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Selection of optimum process parameters is vital for performing a sound grinding operation on Inconel 751 alloy. This paper co-relates the relationship between the most influential input parameters like cutting velocity, depth of cut, feed rate, and environmental conditions to the output parameters, namely, tangential grinding forces, normal grinding forces, temperature, and surface roughness. Three types of machine-learning (ML) algorithms such as support vector machine (SVM), Gaussian process regression (GPR), and boosted tree ensemble techniques are employed to develop a ML model for predicting the output variables during grinding operation of Inconel 751. In order to develop a better ML model, K-fold technique is employed on a total of 81 datasets which are extracted from experimental studies. ML models developed from different algorithms are compared based on performance metrics like R2 score and root-mean-square error (RMSE). GPR algorithm exhibits best results with relatively better R2 score and RMSE value in predicting grinding forces and temperature at wheel work interface. From analyzing the ML models, it is found that cooling environments determined the output grinding parameters to a greater extent when compared with the input grinding parameters. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) alloys are gaining more attention in recent times as biodegradable materials. However, two major problems with Mg alloy implants are bacterial infections and poor corrosion resistance. In this context, a composite surface (Mg–Zn–Dy–Al2O3/HA) is developed using surface modification techniques. First, Al2O3 + HA composite powder is coated on Mg–Zn–Dy alloy to attain coated surface (C-AHa). Next, the C-AHa surface is subjected to friction stir processing to develop composite surface (F-AHa). Microstructural characterization reveals that, the Al2O3 + HA particles were distributed evenly into the Mg–Zn–Dy substrate. Antimicrobial activities against Escherichia coli and Staphylococcus aureus reveal low adhesion of bacteria on the F-AHa sample surface due to low surface energy (37.83 ± 0.22 mN/m) and low surface roughness (0.36 ± 0.1 µm). Further, the cytotoxicity tests confirm that the F-AHa sample shows significant improvement in cell viability (98%) after 7 days and non-toxic against the mouse osteoblast cells. In Vitro corrosion study observations demonstrate that the corrosion rate for the F-AHa sample is decreased by 72% compared to the C-AHa sample. Thus, the results of this study for the fabricated composites are promising for antimicrobial, biocompatible and bioabsorbable temporary implants. [ABSTRACT FROM AUTHOR]

• HDPE/BAG composite feedstock are developed for fused filament fabrication. • Composites show significant strain rate sensitivity under quasi-static conditions. • Compressive modulus and yield strength increase with BAG and strain rate. • All samples exhibit shear-barreling without brittle failure till unloading. • Absorbed energy is dissipated via formation of wrinkles, voids and fibrils. Compressive behavior of additively manufactured bioactive glass (BAG) reinforced high density polyethylene (HDPE) composites under quasi static conditions (0.001, 0.01 and 0.1 s−1 strain rates) is investigated in this work. HDPE feedstock filaments with 5, 10 and 20 wt% of bioactive glass are extruded for fused filament fabrication (FFF) based 3D printing (3DP). Compressive properties are extracted from the stress–strain plots. Elastic modulus and yield strength of the samples increase with filler addition and strain rate. Energy absorption increases with increase in strain rate and BAG content. All the samples exhibit homogeneous ductile deformation with distinct barrelling effect without any visible cracks. Deformation and energy absorption behavior of the tested samples are investigated using micrography. [ABSTRACT FROM AUTHOR]

• Functionally Graded YSZ-IN625 clads show continuous interface without any defects. • Smooth transition in microstructure as a result of Functional grading. • Homogeneous segregation of YSZ particles within YSZ particles as a result of Marangoni flow. • Smaller laser spot size favours strong Marangoni flow within melt pool. M-CrAlY or M-Cr-based bond coats are used as a buffer layer to apply ceramic thermal barrier coatings (TBCs) to metal turbine blades. However, due to oxygen diffusion, thermally grown oxides grow over the bond coat material, leading to coating failure in the components. Therefore, this study attempts to fabricate a novel TBC-coated IN625 without bond coat material using a Functional grading approach. The findings from this study may pave the way for processing functionally graded ceramic materials using Laser Additive manufacturing techniques. This study also evaluates the performance of functional grading in joining dissimilar materials using small spot-size laser sources. In the present study, samples were fabricated for three sample conditions: S1: direct clad, S2: 25% linear grading, and S3: 50% linear grading. The interface between Yttria Stabilized Zirconia (YSZ) and IN625 for the S1 sample showed discontinuous and horizontal cracks along the interface due to steep variations in thermal properties. However, the interface of S2 and S3 samples showed good adhesion and a smooth transition in microstructure between IN625 and YSZ as a result of functional grading. SEM micrographs showed homogeneous YSZ distributions without segregation within the IN625 matrix. This was attributed to strong Marangoni flow as a result of the small spot-size laser beam used in this study. [ABSTRACT FROM AUTHOR]

