Alloy Formation Research Articles

Microstructure and mechanical properties of Ti-Nb alloys: comparing conventional powder metallurgy, mechanical alloying, and high power impulse magnetron sputtering processes for supporting materials screening

At the interface of thin film development and powder metallurgy technologies, this study aims to characterise the mechanical properties, lattice constants and phase formation of Ti-Nb alloys (8–30 at.%) produced by different manufacturing methods, including conventional powder metallurgy (PM), mechanical alloying (MA) and high power impulse magnetron sputtering (HiPIMS). A central aspect of this research was to investigate the different energy states achievable by each synthesis method. The findings revealed that as the Nb content increased, both the hardness and Young’s modulus of the PM samples decreased (from 4 to 1.5 and 125 to 85 GPa, respectively). For the MA alloys, the hardness and Young’s modulus varied between 3.2 and 3.9 and 100 to 116 GPa, respectively, with the lowest values recorded for 20% Nb (3.2 and 96 GPa). The Young’s modulus of the HiPIMS thin film samples did not follow a specific trend and varied between 110 and 138 GPa. However, an increase in hardness (from 3.6 to 4.8 GPa) coincided with an increase in the β2 phase contribution for films with the same chemical composition (23 at.% of Nb). This study highlights the potential of using HiPIMS gradient films for high throughput analysis for PM and MA techniques. This discovery is important as it provides a way to reduce the development time for complex alloy systems in biomaterials as well as other areas of materials engineering.Graphical abstract

Effect of powder and process parameters on in-situ alloying of nitinol during laser powder bed fusion

Powder characteristics such as flow energy, bulk density, compressibility, morphology, particle size distribution (PSD) and laser energy absorbtivity have a significant impact on the Laser Bed Powder Fusion (L-PBF) process. The impact of powder characteristics on in-situ nickel-titanium alloy formation within the L-PBF process is not well understood. In this work, the characteristics of nickel, titanium and two elemental blends of nickel-titanium powder were compared with those of a pre-alloyed nitinol powder. L-PBF solidification tracks were generated using selected powders and characterised for resulting track dimensions and chemical homogeneity. This study demonstrates that the melt homogenisation time and the size of titanium particles relative to nickel particles are critical factors for successful in-situ alloying of nitinol within the L-PBF process. The variation in elemental composition within solidification track cross sections, as measured by EDX point spectra, was found to increase significantly for laser scanning speeds of 400 mm/s and above. Furthermore, the elemental composition inhomogeneity with increasing laser scan speed was found to be significantly more pronounced for a nickel-titanium powder blend of spherical particles with average titanium particle size of 48 μm compared to an otherwise similar blend with an average titanium particle size of 32 μm. There was no significant difference recorded between solidification track widths of in-situ alloyed blends compared to pre-alloyed blends, indicating that optimal hatch spacing for in-situ alloying is likely to be similar to that required for pre-alloyed powders.

Controlling the structure formation of heat-resistant nickel-based alloys, when manufacturing large gas turbine blades

Controlling the structure formation of heat-resistant nickel-based alloys, when manufacturing large gas turbine blades

Crystal Plasticity Finite Element Analyses on the Formability of AA6061 Aluminum Alloy with Different Ageing Treatments

Different ageing treatments have been developed to achieve targeted properties in aluminum alloys through altering microstructures. However, there is a lack of understanding regarding the effect of ageing treatments on the formability of these alloys. In this study, we employed crystal plasticity finite element (CPFE) modeling, in conjunction with the Marciniak-Kuczynski (M-K) approach, to investigate the effects of ageing treatments on the mechanical properties and formability of AA6061 aluminum alloy. The as-received sheet was in the T6 heat treatment state, which was subjected to artificial ageing and pre-ageing, respectively, to achieve two age-hardened alloys with modified precipitation states. The microstructures and crystallographic textures of the three alloys were measured using the electron backscattering diffraction (EBSD) technique, and uniaxial tensile tests were performed along the rolling direction (RD), transverse direction (TD), and diagonal direction (DD, 45° to the RD) for each alloy. The forming limit curve (FLC) of the as-received alloy was determined using the Nakazima test. The dependence of mechanical strength, tensile ductility, and work-hardening behavior on the ageing treatments was clarified. Then, the tensile test results were utilized to calibrate the modeling parameters used in the CPFE model, whereas the FLC predictability of the developed model was validated with the experimental one. In the formability analysis, the effects of the ageing treatment on the FLC exhibit a notable dependency on loading paths, and the pre-aged alloy exhibits better formability than the other two at the plane strain tension state, thanks to its high work-hardening levels. In addition, the deformed textures along the different loading paths and the effects of the initial texture on the FLC are also discussed.

