Corrosion of stainless steels, including the austenitic Fe-Cr-Ni alloys, is associated with MnS inclusions that provide local sites for corrosion pits. Much research effort has been focused on the ...role of MnS in corrosion of conventional (cast and wrought) stainless steel to date, including microanalysis of MnS and the surrounding microchemistry. Herein, it was elucidated that an austenitic stainless steel (type 316L) when manufactured through selective laser melting was able to be produced without MnS inclusions and hence with no accompanying Cr-depletion in the vicinity of MnS, resulting in superior corrosion resistance relative to wrought form.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Laser directed energy deposition (L-DED) is an additive technology that offers a rapid solution for repairing mining components made of High Chromium White Iron (HCWI) on site. However, the refined ...carbide morphology from the rapid cooling in L-DED is detrimental to the wear resistance of the repairs. In this study, two types of powder (Ti powder and TiC powder) were added to improve the wear resistance of L-DED HCWI. The Ti powder addition promoted the formation of in-situ TiC while the TiC powder addition resulted in coarse ex-situ TiC and fine in-situ TiC in the as-deposited microstructure. The addition of both powders destabilised the austenitic matrix (γ-Fe). The wear resistance was investigated by a high stress abrasion test using silica sand (softer than M7C3) and a pin-on-disk wear test using a ruby pin (significantly harder than M7C3). The best wear results were achieved with 6.55 wt% Ti powder addition. This destabilised γ-Fe in the as-deposited microstructure which underwent strain-induced martensite formation during the high stress abrasion wear testing, improving the wear resistance of the alloy. The addition of TiC powder improved the wear resistance in the high stress abrasion test due to the increase in the fraction of carbide. In the pin-on-disk wear test, the alloys with TiC powder addition performed better than the cast sample because a greater amount of γ-Fe matrix in the microstructure provided a better combination of hardness and ductility.
•Successful laser direct energy deposition (L-DED) of high chrome white iron (HCWI) with Ti powder and TiC powder addition.•Alloy containing 6.5%Ti achieved best wear performance in L-DED samples, and almost as good as cast and heat treated HCWI.•The best properties were obtained when there was a strain induced martensite reaction in the matrix phase.•High fraction of carbide is beneficial when using soft abrasives. Austenitic matrix is advantageous under hard counterface.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A first study has been presented on the microstructural evolution of a dual-phase alloy (DSS2507) synthesized by AFSD.•A highly refined and equiaxed austenite/ferrite microstructure was produced by ...CDRX and DDRX mechanisms.•Sigma phase formed in the middle and bottom regions of the deposit due to the multiple thermal cycle and intense straining.•Good tensile strength-ductility properties were attained in the last deposited layers, where sigma phase was excluded.
Additive Friction Stir Deposition (AFSD) is an emerging solid-state metal additive manufacturing (AM) process that offers several key benefits, including high deposition rates and wrought-equivalent mechanical properties even in the as-deposited condition. The work presented is the first study to report on the development of microstructure and mechanical properties of AFSD-processed duplex stainless steel (DSS2507). The banded microstructure of the starting material was remarkably affected by AFSD processing; the austenite grains exhibited a refined and equiaxed morphology, while the ferrite grains appeared slightly larger and elongated. Microstructural observations revealed that the potential mechanism of microstructure evolution in austenite was discontinuous dynamic recrystallization (DDRX), while in ferrite, it was continuous dynamic recrystallization (CDRX). The occurrence of multiple thermal cycles during the AFSD process resulted in σ phase precipitation, which in turn led to considerable variation in mechanical properties with respect to the build direction. The top region of the as-built part with an insignificant σ phase fraction showed improved tensile strength and ductility combination compared to the as-received DSS2507 as well as other AM-processed DSS2507 alloys.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Nanoporous molybdenum oxynitride has been synthesized and studied for the first time as an oxygen reduction catalyst in a 0.1M KCl aqueous solution (pH 5.6). Modified electrodes containing the ...oxynitride catalyst, TIMCAL Super P™ Li carbon as a conducting carbon additive and polyvinylidene fluoride as a binder were prepared, and the ratios of the different components were studied in detail to yield the optimum composition. The oxygen reduction reaction mechanism has been analyzed by the Koutecky–Levich equation using a rotating disk electrode and is in concordance with a four-electron pathway for the molybdenum oxynitride catalyst. Rotating ring-disk electrode experiments have further confirmed the electrocatalytic performance of such oxynitrides toward oxygen reduction, determining an average production of H2O2 of just 2.35%. Finally, we have also compared the performance of vanadium and tungsten oxynitrides under the same conditions as the optimal molybdenum oxynitride.