Ni-rich Phase Research Articles

Investigation of phase transformation and mechanical properties of silicon addition on AlCrFeMnNi high entropy alloys

Abstract This paper examines the impact of silicon in the AlCrFeMnNi high-entropy alloy system, focusing on both its microstructural and mechanical properties. Alloys with varying silicon content (x = 0, 0.3, 0.6, 0.9 atomic ratio) were synthesized using vacuum arc melting. The phase formation of these high-entropy alloys was analyzed using X-ray diffraction to comprehend the alloying process behaviour. The findings revealed that the solidification of the AlCrFeMnNi alloy occurred in dendritically, with dendrite cores containing Cr, Fe, and Ni, while interdendritic regions were enriched in Al and Ni after adding Silicon. Increasing the silicon content from 0 to 0.9 led to significant improvements in microhardness and wear resistance. This improvement is attributed to the reinforcement of grain boundaries provided by silicon. The formation of an Al and Ni rich B2 phase is crucial in resisting dislocation motion and preventing further deformation. Additionally, the addition of silicon led to improved corrosion resistance, as demonstrated by potentiodynamic polarization measurements. However, a trade-off was observed between compressive strength and ductility: compressive strength increased with higher silicon concentrations, but at the expense of ductility.

Effect of alloying elements on coexisting phases and microstructure of M174 heat-resistant aluminum alloy

Abstract This article mainly focuses on high-power density diesel engine piston alloys, with the main component system being M174 heat-resistant aluminum alloy. On this basis, the main heat-resistant alloying elements Cu, Ni, and Fe were optimized and designed. This article is based on Thermo-Calc thermodynamic software, and comprehensively calculates and analyzes the multi-component alloy equilibrium phase diagram and Scheil non-equilibrium solidification of Al-(4-6)Cu-(1.5-3)Ni-(0.7-1.1Fe)-12.5Si-0.85Mg (mt.%) heat-resistant aluminum alloy system. Through the orthogonal experimental method of alloy composition, the phase distribution and microstructure composition of different alloy compositions are obtained. Research has found that Fe-rich phases such as Al5FeSi and Al9FeNi, as well as Ni-rich phases such as A13CuNi, A17Cu4Ni, and Al3Ni, are the main heat-resistant phases of the alloy in the temperature range of 350°C-420°C, providing important support for the high-temperature mechanical properties and creep damage resistance of piston aluminum alloy. At the same time, this article further studies the solidification history and microstructure precipitation of alloys. Fe-rich heat-resistant phases such as Al5FeSi and Al9FeNi have a higher solidification sequence. As primary and secondary phases, it is easy to generate coarse solidified structures. The organizational content is sensitive to the alloy composition. A13CuNi and A17Cu4Ni mainly precipitate in a multi-component eutectic structure, with layered and petal-shaped morphologies. The research results of this article have important theoretical significance and application value for the optimization design of high-power density piston aluminum alloy composition and the coordinated control of multi-phase structure.

Nickel stanogermanides thin films: Phases formation, kinetics, and Sn segregation

Ge1−xSnx thin films with a Sn content of x ≥ 0.1 present a direct bandgap, which is very interesting for the fabrication of efficient photonic devices. The monostanogermanide phase, Ni(GeSn), is promising to form ohmic contact in GeSn-based Si photonic devices. However, the formation kinetics of Ni stanogermanides and the incorporation of Sn in Ni–GeSn phases are not fully understood. In this work, Ni thin films were deposited on Ge and Ge0.9Sn0.1 layers grown in epitaxy on an Si(100) substrate using magnetron sputtering technique. In situ x-ray diffraction measurements were performed during the solid-state reaction of Ni/Ge and Ni/Ge0.9Sn0.1. 1D finite difference simulations based on the linear parabolic model were performed to determine the kinetics parameters for phase growth. The nucleation and growth kinetics of Ni germanides are modified by the addition of Sn. A delay in the formation of Ni(GeSn) was observed and is probably due to the stress relaxation in the Ni-rich phase. In addition, the thermal stability of the Ni(GeSn) phase is highly affected by Sn segregation. A model was developed to determine the kinetic parameters of Sn segregation in Ni(GeSn).

