Mechanical Alloying Technique Research Articles

Effect of Mechanical Alloying on Structural and Electrical Properties of (P<sub>2</sub>O<sub>5</sub>)<sub>(x)</sub>-(Y<sub>2</sub>O<sub>3</sub>)<sub>(0.03)</sub>-(ZrO<sub>2</sub>)<sub>(0.97)</sub> Electrolyte

Pentavalent phosphorous oxide doped yttria-stabilized zirconia (P2O5)X-(Y2O3)0.03-(ZrO2)0.97 with x=0.06 mol.% was achieved via an economical technique using mechanical alloying (MA) technique. Three types of nanocomposite powders of electrolyte were produced by high-energy ball milling with different milling times. The phases of synthesized electrolyte powders and sintered electrolytes were illustrated by X-ray diffraction (XRD). The average particle sizes of powders indicated around (360, 245, and 48) nm at milling duration (1, 10, and 45) hrs, respectively. The XRD analysis results of 1 h MA electrolyte powder obtained tetragonal ZrO2, while the 45 h MA electrolyte manifested a minority phase of monoclinic ZrO2. Then, the XRD of the sintered electrolyte with the optimum electrical properties appeared two phases. The major phase of the tetragonal zirconium yttrium oxide and a minor phase was a monoclinic zirconium oxide. The average grain sizes of the three types of the sintered manufacturing electrolytes were (7.638, 2.642, and 1.245 µm) after the mechanical alloying duration of (1, 10, and 45) hrs, respectively and sintered at 1873 °K. The DC conductivity (σ) studied corresponded to the influence of milling times on the microstructure for each sintered electrolyte. From the results, the synthesized sintered electrolyte with a long MA duration gave a maximum DC (σ) 1.03E-1S.m. And, the DC conductivity (σ) was 1.11E-02 of electrolyte produced with 10 hr mechanical alloying. Otherwise, the lower DC conductivity got with the electrolyte prepared in the lowest milling duration was 8.9 E-2 S.m.

Design and development of Co35Cr5Fe20−xNi20+xTi20 High Entropy Alloy with excellent magnetic softness

The design and development of excellent soft magnetic materials are fascinating research areas in materials science. A series of Co35Cr5Fe20−xNi20+xTi20 (x = 5, 10, 15) High Entropy Alloys (HEAs) were synthesized through mechanical alloying (MA) technique and heat-treated at two different temperatures at 200 °C and 700 °C for 2 h. The XRD analysis confirmed that the HEAs comprised of face-centered cubic (fcc) phase and a minor fraction of an intermetallic R-phase at as-synthesized and annealed state. SEM-EDS observation confirmed the homogeneous compositional distribution and showed that after annealing at 700 °C, tiny spherical particles precipitated over the large grains. The synthesized HEAs showed soft magnetic behavior with low coercivity (12–16 Oe). However, the coercivity decreased more than five times to the initial value after the annealing at 700 °C. Co35Cr5Fe10Ni30Ti20 HEA annealed at 700 °C shows excellent soft magnetic properties with a high value of Ms (78.01 emu/g) and an extremely low value of Hc (1.7 Oe). The found value of the coercivity is the lowest value of the coercivity reported so far for the case of magnetic CoCrFeNiTi based HEAs. In addition, the present work provides a novel design strategy for the development of magnetic HEAs with excellent magnetic softness.

High-Pressure Torsion for Synthesis of High-Entropy Alloys

High-pressure torsion (HPT) is widely used not only as a severe plastic deformation (SPD) method to produce ultrafine-grained metals but also as a mechanical alloying technique to synthesize different alloys. In recent years, there have been several attempts to synthesize functional high-entropy alloys using the HPT method. In this paper, the application of HPT to synthesize high-entropy materials including metallic alloys, hydrides, oxides and oxynitrides for enhanced mechanical and hydrogen storage properties, photocatalytic hydrogen production and high light absorbance is reviewed.