Influence of powder surface chemistry on the defect formation in AlSi10Mg alloy processed via laser powder bed fusion additive manufacturing

In laser powder bed fusion(LPBF) additive manufacturing(AM) of Al alloys, surface chemistry and dissolved gas composition(oxygen/oxides/hydroxides, hydrogen and moisture) of AM powders is a major influencing factor for porosity formation. Therefore, in the present investigation, this aspect is addressed using two sets of virgin AM AlSi10Mg powders, namely, Hi-Ox (2770 ppm oxygen) and Lo-Ox (660 ppm oxygen), to assess the printability under various processing parameters and defect formation in printed parts. Comprehensive and in-depth metallurgical analysis of both powders utilizing multiple characterisation techniques established the presence of various types of oxides/hydroxides with different complex chemistries on the powders’ surface. Enhanced spherical gas porosity and oxide inclusions were witnessed in Hi-Ox print coupons in contrast to the least defects in Lo-Ox coupons rationalized due to surface chemistry difference between the virgin powders. Consequently, the mechanical properties of the Hi-Ox print coupons, even with minimum defect density, are significantly inferior to Lo-Ox specimens. These observations suggest a competing influence of surface chemistry/dissolved gas composition and laser parameters for the processing of both powders. Overall, by correlating the microstructures with processing conditions and oxide concentration, defects morphology, the probable melt pool formation mechanism in LPBF of AlSi10Mg alloy (for high and low oxygen concentration) is elucidated.

Structural correlation and chemistry of molten NaF–ScF3 with dissolved metal aluminium: TG/DTA, XRD, NMR and molecular dynamics simulations

For the first time, the mechanism of metal aluminum dissolution in NaF–ScF3 eutectic melts and the chemical interaction between the constituents of this mixture have been thoroughly studied by a combination of differential thermal analysis (DTA), high temperature and solid-state nuclear magnetic resonance (NMR), and X-ray diffraction (XRD) coupled with the molecular dynamic simulations. The formation of an insoluble Al3Sc alloy in molten (NaF–ScF3)eut system was proven, and the chemical mechanism of this aluminothermic Al3Sc alloy production was elucidated. Corresponding ex situ examinations bring to light the formation of NaScF4 and solid solution of Na3(Al,Sc)F6 in cooled bath. The molecular dynamics calculations of the bath allow us to construct the structural model and to predict viscosity, density and electrical conductivity of the reagent melt to help to optimize the conditions of the alloy synthesis.Graphical abstract

Effect of hydride orientation on tensile properties and crack formation in zirconium alloy cladding tubes

Hydride precipitation and reorientation are of great importance to evaluate considering their detrimental influence on mechanical properties of nuclear fuel claddings. In this work, a fully recrystallized Zr-Sn-Nb cladding tube was hydrided with 120 and 220 wppm concentration, followed by thermo-mechanical treatment to produce specimens with varying hydrogen contents and hydride orientations. Ring tensile test demonstrates that in contrast to circumferential ones, the radial hydrides lead to significant reductions in plastic elongation of cladding tubes. Scatter in values of mechanical properties are observed in the case of 220 wppm radial hydrides, which could be attributed to irregular distribution of interconnected radial hydrides. Microstructure characterization reveals that microvoids initiate at the junction boundaries of hydride platelets under the tension effect of surrounding α-matrix deformation. These microvoids are proposed to propagate along the interior of brittle hydrides, rather than the interface, eventually leading to premature fracture failure given the alignment of radial hydrides perpendicular to the external tensile stress. The presented results are expected to shed light on microcrack initiation and propagation with respect to hydride orientation in zirconium-based nuclear fuel claddings.

