Additively manufactured 316L austenitic stainless steel typically displays a hierarchical microstructure consisting of fine columnar grains, cellular dislocation tangles and nano-inclusions, which ...provides a combination of exceptional strength and ductility. However, the rapidly solidified microstructure often contains significant residual stress and various post-processing heat treatments are generally used to relieve the residual stress and to alter the microstructure and properties. In this work, a 316L austenitic stainless steel additively manufactured by a laser-based powder bed fusion process (selective laser melting, SLM) was for the first time subjected to various heat treatments to systematically study the evolution of residual stress, microstructure and mechanical properties. Significant compressive residual stress was revealed in the core volume of the as-built condition, whilst moderate to full stress relief of 24%, 65% and ~90% was achieved upon 2 h post-processing annealing at 400 and 650 °C and solution annealing at 1100 °C for 5 min, respectively. The extent of stress-relieving is closely associated with the evolution of substructure (i.e., dislocation tangles), which also affects the yield strength. Marked alteration from the as-built metastable microstructure was seen except for the low-temperature treatment at 400 °C. This includes the precipitation of embrittling σ phase or its precursors at 650–800 °C which results in a reduction in ductility. Unlike conventional wrought 316L, no carbide formation was seen in the treatment temperature regime. Recrystallization of columnar grains and coarsening of nano-inclusions took place over time upon solution annealing at 1100 °C, causing softening and unexpected reductions in ductility. This work led to the establishment of heat treatment-property relationships and corresponding microstructural changes, which are of great significance for the component design and structural application of SLM 316L.
•Selective laser-melted 316L austenitic stainless steel was subject to heat treatments from 400 to 1400 °C.•The evolution of residual stress, microstructure, and mechanical properties was systematically studied.•Moderate to full stress relief was achieved upon annealing at 400–650 °C and 1100 °C, corresponding to various declines in yield strength.•Embrittling phase precipitation was observed at 650–800 °C, associated with a reduction in ductility.•Recrystallization and coarsening of oxide inclusions took place at 1100 °C, causing softening and unexpected reduction in ductility.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Magnesium (Mg) based alloys have been extensively considered for their use as biodegradable implant materials. However, controlling their corrosion rate in the physiological environment of the human ...body is still a significant challenge. One of the most effective approaches to address this challenge is to carefully select alloying compositions with enhanced corrosion resistance and mechanical properties when designing the Mg alloys. This paper comprehensively reviews research progress on the development of Mg alloys as biodegradable implant materials, highlighting the effects of alloying elements including aluminum (Al), calcium (Ca), lithium (Li), manganese (Mn), zinc (Zn), zirconium (Zr), strontium (Sr) and rare earth elements (REEs) on the corrosion resistance and biocompatibility of Mg alloys, from the viewpoint of the design and utilization of Mg biomaterials. The REEs covered in this review include cerium (Ce), erbium (Er), lanthanum (La), gadolinium (Gd), neodymium (Nd) and yttrium (Y). The effects of alloying elements on the microstructure, corrosion behavior and biocompatibility of Mg alloys have been critically summarized based on specific aspects of the physiological environment, namely the electrochemical effect and the biological behavior.
Type 316L stainless steel manufactured by laser powder bed fusion (LPBF) in conjunction with appropriate post-treatment has been demonstrated to offer superior pitting resistance and a distinct ...pitting mechanism compared to wrought 316L. This work examines the effect of post-processing annealing time, temperature and microstructural changes on the pitting behaviour of LPBF 316L using potentiodynamic and potentiostatic polarisation in 0.6 M NaCl. Preferential pitting at melt pool boundaries was observed, due to heterogeneity of micro-strain or lattice imperfection. High temperature annealing resulted in the transformation of amorphous oxides with associated Cr-depletion, leading to a reduction of Epit and Erp.
•An essentially porosity-lean 316L stainless steel was prepared by LPBF and subjected to cyclic potentiodynamic and potentiostatic polarisation analysis in 0.6 M NaCl.•Preferential pitting at melt pool boundaries was observed, due to heterogeneity of micro-strain or lattice imperfection.•An increased pitting potential was detected in the LFBF 316L after annealing at 800 °C for 2 h despite the presence of sigma phase formation.•Simultaneous formation of MnS precipitates and coarsened oxides was observed after annealing at 1000–1100 °C and the latter predominantly contributed to a reduced pitting potential.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In the current study, a Ti-6Al-4V alloy plate with a supersaturated martensitic starting microstructure was initially warm rolled, producing a gradient ultrafine-grained (UFG) microstructure ...throughout the thickness: fully equiaxed UFG in the surface layer and a combination of UFG and elongated grains in the center layer. The thermal stability of the warm rolled UFG microstructures was then investigated through the course of post-deformation annealing treatment. Upon annealing, the fully UFG surface layer experienced concurrent α grain growth and β precipitation (i.e. partitioning), whereas the center layer revealed the replacement of partially fragmented α lath by equiaxed grains, most likely through static recrystallization. With increasing annealing time, the overall texture characteristics were mostly preserved for both surface and center layers, apart from a gradual strengthening of the (0°, 0°, 30°) texture component in the surface layer at the expense of the (0°, 0°, 0°) and (0°, 90°, 0°) components. The current post-deformation annealing treatment led to an enhanced tensile elongation of the alloy at the expense of strength, with an increase in the annealing time.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Microalgal species are potential resource of both biofuels and high-value metabolites, and their production is growth dependent. Growth parameters can be screened for the selection of novel ...microalgal species that produce molecules of interest. In this context our review confirms that, autotrophic and heterotrophic organisms have demonstrated a dual potential, namely the ability to produce lipids as well as value-added products (particularly carotenoids) under influence of various physico-chemical stresses on microalgae. Some species of microalgae can synthesize, besides some pigments, very-long-chain polyunsaturated fatty acids (VL-PUFA,>20C) such as docosahexaenoic acid and eicosapentaenoic acid, those have significant applications in food and health. Producing value-added by-products in addition to biofuels, fatty acid methyl esters (FAME), and lipids has the potential to improve microalgae-based biorefineries by employing either the autotrophic or the heterotrophic mode, which could be an offshoot of biotechnology. The review considers the potential of microalgae to produce a range of products and indicates future directions for developing suitable criteria for choosing novel isolates through bioprospecting large gene pool of microalga obtained from various habitats and climatic conditions.
