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Ti-6Al-4V (also called as Ti64) is often used in the aerospace applications for its high strength to weight ratio. Ti64 can be welded by almost all the fusion welding processes but it led to the development of coarse-grained microstructure in the fully deformed zone, severe deformation, and high residual stresses. To reduce these complications, solid state welding processes are now adopted in the aerospace industries because it avoids total melting of materials and provides finer grain structures in the nugget region. Among different solid-state techniques, linear friction welding (LFW) is highly suitable to join the blade to disk assembly in the next generation aero engines. In order to get a joint with higher efficiency, the process parameters such as oscillating frequency, friction pressure, friction time, forging pressure and forging time are to be optimized. Hence, in the current investigation an effort has been made to study the effect of forging pressure on microstructure and tensile properties of LFW Ti64 joints. The tensile strength of the joints was evaluated as per the ASTM standards. The microstructure of various regions of welded joints was examined using optical microscopy (OM) and scanning electron microscopy (SEM). From this study, it is understood that wider interface is observed for lower forging pressure and decrease with increase in forging pressure. The tensile strength increases with increases with forging pressure and it gradually decreases over increasing the forging pressure. The microstructure shows evidence of fine structure in the weld region i.e., FDZ. The TMAZ region of the grain is plastically deformed and reoriented in the direction of the friction motion.

In aerospace and chemical industries, Ti–6Al–4V alloys are mostly used due to outstanding resistance to corrosion and high specific strength. Gas tungsten arc welding (GTAW) process is generally preferred to join Ti–6Al–4V alloy, but width of bead and heat-affected zone are wider in these joints. To overcome these problems, pulsed current gas tungsten arc welding (PC-GTAW), one of the variants of GTAW process, was employed to join Ti–6A–4V alloy. Recently, gas tungsten constricted arc welding (GTCAW) process, a new advanced variant of GTAW process, was developed. It creates high-frequency current level variation in the arc to produce low heat input, narrow fusion zone and heat-affected zone with deeper penetration compared to conventional GTAW and PC-GTAW processes. The present research work is focused to understand the influence of the post-weld heat treatment on tensile properties, microhardness and microstructure of Ti–6Al–4V alloy joints welded by GTAW, PC-GTAW and GTCAW processes. High frequency resulted in appreciable refinements of prior β grains prime to higher tensile properties, hardness and elongation of joints in the as-welded condition. The post-weld heat treatment (PWHT) at 910 °C resulted in enhancement in elongation and deterioration in tensile strength due to coarsening of α and disintegration of α-martensite into symmetrical α and β. However, pulsed gas tungsten constricted arc welded (P-GTCAW) joints showed greater tensile elongation even in PWHT conditions.

Sub-monolayer deposition control of pulsed laser deposition technique has been utilized to grow Ag-Au alloy nanoparticle films of different compositions and mass thicknesses using sequential ablation of pure Ag and Au targets. The films produced at high substrate temperature in single step growth have shown strong localized surface plasmon resonance (LSPR) response, which is systematically red-shifted with Au percentage and film mass thickness. The morphology of the films studied from atomic force microscopy revealed densely packed nanoparticles at all compositions with typical particle number density of ∼1010 - 1011/cm2. The optical response of the films was measured using spectroscopic ellipsometry at different angles of incidence and their effective dielectric response was determined from multiple oscillator modeling. The effective dielectric response was found to well predict the optical transmission spectra and also showed systematic red-shift of interband absorption edge with Au percentage in the films conforming alloy formation, in consistent with the results of X-ray photoelectron spectroscopy. Surface enhanced Raman scattering (SERS) measurements carried out at 488 and 633 nm excitation laser wavelengths revealed that Ag and Ag rich films exhibited relatively higher enhancement of SERS intensity as compared to other composition films. These nanoparticle films were found to be efficient SERS substrates for easy detection of trace dye molecules in nano-molar concentration range. The SERS enhancement was found to depend on film mass thickness and alloy composition dependent LSPR response having close overlap with the laser excitation wavelength.

An experimental study was undertaken to understand the tensile behavior of metal–ceramic composite joint with bolted configuration. Nickel based super alloy (GTM-Su-263) and SiCf/SiC composite were the material systems with an aerospace grade MJ6 bolt of GTM-Su-718. This bolted assembly was pulled at temperatures 25, 600 and 750 °C which were likely to be experienced in a typical aero engine. In case of metal–ceramic composite joint, the net tensile stress decreased from 110 to 88 MPa with increase in temperature from 25 to 600 °C. Similarly, the bearing stress reduced from 146 to 118 MPa. In all the metal–ceramic composite joints, the fracture initiated at the hole edge experienced the maximum tensile stresses. With further increase in temperature, reduction in the net tensile and bearing strength was significant and was attributed to the oxidation of the interface between the fiber and matrix. SEM studies clearly suggested that debonding and fiber pullout resulted in inferior tensile strength properties at elevated temperatures.