Silver nanoflake-mediated anode texture control enabling deep cycling of aqueous zinc-ion batteries

The escalating popularity of aqueous zinc-ion batteries has prompted substantial research efforts directed at mitigating zinc dendrites and parasitic reactions. Modifying Zn foil electrodes with Ag metal/alloy has emerged as an efficacious strategy owing to the exceptional zincophilicity and remarkable electrical conductivity of Ag. Nevertheless, previous studies predominantly rely on either 3D architectures or Ag nanowires/particles. The former approach may increase costs and compromise energy density, while the latter inadequately guides planar zinc deposition. In this work, Ag nanoflakes synthesized by a solution method are employed to control Zn anode texture through a facile drop-casting technique. The nanoflake morphology facilitates the horizontal arrangement of Ag modification layer, thereby readily promoting horizontal zinc deposition. It is also found that the Ag nanoflakes can improve electrolyte wettability, augment anti-corrosion ability, homogenize electric field, diminish nucleation overpotential, reduce desolvation activation energy, impede two-dimensional Zn2+ ion diffusion, reduce exchange current density, lower electrochemical impedances, and result in the formation of AgZn3 alloy. Correspondingly, the zinc stripping/plating reversibility is significantly improved, accompanied by considerably inhibited parasitic reaction, contributing to the realization of deep cycling for both Zn//Zn cell and Zn//MnO2 battery. This study unveils a viable morphology-tailored methodology to achieve dendrite-free characteristic.

Study on mechanism underlying the acceleration of pitting corrosion of B30 copper–nickel alloy by sulfate-reducing bacteria in seawater

In this paper, the relationship between the pitting corrosion formation of B30 copper–nickel (CuNi) alloy and the metabolism of sulfate-reducing bacteria (SRB) was investigated. Combined with the influence of temperature during the actual operation of the cooling systems, the evolution law of the alloy passivation film was analyzed, and the mechanism of SRB promoting the accelerated development of B30 CuNi alloy pitting corrosion was revealed. The results show that SRB significantly promoted the pitting formation and development of B30 CuNi alloy. The maximum pitting depth was 3.9 μm in the sterile system and 15.3 μm with SRB, which was 3.9 times higher than that of sterile system. The loose porous Cu2S film formed by SRB metabolites and copper matrix was easily penetrated by corrosive anions, which promoted copper dissolution and led to pit nucleation. The sulfide adsorbed on the surface prevented or delayed the passivation of B30 CuNi alloy by blocking the adsorption site of O atom, and the corrosion nuclei continued to grow. The non-uniformity caused by the film peeling accelerated the longitudinal development of pitting corrosion, and the expansion and coalescence of adjacent pits caused the transverse development of pitting corrosion. Temperature had a certain influence on the SRB and the formation of B30 CuNi alloy passivation film. The passivation film was formed rapidly at 50 °C with poor quality and the passivation property of Cu2O film was weakened. With the increase of temperature, the pitting potential of sterile system negative shifted from 0.447 to 0.360 V (vs. SCE), while SRB system from 0.340 to 0.198 V (vs. SCE), and the pitting resistance decreased. The passivation film with defects and the Cu2S reduced the barrier efficiency of the film and accelerated the pitting corrosion of B30 CuNi alloy.

Microstructural features and mechanical properties of spray -formed hypereutectic Al-Si-Ti alloy

