Mechanical Alloying Research Articles

Effect of sintering temperature on microstructure and mechanical properties of Ti2AlNb-based composites

Ti2AlNb-based composites are a great choice for achieving high-temperature properties by introducing reinforcement to meet engineering application requirements. In this study, Ti–22Al–25Nb (at.%) alloys and nano-Al2O3/Ti–22Al–25Nb composites were prepared by mechanical alloying (MA) and hot pressing (HP). The effects of sintering temperature on the microstructure and mechanical properties of Ti–22Al–25Nb alloys and Ti2AlNb-based composites were investigated. The sintering temperature effectively regulated the morphology and size of the primary O phase. The addition of Al2O3 particles refined the grain size of the matrix and precipitates, and it induced the phase transformation. When the sintering temperature reached 1350 °C, Ti–22Al–25Nb alloys and Ti2AlNb-based composites obtained a fine and uniform equiaxed microstructure. The hardness and ultimate compressive strength of the composite first increased and then decreased with increasing sintering temperature. Since the addition of Al2O3 particles promoted the precipitation of the ultrafine acicular O phase from the B2 phase, the composite sintered at 1350 °C had the optimal mechanical properties. The hardness of the Ti–22Al–25Nb alloy and Ti2AlNb-based composite was 4.12 GPa and 5.1 GPa, respectively. The ultimate compressive strength of the composite at room temperature (RT) and 650 °C was 2642.3 MPa and 2462.5 MPa, which was 25.8% and 9.6% higher than that of the Ti2AlNb alloy. The strengthening mechanism of the composites mainly includes dispersion strengthening and Orowan strengthening of the nano-Al2O3 particles, as well as precipitation strengthening of the acicular O phase. This study provides a theoretical guidance for designing Ti2AlNb-based composites with excellent high-temperature properties.

Synthesis of nanostructured titanium carbide (TiC) from bitumen coke by mechanical alloying process

AbstractThis study explored synthesizing titanium carbide (TiC) from bitumen coke using mechanical alloying. Initially, raw bitumen coke (5.9 wt.% sulphur) from delayed coking was desulphurized to produce low sulphur coke with a sulphur content of 0.2 wt.% for comparison purposes. Both high and low sulphur coke samples were mechanically alloyed with titanium (Ti) powder in a planetary ball mill under various conditions (milling time, milling speed, and ball‐to‐material ratios [BMR]). TiC was successfully produced from both high sulphur and low sulphur coke samples. The formation of TiC was confirmed by X‐ray diffraction (XRD) analysis. The effects of the experimental parameters on the production of TiC were evaluated. The experimental results showed that the high sulphur coke and Ti were converted into TiC after 10 h milling, whereas the low sulphur coke and Ti were converted into TiC much faster (after 5 h milling) at the same milling speed and BMR. Under the same milling time and BMR, the high sulphur coke and Ti were converted into TiC at 400 rpm, whereas the low sulphur coke and Ti were converted into TiC at 300 rpm. In addition, the high sulphur coke and Ti were converted into TiC when the BMR was 60:1, and the low sulphur coke and Ti were converted into TiC when the BMR was 40:1 under the same milling time and speed. Overall, preliminary results suggest that the conversion of low sulphur coke samples is easier and requires less energy to produce TiC compared to the high sulphur coke samples.

Mechanical properties of high-nitrogen steel produced via selective laser melting using mechanically alloyed and spheroidized powders

In recent years, the development of additive technologies has been one of the priority tasks in the sector. Primarily, additive technologies enable the effective implementation of various design and engineering ideas in high-tech industries, such as the aircraft industry, engine technology, and rocket engineering. The expanded range of standardized materials for additive technologies will facilitate their integration into large-scale production. Of significant interest is the potential use of nitrogen-containing heat-resistant powder alloys to produce complex-shaped aircraft parts using additive technologies. This paper describes the complete process of obtaining samples from powders of alloys with superequilibrium nitrogen content using the selective laser melting (SLM) method. Four different compositions of high-nitrogen steels were obtained through mechanical alloying. Subsequently, the powders of these steels underwent processing using the plasma spheroidization method to be utilized in the SLM process. The SLM method was also employed to produce samples for mechanical tests. Throughout each stage of the process, the powders were thoroughly analyzed. One of the most critical parameters was the nitrogen content in the resulting powders. At each subsequent production stage, its proportion decreased, yet it remained at the superequilibrium content level of 0.13–0.44 wt. %. The mechanical tests confirmed that the alloys fabricated by the SLM method are not inferior in terms of their properties compared to those obtained using classical metallurgical technologies.

