Showing papers by "Defence Metallurgical Research Laboratory published in 2019"

Creep crack simulations using continuum damage mechanics and extended finite element method

Abstract: In the present work, elasto-plastic creep crack growth simulations are performed using continuum damage mechanics and extended finite element method. Liu–Murakami creep damage model and explicit ti...

Superior energy storage performance and fatigue resistance in ferroelectric BCZT thin films grown in an oxygen-rich atmosphere

Abstract: Ferroelectric properties of chemical-solution-deposited Ba0.85Ca0.15Ti0.90Zr0.10O3 (BCZT) thin films in the 200 nm thickness range, grown in air and oxygen-rich atmospheres, were investigated. Oxygen-processed BCZT thin films were found to have very slim hysteresis with higher polarization, lower remanent polarization (Pr), much lower coercivity and much higher dielectric breakdown strength. Those properties resulted in superior energy storage properties. Oxygen-processed BCZT thin films showed an energy storage density (ESD) of 64.8 J cm−3 and energy storage efficiency (ESF) of 73% at 2000 kV cm−1 electric field. Apart from that, the films showed very low leakage current and improved polarization fatigue properties. Oxygen-processed virgin BCZT film displayed maximum polarization (Pmax) of 106 μC cm−2 and Pr of 12.9 μC cm−2, whereas the measured Pmax and Pr of the fatigued film after 1010 switching cycles were 105 μC cm−2 and 13.2 μC cm−2 respectively. BCZT thin films with high ESD and ESF at 2000 kV cm−1 electric field and with excellent fatigue properties could be considered as potential candidates for low and intermediate voltage ferroelectric energy storage applications.

Tensile anisotropy associated microstructural and microtextural evolution in a metastable beta titanium alloy

Abstract: Tensile anisotropy behaviour of metastable beta titanium alloy β-21s (Ti–15Mo–2.7Nb–3Al–0.2Si) sheet in solution treated condition is evaluated at room temperature along three different orientation (rolling direction, 45° to rolling direction and transverse direction). In addition to fractographic studies, the microstructural and microtextural evolution is investigated in the post-tensile deformed condition through optical metallography, scanning electron microscopy (SEM) and Electron Backscattered Diffraction (EBSD). Quantification of mechanical anisotropy by evaluating the % In-Plane Anisotropy (%IPA), Anisotropic Index (δ), yield loci and plastic strain ratio indicated considerable anisotropy in strengths and ductility. Irrespective of testing orientation, the deformed microstructure is characterized by fine to coarse planar slip bands, however the slip bands observed along 45° is relatively widely spaced. The evolution of dislocation density obtained from kernel average misorientation (KAM) maps is unaffected by the tensile testing direction. Although EBSD derived Taylor factor maps revealed slip mediated deformation behaviour dominated by {110} slip systems along all testing directions, the Taylor factor distribution divulged complex dependence on test orientation. Despite weak to moderate microtextural changes are noticed in α-fiber and β-fiber texture components, the textural evolution is strongly influenced by the testing orientation.

Effect of Zr addition on the mechanical properties of Nb Si based alloys

Abstract: In the present study, the effect of Zr addition on the mechanical properties of arc melted hypoeutectic Nb−16 at. %Si alloy has been investigated. The alloys were characterized by scanning electron microscopy (SEM), electron back scattered diffraction (EBSD), hardness test, nanoindentation test, compression test and three point bend test. The desirable phase α−Nb5Si3 phase could be obtained in alloys containing 4 at. % or more Zr. Nanoindentation results showed that the elastic modulus of Nbss phase is not significantly influenced by Zr additions whereas elastic modulus of Nb3Si and α−Nb5Si3phases are considerably improved by Zr additions. The strength, plasticity and room temperature fracture toughness of the alloys are significantly increased with Zr addition. The maximum compressive strength of 2160 ± 80 MPa, plastic strain of 2.6 ± 0.2% and fracture toughness of 14.3 ± 0.3MPam1/2are achieved in alloy with 4 at.% Zr.

Effect of ECAP Die Angles on Microstructure Mechanical Properties and Corrosion Behavior of AZ80 Mg Alloy

Abstract: In this article, the effect of channel angles on material properties was investigated during equal channel angular pressing of AZ80 magnesium alloy using processing route R at 325 °C processing temperature. Channel angles of 90° and 110° and common corner angle 30° have been considered for this study. It has been revealed that the channel angle has a significant influence on deformation homogeneity, microhardness, ultimate tensile strength, ductility and corrosion behavior of Mg alloys. Investigation with reference to as-received AZ80 Mg alloy indicates 18.47% improvement in UTS and 76.07% enhancement in ductility after processing through 3P-90° and 2P-110° ECAP, respectively. Also, the corrosion rate reduces to 89.47% after processing the sample with 3P-110° ECAP die.

