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.

Enhanced tribological performances of nanocrystalline diamond film

Abstract: Diamond films are well known for their outstanding properties such as high hardness, possible low coefficient of friction, high thermal conductivity, excellent biocompatibility and electrical insulation. Diamond films with nanocrystalline grains (grain sizes between 3 and 15 nm) offer further advantages of low compressive stress, low surface roughness, and high amount of surface atoms in relation to volume leading to enhanced surface properties. In view of these, the present investigation is undertaken to explore the possibility of using nanocrystalline diamond (NCD) films in advanced automotive equipment. Accordingly NCD-films have been deposited using a modified hot-filament technique. Tribological behaviour of these films has been evaluated by means of a reciprocating model tribometer with different lubricant qualities. The worn surfaces were examined using scanning electron microscopy (SEM) and 3D white light confocal microscopy. The results show the influences of coating qualities and test conditions on the tribological response. Comparable friction coefficient can be found with high treated and low treated lubricants. These films exhibited negligible wear for the range of load tested.

The quasi-crystalline phase in the Mg—Al—Zn system

Abstract: Shechtman et al.1 have reported a phase in rapidly solidified Al86Mn14 alloy with long-range orientational order, but with icosahedral point-group symmetry, which is inconsistent with lattice translations. However, Pauling2 has argued that the apparent icosahedral symmetry in A186Mn14 alloy is due to directed multiple twinning of cubic crystals with a cube edge of 26.7 A. We report here the powder X-ray diffraction study of a rapidly solidified Mg32(Al, Zn)49 alloy which shows 5–3–2 symmetry diffraction in transmission electron microscopy (TEM). Also reported is a study of rapidly solidified Mg2A13 alloy. The advantage of these alloys is that β-Mg2Al3, which has nearly the same structure as proposed by Pauling for the rapidly quenched Al86Mn14, is an equilibrium phase. This is unlike the Al–Mn system, where, according to Pauling, the cubic phase occurs in a metastable and already twinned form. The present choice of alloy systems makes it possible to compare the X-ray diffraction patterns from the quasi-crystalline phase and a cubic phase with nearly the same structure as proposed by Pauling. We observe that the X-ray diffraction pattern of rapidly solidified Mg32(Al, Zn)49 alloy is distinct from those of the equilibrium phases and that the pattern can be completely indexed to an icosahedral phase. We argue that the above observation is inconsistent with the proposal that the material consists of an aggregate of twinned cubic crystals. Therefore, the alternative is to invoke a quasi-crystalline lattice to explain the observed 5–3–2 symmetry diffraction in TEM.