ABSTRACT In the present study, the effect of the addition of Ti on the microstructural and mechanical properties of hypereutectic (Al/15 wt. %Si) spray-formed (SF) alloys has been investigated and compared with as-cast (AC) alloys. Al/15Si and Al/15Si/2Ti alloys were synthesised by spray forming method. The microstructural features of the alloys were explored under an optical microscope, and a scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis were carried out for phase identification. The phase analysis confirmed the presence of α-Al and Si phases in all the alloys, with additional peaks attributed to Al3Ti and AlSi2Ti present in the Al/15Si/2Ti alloys. The microstructure of the SF1 alloy (Al/15Si) consisted of globular, fine Si phases (primary and eutectic) distributed homogeneously in the equiaxed Al matrix. The addition of Ti to the binary SF1 alloy led to the formation of an SF2 alloy (Al/15Si/2Ti) with a fine intermetallic phase of Al3Ti and further spheroidisation of Si particles. The SF1 and SF2 alloys exhibited 30% and 40% greater microhardness, respectively, than did their corresponding AC alloys. With the addition of Ti, the ultimate tensile strength of the SF2 alloy increased by 19% compared to that of the SF1 alloy. Furthermore, a significant increase in yield strength and ductility was observed in the SF alloys compared to the AC alloys. Adding Ti to hypereutectic Al/15Si alloy via the spray-forming method provides a better alternative material for aerospace and automotive applications.

Laser Irradiation Synthesis of AuPd Alloy with Decreased Alloying Degree for Efficient Ethanol Oxidation Reaction.

The preparation of electrocatalysts with high performance for the ethanol oxidation reaction is vital for the large-scale commercialization of direct ethanol fuel cells. Here, we successfully synthesized a high-performance electrocatalyst of a AuPd alloy with a decreased alloying degree via pulsed laser irradiation in liquids. As indicated by the experimental results, the photochemical effect-induced surficial deposition of Pd atoms, combined with the photothermal effect-induced interdiffusion of Au and Pd atoms, resulted in the formation of AuPd alloys with a decreased alloying degree. Structural characterization reveals that L-AuPd exhibits a lower degree of alloying compared to C-AuPd prepared via the conventional co-reduction method. This distinct structure endows L-AuPd with outstanding catalytic activity and stability in EOR, achieving mass and specific activities as high as 16.01 A mgPd-1 and 20.69 mA cm-2, 9.1 and 5.2 times than that of the commercial Pd/C respectively. Furthermore, L-AuPd retains 90.1% of its initial mass activity after 300 cycles. This work offers guidance for laser-assisted fabrication of efficient Pd-based catalysts in EOR.

Anomalous twin boundary formation in magnesium alloys by rapid solidification

The aim of this work is to investigate the formation of an anomalously high fraction of twin boundaries (TBs) during laser directed energy deposition (DED) of a Mg-3Al-1 Zn (wt.%) alloy. With that goal, single tracks are deposited using different combinations of scan speed and powder feed rate. The melt pool dimensions are related to the DED parameters. Irrespective of the processing conditions, the resulting microstructures are always formed by fine grains with a very weak texture. However, some DED parameter combinations give rise to a fraction of TBs that is significantly higher than that corresponding to a random texture. These TBs are characterized by an irregular morphology and by the presence of segregated atoms, solute clusters, and nanoparticles. Additionally, the lattice in the vicinity of the TBs is highly distorted and contains a high population of stacking faults. All these characteristics set them apart from conventional tensile TBs, which exhibit a large degree of coherency and limited segregation. Rapid solidification is thus presented here as a novel avenue to design TBs with unique properties in Mg alloys. This work paves the way for future studies on grain boundary design via additive manufacturing methods, a field that is still in its infancy.

Iron alloys of volatile elements in the deep Earth's interior.

Investigations into the compositional model of the Earth, particularly the atypical concentrations of volatile elements within the silicate portion of the early Earth, have attracted significant interest due to their pivotal role in elucidating the planet's evolution and dynamics. To understand the behavior of such volatile elements, an established 'volatility trend' has been used to explain the observed depletion of certain volatile elements. However, elements such as Se and Br remain notably over-depleted in the silicate Earth. Here we show the results from first-principles simulations that explore the potential for these elements to integrate into hcp-Fe through the formation of substitutional alloys, long presumed to be predominant constituents of the Earth's core. Based on our findings, the thermodynamic stability of these alloys suggests that these volatile elements might indeed be partially sequestered within the Earth's core. We suggest potential reservoirs for volatile elements within the deep Earth, augmenting our understanding of the deep Earth's composition.