Processing, microstructure and mechanical properties of Ni1.5CoFeCu0.8Al0.2V0.5 high entropy alloy matrix composites reinforced by in-situ synthesized vanadium carbides

Three in-situ synthesized vanadium carbides (in the volume fraction of 5%, 10% and 15%, respectively) reinforced Ni1·5CoFeCu0·8Al0·2V0.5 high entropy alloy (HEA) matrix composites were prepared by adding V and C in equal molar ratio using mechanical alloying and spark plasma sintering techniques. The formation and evolution of vanadium carbide reinforcements as well as their influences on the microstructure and mechanical properties of HEA matrix composite were investigated intensively. The results show that after milling of 70 h part of V and C from raw materials reacted incompletely through the mechanism of solid-state diffusion at the interface, resulting in the generation of V2C and [VC] in the composite powders. Subsequently, owing to the enhanced atomic diffusion during sintering V2C in the intermediate state was further carbonized into [VC] and partial [VC] was transformed to ordered V8C7 in the consolidated composites. The addition of 5 vol% and 10 vol% vanadium carbides resulted in the significant refinement of grains in the HEA matrix due to the grain boundary pinning effect induced by in-situ generated fine reinforcements. However, grains of the composite containing 15 vol% vanadium carbides are coarser than those of the base HEA due to the serious agglomeration of in-situ synthesized reinforcements. With the increase of vanadium carbides content, mechanical properties of the HEA matrix composite do not change monotonously. The composite reinforced by 10 vol% vanadium carbides performs best among the three and its yield strengths at room temperature, 500 °C, 600 °C and 700 °C are about 1.2, 1.4, 2 and 2.5 times, respectively, than those of the base HEA. The improvement in mechanical properties of composite are attributed to grain boundary strengthening and dispersion strengthening caused by in-situ synthesized vanadium carbide nanoparticles.

Ultrastrong nanocrystalline oxide-dispersion-strengthened ferritic alloy with exceptional thermal stability

As structural materials candidates of advanced fission and future fusion reactors, oxide-dispersion-strengthened (ODS) alloys, which are often ultrafine-grained (with a grain size between 100 and 1000 nm), have attracted widespread interest in past decades. However, fabrication of fully dense bulk nanocrystalline ODS alloys has rarely been reported. In this work, a novel Zr-doped nanocrystalline 14YWTZ ferritic ODS alloy (Fe–14Cr–3W-0.4Ti-0.8Zr-0.3Y2O3) was prepared by mechanical alloying and high-pressure consolidation techniques. The high consolidation pressure (4 GPa) endows the bulk nanocrystalline 14YWTZ alloy with a nearly full relative density (~99.5%) and a reasonable tensile elongation. The consolidated nanocrystalline 14YWTZ alloy with an average grain size of ~50 nm shows an ultra-high compressive yield strength of ~2641 MPa. Besides, the alloy exhibits an exceptional thermal stability, i.e., limited grain growth occurs after annealing at a high temperature of 1000 °C. After hot rolling, the alloy retains nanocrystalline microstructures and exhibits an unprecedented tensile yield strength of 2730 MPa, far exceeding those of previous reported ferritic ODS alloys. The high thermal stability of the annealed nanocrystalline 14YWTZ alloys can be ascribed to the combined effects of the thermodynamic multicomponent co-segregation to grain boundaries and strong kinetic Zener pinning by high-density Zr–Ti–Y–O-enriched nanoparticles with an average particle size of ~3.18 nm and a high number density of ~3 × 1024 m−3. The outstanding strength of the present nanocrystalline 14YWTZ alloys primarily originates from the Hall-Petch strengthening of the nanocrystalline matrix, distinguishing them from conventional ODS alloys strengthened by dislocation forest and/or dispersed oxide nanoparticles.