• The isothermal oxidation behavior of LDED Ti-48Al-2Cr-2Nb alloy was investigated. • The oxide-scale consists of TiO 2 , followed by Al 2 O 3 , and a hybrid TiO 2 + Al 2 O 3 layer. • The mass gain curve at 750 °C followed a linear growth trend. • The mass gain curves at 850 °C and 950 °C exhibited parabolic growth patterns. • Severe spallation was observed at temperatures greater than 750 °C for 100 h. This study investigates high-temperature oxidation behavior and kinetics of Laser Directed Energy Deposited (LDED) Ti-48Al-2Cr-2Nb (Ti-48-2-2) alloy at 750 °C, 850 °C, and 950 °C, for 30, 60 and 100 h. Results reveal that the oxide-scale consists of alternating bands of TiO 2 and Al 2 O 3 and its stability is strongly dependent on the oxidation temperature and duration. At 850 °C and 950 °C, the oxide-scale delaminated following 100-h exposure. LDED Ti-48-2-2 exhibited an oxidation rate constant of 0.984 mg2 cm−4 h−1 at 850 °C (100 h) and 2.09 mg2 cm−4 h−1 at 950 °C (100 h), and an activation energy of 83.7 kJ mol−1 (850°–950 °C). LDED Ti-48-2-2 exhibited poor oxidation resistance compared to conventionally processed Ƴ-TiAl alloys. This can be attributed to the absence of N-rich layer and the typical nano-scale α 2 /γ banded lamellar microstructure observed in other processing routes. Post-process heat treatments can be utilized to obtain the desired microstructural features. [ABSTRACT FROM AUTHOR]

Laser Engineered Net Shaping (LENS™), a commercially available additive manufacturing technology, has been used to fabricate dense equiatomic NiTi alloy components. The primary aim of this work is to study the effect of laser power and scan speed on microstructure, phase constituents, hardness and corrosion behavior of laser processed NiTi alloy. The results showed retention of large amount of high-temperature austenite phase at room temperature due to high cooling rates associated with laser processing. The high amount of austenite in these samples increased the hardness. The grain size and corrosion resistance were found to increase with laser power. The surface energy of NiTi alloy, calculated using contact angles, decreased from 61 mN/m to 56 mN/m with increase in laser energy density from 20 J/mm 2 to 80 J/mm 2 . The decrease in surface energy shifted the corrosion potentials to nobler direction and decreased the corrosion current. Under present experimental conditions the laser power found to have strong influence on microstructure, phase constituents and corrosion resistance of NiTi alloy. [ABSTRACT FROM AUTHOR]

The present study aims to comprehend thermo-fluid conditions during laser surface melting (LSM) of Inconel 625 (IN625) alloy using experimental and numerical modelling approaches. Nine tracks were melted on an IN625 plate at different laser powers and scan speeds. Melt pool geometry and grain morphology were evaluated using microscopy techniques. A 3-D finite volume model based on heat conduction solidification equation (HCS model) was used to simulate LSM process. Further, HCS model was expanded to include effects of fluid dynamics (HCS-FD model). Both the numerical models were used to predict melt pool geometry, peak temperatures, temperature gradients and cooling rates. The error in predictions of melt pool geometry from the HCS-FD model was lower when compared to the HCS model. The velocity vectors show a strong surface tension driven flow which has resulted in narrow and deeper melt pools in agreement with the cross sectional images of the melted tracks. Further, solidification characteristics were interpreted to obtain inferences about grain size and morphology. [ABSTRACT FROM AUTHOR]