Дослідження технології зварювання плавленням складнолегованих титанових сплавів

The subject of this article is peculiarities of weld seam formation of complex titanium alloys during electron beam welding in vacuum and argon arc welding. The purpose of this study is to ensure the required level of mechanical properties of welded structures from complex titanium alloys to improve the structure and properties of welded joints. The task: to investigate the processes that are taking place in the zone of thermal influence and to determine their influence on defects formation; to determine the modes of parts welding made of complex titanium alloy; to study the effect of electron beam welding on the materials properties, such as strength, crack resistance, and corrosion resistance. Research results. The thermal cycle influence of welding and subsequent heat treatment on the structural and phase transformations in the weld metal and the heat-affected zone of complex titanium alloy welded joints was studied. It was established that a structure with a metastable β-phase predominance is formed in the weld metal and the zone of welded joints thermal influence, which contributes to the reduction of plasticity and impact toughness. The best combination of the studied welded joint strength and ductility was obtained after heat treatment, annealing at a temperature of 950 °C for 1 h, and cooling in the furnace. The use of filler wire contributes to obtaining an almost uniform structure and the disintegration of metastable phases in the seam as well as in the zone of thermal influence, and the strength limit is 1250 MPa. Conclusions. The influence of filler wires on the obtained samples structure and properties was studied, and the results were discussed depending on possible practical implementations. This article describes the creation and testing of elements of electron beam welding of complex titanium alloys technological process. This makes it possible to widely use welded combined titanium alloys in products of the appropriate purpose. The obtained scientific and practical results lead to increased mechanical properties of complex titanium alloys welded joints to the level of the base metal.

Preparation of a hard AlTiVCr compositionally complex alloy by self-propagating high-temperature synthesis

In this study, an AlTiVCr compositionally complex alloy with a high hardness of 865 ± 34 HV was prepared by a one-step self-propagating high-temperature synthesis (SHS) method using TiO2, V2O5, Cr2O3, and Al as starting materials. Experimental results confirmed the formation of a two-phase alloy having BCC solid solution dendritic grains reinforced by a Ti-rich intermetallic phase. Elemental analysis results confirmed that the Ti at.% in the synthesized alloy was lower than other elements. The addition of extra TiO2 to the reactants, pre-milling of the TiO2-Al mixture, and using the Rutile polymorph of TiO2 instead of Anatase as the starting material increased the atomic percent of Ti. The composition of the proper synthesized alloy was formulated as Al27.3Ti17.2V28.7Cr26.8 which is close to the desired AlTiVCr alloy. To clarify the reaction sequence during the SHS, the binary mixtures were analyzed by thermal analysis. It was postulated that the melting of Al facilitated the reduction reaction of Cr2O3 and VxOy compounds, while TiO2 was the last oxide compound reduced by Al. This hindered the completion of the TiO2 reduction reaction and as a consequence, the unreacted TiO2 entered the slag which lowered the concentration of Ti in the composition of the final alloy.

Exploring the Effects Behind the Outstanding Catalytic Performance of PdAg Catalysts Supported on Almond Shell‐Derived Activated Carbon Towards the Dehydrogenation of Formic Acid

AbstractIn this work, highly efficient carbon‐supported Pd‐based catalysts for formic acid dehydrogenation were synthesized by a straightforward wet impregnation‐reduction method. The carbon support was obtained from a biomass residue (almond shell) prepared via H3PO4‐assisted hydrothermal carbonization (HTC) and thermal activation. This carbon support was doped with nitrogen groups to study the effect on the electronic properties and catalytic performance of the catalysts. Investigating the formation of PdAg alloys with varying Pd : Ag molar ratios resulted in catalysts exhibiting enhanced catalytic activity compared to monometallic Pd counterparts. Notably, the Pd1Ag0.5/NAS catalyst displayed outstanding catalytic performance, achieving an initial TOF of 1716 h−1 (calculated in the first 3 minutes of reaction and expressed per mole of Pd) and maintaining substantial activity over 6 consecutive reaction cycles. This work elucidates the successful synthesis of effective catalysts, emphasizing the influence of nitrogen doping and PdAg alloy composition on catalytic behavior and stability.