Tensile deformation mechanism and failure mode of different microstructures in Ti5Al5Mo5V3Cr alloy

Abstract: Ti 5Al 5Mo 5V 3Cr alloy (Ti-5553) is a high strength near β titanium alloy for aircraft structural applications and has found its specific application in landing gear components. In the present paper a systematic approach was taken to generate and choose three distinct microstructures; one with full β, and the other two with two-phase lamellar α+β microstructures with distinctly different aspect ratios of α precipitates. Tensile behavior of these three microstructures was studied. Few of the distinct observations include 1) Even in the single phase β microstructure, yield strength (YS) was reasonably high, 2) For the two-phase lamellar α+β microstructure high YS and no work hardening were observed, 3) Among the lamellar microstructures, small aspect ratio of α showed much higher YS, but less ductility as compared to the larger aspect ratio of α. Detailed TEM based investigations of deformation micro-mechanisms along with study of eventual failure mechanisms were carried out to explain the above mentioned tensile responses of these microstructures. Differences between the microstructures with small vs. large aspect ratios of α were specifically addressed in terms of tensile behavior and underlying deformation micro-mechanism and failure mode.

Repeated oral dose toxicity study of nickel oxide nanoparticles in Wistar rats: a histological and biochemical perspective

Abstract: Despite the increasing use of nickel oxide (NiO) nanoparticles (NPs), limited information is available on their toxicological effects. Health consequences of 28 days repeated oral exposure to NiO NPs have not been explored thoroughly. Hence, toxicity investigations were performed after 28-day daily exposure in albino Wistar rats with NiO NPs following Organization for Economic Co-operation and Development test guideline 407. Histopathology, biochemical indices including oxidative stress and biodistribution patterns were evaluated to decipher the toxicological impact of NiO NPs. NiO NP characterization by transmission electron microscopy showed an average size of 12.9 (±3.4) nm. Histological studies depicted a prominent impact on the vital organs of the rats. A dose-dependent rise in both aminotransferase enzyme values was recorded in the homogenates of liver and kidney tissues. A significant decrease in superoxide dismutase activity and increase in catalase activity was noted. Further, a dose-dependent decrease in reduced glutathione content was recorded in rats, which suggested generation of reactive oxygen species and oxidative stress. Increase in the malondialdehyde levels was observed with an increase in the dose substantiating the antioxidant enzyme activity profiles. Biodistribution studies indicated maximum accumulation of Ni content in liver followed by kidney. Excretion of Ni was predominantly through feces and a little through renal clearance. Our study indicated that NiO NPs adversely alter the biochemical profile of the rats and cause histological damage. Further investigations are warranted to address the mechanism by which physiological path these NiO NPs exhibit their toxic nature in in vivo.

Structural and magnetic properties of CoMn 2 O 4 synthesized by auto combustion method

Abstract: Combustion synthesized cobalt manganite (CMO) was systematically studied for its structural and magnetic properties. X-ray diffraction (XRD) pattern with high-intensity peaks at appropriate positions revealed the formation of phase pure and highly crystalline CMO. The distorted tetragonal structure of the CMO unit cell suggested the presence of high spin (d4) Jahn–Teller Mn3+ ions. X-ray photoelectron spectra (XPS) supported a mixed spinel with Co2+, Co3+, Mn2+ and Mn3+ cations. Electron microscopy confirmed the formation of submicron-sized CMO particles with well-defined lattice fringes, while low-temperature magnetic investigations revealed that the prepared CMO as a ferrimagnetic spinel due to the presence of uncompensated electronic states. The observed unsaturated magnetization, even at large applied fields, confirmed the high degree of spin-canting due to the existence of Yafet–Kittel spin arrangement.

