Metals and Materials International最新文献

Laser powder bed fusion (LPBF) is one of the most suitable processes in metal additive manufacturing (AM) due to its higher strength and better dimensional accuracy. LPBF has proven to build complicated components like heat exchangers, turbines, intake manifolds, and other aerospace components. These areas have a huge demand of ferrous materials (SS300 series) for better performance. SS316L has good corrosion resistance and better mechanical properties than other stainless steels like SS304. Therefore, SS316L demand has increased in the automobile, aerospace and health care sectors. A comprehensive review of the LPBF AM process on SS316L material was undertaken in the current study. The paper presents the physical, mechanical and microstructural properties of additively manufactured SS316L. The major problems that occur with the LPBF additive manufacturing process are surface roughness, residual stress and distortion also presented in this paper. The prediction of distortion and residual stresses are discussed for different AM process parameters and different simulation software. The effect of post-processing of AM parts is also discussed in detail. This review article will be very helpful for understanding the process parameters, testing methods, post-processing techniques and mechanical properties of LPBF-processed AM SS316L.

The introduction of powder bed fusion (PBF) is crucial for advancing the next-generation automotive industry. However, the PBF faces challenges such as size constraints and difficulties in mass production, necessitating effective welding methods to integrate PBF-produced components with conventionally manufactured counterparts. Among various welding methods, integrating resistance spot welding in the assembly of PBFed products with conventionally fabricated ones may address the inherent PBF challenges. But, our findings revealed that during the resistance spot welding of PBF-fabricated stainless steel (STS) 316L, excessive heat generation caused weld expulsion at relatively low welding current. This expulsion reduced the effective weld volume, resulting in significant degradation in weld strength. To understand the root cause of this phenomenon, this study investigated the origin of the excessive heat and its impact on weldability when connecting the PBFed parts to CRed counterparts. The results show that welding PBF-produced STS 316L to CR-produced STS 316L generated significant heat due to the high surface roughness and unique microstructure of the PBF material. These factors led to weld expulsion and decreased weldability. However, by analyzing these thermal characteristics, we optimized welding parameters and enhanced mechanical properties. Ultimately, we demonstrate that PBF-produced components can be effectively welded to traditionally manufactured parts, providing crucial insights for improving the integration of PBF components in the automotive industry.

Graphic Abstract

Grain boundaries (GBs) are essential in defining the mechanical characteristics and behavior of any polycrystalline material. Their presence has been known to impact the various properties of the materials, including mechanical, thermal, electrical, and optical properties. Interestingly, specific GBs are known to form special faceted structures wherein they adopt a series of distinct planar segments or facets. The presence of faceted GBs has been linked with the anisotropic nature of GB free energies with respect to their inclination, introducing distinct characteristics that significantly influence the overall performance and functionality of materials. Moreover, the formation of faceted GBs increases the total boundary area due to the creation of additional facets. However, as these facets are more energetically favorable, the formation of these faceted GBs leads to a reduction in the overall GB energy. Further, their migration behavior contrasts significantly with that of non-faceted GBs. Understanding the nature of faceted GBs is crucial since they have been closely associated with phenomena such as abnormal grain growth, GB migration, wetting, and diffusion, all of which can result in significant variations in the material’s mechanical, electrical, and thermal properties. In this extensive review article, we have discussed in depth the alteration in the material’s performance incorporated with faceted GBs. Both the experimental and simulation-based investigations have been critically examined and reported to present an informed perspective on recent advancements in this field. Key findings revealed how the faceted GBs contribute to the unique stress responses and alter the energy of the structure, underscoring their role in altering material performance. Finally, we have highlighted prospective research avenues that could help in deepening our understanding of faceted GBs and their impact on material properties.

Graphical Abstract

Clinching technology is a flexible, environmentally friendly and efficient process that enables high-quality connections between homogeneous and heterogeneous materials, and has demonstrated its unique advantages in the transportation and aerospace sectors. This paper presents an overview of the latest developments in clinching technology in terms of the optimization of conventional clinched designs, assisted clinching processes, and structural inspection and prediction. Finally, the future outlook of clinching technology is discussed by focusing on the research results of scholars and future technology trends.