On novel Ni-rich phase formed during aging of an additively manufactured ultra-high strength CoFeNi alloy

The precipitation mechanism of strengthening phase of a body-centered-cubic (BCC) structured CoFeNi multi-principal element alloy produced by additive manufacturing was studied by transmission electron microscopy (TEM) and atom probe tomography (APT). The hardness of CoFeNi alloy achieved the peak value of 554.79 ± 9.86 HV after aging for 160 h at 400 °C. The CoFeNi alloy exhibited an ultrahigh compressive yield strength and ultimate compressive strength up to 1.8 GPa and 2.3 GPa respectively, whilst maintains a strain of 18.9 %. The microstructure of the alloy exhibited nanoscale lamellar Ni-rich phase with high stability homogeneously distributed in BCC matrix after aging at 400 °C. The novel Ni-rich phase containing about 50 at. % Ni with a hexagonal structure is the mainly precipitation strengthening phase, and has coherent orientation relationship with the BCC matrix in the<101>bcc∥<112¯0>Niand 111bcc∥{0001}Ni. Based on the experimental results, the precipitation mechanisms of the Ni-rich phase were discussed in detail. The current work provides a possible new direction to design high-strength alloy by introducing the novel Ni-rich phase.

In-situ synthesis of NiTi shape memory alloys with tunable chemical composition and thermomechanical response by dual-wire-feed electron beam directed energy deposition

In this study, we demonstrate the direct in-situ synthesis of NiTi alloys with tunable chemical composition (Ni/Ti atomic ratio) and corresponding thermomechanical response. This synthesis is achieved by regulating the feeding speed ratio of pure Ni and Ti wires during the additive manufacturing process based on dual-wire-feed electron beam directed energy deposition (EB-DED) technology. Under appropriate process conditions, the resulting NiTi alloys exhibit a controllable evolution around the near-equiatomic composition and display a typical columnar grain morphology characteristic of additively manufactured NiTi alloys. With an increase in Ni content (shifting from Ti-rich to Ni-rich), the second phase particles present in the samples change from Ti-rich phase (Ti2Ni) to Ni-rich phases (such as Ni4Ti3 and Ni3Ti2). The phase transformation temperatures gradually decrease with increasing Ni content, and the predominant matrix phase transitions from martensite to austenite. The as-built NiTi alloy exhibits a typical tensile curve with a good tensile elongation of 11 %, fabricated under suitable composition and microstructure conditions. This result surpasses values reported in current in-situ synthesized NiTi alloys through additive manufacturing methods. Moreover, it almost reaches the levels achieved by additively manufactured NiTi alloys using pre-alloyed raw materials. Furthermore, this study reports, for the first time in the field of in-situ synthesized NiTi alloys, a good tensile shape memory effect, achieving an impressive recovery rate of up to 70 % under a tensile strain of 6 %. This investigation provides a meaningful theoretical perspective and technical strategy for the integrated customization of NiTi alloy components in structure, composition, and function. This low-cost and high-efficiency approach is particularly attractive for the preparation of functional graded, large-scale and disposable NiTi components.

Ni segregation in the oxide film of 15–15Ti austenitic steel at high-temperature CO2

A double-layer oxide film was formed on 15–15Ti exposed to high-temperature CO2, with outer Fe-rich layer and Cr/Ni-rich inner layer comprising Ni-poor and Ni-rich zones. The Ni-poor zone contained Fe-Cr spinel oxides and numerous nanopores, whereas the Ni-rich zone consisted of Fe-Cr spinel oxides and Ni-rich phases with austenite structure. The Ni segregation showed a specific evolution with exposure time and temperature: Ni-poor zones grew up and evolved into a laminar structure as the oxide film thickened. The formation and evolution mechanism of Ni-poor zones and the effect of Ni segregation on the oxidation were discussed in present work.

Effect of deformation twinning on the early oxidation behaviour of 316L steel exposed to liquid lead-bismuth eutectic

Twins were introduced into 316L austenitic stainless steel by shot peening treatments. The twinned 316L was then exposed along with pristine 316L to oxygen-saturated liquid lead-bismuth eutectic at 550 °C for 120 h. We observed that the inner oxide layer on the pristine 316L consisted of Fe–Cr spinel and reticulated nickel-rich phases, whereas that on the twinned 316L consisted of Fe–Cr spinel and Cr2O3 without the nickel-rich phases. The factor contributing to the different microstructure and composition of the oxide layer on pristine and twinned 316L is that the twin boundaries provide additional channels for Cr diffusion into the oxide front, allowing the formation of Cr2O3 and high Cr dense Fe–Cr spinel. As a result, the Ni rich phases do not have sufficient space to exist and are pushed back into the Cr poor steel matrix.