A comprehensive exploration on the development of nano Y2O3 dispersed in AA 7017 by mechanical alloying and hot-pressing technique

The main objective of the present study is to develop AA 7017 alloy matrix reinforced with yttrium oxide (Y2O3, rare earth element) nanocomposites by mechanical alloying (MA) and hot pressing (HP) techniques for armor applications. AA 7017+10 vol % Y2O3 nanocomposites were synthesized in a high-energy ball mill with different milling times (0, 5, 10, and 20 h) to explore the structural refinement effect. The phase analysis and homogeneous dispersion of Y2O3 in AA 7017 nanocrystallite matrix were investigated by X-ray diffraction (XRD), various electron microscopes (HRSEM, and HRTEM), Particle Size Analyzer (PSA), and Differential Thermal Analysis (DTA). The nanostructured powders were hot-pressed at 500 MPa pressure with a temperature of 673k for 1hr. The consolidated sample results revealed significant grain refinement and the enhanced mechanical properties with the function of milling time in which the 20h sample exhibited improvement in the hardness (142 VHN - 260 VHN) and ultimate compressive strength (514 MPa–906.45 MPa) due to effective dispersion of Y2O3. The various strengthening mechanisms namely, grain boundary (27.02–32.69 MPa), solid solution (57.21 MPa), precipitate (189.79–374.62 MPa), Orowan (135.68–206.92 MPa), and dislocation strengthening (84.99–149.82 MPa) were determined and correlated to the total strength.

The effects of structural integrity of graphene on the thermoelectric properties of the n-type bismuth-telluride alloy

This study examines the effects of the structural integrity of graphene on the thermoelectric properties of n-type bismuth telluride alloy. Graphene/Bi2Te2.7Se0.3 composites were prepared via mechanical alloying and spark plasma sintering techniques. Different graphene concentrations (0.05 and 0.5 wt%) and addition times (20 hrs, 10 mins, and 1 min) were considered. The thermoelectric properties were measured, and the results showed that the milling time affects graphene structure as well as its agglomeration. It is revealed that the optimum time to add the two-dimensional filler is during the last phase of mechanical milling as it will preserve graphene’s structure and boost the electrical conductivity. It is also shown that as the milling time of graphene increases, the Seebeck coefficient improves. Even though an increase in the thermal conductivity is expected due to the high electrical conductivity, a clear reduction in the lattice thermal conductivity part was obtained due to the increased scattering at the new interfaces. The figure-of-merit for the optimum sample with 0.05 wt% graphene added in the last 10 mins of milling had an improvement of 19% at room temperature reaching a value of 0.5, and 25% at 160 °C achieving a final value of 0.81.

Enhanced ablation resistance of HfB2-HfC/SiBCN ceramics under an oxyacetylene torch environment

To further improve the ablation resistance of SiBCN ceramics, nanosized HfB2 was introduced by mechanical alloying and subsequent reactive hot-pressing techniques to fabricate HfB2-HfC/SiBCN multiphase ceramics. The mass and linear ablation rates of the 30 vol% HfB2-HfC containing SiBCN ceramics under an oxyacetylene flame for 10 s were lower than those of ZrB2-ZrN/SiBCN and SiBCN, reaching to 0.0025 mg/s and 0.0004 mm/s respectively. Even ablated for 60 s, no trace of cracks appeared on the ablation surface. Oxidation of ceramic matrix, denudation of oxides, erosion by the combustion flow and the re-oxidation of the exposed matrix governed the ablation process.

