Elemental Powders Research Articles

Porous TiFe2 intermetallic compound fabricated via elemental powder reactive synthesis

Porous TiFe2 intermetallic compound fabricated via elemental powder reactive synthesis

Refractory High‐Entropy Alloys Produced from Elemental Powders by Severe Plastic Deformation

A comparative investigation of two fundamentally different approaches for the synthesis, microstructure evolution, and mechanical properties of the refractory high‐entropy alloys (RHEA) HfNbTaTiZr and HfNbTiZr is performed. The two methods comprises conventional arc (button) melting and a powder route based on mechanical alloying and consolidation via severe plastic deformation. In particular, blended elemental powder is pre‐compacted and subjected to one or four passes of equal channel angular pressing (ECAP) at 500 °C and then 10 revolutions of high pressure torsion (HPT) at room temperature to an effective strain between 4 and 40. Some samples are then annealed at 500 °C for 1 h to investigate the thermal stability of the phases. The four ECAP passes at 500 °C do not result in the formation of the body‐centered cubic (BCC) phase typical for the program RHEAs despite the presence of interfacial zones between particles and defect‐driven diffusion. Nevertheless, a single ECAP pass is sufficient to create a solid bulk sample for subsequent HPT. After 10 HPT revolutions, in contrast to melting route resulting in a single BCC phase alloy, both alloys form new phases comprising a Nb‐rich BCC phase and a ZrHf‐rich HCP phase in both alloys.

Microstructures and properties of Al2O3 dispersion-strengthened Cu10Sn oil bearings prepared by solid-liquid doping and reactive synthesis method

To modify the shortcomings of Cu10Sn oil bearing in mechanical performance, this work proposes to prepare the Al2O3 oxide dispersion strengthened (ODS) Cu10Sn oil bearings by reactive synthesis using elemental Sn and Al2O3 ODS-Cu powder, among which the uniformly doped Al2O3 ODS-Cu powder was synthesized through a solid-liquid doping of Al(NO3)3 in CuO powders followed with hydrogen reduction. The effects of Al2O3 content on the microstructure and properties of ODS-Cu powder and ODS-Cu10Sn oil bearings were investigated in details. The results showed that an increase in Al2O3 amount from 0 to 1.5 wt% leads to a decrease in the average particle size of the reduced ODS-Cu powders, and contributes to the significant improvement of radial compressive strength, and Vickers microhardness. The appropriate sintering temperature is approximately 800 °C, which can result in the evenly distributed Al2O3 and well-developed porosity in oil bearing sample after sintering. The corresponding compressive strength and microhardness of ODS1.5-Cu10Sn oil bearing can reach 305 MPa and 208 HV respectively.

Mechanical and tribological characteristics of nickel-rich CoCrCuxFeNi2 high entropy-alloys

This research explores the potential to enhance the copper solubility limit in high-entropy alloys (HEAs) within the CoCrCuFeNi system by increasing the nickel content twofold and applying additional heat treatment. The CoCrCuxFeNi2 HEAs were synthesized through mechanical alloying of elemental powders followed by hot pressing. The study investigated the microstructure and phase composition of CoCrCuxFeNi2 HEAs in relation to varying copper concentrations (x = 0; 0.25; 0.5; 0.75; 1.0). The evaluation of the alloy matrix's chemical composition, which is based on the FCC solid solution, enabled the determination of copper solubility. It was found that doubling the nickel content, relative to the equiatomic ratio, facilitated the formation of HEAs with a homogenous FCC structure for copper concentrations up to x ≤ 0.75. Further heat treatment of these HEAs resulted in an enhanced copper solubility of up to 17.5 at.%. The mechanical and tribological properties of CoCrCuxFeNiy HEAs were also assessed, revealing significant improvements in tensile strength (ranging from 910 to 1045 MPa) and hardness (285–395 HV) for the CoCrCuxFeNi2 alloys. Despite the increased copper solubility limit, the heat treatment process caused a decline in mechanical properties by 35–50 %, attributed to grain size enlargement to 5.5 μm. The CoCrCu0.75FeNi2 and CoCrCuFeNi2 alloys exhibited the lowest wear rates when tested against Al2O3 counterbody, with wear rates of 1,58·10–5 and 1,48·10–5 mm3/(N·m), respectively.