The microstructure and mechanical properties of steel-bonded TiB2 modified by adding Mo2C

In this study, the microstructure and interface of steel-bonded TiB2 were adjusted by adding Mo2C, so as to improve its comprehensive mechanical properties. The addition of Mo2C led to the formation of two kinds of core-rim structures, including TiB2 core-(Ti, Fe, Ni, Cr, Mo)B rim, and TiC core-(Ti, Fe, Ni, Cr, Mo)C rim. Micro - nano scale of TiB2, TiC and (Mo, Cr)C particles were formed in the steel-bonded TiB2. The introduction of Mo element caused the redistribution of elements in Fe-based binder phase, and two types of binder phases were generated, one was Ni-rich binder phase, and the other was Cr-rich binder phase. A full coherent interface was formed between the core and rim phase, and the amorphous metal thin layer was formed between the rim and binder phase. A coherent interface was formed between TiB2 and (Mo, Cr)C phase, (Mo, Cr)C and Ni-rich binder phase, as well as TiB2 and Ni-rich binder phase. Both the coherent interface and amorphous metal thin layer greatly enhanced the interface bonding strength, and improved the strength and toughness of the steel-bonded TiB2. The steel-bonded TiB2 with 6.0 wt% Mo2C exhibited excellent comprehensive mechanical properties, and its relative density, hardness, transverse rupture strength and fracture toughness were 99.94 ± 0.06%, 92.3 ± 0.5 HRA, 1278 ± 37 MPa and 10.90 ± 0.28 MPa·m1/2, respectively.

Cation-exchange-induced structural and chemical modulation of transition metal spinel sulfides to enhance their oxygen evolution performance

Transition metal spinels are promising oxygen evolution reaction (OER) catalysts; however, their rational design has been impeded by their inherent elemental and structural complexities. To alleviate these issues, this paper describes the role of cation exchange in developing active OER catalysts whose chemical and structural features are tailored while their morphology and crystal structure are maintained for enabling a systematic comparison. Through cation exchange, pre-synthesized Co3S4 spinel nanoparticles (NPs) transform into (NixCo3−x)S4 NPs with compositions ranging from Co-rich to Ni-rich phases. Apart from stoichiometry, the atomic disorder and chemical state of the metal cations are amended through excessive interdiffusion and interstitial site preference of the cations, evidently helping boost the catalytic activity. Specifically, (Ni1.2Co1.8)S4—which exhibits an optimal Ni/Co ratio, high structural disorder, and distinct surface chemical states—shows excellent OER performance (overpotential at 10 mA/cm2: 298 mV). In-depth analyses including in situ Raman spectroscopy and DFT calculations indicate that (Ni1.2Co1.8)S4 gradually transforms into OER-active Co/NiOOH—which has a unique electronic structure with strong reaction-intermediate-adsorbing characteristics—during the OER cycles. Overall, the study findings underscore the potency of cation exchange as a tool for controlling structural and chemical features, thereby helping explore complex catalyst materials while enhancing their activity.

Solidification Mechanism of Microstructure of Al-Si-Cu-Ni Alloy Manufactured by Laser Powder Bed Fusion and Mechanical Properties Effect

Based on previous work, where Al-Si-Cu-Ni alloy was successfully manufactured by laser powder bed fusion (PBF-LB/M) technology, in this study, we further observe the microstructure of the alloy, analyze the formation mechanism of the microstructure during solidification, and discuss their implications for the mechanical properties. The results indicate that the microstructure comprises multi-level cellular heterogeneous structures, with an α-Al matrix in the interior of the cellular structure and Cu- and Ni-rich phases clustered at the boundaries, intertwined with the silicon network. During solidification, α-Al solidifies first and occupies the core of the cells, while Si phases and Cu- and Ni-rich phases deposit along the cellular boundaries under the influence of surface tension. During the solidification process of cellular boundaries, influenced by spinodal decomposition and lattice spacing, Si phases and Cu- and Ni-rich phases interconnect and distribute crosswise, collectively forming multi-level cellular structures. The refined cellular microstructure of the PBF-LB/M Al-Si-Cu-Ni alloy enhances the mechanical properties of the alloy. The alloy exhibits a bending strength of 766 ± 30 MPa, a tensile strength and yield strength of 437 ± 6 MPa and 344 ± 4 MPa, respectively, with a relatively low fracture elongation of approximately 1.51 ± 0.07%. Subsequent improvement can be achieved through appropriate heat treatment processes.

