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.

On the ballistic performance of metallic materials

Abstract: The paper presents a ballistic performance index for metallic armour materials in terms of the commonly determined mechanical properties such as strength and modulus. The index is derived using an energy-balance approach, where the kinetic energy of the projectile is assumed to be absorbed by the elastic and the plastic deformation involved in the penetration process as well as the kinetic energy imparted to the target material during deformation. The derivation assumes two distinct stages to exist during the penetration of the projectile. At the striking face of the armour, the material is assumed to flow radially in a constrained deformation region but longitudinally at the rear surface leading to typically observed bulging of the armour without constraint. The index is validated using the available experimental and empirical data obtained in the case of small arm projectiles for an impact velocity of about 800 m/sec. This index is expected to facilitate the development of metallic armour, since the number of the ballistic experiments can be reduced significantly and only the promising materials need to be considered.

Effect of Alloying Elements in Hot-Rolled Metastable β-Titanium Alloys. Part II: Mechanical Properties

Abstract: This paper describes the tensile properties, flow and work-hardening behavior of four metastable β-titanium alloys Ti-5Al-5Mo-5V-3Cr (A1), Ti-5Al-3.5Mo-7.2V-3Cr (A2), Ti-5Al-5Mo-8.6V-1.5Cr (A3), and Ti-5Al-3.5Mo-5V-3.94Cr (A4) in α+β hot-rolled condition. The decreasing order of average strength parameters (σ YS and σ UTS) is A4, A2, A1, and A3. The maximum strength observed in alloy A4 is due to the presence of highest wt. fraction of Cr. The elongation is the maximum and minimum in alloys A3 and A4, respectively. These alloys display moderate to high percent in-plane anisotropy (A IP) and reasonably low anisotropic index (δ) values. Both the A IP and δ values are maximum and minimum in alloys A1 and A3, respectively. The yield locus plots also exhibit the presence of anisotropy due to relatively large differences in yield strength values along tension and compression directions. The flow behavior of alloys A1, A2, and A4 follows Swift equation, while the alloy A3 displays best fit with Holloman equation. The presence of prestrain (e 0) in hot-rolled materials before tensile testing has an important bearing on the flow curves of A1, A2, and A4 alloys. The instantaneous work-hardening rate curves of the alloys A1, A2, and A3 exhibit all the three typical stages (stage I, stage II, and stage III) in RD samples, while the alloy A4 shows the presence of only stage I and stage III. The 45 deg to RD and TD samples of alloys A1, A2, and A4 display only stage I. The stages I and III as well as I and II are present in alloy A3 in 45 deg to RD and TD samples, respectively. Dislocation-controlled strain hardening occurs in all the three stages of these alloys in the absence of stress-induced martensitic transformation (α″) and twinning. Slip is the predominant deformation mechanism during tensile testing. Three types of slip lines, i.e., planar, wavy, and intersecting have been observed close to fracture surfaces of post tensile-tested specimens.

Density functional study of half-metallic property on B2 disordered Co2FeSi

Abstract: First principle calculations on the magnetic properties and spin polarization of the B2 disordered Co2FeSi full Heusler alloy have been carried out along with that of ordered L21 structure. The linear augmented plane wave method, within the LDA+U approximation, gives the magnetic moment value as predicted by Slater-Pauling rule. A small band gap in the minority band structure around the vicinity of the Fermi level results in half-metallicity or 100 % spin polarization in L21 ordered structure. The calculations also showed that the half-metallicity vanishes at moderate percentages of B2 disorders due to creation of new states around the Fermi level in the minority DOS but at low and high levels of disorder, the half-metallicity was retained. The variation in the magnetic moments of Co2FeSi with change in the % disorder was attributed to the changes in the local magnetic moments of Co, Fe, and Si atoms which vary with change in % disorder.

On the die design for Repetitive Upsetting – Extrusion (RUE) process

Abstract: Though the capability of Repetitive Upsetting- Extrusion (RUE) process to produce ultrafine grains in a bulk aluminium alloy has been established, a detailed description on the material flow, deformation homogeneity and the die design requirements to process bulk materials has never been addressed To address these issues commercial pure copper (CP Cu) was subjected up to four cycles of RUE using the die design that has been used by various researchers The RUE processed CP Cu samples when subjected to macrostructure and microstructure evaluation revealed that apart from inhomogeneous deformation, defects such as axial hole/funnel and folds/laps were induced in the processed samples The formation of these defects during RUE is attributed to the current die design Based on a recent study carried out on the extrusion defect – axial hole/funnel, a modified RUE die design has been proposed CP Cu subjected to RUE using the modified die design revealed that the modified die design not only helps in avoiding the defects but also improves the homogeneity

Precipitation Hardening of Cu-3Ti-1Cd Alloy

Abstract: Precipitation strengthening of Cu-3Ti-1Cd alloy has been studied using hardness and tensile tests, electrical resistivity measurements, and transmission electron microscopy. The alloy exhibited a hardness of 117 Hv in solution-treated (ST) condition and attained a peak hardness of 288 Hv after aging at 450 °C for 72 h. Electrical conductivity increased from 7%IACS (International Annealed Copper Standard) in ST condition to 13%IACS on aging at 450 °C for 16 h. The alloy exhibited yield strength (YS) of 643 MPa and ultimate tensile strength (UTS) of 785 MPa in peak-aged (PA) condition. Strengthening in Cu-3Ti-1Cd alloy in PA condition is attributed to solid solution strengthening effect of cadmium (Cd) as well as fine scale precipitation of metastable and coherent β′-Cu4Ti phase. On overaging at 450 or 500 °C, the alloy showed a decrease in hardness as a result of formation of equilibrium precipitate β-Cu3Ti as continuous precipitation within the matrix and as discontinuous precipitation at the grain boundaries. While the tensile properties are better, the electrical conductivity of Cu-3Ti-1Cd alloy is less than that of binary Cu-2.7Ti alloy. The strengthening mechanism is the same in both binary and ternary alloys of Cu-Ti, i.e., precipitation of metastable and coherent β′-Cu4Ti phase.