Onset of tetrahedral interstitial formation in GaAsN alloys

Onset of tetrahedral interstitial formation in GaAsN alloys

The behaviors of He atoms at Ti3SiC2(001)/V(110) interface: A first-principles study

Ti3SiC2 nano-particles and He atom play an important role for the degradation of properties in vanadium alloys under irradiation environment. Herein, the behaviors of He atoms at C-Ti2-H Ti3SiC2(001)/V(110) interface model by first-principles calculations, which is the most thermodynamically stable, is studied to elucidate the effect of Ti3SiC2 nano-particles on the He bubble formation in the vanadium alloys. He atom tends to dissolve at the Ti3SiC2/V interface and at the near Si layer of Ti3SiC2 side at the interface. The vacancy type defects formation energies for V1, C1, C2 and Si, which both lower than V monovacancy formation energy in bulk vanadium, are more likely to form at the interface. Moreover, The existence of monovacancy at the interface makes it easier for neighboring He atoms to dissolve, which has a spatial effect on He atom. The result of the trapping energy and the interface distortion of He atom trapped by Si and V1 vacancies, more He atoms can be trapped as the number of vacancies increases. The diffusion of He atom located at Ti3SiC2 side towards the interface hampered by the small spacing Ti and C atom layers (dlsTi2−C2= 1.18 Å) anddlsTi1−C1 = 1.31 Å) He atom tends to aggerate at the interface due to the higher energy barrier. The Ti3SiC2-praticle/V-matrix interface can act as a sink for He atom. These findings provide a new insight into the understanding about the influence of Ti3SiC2 nano-particles on the mechanisms of He bubble formation and the guidance for further the preparation of vanadium alloys.

Synthesis of Helional by Hydrodechlorination Reaction in the Presence of Mono- and Bimetallic Catalysts Supported on Alumina

Hydrodechlorination reaction of 3-(benzo-1,3-dioxol-5-yl)-3-chloro-2-methylacrylaldehyde in the presence of different low metal content heterogeneous mono- or bimetallic catalysts was tested for the synthesis of the fragrance Helional® (3-[3,4-methylendioxyphenyl]-2-methyl-propionaldehyde). In particular, mono Pd/Al2O3, Rh/Al2O3 or bimetallic Pd-Cu/Al2O3, Rh-Cu/Al2O3 catalysts were tested in different reaction conditions from which it emerged that mono-Rh/Al2O3 was the best performing catalyst, allowing achievement of 100% substrate conversion and 99% selectivity towards Helional® in 24 h at 80 °C, p(H2) 1.0 MPa in the presence of a base. To establish correlations between atomic structure and catalytic activity, catalysts were characterized by Cu, Rh and Pd K-edge XANES, EXAFS analysis. These characterizations allowed verification that the formation of Pd-Cu alloys and the presence of Cu oxide/hydroxide species on the surface of the Al2O3 support are responsible for the very low catalytic efficiency of bimetallic species tested.

Influence of the Cooling Rate on the Heterogeneity of the Structure in the Rapid Quenched Fe – Based Alloys with the Si Addition

The paper presents the results of research from the analysis of primary magnetization curves for Fe based amorphous alloys. Structural defects in the form of pseudodislocation dipoles occur in amorphous alloys. Using the theory developed by H. Kronmuller called the approach to ferromagnetic saturation, it is possible to indirectly observe internal stresses occurring in the volume of amorphous alloys. The magnetic structure is sensitive to all kinds of inhomogeneities that become visible in the process of high-field magnetization. It has been shown that the cooling rate of the liquid alloy has a great influence on the migration of atoms during the solidification process. Longer time of alloy formation causes more atoms to occupy ordered positions, which results in a change in the distance between the magnetic atoms and a higher degree of structure relaxation. This is indicated by a significant difference in the value of the spin wave stiffness parameter Dspf. The structural differences of the alloys were also investigated using a magnetic balance. It has been shown that the cooling rate influences insignificant differences in the course of thermomagnetic curves and the Curie temperature.