Effect of vanadium doping on the electrical charge transport and dielectric relaxation properties of Sodium Bismuth Titanate perovskite

In this work, we report the effect of vanadium doping on the conductivity and relaxation dynamics of the charge carriers in Sodium Bismuth Titanate perovskite material (Na0.5Bi0.5TiO3) prepared by a unique technique which is a combination of chemical and mechanical methods. The parent material was prepared using the citrate auto-ignition method and the mechanical alloying technique was used to incorporate V2O5 in the NBT structure. The X-ray diffraction analysis confirmed the formation of the rhombohedral phase of NBT perovskite with space group R3c in all the compositions. The microstructural analysis was done using Field Emission Scanning Electron Microscopy, Energy-dispersive X-ray spectra, and the elemental mapping of the samples. The conductivity mechanism was analyzed using the complex impedance method. The sample with 15% doping showed the highest conductivity with minimum activation energy. The activation energies for conduction, relaxation, and migration of charge carriers were found to be comparable with each other. The frequency-dependent dielectric data was analyzed using Havriliak–Negami (HN) formalism and suggested non-Debye type relaxation behaviour. The 15% dopped composition showed the highest dielectric strength. The scaling behaviour of impedance and modulus spectra confirmed the temperature-independent conduction and relaxation mechanisms.

Remarkable improvement in high temperature oxidation resistance of WC-12Co by the addition of CrSi2

WC-Co has excellent mechanical properties at a temperature below 700 °C, but above it, the mechanical properties of WC-Co decrease severely because of the oxidation effect. In the present study, the addition of metal silicide of CrSi2 was considered to enhance the oxidation resistance of cementite carbide. The WC-12Co compacts containing 0, 12.5, and 25 wt% CrSi2 were prepared using mechanical alloying and spark plasma sintering techniques at 1150 °C. According to the results of metallographic characterization, the sintered WC-12Co is composed mainly of WC and Co phases. The addition of CrSi2 leads to the formation of new phases as CrSi, CoSi, Co6W6C, and SiC depending on the compact composition. It is found that the WC-12Co compact with 12.5 wt% CrSi2 content exhibits a lower measured density and higher hardness compared to that of CrSi2-free compact. After the first cycle of exposure at 900 °C, the WC-12Co is severely oxidized, forming porous and crack oxide scales. On the contrary, the addition of 12.5 wt% CrSi2 shows the lowest mass gain and displays the most resistance to oxidation attributed to the formation of mainly SiO2 scales. Further increase in CrSi2 concentration, however, the alloy compact experiences breakaway oxidation after the fifth cycle of exposure. Accordingly, it can be proposed that the addition of 12.5 wt% CrSi2 is the most promising composition to allow the cemented carbide used at high temperatures and oxidizing atmospheres.

Magnetic, optical, structural and thermal properties of copper ferrite nanostructured synthesized by mechanical alloying

CuFe2O4 spinel nanostructured were elaborated by mechanical alloying technique from Cu, Cu2O and Fe2O3 under controlled atmosphere with different milling times at room temperature. The CuFe2O4 spinel crystalline has a body-centred tetragonal structure at low temperatures with lattice parameters a ≅ 0.582 nm and c ≅ 0.869 nm and face-centred cubic structure at high temperatures with lattice parameter a ≅ 0.842 nm. The average crystallite size and lattice strain determined from X-ray diffraction for CuFe2O4 are 22.12 ± 5.47 nm and 0.781 ± 0.082 %, respectively. The FTIR-ATR spectra of the samples shows that the vibration around of 400–1000 cm−1 corresponds to the CuFe2O4 absorbed at octahedral and tetrahedral sites. The mechanical alloying process results in CuFe2O4 agglomerated in clusters, which radically change their shape during milling time. Differential scanning calorimetry analysis shows two additional endothermic peaks around 715–781 °C and 863–957 °C, the first peak might be affected to the formation of Cu-Fe-O and the second peak may correspond to the transformation of CuFe2O4 from tetragonal to cubic structure. CuFe2O4 samples milled until 20 h are ferromagnetic at room temperature with saturation magnetization increasing from 29.8 to 59.6 emu/g with increasing the milling time. The coercivity decreases 254 Oe up to 230 Oe when the milling time increases from 0 to 20h.

