Showing papers by "Defence Metallurgical Research Laboratory published in 2012"

Alloy Designation, Processing, and Use of AA6XXX Series Aluminium Alloys

Abstract: The strength-to-weight ratio offered by AA6XXX alloys and their enhanced mechanical properties have become crucial criteria for their use in light weight military vehicles, rockets, missiles, aircrafts, and cars, used for both defence and civil purpose. The focus of this review paper is to put together the latest knowledge available from various sources on alloy design, industrial processing, development of properties, and potential use of AA6XXX alloys. The direct chill (DC) cast AA6XXX wrought alloys which are subsequently processed by fabrication process like hot working, cold working, process annealing, and age hardening heat treatments are the foci of this review though designation section also contains the designations of cast alloys to provide the reader a broad overview on designation. World-wide accepted designations are briefly tabled along with their alloying elements. The effects of the alloying elements which are generally used for AA6XXX wrought alloys are discussed incorporating their interactions during wrought AA6XXX alloy fabrication. The significance of the alloying and also the processing to develop the certain properties and the underlying strengthening mechanisms are discussed. The frequent and versatile uses of these AA6XXX alloys for the structural applications both in defence and civil purpose are put forth.

Effect of amino functionalized MWCNT on the crosslink density, fracture toughness of epoxy and mechanical properties of carbon–epoxy composites

Abstract: Amino functionalized multiwalled carbon nanotubes (A-MWCNTs) reinforced two phase (A-MWNT–epoxy) and three phase (A-MWCNTs–carbon fiber–epoxy) nanocomposites were fabricated with 0.25 wt%, 0.5 wt% and 1.0 wt% loadings of A-MWCNTs. It is observed that, A-MWCNTs can improve the crosslink density of epoxy significantly. Fracture toughness of epoxy matrix is found to increase up to an optimum crosslink density improvement, indicating the role of crosslink density in imparting toughness to epoxy apart from the crack deflection contributions of A-MWCNTs. In addition to that, this study infers that, tensile, flexural properties of the three phase composites are strongly influenced by the fracture toughness changes of the matrices. This study, thus proposes additional mechanisms of toughness enhancements for two phase and mechanical properties enhancements for three phase composites imparted by A-MWCNTs.

High temperature C/C–SiC composite by liquid silicon infiltration: a literature review

Abstract: The ceramic matrix carbon fibre (CMC) reinforced composite has received great attention for use in aerospace engineering. In aerospace, the atmosphere is highly oxidative and experiences very high temperature. In addition to this, the materials require high thermal stability and high abrasion resistance in that atmosphere. The C/C–SiC composite meets with these requirements. In this paper, the C/C–SiC composite by liquid silicon infiltration is reviewed thoroughly.

Nanocrystalline TiN coatings with improved toughness deposited by pulsing the nitrogen flow rate

Abstract: Nanocrystalline titanium nitride (TiN) coatings were deposited on Si (100) substrates using reactive pulsed direct current magnetron sputtering where nitrogen flow rate was pulsed during the deposition. The pulse on time for nitrogen flow rate was 5, 20, 40, 50 and 60 s. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM), micro-Raman spectroscopy and proton elastic backscattering spectroscopy (PEBS) techniques were employed to study the structure and microstructure of the as-deposited coatings. Complete nano-mechanical characterization of the coatings was carried out using nanoindentation, nanoscratch and wear testing techniques. TEM studies revealed the nanocrystalline nature of the coatings with column size between 25 and 30 nm. PEBS analysis revealed an increase in N/Ti ratio from 0.79 to 0.90 in the coatings with increasing pulse on time of nitrogen flow rate. Nanoindentation hardness was found to vary from 17 to 27 GPa and fracture toughness values varied from 2.75 MPa m1/2 to 1.19 MPa m1/2 with increase in pulse on time. The coating deposited at a pulse on time of 20 s was found to exhibit optimal nanoindentation hardness and fracture toughness values of around 18 GPa and 2.12 MPa m1/2, respectively. It is concluded that the pulsing of nitrogen flow rate during reactive deposition of TiN coatings allows one to obtain encouraging combinations of moderate hardness and high toughness.

