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Effect of Isothermal Treatment on Ni3Al Coatings Deposited by Air Plasma Spraying System

Mehmood K., Rafiq M. A., Durrani Y. A., Khan A. N.

Archives of Metallurgy and Materials

2018

Vol. 63, iss. 1

277--283

Ni3Al coatings were obtained on AISI 321 steel samples by air plasma spraying system. The behavior of heat treatment on intermetallic coatings were evaluated after exposure at various temperatures i.e. 500ºC to 800ºC. The stay time in this regard was varied from 10 to 100 hours. The coatings were then characterized by X-Ray diffraction analysis, optical and scanning electron microscopy, eddy current measurements and stress analysis. It was observed that the formation of NiO increases drastically with time and temperature. The hardness of the coating increases with the formation of NiO. It was noted that the residual stresses can be correlated with the formation of NiO. Further, the development of residual stresses can be monitored by a non-destructive technique i.e. eddy current method.

Conduction in nanostructured La1=x Sr x FeO3 (0 <= x <= 1)

Zafar A., Imran Z., Rafiq M. A., Shah S. H., Hasan M. M.

Materials Science Poland

2012

Vol. 30, No. 3

240--247

We investigated electrical properties of nanostructured La1?x Sr x FeO3 (0 <= x <= 1) from 300 K-400 K. The nanostructured La1-x Sr x FeO3 (0 <= x <= 1) was synthesized by citrate gel method requiring no pH control. X-ray diffraction pattern showed that single phase LaFeO3 with an orthorhombic structure was formed. The structure changed into rhombohedral for x = 0.5 and it became cubic for x = 1.0. For x <= 0.5, our material showed non-linear current-voltage characteristics and for x > 0.5 it showed linear current-voltage characteristics. Poole Frenkel type conduction mechanism was found to be operative in LaFeO3 from 300 K-400 K. The experimental values of field-lowering coefficient were by 2.56-6.41 times higher than the predicted value and were attributed to the presence of localized fields. The increase in conductance with Sr content was due to formation of Fe4+ ions in addition to Fe3+ with the increase in Sr content. Impedance spectroscopy and ac conductivity analysis of La1-x Sr x FeO3 (0 <= x <= 1) was also carried out in the temperature range from 300 K-400 K and frequency was varied from 20 Hz - 2 MHz. The ac conduction followed the correlated barrier hopping model in La0.9Sr0.1FeO3.