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.

Particle behaviour during high velocity oxy-fuel spraying

Abstract: A comprehensive one-dimensional model recently developed by the authors is used to investigate particle behaviour associated with the high velocity oxy-fuel (HVOF) spraying process. Using the spraying of WC-12%Co powder as a case study, it is shown that the Knudsen non-continuum effects can have an immense influence on the gas-solid heat and momentum transfer processes. Consistent with actual practical experience during HVOF spraying, the results of this study reveal that the low temperatures provided by the oxy-fuel combustion flame preclude complete melting of many ceramic powders possessing high melting points. However, it is shown that powders of metals and the low melting point alloys can be completely molten in the oxy-fuel flame. With WC-12%Co powder, it is found that only particles smaller than 45 μm in size can be fully molten and this is in excellent agreement with the empirically established HVOF coating practice. The results also indicate that the hypersonic flame accelerates the powder particles to very high velocities, around 700 m s −1 in some instances, and such high particle velocities are primarily responsible for the HVOF technique yielding dense and well-bonded coatings which are superior to plasma-sprayed coatings.

Effect of different reinforcements on composite-strengthening in aluminium

Abstract: In the development of metal-matrix composites, reinforcements of aluminium and its alloys with ceramic materials has been pursued with keen interest for quite sometime now. However, a systematic comparison of the effect of different reinforcements in powder-processed aluminium and its alloys is not freely available in the published literature. This study examines the influence of SiC, TiC, TiB2 and B4C on the modulus and strength of pure aluminium. B4C appears slightly superior as a reinforcement when comparing the effect of SiC, TiC, B4C and TiB2 on specific modulus and specific strength values of composites. However, TiC appears to be a more effective reinforcement, yielding the best modulus and strength values among those considered in this study. The differences in thermal expansion characteristics between aluminium and the reinforcements do not seem to explain this observation. The other advantage of TiC is that it is economically a more viable candidate as compared to B4C and TiB2 for reinforcing aluminium alloys. It is suggested that the superior effect of TiC as a reinforcement is probably related to the high integrity of the bond at the Al-TiC interface.

Correlation between microstructural features and creep strain in a near-α titanium alloy processed in the α+β regime

Abstract: High temperature creep is an important property of titanium alloys used in aeroengines. Creep resistance of titanium alloys generally varies with heat treatment, temperature and cooling rate. Both the parameters affect the morphology and topology of the α (HCP) and β (BCC) phase present in the material. Various theories have been proposed in the literature to explain (i) the increase in creep strain with decreasing solution treatment temperature and (ii) the U-shaped variation of creep strain with cooling rate. Some of these theories are quite contradictory. An attempt is made here to systematically (a) evaluate and establish a direct microstructure–mechanical property correlation and (b) to explain the observed variation in the creep behaviour of a near-α titanium alloy IMI 834. The results obtained indicate that the observed U-shaped variation of creep curve is due to the counter acting nature of various microstructural features present in the material.