Microstructure and oxidation behavior of an Al–Ni–Cr–Cu–MoO3–SiO2 composite coating on low-carbon steel

In the present study, an Al–Ni–Cr–Cu–MoO3–SiO2 composite coating with varying elemental compositions was deposited using the mechanical alloying technique. The composite coating structure before and after an oxidation test was studied using X-ray diffraction (XRD), three-dimensional optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). A cyclic oxidation test was conducted in an 800 °C air atmosphere for 10 cycles (200 h). Based on the XRD, SEM, and EDX analyses, the coating comprised composite-refined Al, Ni, Cr, and Cu particles as well as coarse SiO2 particles. The composite coating had a thickness in the range of 36–59 μm, with good and continuous adherence to the substrate. The cyclic oxidation curve of the composite coating followed a parabolic rate law. The sample that contained 5.3 wt% MoO3 showed the best oxidation resistance after 10 oxidation cycles at 800 °C. This sample had a lower mass gain than the other samples. Moreover, this sample had a Kp of 1.2 × 10−3 mg2/cm2·s. Protective Al2O3 oxides formed on the composite coating surface with a thickness of 0.75–1.89 μm. This oxide scale was dense and fully adhered to the coating, thereby improving oxidation resistance.

Production of Al based Composites Reinforced with FeAl Intermetallic Particles by Mechanical Alloying

In this research project, Al matrix composite materials reinforced with 5 and 10 (wt.%) of FeAl intermetallic particles were synthesized by Mechanical Alloying (MA) at a speed of 250 RPM for 2, 5, 10 and 15 h of milling time. The results showed that composite materials can be obtained at low energy conditions with improved dispersion of the reinforcement in the Al matrix compared to those obtained by conventional techniques. The composites powders obtained by mechanical alloying at different milling times were studied by Scanning Electron Microscopy (SEM) in order to characterize the morphology and particle size. X-Ray Diffraction (XRD) was used to study the structural evolution of the system as the initial powders were subjected to different milling times, thus obtaining the evolution of the present phases, changes in lattice parameters and crystallite size. This work demonstrates the viability of the MA technique to produce composite materials with a homogenous distribution of the reinforcement particles with a great degree of control in the process, which would be very difficult to reproduce by conventional synthesis methods.

Composite and Surface Functionalization of Ultrafine-Grained Ti23Zr25Nb Alloy for Medical Applications.

In this study, the ultrafine-grained Ti23Zr25Nb-based composites with 45S5 Bioglass and Ag, Cu, or Zn additions were produced by application of the mechanical alloying technique. Additionally, the base Ti23Zr25Nb alloy was electrochemically modified in the two stages of processing: electrochemical etching in the solution of H3PO4 and HF followed by electrochemical deposition in Ca(NO3)2, (NH4)2HPO4, and HCl. The in vitro cytocompatibility studies were also done with comparison to the commercially pure titanium. The established cell lines of Normal Human Osteoblasts (NHost, CC-2538) and Human Periodontal Ligament Fibroblasts (HPdLF, CC-7049) were used. The culture was conducted among the tested materials. Ultrafine-grained titanium-based composites modified with 45S5 Bioglass and Ag, Cu, or Zn metals have higher biocompatibility than the reference material in the form of a microcrystalline Ti. Proliferation activity was at a stable level with contact with studied materials. In vitro evaluation research showed that the ultrafine-grained Ti23Zr25Nb-based composites with 45S5 Bioglass and Ag, Cu, or Zn additions, with a Young modulus below 50 GPa, can be further used in the biomedical field.

