion and recrystallization of Ni-5 wt.%Al coatings. Atmospheric plasma spray (APS) and detonation spray (DSC) techniques were used to deposit Ni-5 wt.%Al coatings on IN718 substrates. The coatings were examined using HT-XRD at ambient conditions (25 °C) up to high temperatures (1150 °C) under a vacuum pressure of around 10−4 mbar. Coefficients of thermal expansion (CTE), crystallite size (D) and lattice strain (ε) were determined by the Scherer and Williamson-Hall (W-H) method with a uniform strain model (UDM) using x-ray peak profile analysis (XPPA). The microstructure of the Ni-5 wt.%Al coatings was analyzed by field emission scanning electron microscopy (FESEM). No phase changes were observed in either coating, as the Ni-5 wt.%Al coatings consisted mainly of γ-Ni crystals with a face-centered cube (FCC) phase in both coating techniques. Lattice parameters as a function of temperature were used to calculate linear thermal expansion coefficients. The linear thermal expansion of Ni-5 wt.%Al coatings deposited by both thermal spray methods was discussed on the basis of process-induced microstructures. © 2023, ASM International.Item Understanding early-stage oxidation mechanism of Crofer 22 APU solid oxide fuel cell steel interconnect using glow discharge optical emission spectroscopy and grazing incidence X-ray diffraction(Elsevier B.V., 2023) Naik, M.; Santhy, K.; Rajasekaran, R.Crofer 22 APU is used as metallic interconnects in stacking solid oxide fuel cells (SOFCs) operated at elevated temperatures (above 700 °C) owing to their excellent oxidation resistance. Understanding the protective layer formation in the initial oxidation stage would be useful for optimizing and designing protective coatings for extended life. Initial stage oxidation of Crofer 22 APU steel using surface analytical tools such as glow discharge optical emission spectroscopy (GD-OES), grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy, and atomic force microscopy (AFM) are studied in the paper. An oxidation test on as-received Crofer 22 APU steel was carried out in a controlled atmosphere (0.01 Pa) in an in-situ high-temperature X-ray diffraction (XRD) stage at 950 °C. Normal XRD showed no indication of oxidation, while GIXRD revealed the formation of two-layer oxides: Top layer spinel MnCr2O4 and fine-grained inner layer Cr2O3, which was confirmed and quantified by GD-OES depth profiling. The Cr2O3 formed initially led to the formation of MnCr2O4 spinel during the initial stage. The rapid diffusion of Mn through the fine-grained Cr2O3 layer results in an increased growth rate of MnCr2O4 spinel on the top of the fine-grained Cr2O3 layer. © 2023 Elsevier B.V.Item High temperature sliding wear behavior of detonation sprayed Ni-5wt%Al coating(Elsevier Ltd, 2023) N, P.; N.l, P.; P, S.B.; G, S.; Rajasekaran, R.The tribological behavior of detonation (DSC) sprayed Ni-5%wtAl coatings at room temperature (25 °C) and elevated temperature (850 °C) has been studied in this work. Dry sliding wear experiments were done by using alumina (Al2O3) ball-on-disc tribometer. FESEM-EDS and a non-contact 3D profilometer microanalysis were used to evaluate the worn scar and wear rate and identify the wear mechanism. X-ray diffraction (XRD) investigation indicated that the Ni-5wt%Al coating predominantly consists of γ-Ni phases at 25 °C and 850 °C conditions. The phase evolution, thermal expansion, crystallite size, and lattice strain were evaluated using in-situ high-temperature X-ray diffraction (HT-XRD). The crystallite size (D) and lattice strain (ε) were determined by Williamson-Hall analysis using a uniform deformation model (UDM), employing X-ray peak profile analysis (XPPA). In high-temperature conditions, the thermal expansion mismatch between the coating and substrate is negligible, with reduced spallation and cracking at the interface. The findings of the wear tests revealed that as the temperature increased, the coefficient of friction (CoF) and wear rate (ω) significantly decreased as the wear mechanism changed from abrasive to adhesive. The improvement of wear resistance of Ni-5wt%Al coating at high temperatures has been evaluated and discussed from the perspective of thermal expansion and tribo-layer formation. © 2023 Elsevier B.V.