Improvements of machinability of aerospace-grade Inconel alloys with ultrasonically assisted hybrid machining

Aerospace-grade Ni-based alloys such as Inconel 718 and 625 are widely used in the airspace industry thanks to their excellent mechanical properties at high temperatures. However, these materials are classified as ‘difficult-to-machine’ because of their high shear strength, low thermal conductivity, tendency to work-harden and presence of carbide particles in their microstructure, which lead to rapid tool wear. Machining-induced residual stresses in a machined part is an important parameter which is assessed since it can be used to evaluate overall structural resilience of the component and its propensity to fatigue failure in-service. Ultrasonically assisted turning (UAT) is a hybrid machining technique, in which tool-workpiece contact conditions are altered by imposing ultrasonic vibration (typical frequency ~ 20 kHz) on a tool’s movement in a cutting process. Several studies demonstrated successfully the resulting improvements in cutting forces and surface topography. However, a thorough study of UAT-induced residual stresses is missing. In this study, experimental results are presented for machining Inconel 718 and 625 using both conventional turning (CT) and UAT with different machining parameters to investigate the effect on cutting forces, surface roughness and residual stresses in the machined parts. The study indicates that UAT leads to significant cutting force reductions and improved surface roughness in comparison to CT for cutting speeds below a critical level. The residual stresses in machined workpiece show that UAT generates more compressive stresses when compared to those in CT. Thus, UAT demonstrates an overall improvement in machinability of Inconel alloys

Modelling strain localization in Ti-6Al-4V at high loading rate: a phenomenological approach

A phenomenological approach based on a combination of a damage mechanism and a crystal plasticity model is proposed to model a process of stain localization in Ti-6AI-4V at a high strain rate of 103 s-1. The proposed model is first calibrated employing a 3D representative volume element model. The calibrated parameters are then employed to investigate the process of onset of strain localization in the studied material. A suitable mesh size is chosen for the proposed model by implementing a mesh-sensitivity study. The influence of boundary conditions on the initiation of the strain localization is also studied. A variation of crystallographic orientation in the studied material after the deformation process is characterized, based on results for different boundary conditions. The study reveals that the boundary conditions significantly influence the formation of shear bands as well as the variation of crystallographic orientation in the studied material. Results also indicate that the onset of strain localization can affect considerably the material’s behaviour

Nanocrystalline Co3-XNixO4 with Low Ni Concentration: Enhanced Oxygen Evolution Activity Compared to Co3O4

by A. Singhal and Anuj Bish

Direct formic acid electro-oxidation on Pt Doped and Undoped La1-xSrxCoO3: activity suppression due to proton reduction reaction

Combustion synthesized Pt-doped and undoped La1-xSrxCoO3 are utilized for formic acid electro-oxidation. Cyclic-voltammetry (CV) during formic acid electro-oxidation demonstrates that the oxidation current initially increases and then decays to zero on both the catalysts. This implies that the HCOOH possibly has some poisoning effect on the catalysts. Both materials show a unique reduction peak in the oxidation scan right after the addition of HCOOH in the electrolyte, demonstrating a reduction process in the oxidation cycle. When HCOOH is replaced by potassium formate, the reduction peak is found absent. Further, significant increase in the current is observed in the case of La1-xSrxCoO3. This confirms that the protons which are generated during the electro-oxidation of HCOOH are reduced on the catalyst's surface generating the reduction peak in the CV. This process suppresses the counter-reaction to diminish the current. Instead of protons, K+ ions are generated with potassium formate which greatly prevents the proton reduction reaction and leads to the formate ion oxidation. Only CO2 was evolved during the electro-oxidation which was confirmed through gas chromatography. Further investigations reveal that apart from proton reduction reaction, Pt-doped La1-xSrxCoO3 gets poisoned in presence of CO2 also; the main oxidation product of both HCOOH and KCOOH.by Anuj Bisht and Sudhanshu Sharm

Enhanced oxygen evolution activity of Co3?xNixO4 compared to Co3O4 by low Ni doping

We herein report a series of nanocrystalline Ni-doped Co3O4: Co3?xNixO4 (0.0075???x???0.30) with a nickel doping percentage from 0.25 to 10 atomic percent synthesized using solution combustion method. These oxides are characterized by XRD and show pure nanocrystalline phase of Co3O4 with no separated peaks related to Ni/NiOx and confirms that Ni has been substituted in the lattice. TEM results indicate that the morphology and size of all the compounds are similar. Electrochemical measurements indicate that Co3O4 and Co3?xNixO4 are active for oxygen evolution reaction (OER) and also shows that low amount of nickel doping in Co3O4 can remarkably enhance OER activity in neutral, alkaline and buffer (pH-7) electrolytes. Out of all compositions, 0.5% Ni-doped Co3O4 (Co2.985Ni0.015O4) seems to be more active than Co3O4 in terms of both current density and onset potential in K2SO4 medium. The enhancement in terms of OER activity, however, decreases until the doping concentration reaches beyond 0.5%. Phosphate buffer solution (PBS) studies reveal that Co3O4 and 0.5% Ni-doped Co3O4 show OER at near thermodynamic potential. Detailed x-ray photoelectron spectroscopy (XPS) studies have indicated that surface oxygen (lattice oxygen) concentration is an important factor in deciding the OER activity which is highest for 0.5% Ni doped Co3O4 (Co2.985Ni0.015O4) and hence gives the highest OER activity.by Aditi Singha, Anuj Bisht and Silvia Irust

Pt doped and Pt supported La1-xSrxCoO3: lower activity of Pt4+ towards the CO poisoning effect in formic acid and methanol electro-oxidation compared to Pt metal