Production and Characterization of Ni0.50 Al0.50 and Ni0.55 Al0.45 Powders by Volume Combustion Synthesis

Nickel aluminide (NiAl) is an essential intermetallic material with a high melting point and excellent high temperature corrosion resistance. It is a solid solution of Ni and Al in 40-61 mol.% Ni range. In this study, Ni0.50Al0.50 and Ni0.55Al0.45 powders were formed by using nickel and aluminum elemental powders through volume combustion synthesis (VCS). MgO powder was utilized as the thermal diluent. According to adiabatic temperature calculations, MgO was added to the reactant mixture in 10-40 vol.% range for preventing the melting and sintering of the formed Ni0.50Al0.50 and Ni0.55Al0.45 particles. After VCS, the products were ground into powder form and leached in 3M HCl solution in order to remove the MgO particles. After VCS, the samples which were obtained with 10 - 30 vol.% MgO addition were quite hard and difficult to grind. This indicated the partial sintering of the formed particles. It was relatively easier to grind into powder form the samples which contained 40 vol.% MgO. Therefore, it was determined that the most suitable MgO ratio for the formation of Ni0.50Al0.50 and Ni0.55Al0.45 powders was 40 vol.%. Formed powders were mostly in 5-100 µm particle size range. The formation of single phase pure powders was confirmed by the XRD analyses. A shift of about 0.1 degrees to higher 2-theta values was determined in the XRD peaks of the Ni0.55Al0.45 powder as compared to the Ni0.50Al0.50 phase, after annealing the powders. The results were in agreement with the crystallographic data.

Laser additive manufacturing of Cu–Cr–Nb alloys by using elemental powder

Laser additive manufacturing of Cu–Cr–Nb alloys by using elemental powder

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.

A Multivariate 2D Metal-Organic Framework with Open Metal Sites for Catalytic CO2 Cycloaddition and Cyanosilylation Reactions.

This work reports the synthesis of a dual functional 2D framework, {[Zn2(4-tpom)2(oxdz)2]·4H2O}n (1), at room temperature, where a bent dicarboxylate, oxdz2- (4,4'-(1,3,4-oxadiazole-2,5-diyl)dibenzoate), and a neutral flexible N-donor linker, 4-tpom (tetrakis(4-pyridyloxymethylene)methane), are utilized. Its single-crystal X-ray analysis indicated a 2-fold interpenetrated 2D framework having tetracoordinated Zn(II) centers and dangling pyridyl groups. Its further characterization was carried out with elemental microanalysis, FTIR spectroscopy, TG analysis, and powder X-ray diffraction. The tetracoordinated Zn(II) centers as active Lewis acidic sites and the N atoms of 4-tpom as Lewis basic sites in 1 are explored for its functioning as a heterogeneous catalyst in two important reactions, (i) cycloaddition of CO2 with various epoxides and (ii) cyanosilylation reaction under solvent-free conditions. We could successfully show the cycloaddition of styrene oxide with CO2 (99% conversion) under balloon pressure with low catalyst (0.2-0.3 mol %) and cocatalyst (0.5-0.75 mol %) loadings, which is otherwise difficult to achieve. It was observed that all the substrates (aromatic and aliphatic), irrespective of their sizes, showed conversion percentage >99%. In the cyanosilylation reaction, a conversion of 96% was obtained with 1.5 mol % of 1 at room temperature for 12 h. This framework emerged as an excellent recyclable catalyst for both the reactions.

