Effect of post weld heat treatment on the microstructure and mechanical properties of gas tungsten arc welded Al0.3CoCrFeNi high entropy alloy

The authors gratefully acknowledge ECR-SERB (grant number ECR/2017/001278 ) for funding the project and FE-SEM & TEM facility at Department of MSME, IIT Hyderabad . We thank Chenna Krishna for providing the starting material and we also thank Radha Ambe for discussions in the manuscript. JPO acknowledges funding by national funds from FCT - Fundação para a Ciência e a Tecnologia, I.P. , in the scope of the projects LA/P/0037/2020 , UIDP/50025/2020 and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication – i3N. Publisher Copyright: © 2023 The Author(s)In this work, a single-phase Al0.3CoCrFeNi high entropy alloy is successfully joined by gas tungsten arc welding (GTAW). Microstructural analysis revealed the presence of equiaxed grains and annealing twins in the base material, while the same FCC structure with coarse grains and columnar dendrites are identified in the heat-affected zone and fusion zones, respectively. Further, post-weld heat treatment (PWHT) of the welded joint at 1100 °C for 1hr facilitates the formation of B2/BCC precipitates in the FCC matrix. The as-received material showed an ultimate tensile strength of 570 MPa and elongation of 83 %. The joint efficiency is 82 %, which is attributed to the large grain size that developed in the fusion zone. The PWHT material had an improved joint efficiency of 92 %, attributed to BCC/B2 precipitates forming within the FCC matrix. This research highlights the role of PWHT in obtaining high-performing HEA joints.publishersversionpublishe

Process-microstructural features for tailoring fatigue strength of wire arc additive manufactured functionally graded material of SS904L and Hastelloy C-276

Many engineered components on subjecting to critical environments require properties that slightly differs with location in the fabricated part. The inadequate understanding of wire arc additive manufacturing (WAAM) process-microstructural features correlation brings interests on the structural reliability of functionally graded materials (FGM), which limits the extensive use of this cutting edge technology. Gas metal arc welding (GMAW) based WAAM process was adopted to fabricate the FGM of super austenitic stainless steel SS904L and Hastelloy C-276 with excellent bonding. The micrographs revealed that the WAAM processed FGM was mainly composed of columnar and equiaxed dendrites and had noticeable inhomogeneous features along the built direction. Tensile test results of sample along the built direction revealed a yield strength of 311.08 MPa and tensile strength of 680.73 MPa. Cyclic loading results depicted that the WAAM processed FGM has a fatigue resistance of 156 Mpa after sustaining 2 × 106 cycles. As a result of the varying microstructural characteristics along the built direction, the failure was initiated and fractured at the SS904L weaker region. © 2020 Elsevier B.V

Effect of double-side welding on the microstructural characteristics and mechanical performance of dissimilar AA6061-AA5052 aluminium alloys

In this study, cold metal transfer (CMT) based double-side welding process was employed to weld AA5052-H32 and AA6061-T6 plates having a thickness of 6 mm. The microstructure and mechanical integrity of the weldment was examined systematically. Symmetric and defect free joint with full penetration was achieved. The multiple heating and cooling cycles during CMT welding did not affect the weldment while the microstructure comprised of columnar and equiaxed dendrites and the heat affected zone (HAZ) width was < 50 µm at all interfaces. Precipitates such as Al3Mg2, Mg2Si, and α-Al(FeMn)Si were observed in the fusion zone. Intergranular Al-Si eutectic structure along with few microliquefaction cracks were noticed in the α-Al matrix. The maximum tensile properties for double-side welded joint were 214 MPa and 12.30 % with a joint efficiency of 70.68 %. Tensile specimens underwent ductile fracture in the weaker AA5052-H32 side with confined plastic deformation

Comprehensive \u3ci\u3ein vitro\u3c/i\u3e and \u3ci\u3ein vivo\u3c/i\u3e evaluation of therapeutic potential of Bacopa-derived asiatic acid against a human oral pathogen \u3ci\u3eStreptococcus mutans\u3c/i\u3e

Dental caries is a common human oral disease worldwide, caused by an acid-producing bacteria Streptococcus mutans. The use of synthetic drugs and antibiotics to prevent dental caries has been increasing, but this can lead to severe side effects. To solve this issue, developing and developed countries have resorted to herbal medicines as an alternative to synthetic drugs for the treatment and prevention of dental caries. Therefore, there is an urgent need for plant-derived products to treat such diseases. Bacopa monnieri, a well-documented medicinal plant, contains 52 phytocompounds, including the pentacyclic triterpenoid metabolite known as asiatic acid (ASTA). Hence, this study aimed to demonstrate, for the first time, the antibacterial activity of phytocompound ASTA against S. mutans. The findings revealed that ASTA significantly inhibited the growth of S. mutans and the production of virulence factors such as acidurity, acidogenicity, and eDNA synthesis. Molecular docking analysis evaluated the potential activity of ASTA against S. mutans virulence genes, including VicR and GtfC. Furthermore, toxicity assessment of ASTA in human buccal epithelial cells was performed, and no morphological changes were observed. An in vivo analysis using Danio rerio (zebrafish) confirmed that the ASTA treatment significantly increased the survival rates of infected fish by hindering the intestinal colonization of S. mutans. Furthermore, the disease protection potential of ASTA against the pathognomonic symptom of S. mutans infection was proven by the histopathological examination of the gills, gut, and kidney. Overall, these findings suggest that ASTAmay be a promising therapeutic and alternative drug for the treatment and prevention of oral infection imposed by S. mutans