Ti–6Al–4V alloys are perfectly suited for fan compressor blade material in advanced aero engine components due to outstanding resistance to corrosion and specific strength was high in both room temperature and elevated temperature. For autogeneous welding of thin sheets of Ti–6Al–4V alloy, the gas tungsten constricted arc welding (GTCAW) was established to be beneficial than the gas tungsten arc welding process. The performance of welded joints depends on the fusion zone grain size (FZG) and fusion zone hardness (FZH), which need to be suitably optimized and controlled to attain advantageous mechanical characteristics of the joint. Hence, in this research study, efforts were taken to develop empirical relationships for predicting the FZH and FZG incorporating very important GTCAW parameters. Parameter optimization was performed using response surface methodology. Additionally, the influence of GTCAW parameters on FZG and FZH was analyzed. From the results, it is inferred that the inter-pulse frequency has better influence on FZG and FZH compared to other parameters.

Titanium and its alloys have been considered as one of the best engineering materials for industrial applications. Excellent combination of properties such as high strength to weight ratio, excellent resistance to corrosion makes them attractive materials for many industrial applications. Recently, considerable research has been performed on Gas Tungsten Constricted Arc welding (GTCAW) process and reported advantages include, lower heat input, reduced residual stresses and distortion. In this investigation, tensile properties of GTCA welded Ti-6Al-4V alloy joints were evaluated. Single pass, autogeneous welds free from volumetric defects were fabricated using optimized GTCAW parameters. The joints were characterized using optical microscopy, scanning electron microscopy and microhardness, survey. Tensile properties of the joints were overmatching with the base metal. The alpha and granular beta grains in the base metal were changed into short acicular alpha martensitic structure in the fusion zone as a result of GTCAW

Thin sections of Ti6Al4V based aeroengine structural material was refurbished using laser metal deposition (LMD) technique. The thermal gradient and cooling rate was strategically controlled through the appropriate selection of laser process parameter such as laser power, scan speed and powder feeding rate. At a laser power of 1500 W and at a scan speed of 600 mm/min, the deposited layer is free of cracks and pores with good metallurgical bonding to the substrate as well as between the layers. The β to αˈ martensite phase transformation was prevalent in the deposited region which marginally increased the hardness. The ultimate tensile strength (UTS) of LMD was found to be 900 MPa which is slightly lower than the base UTS of 950 MPa. The LMD fails due to brittle fracture with traceable elongation.

A tetradentate nitrogen donor [N4] macrocyclic ligand, 1,3,7,9-tetraaza-2,8-dithia-4,10-dimethyl-6,12-diphenylcyclododeca-4,6,10,12-tetraene has been synthesized by using thiourea and benzoylacetone. Complexes of Mn(II), Co(II), Ni(II), and Cu(II) have been synthesized with this ligand and characterized by element chemical analysis, molar conductance, magnetic susceptibility, mass, 1H nuclear magnetic resonance, Fourier transform–infrared, electronic, and electron paramagnetic resonance spectral studies. The molar conductance measurements of Mn(II), Co(II), and Cu(II) complexes in dimethyformamide correspond to nonelectrolytes, whereas Ni(II) complex is a 1: 2 electrolyte. The complexes are high-spin except for Ni(II) which is diamagnetic. Octahedral geometry has been assigned for Mn(II) and Co(II) complexes, square planar for Ni(II) and tetragonal geometry for Cu(II). The ligand and its complexes were screened in vitro against two pathogenic fungi (Fusarium moniliformae and Rhizoctonia solani) and bacter...

Welding is an integral part of the fabrication process for realization of the components and sub-components for any structural system. The weld process and the evaluation of the weld zone properties become more significant for the critical application like structural components of an aero engine. Standard tensile testing of the welded specimens provides the ductility for the composite joint i.e. the parent, heat affected zone and the weld zone. Standard bend tests (Three point bend) are specified as the qualitative tests for evaluating the ductility of the welded joints. For these bend tests, the ductility of the parent specimens are utilized for calculating the bend test parameters and the bend angles are specified after performing the tests on the parent specimens. But during the bend tests on the TIG welded specimens of specific materials and the thickness combinations like Ti-64 with thickness of 1.2 and 4.0 mm, it was observed that the specimens used to get fractured during bend tests before the specified bend angle is achieved. Though this suggests that the ductility of the welded joint is lesser than that of the parent specimens, it is not quantified with the premature failure of the test specimen. In the present study, bend tests on these material samples are performed on TIG welded specimens. Load and the displacement were monitored during the bend tests and maximum plunger depth and bend angle was recorded. A term called virtual plunger diameter is introduced in this work. Based on this plunger depth, span length, virtual plunger diameter is estimated at the onset of the fracture. From this plunger diameter the ductility of the weld joint is recalculated and is found to be lesser than the ductility of the welded joint as observed during the tensile test. The proposed bend test result analysis technique provides the quantitative results i.e. weld ductility from the bend test data.Copyright © 2013 by ASME