Investigation of the effect of SiC additions on the high-temperature oxidation behavior of combustion-synthesized MoSi2

In this study, the effect of the weight percentage of SiC on the high-temperature oxidation behavior of MoSi2-Xwt. % SiC composite (X = 0, 10, 20, 30) was studied. The composites were produced from elemental powder compacts of molybdenum, silicon and carbon (where applicable) by combustion synthesis and subsequent sintering method. Additionally, a series of each synthesized powder was mixed with 5 wt% bentonite and consequently sintered. The sintered specimens were then subjected to oxidation at 1100 °C. Microstructure and phase analysis of the oxidized samples were investigated by X-ray diffraction (XRD) and a scanning electron microscope equipped with energy-dispersive spectroscopy (SEM-EDS). Surface and cross-sectional examinations of the samples after oxidation revealed that all samples possessed good oxidation resistance in the way that no spallation was observed between the oxide layer and the substrate. The highest oxidation resistance at 1100 °C was observed in the sample with MoSi2 (without SiC) containing bentonite (AB0). This sample showed only 0.75% weight gain after 50 h of oxidation, which is probably due to the effective role of bentonite in decreasing the open porosities, and further reducing the oxygen penetration path during the oxidation process.

Analysis of initial stage of liquid-phase sintering by combined multi-phase-field/discrete-element method

A combined multi-phase-field/discrete-element method in two dimensions is applied to the liquid phase sintering process of blended elemental powders. The boundary migration, diffusion of elements, and phase transformation between two dissimilar particles are calculated using a multi-phase-field method for sintering based on Gibbs energy functions. The sintering shrinkage is computed with the discrete-element method taking account of the neck size and sintering force, which are obtained from a multi-phase-field simulation. In this study, a pair or small cluster consisting of two elemental powders in a binary eutectic alloy is used as a model system. First, the formation of a liquid phase around the contact area between two dissimilar particles above the eutectic temperature of the system, and the motions of the particles due to grain boundary sliding along the liquid films are confirmed. Second, an Sn–Bi system is selected as the real eutectic system, and the sintering behavior of powder compacts with various mixing ratios of Sn and Bi particles is demonstrated. Finally, transient liquid-phase sintering of Sn–Bi system is simulated, that is, the generation and extinction of the liquid phase due to interdiffusion between Sn and Bi particles are calculated.

Multi-Scale Cu-Cr Composites Using Elemental Powder Blending in Laser Powder-Bed Fusion

Cu-Cr-based alloys are good candidates for thermo-electrical applications because of their excellent combination of mechanical, thermal, and electrical properties. However, tailoring their microstructure via traditional processes such as sintering and casting remains a challenging task. Herein, we introduce a strategy to fabricate multiscale Cu-25Cr composites. This is achieved through in-situ alloying from elemental powder blending in laser powder-bed fusion. The process is monitored layer-by-layer using synchrotron X-ray microtomography. We show that by changing the melt-pool size and its overlap, one can produce multiscale Cu-Cr composites with coarse (∼50µm) and fine Cr-spheroids (<500 nm) while controlling their spatial distribution. Coarse Cr particles are preferentially located at the melt pool boundaries while fine spherical Cr particles are distributed in the melt pool interior. Spatial variations in mechanical properties are revealed using nanoindentation mapping. This strategy opens new opportunities to optimize multiscale metal matrix composite through the manipulation of the scanning strategy.

Mekanik alaşımlama ile üretilen Al4.5Cu/TiO2 kompozitlerinin mikroyapı, sertlik ve termal özellikleri

Al4.5Cu/TiO2 composites were fabricated from their elemental powders by the mechanical alloying method. Microstructural and thermal properties of the composites were investigated by a combination of differential thermal analysis (DTA), scanning electron microscopy with energy dispersive X-ray detection (SEM-EDX), and X-ray diffraction (XRD). Microstructural evolutions, phase transformations, and crystallite size changes were investigated depending on the milling time. XRD and SEM results showed that there were a more homogeneous structure and shrinkage in grain size due to the increased milling time. The DTA results showed an endothermic peak of around 650 oC which indicates the melting temperature of Al. Besides, the mechanical properties of the pressed and sintered composites were investigated by Vickers micro-hardness testing. The results showed that microhardness values significantly increased as milling time increased from 5h to 10h. The maximum microhardness value of 173±10 HV was obtained for Al4.5Cu with 20 wt% TiO2 composite after milling for 10h.