Compositional alteration of low dimensional nickel sulfides under hydrogen evolution reaction conditions in alkaline media

Developing cost-effective electrodes for electrochemical water splitting with minimal kinetic losses remains a primary challenge in water electrolysis. Nickel-based dichalcogenides, particularly sulfides, have emerged as promising candidates for the hydrogen evolution reaction (HER). However, the stability of various nickel sulfide (NixSy) phases under cathodic potentials in alkaline electrolytes is subject to debate. In this study, we investigate the HER activity and durability of both 2-dimensional (2D) and 3-dimensional (3D) NixSy nanostructures with diverse chemical compositions. Through cross-correlation analysis of spectroscopic and electrochemical characterization data, we elucidate the transformation behavior of these materials under operating conditions. Our findings reveal that NiS2 tends to undergo conversion to nickel hydroxide (Ni(OH)2), while Ni-rich phases like Ni3S4 and NiS exhibit greater stability. Furthermore, we demonstrate that in 3D nanostructures, the initial formation of a protective hydroxide layer on the surface inhibits further sulfide transformation. This nickel sulfide/hydroxide composite shows an improved HER activity with lower onset potential (−0.25 V), Tafel slope (105 mV s−1), and charge transfer resistance (17.3 Ω).

Microstructure and mechanical properties of cast, eutectic Al-Ce-Ni-Mn-Sc-Zr alloys with multiple strengthening mechanisms

The effects of Ni additions on microstructure and microhardness of near-eutectic Al-9Ce-xNi-0.75Mn-0.18Sc-0.12Zr (x = 2.5, 3.2, and 3.9 wt.%) alloys are investigated for various cooling rates. The as-cast microstructure consists of fine, micron-scale Al11Ce3 and Ni-rich phases formed during eutectic solidification. Two Ni-rich phases are observed: (i) Al27Ce3Ni6 at higher Ni contents and slower solidification rates, and (ii) Al9(Ni,Mn,Fe)2 at lower Ni contents and faster solidification rates. While these Ni-containing alloys have higher microhardness than a Ni-free control alloy, varying the Ni concentration in the 2.5–3.9 wt.% range does not significantly affect the microhardness, indicative of competing strengthening and weakening effects from adding Ni. The alloy with intermediate Ni content (3.2 wt.%) is selected for further microstructural and mechanical characterization. It contains four coarsening-resistant strengthening constituents: (i) micron-scale Al11Ce3 and (ii) Al27Ce3Ni6 or Al9(Ni,Mn,Fe)2 platelets, all formed during eutectic solidification, (iii) L12-Al3(Sc,Zr) nanoprecipitates formed on aging, and (iv) Mn atoms in solid solution in the α-Al matrix. The combined strengthening mechanisms impart high strength at ambient and elevated temperatures, as measured by microhardness (as a function of aging time), by compression and tensile experiments, and by compressive creep measurements. Alloys previously reported in the literature - with various combinations of one, two or three of these four strengthening phases - show lower hardness and creep resistance, indicating that cumulative strengthening can be achieved when combining mechanisms; the present alloy containing all four phases shows a remarkably high creep threshold stress of 62 MPa at 300 °C.