Mechanical alloying of AlCoCrFe and AlCoCrFeNi: Design and experimental evaluation of medium- and high-entropy alloy particles for cold spraying

The manufacturability of equiatomic high-entropy alloy (HEA) particles with single- and dual-phase crystal structures using the high-energy mechanical alloying (HE-MA) method was explored in this study. Following a material design-of-experiment (DoE) curriculum, particles were synthesized in a planetary mill. Milling times varied while operating under two distinct HE-MA manufacturing regimes: the conventional approach (simultaneous milling of constituent elements) and the sequential method (progressive milling with the introduction of elements in a specific order). Within the conventional regime, equiatomic AlCoCrFe and AlCoCrFeNi blends were milled, focusing on the influence of incorporating nickel (Ni) as a transient element into the base composition. This led to an equivalent particle size distribution ranging from 5 to 100 μm. Notably, the presence of Ni resulted in an increased fraction of the face-centered cubic (FCC) phase, coupled with a simultaneous reduction in grain and crystallite sizes, thereby enhancing the overall material strength. This knowledge was applied to the design and synthesis of a target equiatomic FeNiCoCrAl HEA system. In this context, individual elements were added to the starting/milled Fe + Ni alloy at four-hour intervals, in line with the sequential milling regimen. The results showed an interesting evolution: the conventionally milled AlCoCrFeNi particles exhibited a dual-phase body-centered cubic (BCC) and FCC structure, with a composition of 55% BCC and 45% FCC phase fractions, while the sequentially milled FeNiCoCrAl particles demonstrated a single-phase BCC structure after 24 h of milling.

Heterogeneous grain structure in biodegradable Zn prepared via mechanical alloying and laser powder bed fusion for strength-plasticity synergy

ABSTRACT This study presented a unique process of mechanical alloying (MA) and laser powder bed fusion (LPBF) to prepare heterogeneous grain structure (HGS) Zn with strength-plasticity synergy. The results showed that the MA-treatment significantly refined the grain sizes of Zn to nano-scale and contributed to the formation of HGS powders. Moreover, the ultra-fast heating and cooling of LPBF process inhibited the grain growth and resulted in a specific core/shell HGS, wherein the cores (micron-grains) were surrounded by interconnected shells (nano-grains). Notably, the prepared HGS Zn demonstrated synergistically improved compressive yield strength (2.1 times) and plasticity (58%) compared with the homogeneous coarse-grained counterparts. This impressive strength-plasticity synergy was primarily attributed to high back stress and dislocation pile-ups generated by the deformation incompatibility between the nano-grained shells and micron-grained cores. These findings open up new fields for MA and LPBF in the preparation of HGS metals and their applications in solving strength-plasticity tradeoff.

Mechano-Synthesis, Structure, and Thermal and Magnetic Behaviors of the New Compound Mn1.2Co0.05Fe0.7P0.45Si0.5B0.05

The Mn1.2Co0.05Fe0.7P0.45Si0.5B0.05 compound has been systematically synthesized by mechanical alloying for 15 h, followed by annealing with two heating cycles at 1373 K for 2 h and 1073 K for 24 h. The powder that was milled for 15 h revealed the main hexagonal-Mn2P-type phase and the minor cubic-Mn3Fe2Si phase through X-ray diffraction examination. After annealing the same powder at 1373 K for 2 h and again at 1073 K for 24 h, the refined phase was the unique (Mn, Fe)2(P, Si) type with a hexagonal structure. For the mechanically alloyed powder, the final crystallite size was approximately 20 nm, and it rose to 95 nm during the annealing process. Further, a large amount of lattice microstrain was achieved as a result of high-energy milling (about 0.75%). Over the whole temperature range of 373 to 923 K, the thermal analysis showed several overlapping exothermic peaks, which indicated the improvement of the microstructure after the structural relaxation and reordering process. Moreover, the Curie temperature of the alloy was retrieved at approximately 675 K. According to an analysis of the magnetic properties, the mechanically alloyed powder exhibited an exceptional soft ferromagnetic state after 15 h of milling, and the annealed alloy showed superparamagnetic characteristics.