Pt-supported La1–xSrxCoO3 and Pt-doped La1–xSrxCoO3 are synthesized using chemical reduction and solution combustion method, respectively. Chemical reduction is carried out using formaldehyde as a reducing agent giving Pt-supported La1–xSrxCoO3. Solution combustion method is used to prepare Pt-doped La1–xSrxCoO3. Detailed characterization using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area measurement, and transmission electron microscopy (TEM) is carried out to distinguish the Pt-supported and Pt-doped compounds in terms of their morphology and Pt oxidations states. TEM results indeed show the differences in their morphology. Further, electrochemical measurements are performed in neutral medium to differentiate their electrochemical activity. Cyclic voltammetry (CV) shows noticeable differences between Pt-supported La1–xSrxCoO3 and Pt-doped La1–xSrxCoO3. Importantly, our results show that Pt4+ in doped compound has poor to zero electrocatalytic activity toward formic acid and methanol electro-oxidation in comparison to Pt0 in supported compound. This study shows that metallic Pt in zero oxidation state is a superior catalyst to Pt in +4 oxidation state.by Anuj Bisht et al

Understanding the electrochemical differences of Pt doped and Pt supported over CeO2

Pt supported over CeO2 (Pt on CeO2) and Pt doped CeO2 (Pt in CeO2) are synthesized using chemical reduction and solution combustion method. In chemical reduction two different reducing agents are used namely; hydrazine hydrate and formaldehyde giving Pt supported over CeO2. Solution combustion method is used to prepare Pt doped CeO2. Detailed characterization using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area measurement and transmission electron microscopy (TEM) is carried out to distinguish the Pt supported and doped compounds. XRD and TEM results have clearly shown the differences in the structure and morphology, however, BET results do not show significant differences. Further, electrochemical measurements are performed in neutral medium to differentiate the electrochemical activity. Cyclic voltammetry (CV) indeed shows noticeable differences between Pt supported over CeO2 and Pt doped CeO2. CeO2 alone has also shown different electrochemical behavior compared to the Pt containing CeO2. Considering oxygen evolution reaction (OER) as a model reaction, Tafel slope measurements are performed for CeO2, Pt supported over CeO2 and Pt doped CeO2 to observe the differences. It was noted that CeO2 and Pt doped CeO2 showed similar Tafel slope indicating the same mechanism, while Pt supported over CeO2 showed different Tafel slopes, hence the different mechanism.Sudhanshu Sharma et al.

La0.80Sr0.20CoO3 as a noble-metal-free catalyst for the direct oxidation of formic acid under zero applied potential

Direct oxidation of formic acid to CO2 using noble-metal-free La0.80Sr0.20CoO3 is demonstrated in this study. The catalyst was able to oxidize HCOOH without any externally applied potential. The activity of La0.80Sr0.20CoO3 is compared with that of Pt nanoparticles. It is observed that the amount of CO2 generated using La0.80Sr0.20CoO3 is five times higher than that generated with Pt nanoparticles. The experimental observations are supported by DFT calculations, which reveal the role of the lattice oxygen in La0.80Sr0.20CoO3 in the catalytic effect. The Sr ions were not found to have any appreciable role in the dissociation step. Weak binding of CO2 involving energy changes of the order of ?1?kcal/mol indicated the ease of CO2 desorption from the catalyst surface, thus making the catalyst highly active for electrochemical HCOOH oxidation.by Anuj Bisht Phanikumar Pentyala, Parag A.Deshpande and Sudhanshu Sharm

Microstructural and crystallographic response of shock-loaded pure copper

Microstructural and crystallographic aspects of high-velocity forming or ``rapid'' forming of rolled sheets of pure copper have been investigated in this work. Significant changes in crystallographic orientation and microstructure were observed when thin (0.5 mm) metal sheets of annealed copper were subjected to high strain rate deformation in a conventional shock tube at a very low impulse magnitude (similar to 0.2 N s), which is inconceivable in conventional metal forming. Shock-loaded samples show characteristic texture evolution with a high brass {110} < 112 > component. A significant change in grain orientation spread was observed with increasing amount of effective strain without any drastic change in grain size. The texture after deformation was found to be strain-dependent. The path of texture evolution is dependent on the initial texture. Misorientation was limited to less than 5 degrees. Deformation bands and deformation twins were observed. There was a decrease in twin Sigma 3 coincidence site lattice (CSL)] boundary number fraction with increasing strain due to the change in twin boundary character to high-angle random boundary (HARB) as a result of dislocation pile up. The study shows the probability of a high-velocity shock wave forming pure Cu

Effect of stacking fault energy on the evolution of microstructure and texture during blast assisted deformation of FCC materials

Effect of stacking fault energy (SFE) on microstructural and crystallographic aspect of high-velocity deformation of FCC metals (Ni, Cu, and austenitic stainless steel) via blast assisted deformation have been investigated in this work. Microstructural changes have been probed via XRD line profile analysis and electron back-scattered diffraction methods along with TEM analysis for selected samples. The texture of all deformed material tends towards a developed a-fiber, which is observed to be strain-dependent. The relative fraction of Brass to Goss texture components increases with a decrease in SFE. The annealing twin boundaries, present in the initial material, transform in segments or full to high angle random boundary in all the material due to the dislocation pile-up. However, the microstructure of the deformed material depends heavily on the SFE, with nickel showing dislocation cells, and, austenitic stainless steel (ASS) has a mix of features of homogeneous dislocation, deformation bands, and deformation twins. Relatively thick deformation twins form in grains having orientations other than {110} plane normal to the blast direction. The overall microstructure of ASS gives an impression of a superimposed microstructure. Such structure is expected to be a result of shock passage through the material followed by macroscopic straining. No such superimposed microstructure has been observed in nickel which is attributed to recovery behavior prevalent in high SFE materials