Effect of high-energy shot peening process on the oxidation behaviour of AISI 321 stainless steel at 900 °C

ABSTRACT The present work comparatively investigates the oxidation behaviour of AISI 321 austenitic stainless steel at 900 °C in Ar-21vol.%O2 in two conditions of solution annealed (SAed) and after a high-energy shot peening process (HESPed). Kinetic observations indicated that during the initial 25 h of oxidation, the HESPed sample exhibits higher oxidation kinetics. However, as oxidation progresses, the kinetics of the SAed sample surpasses in a way that after 150 h, the weight gain for SAed is 0.93 mg/cm2, and for HESPed, it is 0.71 mg/cm2. GI-XRD results after 150 h of oxidation revealed similar oxide phases on both samples, including (Cr,Fe)2O3, Mn(Fe,Cr)2O4, and Fe2O3. An important point is that the oxide formed on the surface of the SAed sample, unlike HESPed, undergoes severe spallation and cracking after 150 h, leading to sub-surface oxidation and the formation of Ni-rich oxide phases such as Ni(Fe,Cr)2O4. The enhancement observed in the oxidation performance of the HESPed sample can be ascribed to the augmented density of high-diffusivity paths, a consequence of the high-energy shot peening process, and the prompt development of uniform inner Si-rich and intermediate Cr-rich oxide layers.

Effect of heat treatment on the microstructure and superelasticity of NiTi alloy via selective laser melting

In this study, a Ni50.4Ti49.6 shape memory alloy (SMA) was fabricated by selective laser melting (SLM), and it is found that heat treatments were effective to change the phase transformation behavior, microstructure, and superelasticity under compression for SLM Ni50.4Ti49.6. Detailed results based on EBSD demonstrated that, for SLM Ni50.4Ti49.6 during solid solution and aging (450 °C) treatment, the ultrafine cellular and columnar grains (∼16.5 μm) in as-fabricated Ni50.4Ti49.6 became equiaxed grains (∼70.2 μm), and the frequency of low-angle grain boundaries (26.7%→13.5%) and kernel average misorientation (0.37 → 0.21) decreased. The SEM and TEM analyses show that Ti-rich Ti2Ni/Ti4Ni2Ox and Ni-rich Ni4Ti3 precipitate phases were formed in the matrix simultaneously. After solid solution treatment, the size and distribution of Ti2Ni/Ti4Ni2Ox almost unchanged with aging temperature increasing from 350 °C to 550 °C, however, the size of Ni4Ti3 in aging-treated NiTi samples increased with aging temperature obviously, and it is interesting to find that the distribution of Ni4Ti3 became uneven and dislocation networks were formed in the matrix when the aging treatment reached up to 550 °C, which originated from the internal stress generated by supersaturated Ni atoms. Furthermore, the results of superelasticity for aging-treated NiTi demonstrated that the characteristics of Ni4Ti3 precipitate phase were powerful to influence the process of superelasticity decay/fatigue instead of determining the ultimately recovery strain after 10 compressive cycles. The aging-treated NiTi with evenly-distributed, high-density, and relatively-small Ni4Ti3 precipitate phase shows minimum recovery strain at 1st cycle compression and best superelasticity stability among three aging-treated NiTi, which was attributed to strong obstruction effect of these Ni4Ti3 precipitate for the occurrence of stress-induced martensitic transformation process and formation of dislocations. In contrast, the aging-treated NiTi with unevenly-distributed and low-density Ni4Ti3 precipitate shows maximum recovery strain at 1st cycle compression and worst superelasticity stability. These results in this work can bring some meaningful insights into tailoring the microstructure and superelasticity of SLM NiTi SMAs.

In-situ alloying laser powder bed fusion of Ni-Mn-Ga magnetic shape memory alloy using liquid Ga

Ni-Mn-Ga-based magnetic shape memory alloys can exhibit large magnetic field induced strains (MFIS). Recently, additive manufacturing techniques, especially laser powder bed fusion (L-PBF), have been successfully used to manufacture functional polycrystalline Ni-Mn-Ga with complex geometries, such as ‘bamboo-grained’ lattice structures. However, previous approaches of L-PBF of Ni-Mn-Ga have used pre-alloyed powders, which can limit the compositional freedom of the manufactured devices. This study explores, for the first time, the feasibility of an in-situ L-PBF alloying approach using a powder blend of elemental Ni, Mn, and Ga. Promising results were obtained despite the significant differences between the elemental Ni and Mn powders and the liquid Ga. The microstructure of the as-built sample showed distinct stripe patterns from the 14 M structure confirmed by XRD analysis. Heat-treatment significantly improved chemical homogeneity, dissolved the Ni-rich phase but couldn’t dissolve MnO hindering the shape memory effect.