Ni(II)-Metal-organic framework based on 3,3′-di(1H-imidazol-1-yl)-1,1′-biphenyl: Synthesis, structure and luminescence detection

A new metal–organic framework material [Ni(L)(pda)(H2O)2]•2H2O (1) was synthesized by a solvothermal reaction of 3,3′-di(1H-imidazol-1-yl)-1,1′-biphenyl (L) and 1,4-Phenylenediacetic acid (H2pda) with Ni(NO3)2·6H2O. Crystal properties were characterized by elemental analysis (ER), infrared spectroscopy (IR), thermogravimetric analysis (TGA), and powder X-ray diffraction (PXRD), and it was found that 1 has excellent thermal and structural stability. Furthermore, through fluorescence luminescence experiments, 1 exhibits excellent recognition performance for antibiotics, Fe3+, Cr(Ⅵ) and acetone molecules, which has potential application value.

Continuous synthesis of high-entropy alloy nanoparticles by in-flight alloying of elemental metals

High-entropy alloy (HEA) nanoparticles (NPs) exhibit unusual combinations of functional properties. However, their scalable synthesis remains a significant challenge requiring extreme fabrication conditions. Metal salts are often employed as precursors because of their low decomposition temperatures, yet contain potential impurities. Here, we propose an ultrafast (< 100 ms), one-step method that enables the continuous synthesis of HEA NPs directly from elemental metal powders via in-flight alloying. A high-temperature plasma jet ( > 5000 K) is employed for rapid heating/cooling (103 − 105 K s−1), and demonstrates the synthesis of CrFeCoNiMo HEA NPs ( ~ 50 nm) at a high rate approaching 35 g h−1 with a conversion efficiency of 42%. Our thermofluid simulation reveals that the properties of HEA NPs can be tailored by the plasma gas which affects the thermal history of NPs. The HEA NPs demonstrate an excellent light absorption of > 96% over a wide spectrum, representing great potential for photothermal conversion of solar energy at large scales. Our work shows that the thermal plasma process developed could provide a promising route towards industrial scale production of HEA NPs.

Additive manufacturing of defect-free TiZrNbTa refractory high-entropy alloy with enhanced elastic isotropy via in-situ alloying of elemental powders

Laser powder-bed fusion (L-PBF) additive manufacturing presents ample opportunities to produce net-shape parts. The complex laser-powder interactions result in high cooling rates that often lead to unique microstructures and excellent mechanical properties. Refractory high-entropy alloys show great potential for high-temperature applications but are notoriously difficult to process by additive processes due to their sensitivity to cracking and defects, such as un-melted powders and keyholes. Here, we present a method based on a normalized model-based processing diagram to achieve a nearly defect-free TiZrNbTa alloy via in-situ alloying of elemental powders during L-PBF. Compared to its as-cast counterpart, the as-printed TiZrNbTa exhibits comparable mechanical properties but with enhanced elastic isotropy. This method has good potential for other refractory alloy systems based on in-situ alloying of elemental powders, thereby creating new opportunities to rapidly expand the collection of processable refractory materials via L-PBF.

Features of Microstructural Evolution and Corrosion Behavior of Ti6Al4V Titanium Alloy Fabricated from Elemental Powder Blends

Sintered Ti6Al4V titanium alloys prepared from TiH2/60Al40V powder blends under various technological conditions were studied. The microstructural evolution was investigated by X-ray diffraction, scanning electron microscopy, optical microscopy, and energy dispersive X-ray analysis. The corrosion resistance of sintered titanium alloy was evaluated by the static immersion test in 40 wt.% H2SO4 acid, according to ASTM standard G31-72(2004). Depending on powder metallurgy processing parameters (compaction pressure or sintering temperature), the Ti6Al4V alloy was obtained with various structural features (porosity and structural heterogeneity). It was shown that those structural features of sintered Ti6Al4V titanium alloy are a key microstructural factor that determines their corrosion resistance. For instance, an increase in porosity leads to enhanced corrosion resistance. Based on the current research, the optimal manufacturing regimes of powder metallurgy of Ti6Al4V titanium alloy ensure the achievement of characteristics sufficient for practical use in aggressive conditions of the chemical industry were obtained.

Effect of Sintering Temperature on Microstructure Characteristics of Porous NiTi Alloy Fabricated via Elemental Powder Sintering.