Synthesis of Ni-Cr-B-Si-Fe-based interlayer alloy for transient liquid phase bonding of Inconel 718 superalloy by mechanical alloying process

A Ni-Cr-B-Si-Fe-based filler alloy powder has been synthesized by mechanical alloying technique in a high-energy ball mill to join Inconel 718 (IN 718) by transient liquid phase (TLP) bonding. The structural analysis of the synthesized alloy powders was done by field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), field emission transmission electron microscope (FETEM), and laser particle size analyzer (LPSA). Thermal characterization was done by differential scanning calorimetry (DSC). The particle size of 60-h milled powders was found to be 15.4 μm and exhibits equiaxed shapes. Analysis of results reveals that during the milling process, elemental powder mixture gradually transforms to a nano-crystalline non-equilibrium face-centered cubic structured (FCC) Ni (Cr, Fe, Si, B) solid solution alloy. For the powder after 60-h milling, the crystallite size measured by XRD was found to be 4.0 nm. The lattice constant of nickel in the milled powder mixture decreased up to 5 h of milling and increased with a further increase in milling time. Dissolution of Si, B, Cr, and Fe into the Ni matrix resulted in the change of lattice constant of the alloy powder. The DSC result of 60-h milled powders reveals an endothermic peak at 1023.5 °C, which is attributed to the melting of the alloy powder. The activation energy of the milled powder reduced with milling time; as a result, the diffusivity of the elements in the filler metal increased. The activation energy of the 60-h milled alloyed powders was found to be 2714.67 KJ/mol. IN 718 superalloy was joined by the TLP bonding process. The microstructure of the TLP-bonded IN 718 joints showed three distinct zones in the bond area. Increasing the bonding temperature from 1050 to 1100 °C resulted in a 21% increase in the shear strength of TLP-bonded IN 718 alloy.

Desorption properties of mechanically milled MgH2 with double catalysts Ni and SiC

The study of the MgH2 double-catalyzed Ni and SiC based storage system has been done. The objective of this study is to improve the hydrogen desorption temperature and the hydrogen desorption capacity. The material preparation was done through mechanical alloying technique. In this method, the milling of the material was carried out within 5 hours, 10 hours and 15 hours, with the ratio of the ball to the powder was and the speed of 350 rpm with the catalyst insertion catalyst by 5 wt% and 10 wt% SiC. Results from XRD measurements revealed that the sample was successfully reduced to a nanocrystal scale. The phase emerging from the XRD observation is the phase MgH2 as the main phase and followed by Ni and SiC phase as the minor phase. From the observation with SEM showing irregular particle shape, the particle size in the sample is not homogeneous because of the agglomeration effect and cold welding that causes the particle size to look large. The hydrogen release capacity was obtained in the samples which were milled for 10 hours at the weight of 5 wt% Ni-SiC catalyst with the release of 2.6 wt%. Based on observation with thermogravimetric analyzer (TGA), the lowest temperature was obtained in the samples which were milled 10 hours with catalyst 5 wt% SiC, which was 365 °C.

Effect of graphene nanoparticles on the physical and mechanical properties of the Al2024-graphene nanocomposites fabricated by powder metallurgy

Recently, a growing interest has been dedicated towards improving the properties of Al alloys for use in various industrial applications. In this sense, mechanical alloying technique followed by sintering process at 460 and 560 °C in argon atmosphere was used to prepare Al2024 alloy matrix nanocomposites-reinforced by different graphene contents up to 2 wt%. Both XRD technique and TEM were employed to characterize the prepared nanocomposites powders. Microstructure analysis was performed on the sintered composites using SEM. Moreover, the relative density, corrosion rate, thermal expansion and electrical properties of the sintered nanocomposites were measured. Furthermore, their mechanical properties were measured with ultrasonic non-destructive technique. SEM and TEM micrographs revealed a uniform distribution of graphene in the Al alloy matrix. The relative density, coefficient of thermal expansion (CTE) and electrical conductivity of the specimens sintered at 460 °C decreased until reached 90.9%, 13.6 × 10−6/°C and 8.41 × 105 S/m, respectively as the graphene content increased to 2 wt%, while they increased to 93.8%, 1.5 × 10−6/°C and 4.20 × 106 S/m as the sintering temperature increased to 560 °C. On the other hand, the mechanical properties of the nanocomposites such as microhardness, elastic modulus and yield strength were enhanced to 155, 134 and 97%, respectively after adding 2 wt% graphene and sintering at 560 °C. Additionally, the corrosion rate decreased from 5.74 to 2.73 and 5.34 to 2.59 for the sample having 2 wt% graphene and sintered at 460 and 560 °C with increased the exposure from 24 to 144 h, respectively.