Effects of Low Nickel Content on Microstructure and High-Temperature Mechanical Properties of Al-7Si-1.5Cu-0.4Mg Aluminum Alloy

In this paper, the effects of Ni content on the room and elevated temperature (250 °C) tensile strength of Al-7Si-1.5Cu-0.4Mg-0.3Mn-0.1RE-xNi (x = 0, 0.3, 0.6, 0.9 wt.%) alloys were investigated, along with microstructure characterization and tensile testing. In the as-cast state, the dominant Ni-rich phases were primarily the γ-Al7Cu4Ni and δ-Al3CuNi phases. Following the solution heat treatment, a significant reduction in the γ-Al7Cu4Ni phase was noted, accompanied by the emergence of numerous small ε-Al3Ni phases. Both room temperature strength and high temperature strength at 250 °C exhibited a consistent increase with rising Ni content, reaching 405 MPa and 261 MPa, respectively, at 0.9 Ni content, which were increased by 6.4% and 16.8%, respectively, compared with 0 Ni content. The elongation exhibited an oscillating increase within the Ni content range of 0 to 0.6, reaching peak values of 2.6% in room temperature and 4.3% in high temperature at 0.6 Ni, followed by a rapid decline. At 0.6 Ni content, the alloy demonstrated a well-balanced combination of mechanical properties, featuring commendable strength and plasticity.

Intolerance of Ruddlesden-Popper La2NiO4±δ Structure to a-Site Cation Deficiency

Mixed ionic-electronic conductors derived from Ruddlesden-Popper Ln2NiO4+δ (Ln = La, Pr, Nd) attract significant attention as oxygen electrode materials for solid oxide fuel and electrolysis cells. However, literature data on the impact of A-site deficiency on the phase relationships and functional properties of Ln2NiO4+δ-based phases are contradictory. While some works report an accommodation of A-site vacancies up to x = 0.15 in La2-x NiO4±δ, others indicate difficulties in the synthesis of single-phase La2-x NiO4+δ even for low x values. The present work explores the impact of the nominal A-site deficiency on the phase composition and electrical transport properties of La2-x NiO4±δ ceramics.Ceramics with the nominal composition La2-x NiO4±δ (x = 0, 0.02, 0.05, 0.10) were synthesized by the glycine-nitrate technique and sintered at 1350-1450°C. While XRD analysis suggested the formation of single-phase materials with orthorhombic K2NiF4-type structure, the lattice parameters remained independent of composition within the experimental uncertainty. Neutron diffraction studies of x = 0 and 0.05 samples revealed that the lattice parameters, La:Ni atomic ratio (2:1) and oxygen sites occupancy remain identical for both samples, while the presence of impurity NiO phase (0.4 wt.%) was detected for La1.95NiO4±δ. SEM/EDS inspection of ceramic samples confirmed the presence of nickel-rich inclusions for x ≥ 0.02, which could not be eliminated by increasing the temperature and time of sintering. The volume fraction of inclusions increased with x. The experimental observations are supported by the atomistic simulations showing that the coexistence of cation-stoichiometric La2NiO4+δ with nickel-rich La4Ni3O10 or NiO is more favorable compared to cation-deficient La1.95NiO4±δ. Molecular dynamics simulations of La1.95NiO4±δ lattice demonstrated that the introduction of La vacancies leads formation of instability zone in the rock-salt-type layer and destabilization of the crystal lattice. The intolerance of La2NiO4+δ lattice to A-site vacancies and coexistence of La2NiO4+δ with traces of Ni-rich secondary phase in the samples with the nominal composition La2-x NiO4±δ results in an insignificant variation of electrical transport properties with x. Acknowledgements This work was developed within the scope of the project CARBOSTEAM (POCI-01-0145-FEDER-032295) funded by FEDER through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) and by national funds through FCT/MCTES, and the project CICECO-Aveiro Institute of Materials (UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020) financed by national funds through the FCT/MCTES (PIDDAC). A.B. acknowledges the PhD scholarship by the FCT (grant SFRH/BD/150704/2020). This work was partially supported by the National Science Centre, Poland, grant UMO-2020/37/B/ST8/02097.