Effect of Milling Time on the Structure Stability of FeMnNiCrAl Non-equiatomic High-Entropy Alloy

A non-equiatomic Fe34.9Ni30.2Mn18.6Cr9.3Al7 high-entropy alloy (HEA) was synthesized by mechanical alloying using different milling times. To study the effect of milling time on the structure stability, X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive X-ray spectroscopy were conducted. For comparison, an Al-free alloy (Fe37.5Ni32.5Mn20Cr10) was produced at 25 h milling. XRD indicated a single FCC phase alloy after 5 h milling time and a dual FCC and BCC phase at 25 h milling time. Clearly, it is found that Al addition is not necessarily the main factor leading to BCC phase formation as reported for similar HEAs produced by casting route. Increasing the milling time, the lattice strain increased reaching an average maximum value of 0.8% with an increase in d-spacing while the crystallite size was reduced to about 5.7 nm. A dual-phase structure formation was related to a decrease in the accumulated strain (ca.32%) confirming a strain-induced transformation.

Synthesis of (TiTaNb)<sub><i>x</i></sub>Hf<sub><i>y</i></sub>Zr<sub><i>z</i></sub>C high-entropy carbides resistant to high thermal oxidation by mechanical alloying and spark plasma sintering

This study presents the synthesis of (TiZrHfTaNb)C, (TiTaNb)0.45Hf0.275Zr0.275С and (TiTaNb)0.3Hf0.35Zr0.35С single-phase, high-entropy carbides through mechanical alloying and plasma sintering. High-entropy carbides hold promise for applications in jet engine components. We identified optimal mechanical alloying conditions to achieve powder homogeneity and minimize iron fouling. The microstructure, phase, and chemical compositions of the samples were investigated. At 1600 °C, a sample with a face-centered cubic (FCC) lattice and low content of zirconium and hafnium oxides was formed. Elevating the sintering temperature to 2000 °C facilitated oxide dissolution and the formation of single-phase, high-entropy carbides. The microhardness of the samples ranged from 1600 to 2000 HV, while the compressive strength varied between 600 and 800 MPa. Plasma heating tests demonstrated excellent resistance to thermal oxidation for (TiTaNb)0.3Hf0.35Zr0.35С, withstanding temperatures up to 2250 °C.

Transitional and refractory elements-based high entropy alloy developed through mechanical alloying and microwave sintering: Tribological and corrosion responses

Over the last decade, High Entropy Alloys (HEAs) gained recognition in various sectors (nuclear, aerospace, marine, and biomedical) due to their excellent strength, thermal stability, biocompatibility, wear and corrosion characteristics. This study deals with the development of a novel HEA through a microwave-assisted powder metallurgy, which is an economical approach and overcome the limitations of conventional fabrication techniques. A series of multi-principal alloys are developed, and noted that the HEA is developed through 15 h of ball milling of metallic powders followed by compaction and microwave sintering at 1400 °C at controlled heating and cooling rates. Thus, developed alloys were further examined to record their mechanical properties, tribological, and corrosion responses. The microstructural and metallurgical changes were recorded using Field Emission Scanning Electron Microscopy (FESEM), X-Ray Diffraction (XRD), and X-Ray Photoelectron Spectroscopy (XPS). Finally, the tribological and corrosive responses were recorded using a multifunctional tribometer and a potentiostat (potentiodynamic polarization and electrochemical impedance spectroscopy (EIS)). It is observed that the 1400 °C sintered HEA exhibited superior mechanical, tribological, and corrosive properties. It is worth hypothesizing that the transformation of dual phases (BCC and FCC) to the single BCC phase was responsible for the exceptional properties. Hence, this affordable fabrication approach can be used to develop bulk HEAs to explore other functional characteristics in the future.

Cobalt ferrite induced enhancement in the thermoelectric properties of zinc oxide composites

Thermoelectric (TE) material devices can be treated as an initiative to reduce global warming by scavenging waste heat and recycling it into useful electrical energy. In dual-phase materials, the energy filtering mechanism serves a significant role to enhance power factor by controlled electrical conductivity and Seebeck coefficient in connection with carrier concentration and carrier mobility. Here we performed the preparation of Cobalt Ferrite (CF) using mechanical alloying and the cf@zno composites via solid state reaction technique by varying stoichiometric weight between CF and ZnO. The magnetic, electric, and optical properties of the samples exposed the influence of CF on the TE properties of ZnO matrix. The cf7.5wt%@zno sample shows greater carrier mobility and moderate carrier concentration results the improved electrical conductivity value 4235 Sm−1 and hence achieved highest power factor 439 μWm−1K−2.