Swaging and heat treatment studies on sintered 90W–6Ni–2Fe–2Co tungsten heavy alloy

Abstract: The effect of swaging deformation and low temperature aging on mechanical properties of tungsten heavy alloy (90W–6Ni–2Fe–2Co) was studied. The alloy was prepared by conventional hydrogen sintering followed by vacuum heat treatment and swaging with varying reductions in area (ranging from 10 to 75%). The swaged samples were aged in nitrogen atmosphere at temperatures ranging from 300 to 1100 °C followed by microstructure and mechanical property evaluation. Both microstructure and mechanical properties were sensitively dependent on the amount of deformation imparted during swaging. Subsequently, aging also influenced the properties depending upon the aging temperature. Detailed fractographic study revealed that the fracture mode of the alloy changed from intergranular to transgranular mode depending upon thermo-mechanical processing. Aging treatment after swaging affected the fracture morphology of alloy considerably. Samples aged at 500 °C showed predominant transgranular failure of tungsten grains, whereas the one heat treated at 700 °C showed increasing evidence ductile tear. Based on the results, an approach for optimizing mechanical properties that involves heat treatment and swaging operation was proposed.

Strength of hot pressed ZrB2–SiC composite after exposure to high temperatures (1000–1700 °C)

Abstract: Residual strength (room temperature strength after exposure in air at high temperatures) of hot pressed ZrB2–SiC composites was evaluated as function of SiC contents (10–30 vol%) as well as exposure temperatures for 5 h (1000–1700 °C). Multilayer oxide scale structures were found after exposures. The composition and thickness of these multilayered oxide scale structure was dependent on exposure temperature and SiC contents in composites. After exposure to 1000 °C for 5 h, the residual strength of ZrB2–SiC composites improved by nearly 60% compared to the as-hot pressed composites with 20 and 30 vol% SiC. On the other hand, the residual strength of these composites remained unchanged after 1500 °C for 5 h. A drastic degradation in residual strength was observed in composites with 20 and 30 vol% SiC after exposure to 1700 °C for 5 h in ZrB2–SiC. An attempt was made to correlate the microstructural changes and oxide scales with residual strength with respect to variation in SiC content and temperature of expsoure.

Ballistic Studies on TiB2-Ti Functionally Graded Armor Ceramics

Abstract: The objective of this paper is to discuss the results of the ballistic testing of spark plasma sintered TiB2-Ti based functionally graded materials (FGMs) with an aim to assess their performance in defeating small-calibre armor piercing projectiles. We studied the efficacy of FGM design and compared its ballistic properties with those of TiB2-based composites as well as other competing ceramic armors. The ballistic properties are critically analyzed in terms of depth of penetration, ballistic efficiency, fractographs of fractured surfaces as well as quantification of the shattered ceramic fragments. It was found that all the investigated ceramic compositions exhibit ballistic efficiency (eta) of 5.1 -5.9. We also found that by increasing the thickness of FGM from 5 mm to 7.8 mm, the ballistic property of the composite degraded. Also, the strength of the ceramic compositions studied is sufficient to completely fracture the nose of the pointed projectile used. Analysis of the ceramic fragments (2 mu m-10 mm) showed that harder the ceramic, coarser were the fragments formed. On comparing the results with available armor systems, it has been concluded that TiB2 based composites can show better ballistic properties, except B4C. SEM analysis of the fragments obtained after testing with FGM showed formation of cleavage steps as well as presence of intergranular cracks, indicating that the FGM fractured by mixed mode of failure. It can be concluded that the FGM developed has lower ballistic properties compared to its monolith TiB2-20 wt.% Ti.

Influence of minor addition of boron on tensile and fatigue properties of wrought Ti–6Al–4V alloy