The control of microstructure, texture and deformation inhomogeneity is critical for the hot working of titanium alloys and to optimize their mechanical properties. Herein, a new approach to control ...the grain refinement, texture and deformation anisotropy of commercial purity titanium (CP–Ti) was established through hot working of a martensitic starting microstructure. The deformation characteristics of the martensitic CP-Ti were investigated through uniaxial hot compression testing at 800 °C and compared with the same alloy with an equiaxed starting microstructure. The associated microstructure, texture development and grain refinement mechanisms were elucidated using electron backscatter diffraction (EBSD) and flow behavior analysis. The equiaxed microstructure displayed a typical flow behaviour of metals undergoing continuous dynamic recrystallization (CDRX). This was accompanied by moderate grain refinement to ∼8.2 μm and macroscopically non-uniform expansion of specimen. In comparison, the martensitic microstructure revealed a stress-strain curve of continuous softening beyond the peak strain. An enhanced grain refinement to ∼5 μm was obtained also via CDRX in the form of kinking of laths and progressive lattice rotation without noticeable macroscopic deformation anisotropy. This distinct deformation behaviour was mainly attributed to the unique microstructure and texture formed through the martensitic transformation, which altered the activation of slip systems, grain refinement kinetics and texture development during hot deformation.
•The grain refinement of CP-Ti was remarkably enhanced by transforming the starting microstructure from equiaxed coarse grains into martensite prior to hot deformation at 800 °C.ii.A markedly weakened texture was developed in the deformed martensitic CP-Ti due to multiplication of α variant formation from a given β grain through the β.→α transformation, which also contributed to reduced deformation anisotropy.iii.The equiaxed and martensitic CP-Ti were both refined via continuous dynamic recrystallization while the martensitic Ti exhibited enhanced grain refinement mainly due to a refined lath thickness and randomized orientation, which enabled lath kinking and activation of <c+a> slip during deformation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In the current study, ultrafine equiaxed grains with a size of 150 to 800 nm were successfully produced in a Ti-6Al-4V alloy through thermomechanical processing of a martensitic starting ...microstructure. This was achieved through a novel mechanism of grain refinement consisting of several concurrent processes. This involves the development of substructure in the lath interiors at an early stage of deformation, which progressed into small high-angle segments with increasing strain. Consequently, the microstructure was gradually transformed to an equiaxed ultrafine grained structure, mostly surrounded by high-angle grain boundaries, through continuous dynamic recrystallization. Simultaneously, the supersaturated martensite was decomposed during deformation, leading to the progressive formation of beta phase, mainly nucleated on the intervariant lath boundaries.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Tempering has been used as a method to develop a range of dual phase steels with the same martensite morphology and volume fraction, but containing phases with different relative strengths. These ...steels were used to examine the strain partitioning between the two constituent phases experimentally through mechanical testing and numerically through finite element modelling. It was found that increasing the differential in strength between the two phases not only produces regions of high strain, but also regions of low strain. On average, a larger difference in strength between the phases increased the strain carried by the softer phase. There was no discernible preferential strain localisation to the ferrite/martensite interface, with the regions of strain localisation being determined by the morphology of the microstructure. A direct correlation between the average strain in the ferrite, and the measured ductility has been found.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The influence of surface roughness and impact energy on the hydrodynamic behavior of water droplets impinging upon dry and rigid surfaces of known roughness has been investigated experimentally. The ...influence of these two parameters on the droplet maximum spreading diameter, slip length during droplet recoil, dynamic contact angle, contact angle hysteresis, and apparent contact angle of droplets at rest has been determined. Based on the quantitative assessment, a correlation for the maximum spreading diameter in terms of the nondimensional parameter (We/Oh) and surface roughness ratio (R a/d o) was derived. We propose to use surface roughness “R a” rather than using the contact angle for correlation as contact angles cannot be known a priori, whereas surface roughness can be determined beforehand. The wetting state of a droplet depends on the combined influence of droplet impact energy and surface roughness. While increasing impact energy increases the spreading, higher surface roughness resists the droplet from spreading. Low impact energy and a smoother surface tend toward the Cassie–Baxter wetting state, whereas high impact energy and rough surfaces propel the droplet toward the Wenzel state of wetting.
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IJS, KILJ, NUK, PNG, UL, UM
Aluminium – Interstitial Free (IF) steel multilayered composite sheets with different volume fractions of aluminium were produced by accumulative roll bonding (ARB) and Asymmetric Accumulative Roll ...Bonding (AARB). The IF steel and Al alloy (AA1050) sheets were stacked in a sandwich like structure and roll-bonded by two passes with varying roll diameter ratios (dr) equal to 1 and 2 for ARB and AARB processes, respectively. This work focused on a study of the effect of shear strain mode on the formation of the interface zone. The interface zone thickness, which formed by intermixing and diffusion, was characterised by different techniques including STEM-EDS line scan, HRTEM and Atom Probe. Furthermore, finite element simulations of both processes were conducted to determine the level of shear strain at the interfaces. It was demonstrated that the width of the interface zone directly correlates with the magnitude of shear strain and architecture of the hybrid material.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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