Laser powder bed fusion of an ultrafine microstructural in-situ TiB2/Al composite with excellent mechanical properties and thermal stability at elevated temperatures

Additive manufacturing of lightweight and heat-resistant aluminum-based materials has received ever increasing interest for obtaining high specific strength and complex-shaped components serving at elevated temperatures in aerospace industry. In this study, an in-situ TiB2 particle reinforced Al–Cu–Mg–Fe–Ni (Al2618) alloy was additive manufactured by laser powder bed fusion (L-PBF) with excellent printability. The as-printed TiB2/Al2618 composite presented a fully equiaxed and remarkably refined grain structure with an average size of ∼1 μm. The intermetallic phases in the Al matrix exhibited an ultrafine cellular structure owing to the rapid solidification by L-PBF. The ultrafine microstructure showed excellent thermal stability at elevated temperatures due to the synergic effects of TiB2 particles and Fe, Ni-rich coarsening-resistant intermetallic phases. The L-PBF TiB2/Al2618 composite has shown superior mechanical performance at elevated temperatures both in tensile strength and in strength retention after thermal exposure among typical L-PBF and wrought Al alloys. This work inspires the design of heat-resistant metal matrix composites (MMCs) with advanced high-temperature mechanical performance enabled by additive manufacturing for potential industrial applications.

Structure and magnetism of AlCoCrCuFeNi high-entropy alloy

We report on the investigation of magnetic and structural properties of AlCoCrCuFeNi, which is known to crystallize in a dual phase solid solution: the face-centred cubic (FCC) or the body-centred cubic (BCC). The results of neutron (NPD) and synchrotron powder diffraction (SXRD) allow to partially resolve magnetic information coming from BCC and FCC phases, which is impossible in the bulk magnetic measurements. Electron diffraction (PED) revealed that AlCoCrCuFeNi forms dendritic microstructure with the Cu-rich FCC phase and the Ni-rich BCC phase. Lattice parameters obtained from PED method are in good agreement with parameters obtained after refinement on the basis of powder X-ray diffraction measurements. The local crystal and electronic structure around Co was studied using Co K X-ray Absorption Spectroscopy (XAS). The magnetic measurements show that AlCoCrCuFeNi reveal a ferromagnetic transition at about 330 K and displays magnetic hysteresis loop at the room temperature. Results from NPD suggest that the magnetic moment is mostly located in the BCC subsystem. The alloy shows soft magnetic properties. Saturated magnetizations (Ms), remanence ratio (Mr/Ms) and coercivity (Hc) of the cast are estimated to be 45.10 emu/g, 5.1 % and 56 Oe at 300 K, respectively. Finally, the BCC-FCC phase transformation up to 673 K (400 °C) was investigated using temperature dependent NPD, where a possible second BCC phase was identified.

Wear and corrosion resistance of Al1.2CoCrFeNiScx high entropy alloys with scandium addition

The present study focuses on investigating the microstructure, hardness, wear, and corrosion resistance of Al1.2CoCrFeNiScx high entropy alloys, where the Sc content (x) varies between 0, 0.1, 0.2, and 0.3. The results indicate that the addition of Sc promotes the formation of the FCC phase and improves the hardness and wear resistance, but reduces the corrosion resistance of the alloy. The alloy's evolution can be observed as a transition from a single BCC phase to a combination of Fe, Cr-rich BCC phase, Al, Co, Ni-rich BCC phase, and Ni, Sc-rich FCC phase. As the Sc content increases from 0 to 0.3, the hardness increases from 438 HV to 581 HV, representing a 32.6 % increment. This increase can be mainly attributed to grain size strengthening and solid solution strengthening. Additionally, the average friction coefficient experiences a notable reduction from 0.999 to 0.574, indicating a 42.5 % decrease. With respect to wear resistance, the Al1.2CoCrFeNiSc0.3 alloy exhibits superior performance, demonstrated by its lower friction coefficient, reduced wear rate, and smaller volume, width and depth of wear marks. Furthermore, the addition of Sc to the Al1.2CoCrFeNiScx alloys leads to an overall decrease in corrosion potential, accompanied by an increase in corrosion current density, suggesting that Sc has a detrimental effect on the corrosion resistance of the alloy. Moreover, the Al1.2CoCrFeNi alloy displays pitting corrosion, while the Al1.2CoCrFeNiScx alloys demonstrate intercrystalline corrosion, which preferentially occurs on the Ni, Sc-rich phase due to the high electrochemical activity and low equivalent chemical potential.