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.

Foaming experiments on LM25 alloy reinforced with SiC particulates

Abstract: Al–Si–Mg/SiCP foams were prepared by melt processing route with TiH2 as the blowing agent The effects of foaming temperature (640 and 670 °C), SiCP size (12 and 21 μm), and volume % (5–20) on liquid foam expansion and subsequent collapse were studied Irrespective of the particle size, significant collapse was observed in the liquid foam at 670 °C At the lower foaming temperature of 640 °C, the liquid foam collapse was low to moderate, with finer and higher (15/20%) contents of SiCp resulting in low collapse and the best overall quality Preferential segregation of particles to gas/metal interface, postulated by earlier investigators, was not observed in the present case The presence of SiC within the cell walls induced brittleness, and created irrecoverable damage during the initial phase of compressive deformation The compressive strength of the foams was lower than theoretical predictions Minor defects such as porosity, present within the cell walls, might be responsible in lowering of the compressive strength

An Investigation into Hot Deformation Characteristics and Processing Maps of High-Strength Armor Steel

Abstract: The isothermal hot compression tests of high-strength armor steel over wide ranges of strain rates (0.01-10 /s) and deformation temperatures (950-1100 °C) are carried out using Gleeble thermo-simulation machine. The true stress-strain data obtained from the experiments are employed to establish the constitutive equations based on the strain-compensated Arrhenius model. With strain-compensated Arrhenius model, good agreement between the experimental and predicted values is achieved, which represents the highest accuracy in comparison with the other models. The hot deformation activation energy is estimated to be 512 kJ/mol. By employing dynamic material model, the processing maps of high-strength armor steel at various strains are established. A maximum efficiency of about 45% of power dissipation is obtained at high temperature and low strain rate. Due to the high power dissipation efficiency and excellent processing ability in dynamic recrystallization zone for metal material, the optimum processing conditions are selected such that the temperature range is between 1050 and 1100°C and the strain rate range is between 0.01 and 0.1/s. Transmission electron microscopy observations show that the dislocation density is directly associated with the value of processing efficiency.

Constitutive Modeling of Hot Deformation Behavior of High-Strength Armor Steel

Abstract: The hot isothermal compression tests of high-strength armor steel under a wide range of deformation temperatures (1100-1250 °C) and strain rates of (0.001-1/s) were performed. Based on the experimental data, constitutive models were established using the original Johnson-Cook (JC) model, modified JC model, and strain-compensated Arrhenius model, respectively. The modified JC model considers the coupled effects of strain hardening, strain rate hardening, and thermal softening. Moreover, the prediction accuracy of these developed models was determined by estimating the correlation coefficient (R) and average absolute relative error (AARE). The results demonstrate that the flow behavior of high-strength armor steel is considerably influenced by the strain rate and temperature. The original JC model is inadequate to provide good description on the flow stress at evaluated temperatures. The modified JC model and strain-compensated Arrhenius model significantly enhance the predictability. It is also observed from the microstructure study that at low strain rates (0.001-0.01/s) and high temperatures (1200-1250 °C), a typical dynamic recrystallization (DRX) occurs.