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.

Effects of Cold Work on Precipitation Hardening of Cu-4.5 mass%Ti Alloy

Abstract: The structure and properties of a solution treated, cold worked and aged Cu-4.5%Ti alloy were studied by means of optical, scanning and transmission electron microscopy as well as hardness, tensile tests and electrical conductivity measurements. Prior cold work (rolling) increases the peak hardness from 340 to 425 VHN, the tensile strength from 890 to 1380 MPa and the conductivity from 10 to 25% IACS on aging the alloy in the temperature range from 400 to 450°C. Maximum strengthening of the alloy is attributed to the precipitation of a coherent, metastable β' phase (Cu 4 Ti). The alloy is deformed through profuse twinning. The ductile mode of fracture of the aged alloy is not affected by the prior cold work.

Laves phase in superalloy 718 weld metals

Abstract: The important consequence of the solidification in cast or welded superalloy 718 is the segregation of Nb and the formation of laves phase. Laves phase is a brittle intermetallic topologically close-packed phase with hexagonal structure, known for its detrimental effect on mechanical properties at room temperature [1]. Although data available with regard to wrought materials is somewhat elaborate it is not true for welds in general and for electron beam welds in particular. In this letter the formation of laves phase in high heat input gas tungsten arc (GTA) and low heat input electron beam (EB) welds of 2 mm thick superalloy 718 in as-welded and post-weld heat treated (PWHT) conditions is evaluated. The results have a bearing on the tensile ductility and other properties of welds. Sheets of superalloy 718 of thickness 2 mm in solution treated condition (chemical composition in Table I) were autogenously welded by automatic GTA and EB welding processes, resulting in full penetration using the weld process parameters listed in Table II. The as-welded samples were subjected to two PWHT schedules: direct duplex ageing and solution treatment followed by ageing. Solution treatment was carried out at 980 °C for 20 rain with air cooling and the duplex ageing was carried out at 720 °C for 8 h with furnace cooling to 620 °C for 8 h with air cooling. The as-welded and heat treated samples were then subjected to scanning electron microscopic (SEM) examination and quantitative electron probe micro-analysis (EPMA) for the analysis of microsegregation of elements and determination of the formation of laves phase. Figs 1 and 2 show SEM micrographs of the aswelded microstructures of EB and GTA weld metals, respectively. Essentially, the solidified structure is of dendritic type. EB weld metal showed relatively finer

Elevated-temperature oxidation behavior of titanium silicide and titanium silicide-based alloy and composite

Abstract: The oxidation behavior of Ti5Si3 has been studied in air in the temperature range of 1200 °C to 1400 °C. The oxidation kinetics is slower than that predicted by the parabolic-rate law equation at 1200 °C, but is sharply enhanced beyond a temperature of 1300 °C. The oxidation kinetics of a Ti5Si3-8 wt pct Al alloy and a Ti5Si3-20 vol pct TiC composite at 1200 °C has also been investigated and compared to that of Ti5Si3. Alloying with Al does not alter the oxidation resistance much, but the presence of TiC reinforcements enhances the rate of oxidation significantly. The oxidation products have been identified and the mechanism of oxidation has been analyzed using thermodynamic and kinetic considerations.