Comprehensive in vitro and in vivo evaluation of therapeutic potential of Bacopa-derived asiatic acid against a human oral pathogen Streptococcus mutans

Dental caries is a common human oral disease worldwide, caused by an acid-producing bacteria Streptococcus mutans. The use of synthetic drugs and antibiotics to prevent dental caries has been increasing, but this can lead to severe side effects. To solve this issue, developing and developed countries have resorted to herbal medicines as an alternative to synthetic drugs for the treatment and prevention of dental caries. Therefore, there is an urgent need for plant-derived products to treat such diseases. Bacopa monnieri, a well-documented medicinal plant, contains 52 phytocompounds, including the pentacyclic triterpenoid metabolite known as asiatic acid (ASTA). Hence, this study aimed to demonstrate, for the first time, the antibacterial activity of phytocompound ASTA against S. mutans. The findings revealed that ASTA significantly inhibited the growth of S. mutans and the production of virulence factors such as acidurity, acidogenicity, and eDNA synthesis. Molecular docking analysis evaluated the potential activity of ASTA against S. mutans virulence genes, including VicR and GtfC. Furthermore, toxicity assessment of ASTA in human buccal epithelial cells was performed, and no morphological changes were observed. An in vivo analysis using Danio rerio (zebrafish) confirmed that the ASTA treatment significantly increased the survival rates of infected fish by hindering the intestinal colonization of S. mutans. Furthermore, the disease protection potential of ASTA against the pathognomonic symptom of S. mutans infection was proven by the histopathological examination of the gills, gut, and kidney. Overall, these findings suggest that ASTA may be a promising therapeutic and alternative drug for the treatment and prevention of oral infection imposed by S. mutans

Effect of double-side welding on the microstructural characteristics and mechanical performance of dissimilar AA6061-AA5052 aluminium alloys

In this study, cold metal transfer (CMT) based double-side welding process was employed to weld AA5052-H32 and AA6061-T6 plates having a thickness of 6 mm. The microstructure and mechanical integrity of the weldment was examined systematically. Symmetric and defect free joint with full penetration was achieved. The multiple heating and cooling cycles during CMT welding did not affect the weldment while the microstructure comprised of columnar and equiaxed dendrites and the heat affected zone (HAZ) width was < 50 µm at all interfaces. Precipitates such as Al3Mg2, Mg2Si, and α-Al(FeMn)Si were observed in the fusion zone. Intergranular Al-Si eutectic structure along with few microliquefaction cracks were noticed in the α-Al matrix. The maximum tensile properties for double-side welded joint were 214 MPa and 12.30 % with a joint efficiency of 70.68 %. Tensile specimens underwent ductile fracture in the weaker AA5052-H32 side with confined plastic deformation. © 2022 Elsevier B.V

Microstructure and mechanical properties of wire arc additive manufactured bi-metallic structure.

Wire arc additive manufacturing (WAAM) with better material utilisation efficiency and higher deposition rate was employed to fabricate bi-metallic structure (BMS) of non-stabilised austenitic stainless steel (SS904L), and solid solution strengthened Hastelloy C-276. The micrographs confirmed the existence of directionally elongated, columnar, and equi-axed dendrites in the BMS. Significant grain coarsening was observed in the re-melted layers. The tensile properties of Hastelloy C-276 and SS904L were comparable with wrought counterparts, while the bi-metallic interface sample fractured in the SS904L side. The presence of secondary phases and varying microstructure along the building direction is responsible for the anisotropy in mechanical properties. Microhardness results revealed the steep increase at the bi-metallic interface due to the dilution of elements between two materials. © 2020 Institute of Materials, Minerals and Mining. Published by Taylor & Francis on behalf of the Institute

Microstructure and Mechanical Properties of Dissimilar Aluminum Alloys AA5052-H32 and AA2219-T31 Welded Using Cold Metal Transfer Process

Lightweight structures fabricated from dissimilar aluminum alloys in aerospace and marine industries involve a lot of welding. Aluminum alloys AA5052-H32 and AA2219-T31 were successfully welded with the low heat input welding technology, the cold metal transfer (CMT) process. Microstructures indicated the existence of finer equiaxed dendrites and strengthening precipitates in the weld metal (WM). The microliquefaction cracks were discontinuous and propagated along the grain boundaries and with the grains of α-Al matrix in the WM. The tensile properties of the dissimilar welded joint attained a joint efficiency of 70.1 % and fracture ended in ductile nature with dimples and microvoids. The heat affected zone was narrow and noticed a drop in the hardness at both the interfaces caused by a softening phenomenon, ending up with coarse precipitates having lower hardness. Copyright © 2021 by ASTM International