Abstract: Addition of boron to cast Ti–6Al–4V alloy leads to significant refinement in grain size, which in turn improves processibilty as well as the mechanical properties of the as-cast alloy. Room temperature tensile and fatigue properties of Wrought Ti–6Al–4V–B alloys with B up to 0.09 wt.% are investigated. Thermo-mechanical processing at 950 °C caused kinking of α lamellae and alignment of TiB particles in the flow direction with a negligible change in prior β grain and colony sizes, indicating the absence of dynamic recrystallisation during forging. Characterisation with the aid of X-ray and electron back scattered diffraction reveal a strong basal texture in B free alloy which gets randomised with the 0.09B addition in the forged condition. Marginal enhancement in tensile and fatigue properties upon forging is noted. B free wrought Ti–6Al–4V alloy exhibits better tensile strength as compared to B containing alloy, due to the operation of 〈 c + a 〉 slip on pyramidal planes with high value of CRSS as compared to 〈 a 〉 slip on basal and prismatic planes. Decrease in fatigue strength of Ti–6Al–4V–0.04B in as-cast and the wrought state is observed due to increase in the volume fraction of grain boundary α phase with B addition, which acts as a crack nucleation site. No significant effect of TiB particles on tensile and fatigue properties is observed.

Effect of mode of deformation by rolling on texture evolution and yield locus anisotropy in a multifunctional β titanium alloy

Abstract: Present work describes the evolution of texture during different modes of deformation by cold rolling of a Gum metal or multifunctional β titanium alloy. The cold rolled materials exhibit the presence of β and small amount of stress induced martensitic (α″) phases. The development of texture has been explained in terms of α and γ fibres. The effect of different modes of rolling results in different patterns of changes in the intensities of texture components in the α fibre. The overall intensity of γ fibre reduces with increase in cold rolling reduction in TCR, MCR and CR specimens although distribution of intensities is different in each case. Texture hardening occurs with increase in rolling reductions in all the modes of rolling. The extent of anisotropy is maximum in MCR while it is minimum in CR specimens.

Effect of matrix on the ballistic impact of aramid fabric composite laminates by armor piercing projectiles

Abstract: Ballistic impact performance of aramid fiber fabric-epoxy and aramid fiber fabric-polypropylene (PP)-based composite laminates has been studied against 7.62 mm armor piercing projectiles. Twaron® was used as aramid fiber fabric in the composites. Role of matrix on the damage pattern has been investigated by impacting the composites of different thickness with projectiles having different strike velocity (SV). Ballistic limit (BL) for each composite has been estimated through correlation of SV and residual velocity (RV) of the projectile by usual V50 method. Ballistic limit was found to vary linearly with composite laminate thickness. Twaron®-PP composites exhibited higher ballistic limit compared toequivalent thickness of Twaron®-epoxy composites. Epoxy-based composites exhibited localized damage mode compared to a global mode of failure in PP-based composites. Scanning electron microscopy revealed that fibers in Twaron®-epoxy composites failed largely by shear while tensile mode of failure was observed for Twaron®–PP composites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Influence of Rotational Speed on Microstructure and Mechanical Properties of Dissimilar Metal AISI 304-AISI 4140 Continuous Drive Friction Welds

Abstract: Fundamental investigation of continuous drive friction welding of austenitic stainless steel (AISI 304) and low alloy steel (AISI 4140) is described. The emphasis is made on the influence of rotational speed on the microstructure and mechanical properties such as hardness, tensile strength, notch tensile strength and impact toughness of the dissimilar joints. Hardness profiles across the weld show the interface is harder than the respective parent metals. In general, maximum peak hardness is observed on the stainless steel side, while other peak hardness is on the low alloy steel side. A trough in hardness distribution in between the peaks is located on the low alloy steel side. Peak hardness on the stainless steel and low alloy steel side close to the interface increases with a decrease in rotational speed. All transverse tensile joints fractured on stainless steel side near the interface. Notch tensile strength and impact toughness increase with increase in rotational speed up to 1 500 r/min and decrease thereafter. The mechanism of influence of rotational speed for the observed trends is discussed in the torque, displacement characteristics, heat generation, microstructure, fractography and mechanical properties.

Experimental and analytical study of high velocity impact on Kevlar/Epoxy composite plates

Abstract: In the present study, impact behavior of Kevlar/Epoxy composite plates has been carried out experimentally by considering different thicknesses and lay-up sequences and compared with analytical results. The effect of thickness, lay-up sequence on energy absorbing capacity has been studied for high velocity impact. Four lay-up sequences and four thickness values have been considered. Initial velocities and residual velocities are measured experimentally to calculate the energy absorbing capacity of laminates. Residual velocity of projectile and energy absorbed by laminates are calculated analytically. The results obtained from analytical study are found to be in good agreement with experimental results. It is observed from the study that 0/90 lay-up sequence is most effective for impact resistance. Delamination area is maximum on the back side of the plate for all thickness values and lay-up sequences. The delamination area on the back is maximum for 0/90/45/-45 laminates compared to other lay-up sequences.