SnO-GeO2-Sb2O3 glass anode network mixed with different Ba2+ fractions: Investigations on Na-ion storage capacity and stability

Abstract: Microstructure and electrochemical characteristics of glass anode composition (100-x) (0.7[0.625SnO-0.375GeO2]-0.3Sb2O3)-xBaO (x = 0, 2, 4, 6 and 8 mol%, labeled as Bx) for the sodium battery is analyzed. The absence of peaks in the XRD traces related to glass former (Sb2O3) after discharging is directly confirmed that the antimony content retains its amorphous phase even after the samples are being discharged. Several nanosized amorphous intermediate domains are precipitated in the bright region of Sn-Ge-Sb glass network as appeared in TEM results. Except for the sample B6, all the other samples exhibited two sloping sodiation and de-sodiation plateaus which are almost constant at around 0.62 V and 0.14 V due to the formation of amorphous intermediates domains such as Na9Sn4 and NaSn3 in the glass network. The initial discharge capacity achieved to be highest for B6 sample (838 mA h g−1) and loss of discharge capacity is up to ~31.18% even at high rate 5C. A systematic study can monitor the stable cycle performance and shed light on the design of target glass anode with high capacity and stability.

Deformation behaviour of an as-cast nickel base superalloy during primary hot working above and below the gamma prime solvus

Abstract: Primary hot working behaviour of an as-cast nickel base superalloy has been evaluated by carrying out isothermal hot compression tests both above and below the gamma prime solvus. The flow (yield σ0, peak σp, steady state σss) stress of the material was found to be highly temperature sensitive when deformed below the gamma prime solvus. The coherent gamma prime precipitates present in the material were found to be sheared by the moving dislocations in this regime. The material was relatively insensitive to temperature changes above the gamma prime solvus and exhibits discontinuous dynamic recrystallization (DDRX) when deformed between 1100 °C – 1140 °C and 6 × 10−3 to 10−2/sec with a characteristic efficiency value of 48% as defined by dynamic materials modeling. The kinetics of DDRX was evaluated by carrying out hot compression tests up to a strain of 140% under peak efficiency conditions. The friction corrected flow curve was used to estimate the critical strain (ec) for DDRX initiation and the saturation stress (σsat) for dynamic recovery. The fraction recrystallized (XDDRX) estimated using the flow curve analysis was found to correlate well with the quantitative microstructural observations. The activation energy map developed using the back stress corrected flow stress and the true stress exponent revealed that glide along with diffusion controlled climb as the rate controlling mechanism. Side-pressing test was used to validate the experimental findings and also to establish a suitable thermo-mechanical processing schedule to achieve an order of grain refinement. The results obtained are presented and discussed here.

Stress compensated MEMS magnetic actuator based on magnetostrictive Fe65Co35 thin films

Abstract: We have developed a stress compensated MEMS magnetic actuators based on Fe65Co35 thin films. The magnetic actuator was designed for ˜ 25 kHz mechanical resonance frequency using a finite element method. The cantilever layer stack consists of Si/SiO2/Fe65Co35 multilayers where silicon dioxide (SiO2) layer stress is compressive and Fe65Co35 layers is tensile in nature. The bilayer combination nullifies the film stress which result to a stress compensated undeformed released micro-actuator. Further, cantilevers are mounted on a piezo-disk and the experimental resonance frequency measured using laser Doppler vibrometer was found to be around 25.275 kHz which is close to simulated resonance frequency. Using cantilever deflection method, the magnetostriction coefficient (λ) measured was found to be ˜135 ppm. This study also suggests the possibility to realize variety of stress compensated magnetic MEMS devices based on stress compensation in bilayers. Further, the results also indicate that the compensation mechanism can be applied to magnetic MEMS devices for reliable device fabrication and operation. The developed magnetostrictive micro-actuator has potential applications in magnetic MEMS for low field sensing and actuation applications.

Ferromagnetism in the multiferroic alloy systems BiFeO3-BaTiO3 and BiFeO3-SrTiO3: Intrinsic or extrinsic?

Abstract: Among the different bulk alloys of the room temperature multiferroic compound BiFeO3, alloying with ATiO3 (A = Ba, Sr, Pb) is interesting as they have been reported to induce ferromagnetism under certain conditions. While this makes them interesting as potential multiferroic magnetoelectric materials, there is a lack of clarity on the origin of ferromagnetism in these systems. We have performed a detailed magneto-structural analysis on two alloys, namely, BiFeO3-BaTiO3 and BiFeO3-SrTiO3, and found the systems' propensity for the formation of ferrimagnetic hexaferrite (BaFe12O19 and SrFe12O19) phases. Though insignificantly small to the extent of being undetectable by x-ray powder diffraction, we prove that the ferromagnetic character of the specimen is entirely due to spontaneous precipitation of the hexaferrite grains. While our results suggest that care should be exercised before attributing ferromagnetism in such alloy systems as intrinsic to the perovskite phase, the propensity for the spontaneous precipitation of the hexaferrite phase in these multiferroic alloy systems is encouraging as it provides an opportunity for designing self-grown ferroelectric-ferromagnetic composites with good magnetoelectric coupling.

