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

Pt⁴⁺ as an Active Site for Oxygen Evolution Reaction in La_1–<i>x</i>Sr<i>_x</i>Co_1–<i>y</i>Pt<i>_y</i>O₃

This study presents an investigation on the role of Pt4+ in Pt-doped La1–xSrxCoO3 (LSPtCO) perovskite for oxygen evolution reaction (OER) activity. LSPtCO with Pt in the +4 oxidation state shows the highest activity for OER in comparison to undoped La1–xSrxCoO3 (LSCO) and Pt metal-supported LSCO (Pt is in the zero oxidation state). These results indicate that a high oxidation state of Pt is favorable for the OER activity. Pt4+ is also shown as the active center for the OER reaction as its reductive treatment decreases the OER activity significantly. Thus, the formation of high-valent Pt is a key factor in fabricating an active OER catalyst. While Pt metal may not be a good catalyst for OER, Pt4+ is significantly superior, especially in LSCO

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

Lithium-Ion Battery Power Performance Assessment for the Climb Step of an Electric Vertical Takeoff and Landing (eVTOL) Application

High power is a critical requirement of lithium-ion batteries designed to satisfy the load profiles of advanced air mobility. Here, we simulate the initial takeoff step of electric vertical takeoff and landing (eVTOL) vehicles powered by a lithium-ion battery that is subjected to an intense 15C discharge pulse at the beginning of the discharge cycle followed by a subsequent low-rate discharge. We conducted extensive electrochemical testing to assess the long-term stability of a lithium-ion battery under these high-strain conditions. The main finding is that despite the performance recovery observed at low rates, the reapplication of high rates leads to drastic cell failure. While the results highlight the eVTOL battery longevity challenge, the findings also emphasize the need for tailored battery chemistry designs for eVTOL applications to address both anode plating and cathode instability. In addition, innovative second-use strategies would be paramount upon completion of the eVTOL services

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

Shear band widening mechanism in Ti–6Al–4V under high strain rate deformation

In this study, mechanical properties and microstructural investigation of Ti64 at high strain rate are studied using a split-Hopkinson pressure bar method under compression for temperatures up to 800 °C. Flow softening in the mechanical response of material to such loading conditions hints at instability in compression, which increases with an increase in temperature. Microstructural characterization of the deformed material is characterized using the electron-backscattered diffraction technique. It reveals the presence of instabilities in Ti64 in the form of a fine network of shear bands. The shear band width grows with an increase in temperature along with the area fraction of shear band in the material, displaying its improved capacity to contain microstructural instabilities at higher temperature. After a detailed microstructural investigation, a mechanism for shear band widening is proposed. Based on this mechanism, a path generating nuclei within shear bands is discussed

Characterisation of additively manufactured metallic stents

This paper focuses on microstructural characterisation of metallic stents produced with additive manufacturing, a promising technique to deliver patient-specific stents. A 316L stainless steel tube, manufactured by selective laser melting (SLM), and a 316L stainless steel stent were investigated. Specimens were prepared for microstructural studies through sectioning, mounting, grinding and metallurgical polishing procedures. Microstructures were examined employing a JEOL 7100F scanning electron microscope, with simultaneous elemental analysis using energy dispersive x-ray spectroscopy (EDS) and orientation analysis with electron backscatter diffraction. The obtained results showed that a center of the selective laser melted (SLMed) tube had a columnar and coarse grain microstructure, with high-angle grain boundaries. The EDS analysis confirmed that the composition of the SLMed tube were similar to those of commercial stent, but with some differences in weight fractions of alloy elements

Tailoring of the Anti-Perovskite Solid Electrolytes at the Grain-Scale

The development of thin, dense, defect-free solid electrolyte films is key for achieving practical and commercially viable solid-state batteries. Herein, we showcase a facile processing pathway for antiperovskite (Li2OHCl) solid electrolyte materials that can yield films/pellets with very high densities (∼100%) and higher conductivities compared with conventional uniaxially pressed pellets. We have also achieved close to 50% improvement in the critical current density of the material and an improved lithiophilicity due to the surface nitrogen enrichment of the processed pellets. Distribution of relaxation time analysis supports the contributions from “faster” transport mechanisms for the antiperovskite films/pellets developed using the new protocol. Overall, the results highlight the feasibility of our new processing pathway for engineering antiperovskite solid electrolytes at the grain scale as a highly desirable approach for practical all-solid-state batteries