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Conventional fusion welding process exhibited difficulties in joining Al alloys at the relatively high processing temperature above the melting temperature due to their high coefficient of thermal expansion and thermal conductivity, which cause pore formation and large distortion during solidification, resulting in significant deterioration of mechanical properties in welds. Friction stir welding (FSW), one of solid-state joining methods, was developed as a special welding technique for Al alloys invented at The Welding Institute (TWI) in 1991. Since FSW can be performed below the melting point of Al alloys, the formation of pores and large distortion are greatly inhibited at the weld regions. However, both grain coarsening and dissolution of precipitates during FSW lead to the material softening, which reduces the joint efficiency. While, at a lower processing temperature, the material flow between the rotating tool and workpieces becomes insufficient, generating welding defects. Linear friction welding (LFW) is another solid-state joining process that is suitable for manufacturing Ti-6Al-4 V alloy blade disks, i.e., blisks in the field of aircraft engines. This is caused by a low thermal conductivity of the Ti alloys, suppressing the formation of softening and heat-affected zones under any processing conditions during LFW. The high-pressure LFW process is expected to be a promising process also for producing high-efficiency Al alloy weldments. However, the knowledges and benefits of LFW process for metallic materials with high thermal conductivity such as Al alloys are not well-known. Therefore, this article summarizes the latest reported results on welding temperature, microstructure evolutions, mechanical properties and joint efficiency of LFW Al alloy joints to better utilize the LFW process. Finally, the conclusions of this article including suggestions for further research and development in the Al alloy joints in LFW are provided.

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Ultrasonic shot peening (USP) is an advanced surface treatment technique that enhances the mechanical performance of metallic materials. This study systematically investigates the effects of USP on the hydrogen embrittlement (HE) resistance of 316L stainless steel. By varying the shot peening energy, we evaluate surface deformation, microstructural evolution, and resultant mechanical properties and these effects on the HE. In order to validate the improvement of HE resistance, mechanical tests such as SSRT and hardness tests with/without hydrogen charging conditions, and hydrogen contents are measured through TDS analyses. A finite element (FE) model is employed to predict stress distributions, and also performed to validate and quantify the effect of peening on the improvement of mechanical properties based on these experimental results. The results demonstrate that USP significantly improves HE resistance by inducing compressive stress and refining the microstructure. The validated FE model provides insights for optimizing USP parameters, highlighting USP as a promising technique for enhancing material reliability in hydrogen environments.

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The microstructural evolution and mechanical characteristics of CoCrFeMnNi high entropy alloy (HEA) joined to 316 L stainless steel (SS316L) were investigated by performing diffusion bonding at temperatures ranging from 975 °C to 1050 °C under a compressive pressure of 5 MPa. The diffusion-bonded samples were examined microstructurally with a Scanning Electron Microscope (SEM) equipped with an Energy Dispersive Spectrometer (EDS), Electron Back Scattered Diffraction (EBSD) and X-ray Diffraction (XRD) analyses, and the mechanical responses of the joints were assessed based on the fracture energy calculation from the shear test results. The CoCrFeMnNi-HEA was successfully joined to SS316L preserving a single face centred cubic (FCC) phase solid solution within the diffusion zone. Increasing the bonding temperature led to widening the diffusion zones and microstructural changes such as grain growth, which became more prominent, particularly for temperatures equal to 1025 °C and beyond. The optimum bonding temperature was observed to be 1000 °C, corresponding to a total diffusion width of 10.5 μm. These diffusion joints were characterised by the moderate presence of interfacial pores and the highest fracture energy.

Graphical Abstract

This study presents a critical evaluation of the contour method and synchrotron X-ray diffraction strain tomography for the reconstruction of residual elastic strains, focusing on quench-induced cracking in carbon steel components. Using the OxCM contour solver with both optical and contact profilometry, and strain tomography via the exCaking method and Rietveld refinement, the strengths and limitations of each technique are explored. High-resolution data acquisition is emphasized as essential for accurately resolving material discontinuities. The analysis also investigates the link between residual elastic strains and quench cracking, and assesses how data processing, specifically the application of a smoothness factor to capture the main features of the experimental data, affects the accuracy and reliability of contour method reconstructions.

Graphical Abstract

Direct aging (DA), a post-heat treatment process that omits the solution treatment step, was applied to study its effects on the microstructure and mechanical properties of an A20X aluminum alloy fabricated by laser powder bed fusion (LPBF). The chemical heterogeneity in the as-built (AB) microstructure, characterized by Ti- and Cu-enriched cell boundaries, facilitates the rapid formation of nanosized precipitates during DA. Precipitation initiated at the cell boundaries and progressed into the matrix, with the size and density of Ω and θ′ phases increasing with aging time. DA slightly enhanced tensile strength compared to the AB condition; however, excessive aging time led to strength reduction owing to excessive precipitate coarsening along the cell boundaries. Additionally, aging mitigated dynamic strain aging, as evidenced by the reduced frequency of serrated flows that results in the ductility recovery in the full-aged sample. These findings emphasize the critical role of DA in tailoring the mechanical properties of LPBF A20X alloys, offering a simplified pathway for optimizing high-strength aluminum additive manufacturing components.

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