Effect of cyclic heat treatment on the microstructure and mechanical properties of W-Ni-Co alloys

Abstract: Current generation heavy alloys with enhanced static as well as high strain rate properties are based on W-Ni-Co alloys. These alloys are subjected to a cyclic heat treatment to obtain fine tungsten precipitates in the matrix and to realise superior mechanical properties. The present study is focused on processing 92W-5Ni-3Co alloy using a post-sintering cyclic heat treatment to obtain fine tungsten precipitates in the matrix. As-sintered alloys and cyclic heat treated (in vacuum) alloys are then subjected to (i) vacuum heat treatment with oil quenching and (ii) nitrogen heat treatment with water quenching. A comparison has been drawn based on microstructural features and mechanical properties, between the alloys processed (i) with and without cyclic heat treatment and (ii) with oil and water quenching. This study thus helps in understanding the effect of cyclic heat treatment and quenching medium on the microstructure and mechanical properties of W-Ni-Co alloys.

Post-processing of Ni-Cr-Al 2 O 3 Thermal Spray Coatings Through Friction Stir Processing for Enhanced Erosion–Corrosion Performance

Abstract: Thermal spray coatings are widely used for addressing erosion problems in fluid machineries However, the presence of splat boundaries, non-homogeneous microstructure and element segregation limits their performance In this study, we developed Ni-Cr-40Al2O3 coatings on stainless steel (SS316L) substrate using high-velocity flame spray followed by post-processing using friction stir processing The performance of as-sprayed and processed coatings was evaluated in slurry erosion, erosion–corrosion and pure corrosion in 35% NaCl solution As-sprayed coating showed lower erosion and erosion–corrosion resistance compared to stainless steel Friction stir processing resulted in significant microstructure refinement concurrent with enhanced hardness and fracture toughness of the developed coating At oblique impingement angle, the processed coating showed nearly 30% to twofold higher erosion and erosion–corrosion resistance compared to stainless steel substrate During pure erosion at normal impingement, both as-sprayed and processed coating showed higher volume loss However, during erosion–corrosion at normal impingement, the processed coating was able to demonstrate similar volume loss as that of the substrate In addition, the processed coating showed significant improvement in the corrosion performance as well The study showed that friction stir processing could be a promising pathway to unravel the deleterious effects of inherent non-homogeneities in thermal spray coatings

Superior ballistic performance of high-nitrogen steels against deformable and non-deformable projectiles

Abstract: Hot-rolled high-nitrogen steel (HNS) plates were evaluated against AK-47 mild steel core (7.62 mm × 39 mm, deformable) and 14.5 mm armour piercing (AP) (14.5 mm × 114 mm, hard steel core) projectiles. The ballistic results of HNS plates were compared with conventionally used Rolled Homogeneous Armour (RHA) steel plates. The ballistic tests on HNS and RHA steel plates with different thicknesses were conducted against AK-47 mild steel core and 14.5 mm AP projectiles at velocities of 740 ± 10 m/s and 1000 ± 10 m/s respectively, in order to find out the minimum thickness required to stop the projectile without perforation. In comparison to RHA steel, HNS exhibited higher ballistic performance (in terms of minimum areal density required) against both AK-47 mild steel core and 14.5 mm armour piercing projectiles. The ballistic results against 14.5 mm AP was studied using an analytical model reported in literature. Detailed post ballistic (microstructural and hardness measurements) investigations were carried out to understand the ballistic performance of the two steels. Further, an attempt has been made to correlate the initial microstructure and mechanical properties with the failure mechanisms activated during ballistic impact and the resulting ballistic performance.

Structural and spectroscopic characterization of bismuth-ferrites

Abstract: BiFeO3 based materials are currently one of the most studied multiferroics due to their possible applications at room temperature. In this study two sets of BFO are synthesized at different sintering temperatures i.e. BFO-1 and BFO-2, synthesized at a calcination temperature of 650° C and sintering temperature of 750° C and 820° C respectively. The structural characterization is studied using XRD. BFO-2 which is sintered at a temperature of 820° C shows much better properties as well as rhombohedral structure in comparison to the hexagonal counterpart in case of BFO-1. In addition to this the spectroscopic diagnosis using FTIR and Raman spectroscopic techniques are also highlighted here.