The Effect of Ball Size on Hardness of Mechanically Alloyed Al-10wt.%Ti Powders

Particle size and hardness of Al-10%wt.Ti powders due to the influence of ball diameter have been carried out using mechanical alloying techniques. The milling device used consisted of a Fritsch Pulverisette-5 planetary type ball mill with the rotational speed of about 360 rpm and balls size of 10, 15 and 20 mm. The materials used are stearic acid which was used as a process control agent, aluminum and titanium powders. A mixture of aluminum and titanium powders has the composition of Al-10wt.%Ti. The Al-10wt.%Ti powders, stearic acid and stainless-steel balls were added to the Fritsch Pulverisette-5 planetary in the argon gas environment. The weight ratio of stainless steel balls to the Al-10wt.%Ti powder was 20 : 1. The mixing time process was carried out for 5, 10, 15, 20 and 30 hours, respectively. Changes in phase compositions of these Al-Ti powders under different ball mill sizes were examined by XRD, and the optimum experimental parameter was obtained: the ball mill size was 20 mm. It was found that from the diffraction patterns of the Al-10wt.%Ti powders, the peaks of titanium begin to disappear with the increasing of the milling time, which indicates the increasing degrees of alloying of titanium atoms in the aluminum matrix. The microhardness test results showed that the hardness increases with increasing ball size.

Crystal Structure and Colorimetric Behavior of Low Melting Point Ternary Alloy

Elements of high purity (99.999) ,were used to prepare the alloy , Bi ,Sn,Zn and Cu .Two types alloy Bi – Sn – Zn and Bi – Sn – Cu were prepared by mechanical alloying technique (MA) .Annealing at 100 °Cfor 8 hours was applied for the resulting alloys . X-ray diffraction and differential scanning colorimetriy were tested for the two types of alloy before and after annealing. The best results was noticed in the ternary alloythat prepared at 4 hours milling time ,and annelid at 100 °C, for 8 hours ,under static air.

Optimal performance of Cu1.8S1\u2212xTex thermoelectric materials fabricated via high-pressure process at room temperature

Cu1.8S has been considered as a potential thermoelectric (TE) material for its stable electrical and thermal properties, environmental benignity, and low cost. Herein, the TE properties of nanostructured Cu1.8S1−xTex (0 ⩽ x ⩽ 0.2) bulks fabricated by a facile process combining mechanical alloying (MA) and room-temperature high-pressure sintering (RT-HPS) technique were optimized via eliminating the volatilization of S element and suppressing grain growth. Experimentally, a single phase of Cu1.8S was obtained at x = 0, and a second Cu1.96S phase formed in all Cu1.8S1−xTex samples when 0.05 ⩽ x ⩽ 0.125. With further increasing x to 0.15 ⩽ x ⩽ 0.2, the Cu2−zTe phase was detected and the samples consisted of Cu1.8S, Cu1.96S, and Cu2−zTe phases. Benefiting from a modified band structure and the coexisted phases of Cu1.96S and Cu2−zTe, the power factor is enhanced in all Cu1.8S1−xTex (0.05 ⩽ x ⩽ 0.2) alloys. Combining with a drastic decrease in the thermal conductivity due to the strengthened phonon scatterings from multiscale defects introduced by Te doping and nano-grain boundaries, a maximum figure of merit (ZT) of 0.352 is reached at 623 K for Cu1.8S0.875Te0.125, which is 171% higher than that of Cu1.8S (0.130). The study demonstrates that doping Te is an effective strategy to improve the TE performance of Cu1.8S based materials and the proposed facile method combing MA and RT-HPS is a potential way to fabricate nanostructured bulks.