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A series of quaternary Zn-Al-Cu-Li alloys with different weight fractions of Cu, Al, and Li were developed and investigated for potential application in high load bearing bioresorbable implants. The ...developed alloys provided various fractions of binary and ternary intermetallic structures, which resulted in formation of multiphase microstructures containing a zinc-rich η-phase and LiZn4 and CuZn4 phases. The intermetallic phases promoted grain refinement and a good combination of mechanical properties. The developed Zn-2Al-4Cu-0.6Li alloy showed strength and ductility close to commercially pure Ti alloys with a UTS value of ∼535 MPa and elongation of 37%. The examination of in vitro corrosion behavior of the developed alloys in the modified Hanks’ solution revealed suitable corrosion rates (∼38.5 μm/year). The moderate corrosion rate was controlled by the formation of a homogeneous layer of stable corrosion products that protected the alloys from the corrosive environment, particularly in the late stages of immersion. The developed alloys with the most promising mechanical and corrosion properties appeared to be biocompatible to mouse fibroblast cells and human umbilical mesenchymal stem cells, making them suitable candidates for implant applications.
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•AA6063 via additive friction stir deposition (AFSD) refines the harmful Fe containing particles present in the swarf and exhibits a relatively refined and equiaxed grain structure.•A precipitation ...gradient is formed during AFSD but post heat treatment readily produces a uniform structure.•Heat-treated AFSD AA6063 shows a wrought-like property.
Additive friction stir deposition (AFSD) is an emerging additive manufacturing technology with the unique capability to create large-scale, free-form depositions without melting. It has the added benefit of accepting input material that is readily formed from swarf. The present work addresses questions that have arisen over the impact of the process on the precipitation in 6063 aluminium alloys (AA6063). The mechanical properties and microstructure throughout the deposit was assessed and characterized in T4, T5 and T6 conditions using a combination of transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). In the as-deposited condition, the degree of precipitation was highly heterogeneous across the different printed layers, resulting in a significant hardness gradient from the bottom to the top of the deposit. Such gradients in hardness and precipitation could be eliminated through the use of a T6 heat treatment. Additionally, the EBSD result shows that the deposited AA6063 exhibited a relatively refined and equiaxed grain structure, which evolved via continuous dynamic recrystallization during deposition. These results emulate those observed for 6xxx-series alloy deposits formed from primary material. This work demonstrates the capacity of AFSD as a viable method of solid state Al recycling, creating depositions with wrought-like properties when an adequate post-deposition heat treatment is conducted.
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Two groups of martensitic alloys were examined for changes induced by deep cryogenic treatment (DCT). The first group was a range of binary and ternary compositions with 0.6 wt % carbon, and the ...second group was a commercial AISI D2 tool steel. X-ray diffraction showed that DCT made two changes to the microstructure: retained austenite was transformed to martensite, and the dislocation density of the martensite was increased. This increase in dislocation density was consistent for all alloys, including those that did not undergo phase transformation during DCT. It is suggested that the increase in dislocation density may be caused by local differences in thermal expansion within the heterogeneous martensitic structure. Then, samples were tempered, and the cementite size distribution was examined using small angle neutron scattering (SANS) and atom probe tomography. First principles calculations confirmed that all magnetic scattering originated in cementite and not carbon clusters. Quantitative SANS analysis showed a measurable change in cementite size distribution for all alloys as a result of prior DCT. It is proposed that the increase in dislocation density that results from DCT modifies the cementite precipitation through enhanced diffusion rates and increased cementite nucleation sites.