Synergic effect of multi-walled carbon nanotubes and gold nanoparticles towards immunosensing of ricin with carbon nanotube–gold nanoparticles–chitosan modified screen printed electrode

Abstract: An amperometric immunosensor for the specific detection of Ricinus communis is reported. Screen printed electrodes (SPEs) were modified with gold nanoparticles (GNPs) loaded multiwalled carbon nanotubes (MWCNTs)–chitosan (Ch) film. The ratio of MWCNT and GNP was optimised to get best electrochemically active electrode. Sandwich immunoassay format was used for the immunosensing of ricin. The revealing antibodies tagged with the enzyme alkaline phosphatase (ALP) converts the substrate 1-naphthyl phosphate into 1-naphthol that was determined with the amperometric technique. The amperometric current obtained was correlated with the concentration of ricin. The prepared GNP–MWCNT–Ch–SPE showed high stability due to the Ch film, short response time with good reproducibility and increased shelf life of the electrodes immobilised with antibodies. The electrochemical activity of the electrode improved because of optimization of composition of CNTs and gold nanoparticles. Under the optimal conditions, the modified electrode showed a wide linear response to the concentration of ricin in the range of 2.5–25 ng mL−1 with a limit of detection of 2.1 ng mL−1 and with a relative standard deviation of 5.1% and storage life of 32 days.

Effect of W co-doping on the optical, magnetic and electrical properties of Fe-doped BaSnO3

Abstract: The effect of W co-doping on the optical, magnetic and electrical properties of Fe-doped BaSnO 3 has been studied. Polycrystalline BaSnO 3 , BaSn 0.96 Fe 0.04 O 3 and BaSn 0.95 Fe 0.04 W 0.01 O 3 samples were prepared using solid state reaction. In the analysis of powder X-ray diffraction patterns, the samples were found to be free of secondary phases. Diffuse reflectance spectra evidenced the substitution of Fe and W for Sn in the host BaSnO 3 . Micro-Raman spectra confirmed the existence of oxygen vacancies in the samples. Upon W-1% co-doping, the ferromagnetic character of Fe-4% doped BaSnO 3 is suppressed drastically and its Curie temperature is reduced to 310 K from 462 K. The existence of F-centers and ferromagnetic interactions at room temperature is evidenced by the electron paramagnetic resonance and ferromagnetic resonance signals observed in the electron spin resonance spectra of the undoped and Fe-4% doped, (Fe-4% and W-1%) co-doped BaSnO 3 samples respectively. Suppression of ferromagnetism upon W co-doping is due to the fact that each W 6+ ion donates two electrons to the host lattice and it reduces the number of oxygen vacancies that are essential for ferromagnetism to exist in the Fe-doped BaSnO 3 samples.

Charge transfer on the metallic atom-pair bond, and the crystal structures adopted by intermetallic compounds.

Abstract: It has been argued in our recent papers that the heat of formation of intermetallic compounds is mostly concentrated in the nearest neighbor unlike atom-pair bonds, and that the positive term in Miedema's equation is associated with charge transfer on the bond to maintain electroneutrality. In this paper, taking examples of some well populated crystal-structure types such as MgCu2, AsNa3, AuCu3, MoSi2 and SiCr3 types, the effect of such charge transfer on the crystal structures adopted by intermetallic compounds is examined. It is shown that the correlation between the observed size changes of atoms on alloying and their electronegativity differences is supportive of the idea of charge transfer between atoms. It is argued that the electronegativity and valence differences need to be of the required magnitude and direction to alter, through charge transfer, the elemental radius ratios RA/RB to the internal radius ratios rA/rB allowed by the structure types. Since the size change of atoms on alloying is highly correlated to how different RA/RB is from the ideal radius ratio for a structure type, the lattice parameters of intermetallic compounds can be predicted with excellent accuracy knowing RA/RB. A practical application of the approach developed in our recent papers to superalloy design is presented.