To investigate the effect of the sintering temperature on the microstructure characteristics of porous NiTi alloys, two types of porous NiTi alloys with equal atomic ratios were fabricated via elemental powder sintering at 950 °C and 1000 °C. Afterwards, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were collectively applied to investigate the pore characteristics and microstructure of the fabricated porous NiTi alloy. The results show that when the sintering temperature increases from 950 °C to 1000 °C, the average pore size increases from 36.00 μm to 181.65 μm, owing to the integration of these newly formed small pores into these pre-existing large-sized pores. The measured density increases from 2.556 g/cm3 to 3.030 g/cm3, while the porosity decreases from 60.4% to 51.8%. This is due to the occurrence of shrinkage after the sufficient diffusion of atoms. Furthermore, the characterization results confirm that a change in the sintering temperature would not change the phase types within a porous NiTi alloy; namely, the matrix consists primarily of B2 NiTi, with a significant amount of Ni4Ti3 precipitates and a small amount of Ni3Ti precipitates and Ti2Ni precipitates. However, as the sintering temperature increases, the number of Ni4Ti3 precipitates decreases significantly. The formation of a Ni4Ti3 phase in the present study is closely related to the enrichment of Ni content in the matrix owing to the diffusion rate difference between Ni atoms and Ti atoms and the absence of a transient liquid phase (TLP) during the sintering process owing to the relatively low sintering temperature (lower than the eutectic temperature). Moreover, the increasing sintering temperature speeds up the atom diffusion, which contributes to a reduction in the enrichment of Ni as well as the number of formed Ni4Ti3 precipitates.

A Comprehensive Study on Hot Deformation Behavior of the Metastable β Titanium Alloy Prepared by Blended Elemental Powder Metallurgy Approach

A Comprehensive Study on Hot Deformation Behavior of the Metastable β Titanium Alloy Prepared by Blended Elemental Powder Metallurgy Approach

Influence of the sintering method on microstructure and microhardness of AlCuNiSnZn-based high-entropy brasses and bronzes obtained by powder metallurgy

The present report focused on synthesizing and characterizing a series of AlCuNiSnZn alloys obtained by powder metallurgy as a new family of high-entropy brasses and bronzes. The (AlCuNi)80Sn10Zn10 and (AlCuNi)70Sn15Zn15 alloys were obtained by mechanical alloying and sintering, evaluating two sintered methods: high-frequency induction heat and conventional. After 10 h of mechanical alloying, the elemental powder mixture formed solid solutions of face-centered cubic (FCC-α) and body-centered cubic (BCC-β) phases. However, the solid solutions, after sintering, were decomposed into a mixture of γ Ni2Zn11, AlNi, and Cu2Ni3Sn3 phases. The (AlCuNi)80Sn10Zn10 system sintered by high-frequency induction heat exhibits a microhardness value of ∼501 HV±17, while that obtained by the conventional method was ∼320 ± 21 HV. The results showed that it is convenient to maintain the BCC/FCC solid solutions after sintering due to their stability and properties. In addition, it is necessary to design alloys with lower values of ΔHmix to improve the microhardness.

Deposition of NiAl/Al3Ni2(CrB2) Coatings from Ni, Al and CrB2 Powders Using Mechanical Synthesis in Planetary Ball Mill.

Interest in composite thick coatings with an intermetallic matrix stimulates the development of new deposition techniques like the co-milling of pre-alloyed NiAl powder with platelet-shaped substrates. Obtained coatings were up to several micrometers thick as cold-welding of intermetallic particles was effective only at the start of this process, while later, chipping prevailed over added material. The present experiment covered the co-milling in the planetary ball mill of Ni and Al elemental powders (1:1 molar ratio) with AISI 304 steel platelets for 32 h at 300 rpm. Next, this process was repeated with an admixture of 15 wt.% of CrB2 powder. In both cases, their milling succeeded in producing up to a 200 μm coating after 4 h. The use of light, scanning and transmission electron microscopy (LM/SEM/TEM) helped to establish that the coatings had gradient microstructures with more refined crystallites of NiAl, Al3Ni2 and CrB2 closer to the surface. With the addition of a ceramic phase, the coatings presented higher hardness and lower friction during dry wear tests both at RT and at 500 °C.