•Additive friction stir deposition (AFSD) of Ti6Al4V was performed using a new tool and various deposition parameters.•AFSD of Ti6Al4V produced fully dense and homogeneous microstructures with ...excellent properties in the as-deposited state.•Significant microstructural refinement is achieved by the reduction of deposition temperature.•The fine structured printed material exhibited mechanical properties better than other additive processes.
The additive friction stir deposition (AFSD) of Ti6Al4V alloy was successfully performed over a wide processing window. The microstructures were examined based on the high atemperature β grain size, grain boundary α formation and the propensity of variant selection as a function of process parameters. The analysis revealed that a reduction in deposition temperature could be achieved by the change in AFSD parameters, resulting in major reduction of prior β grain size and refinement of as-deposited α phase structure. This resulted in significant improvements of ductility and strength in the as-deposited state with ductility values up to ∼20% and maximum yield and ultimate tensile strengths values of 1010 MPa and 1233 MPa, respectively.
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The deformation behaviour of three direct laser fabricated AlxCoCrFeNi high entropy alloys were examined. One alloy had a face-centered cubic (x = 0.3) structure, one had a two-phase structure ...comprising an ordered (B2) and disordered BCC phase (x = 0.85), and the third alloy contained a mixture of all three phases (x = 0.6). The deformation behaviour of all three alloys was examined by mechanical testing, scanning electron microscopy and transmission electron microscopy. The dislocation density of specimens was measured using x-ray diffraction. For the FCC alloy, it was found that the correlation between dislocation density, applied stress and compressive strain all benchmark closely with the behaviour of austenitic stainless steel. It is therefore found that this alloy does not show any unique deformation behaviours of note, and like austenitic steels, show a low yield point, moderately high work hardening rates and excellent plasticity. For the case of the alloy with a high aluminium concentration, which had a two-phase B2+BCC microstructure, an exceptionally high yield strength of 1400 MPa was observed. Nano-hardness examination of this alloy showed that the B2 phase had an exceptionally high hardness value. Since the alloy contained a large volume fraction of this hard intermetallic B2 phase, is was concluded that the B2 phase is responsible for the high strength of this alloy. It was shown that this alloy behaves like a composite, and its strength can be predicted closely using a simple rule of mixtures approach. The poor tensile ductility of BCC high entropy alloys has been suggested to be the result of the inability of the B2 phase to accommodate shape change, leading to interphase cracking that results in brittle fracture characteristics.
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•The difference in the mechanical properties of the FCC and BCC AlxCoCrFeNi high entropy alloys were analysed.•The high strength of BCC HEA was due to high concentration of B2 phase and explained by simple rule of mixtures.•The slip systems in BCC HEA was analysed using slip line trace analysis.•The BCC HEAs deform by slip along (110) and (112) planes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
High entropy alloys (HEAs) show promise as materials for structural applications, even at elevated temperatures. However, their wear behaviour over a wide range of temperatures has not been ...extensively studied. CoCrFeMnNi and AlxCoCrFeNi HEAs were subjected to pin-on-disc dry sliding wear at temperatures between 25 °C and 900 °C against an alumina ball, and the tribological performance benchmarked against AISI 304 and Inconel 718. A detailed characterisation of the wear tracks using electron microscopy and surface profilometry revealed a transition in wear mechanism from abrasive wear at room-temperature to oxidative and delamination wear above 600 °C. The wear performance of the HEAs, AlCoCrFeNi in particular, is substantially enhanced with increasing temperature, surpassing that of Inconel 718 at 900 °C. The enhanced wear performance of the HEAs above 600 °C is attributed to the formation of a compact oxide scale in the contact region, and relative subsurface strengthening in the form of a fine-grained recrystallised structure containing precipitation hardening phases.
•The wear behaviour of various high entropy alloys up to 900 °C is analysed.•Wear rates of high entropy alloys decreases with increasing temperature.•High wear resistance of AlCoCrFeNi due to alumina scale and σ-phase precipitation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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