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.

Precipitation hardening of Cu-Ti-Cr alloys

Abstract: Precipitation hardening of Cu-4Ti-1Cd alloy has been studied using hardness measurements and transmission electron microscopy. This alloy exhibited hardness of 238 Hv in solution treated (ST) condition and attained peak hardness of 318 Hv after ageing at 450°C for 40 h. Electrical conductivity of Cu-4Ti-1Cd alloy increased from 5.7 %IACS (International Annealed Copper standard) in ST condition to 8.9 %IACS on ageing at 450°C for 16 h. This alloy exhibited markedly higher yield strength (751 MPa in the peak-aged condition) compared to Cu-4.5Ti alloy but the increase in UTS due to cadmium addition was less significant. The higher yield strength of ternary alloy in peak aged condition is due to the solid solution strengthening of cadmium as well as the presence of β′-Cu4Ti precipitate. On over-ageing the alloy showed a decrease in hardness as a result of formation of equilibrium precipitate, β-Cu3Ti. Optical microscopy reveals single phase with equiaxed grains in solution treated condition. A coherent, metastable phase β′-Cu4Ti is responsible for high strength and hardness in peak aged condition. The over-ageing in this alloy shows the formation of cellular structure at the grain boundaries of the matrix phase.

Tensile Properties of Ni-Based Superalloy 720Li: Temperature and Strain Rate Effects

Abstract: Tensile properties, deformation, and fracture behavior of a wrought nickel-base superalloy 720Li have been studied in standard solutionized and two-stage-aged condition in the temperature range of 25 °C to 750 °C. Effect of strain rate on tensile behavior was assessed at 25 °C, 400 °C, and 750 °C at five strain rates that range between 10−5 s−1 and 10−1 s−1. The yield strength and ultimate tensile strength of the alloy remained unaffected by temperature until about 600 °C and 500 °C, respectively, typical of superalloys strengthened by fine and coherent intermetallic Ni3Al-based precipitates. The flow stress of the alloy was found to be insensitive to the strain rates studied at 25 °C and 400 °C. However, at 750 °C, the flow stresses showed strain rate sensitivity at strain rates 10−3 s−1, and at lower strain rates, tensile instability was seen to set in immediately after yielding. The alloy exhibited ductile dimple fracture at all the temperatures and strain rates studied. Microstructural investigations indicate that in regimes where flow stresses are insensitive to strain rate, deformation occurs through heterogeneous planar slip, whereas in strain rate sensitive regimes, thermally activated diffusion processes promote homogeneous deformation.