Defence Metallurgical Research Laboratory

About: Defence Metallurgical Research Laboratory is a facility organization based out in Hyderabad, India. It is known for research contribution in the topics: Microstructure & Alloy. The organization has 1208 authors who have published 2662 publications receiving 51663 citations.

Formation of TiN whiskers through carbothermal reduction of TiO2

Abstract: Formation of TiN whiskers through carbothermal reduction of TiO2 in nitrogen was studied. Effect of (i) addition of potassium (K2CO3) and nickel (NiCl2), (ii) reaction temperature on the formation of whiskers was studied. Addition of K2CO3 has strong influence on the formation whiskers. The yield of whisker was maximum at 920–1000°C. At higher temperatures, formation of particulates of TiN was the dominant process. Increase in K2CO3 concentration increased the formation of (i) whiskers at low temperatures 815°–920°C, (ii) particulates at high temperatures 1000°–1100°C. A vapor-liquid-solid growth mechanism of whisker formation was identified. K2CO3 has been identified as an essential constituent for the formation of a low melting liquid by reaction with TiO2 and NiCl2. Continuous supply of TiO, nitrogen and CO to this complex K-Ni-Ti liquid droplet lead to the precipitation of TiN whisker.

Dynamic hardness of detonation sprayed WC-Co coatings

Abstract: The objective of the present work was to determine the dynamic hardness of WC-Co coatings from the dynamic hardness of the coating substrate system. It was also the purpose of this work to evaluate the influence of coating composition, coating thickness, and substrate materials on the dynamic hardness of the coating. To achieve the above-mentioned objectives, WC-12%Co and WC-17%Co coatings were deposited by detonation spraying on three different substrate materials: mild steel, commercially pure (CP) aluminum, and CP titanium. The dynamic hardness of the coating/substrate composite was evaluated by a drop weight system. The dynamic hardness of the coating independent of the substrate was determined from the dynamic hardness of the coating/substrate composite.

Charge transfer on the metallic atom-pair bond, and the crystal structures adopted by intermetallic compounds.

Abstract: It has been argued in our recent papers that the heat of formation of intermetallic compounds is mostly concentrated in the nearest neighbor unlike atom-pair bonds, and that the positive term in Miedema's equation is associated with charge transfer on the bond to maintain electroneutrality. In this paper, taking examples of some well populated crystal-structure types such as MgCu2, AsNa3, AuCu3, MoSi2 and SiCr3 types, the effect of such charge transfer on the crystal structures adopted by intermetallic compounds is examined. It is shown that the correlation between the observed size changes of atoms on alloying and their electronegativity differences is supportive of the idea of charge transfer between atoms. It is argued that the electronegativity and valence differences need to be of the required magnitude and direction to alter, through charge transfer, the elemental radius ratios RA/RB to the internal radius ratios rA/rB allowed by the structure types. Since the size change of atoms on alloying is highly correlated to how different RA/RB is from the ideal radius ratio for a structure type, the lattice parameters of intermetallic compounds can be predicted with excellent accuracy knowing RA/RB. A practical application of the approach developed in our recent papers to superalloy design is presented.