Exploring the microstructure, mechanical properties, and corrosion resistance of innovative bioabsorbable Zn-Mg-(Si) alloys fabricated via powder metallurgy techniques

Zinc alloys belong to the widely studied materials for applications like medical devices, however, they often encounter an inappropriate combination of mechanical/corrosion/biological properties. In this respect, we produced the Zn–1Mg and Zn–1Mg–1Si containing biologically friendly elements with potential strengthening effects on zinc matrix by powder metallurgy methods including mechanical alloying, spark plasma sintering, and extrusion further enabling the formation of materials with unique extremely fine-grained microstructures. The systematic study of these materials showed the possibility of reaching homogeneous nano-grain microstructure and high strength values exceeding 450 MPa in tension. Selected chemical composition and processing methods led also to slightly decreased wear and corrosion rates and rather uniform corrosion.

Effect of Ball Diameter on Mechanical Alloying Process for the Production of Dispersion Strengthened Tungsten

Effect of Ball Diameter on Mechanical Alloying Process for the Production of Dispersion Strengthened Tungsten

WC-based cemented carbide with NiFeCrWMo high-entropy alloy binder as an alternative to cobalt

In the current work, a nanostructured NiFeCrWMo high entropy alloy (HEA), synthesized by mechanical alloying, was used as the alternative binder phase for substituting Co to fabricate WC–HEA cemented carbides by electron–beam sintering (EBS). The microstructure and mechanical properties of initial powder mixtures and sintered samples were studied using X-ray diffraction analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy (EDS), indentation technique and compression tests. NiFeCrWMo HEA does not have direct interaction with WC, but at the boundaries between WC and HEA particles (Ni, Fe, Cr)xWyCz complex carbide is formed as result of reduction processes during sintering. The results show that WC–HEA cemented carbide has better performances than the commercial WC–8Co-cemented carbide prepared by EBS. The NiFeCrWMo HEA binder significantly slows down the growth of WC grains due to the sluggish diffusion effect and the formation of a small amount of complex carbide, and, compared to Co, improves the mechanical properties, provides an excellent combination of microhardness (18.9 ± 0.4 GPa) and fracture toughness (11.4 ± 0.3 MPa m1/2). Therefore, the NiFeCrWMo high entropy alloy can potentially become a binder for WC cemented carbides.

Role of process control agent in the production of Al2O3-reinforced titanium matrix composites

Metal Matrix Composites (MMCs) have recently been preferred over traditional materials in many engineering applications. Titanium matrix composites (TMCs) are used in the automotive, aerospace and defence industries thanks to their exceptional strength, high fatigue strength, good corrosion resistance and high elastic modulus. Some of the most used reinforcement materials for TMCs are SiC, Zr2O3, Al2O3, graphene, carbon nanotube (CNT) and TiC. In this study, TMCs reinforced Al2O3 were produced via conventional powder metallurgy (PM) and ultrasonic-assisted mixing. An Al2O3 in varying amounts (5 and 10 wt%) was incorporated into the TMCs via mechanical alloying (MA) for 5 h in a high-energy ball mill and using different process control agents (PCA, Stearic acid (SA), Polyvinyl Alcohol (PVA), Ethanol). The mechanically alloyed (MA'ed) powders were compacted by a hydraulic press under uniaxial pressure of 450 MPa and sintered at 1200 °C for 2 h in an argon atmosphere. The microstructural, mechanical and tribological properties of Ti-xAl2O3 powders and bulk samples were investigated. The highest hardness and the lowest specific wear rate were found in specimens reinforced with 5 wt% Al2O3, using ethanol as PCA, and produced by ultrasonic-assisted mixing, but the same specimen had the lowest compressive strength.

Mechanical alloying and direct powder forging of Ni–20Cr–20Fe-0.08C alloy

In the present work Ni–20Cr–20Fe-0.08C nickel-based alloy was prepared by mechanical alloying followed by direct powder forging. Mechanical alloying (MA) of the elemental powders corresponding to a starting composition of Ni–20Cr–20Fe-0.08C (without process control agent) was carried out in a high energy attritor mill (Simoloyer). X-ray diffraction studies indicated that a single phase (γ) solid solution was obtained at 8 h of milling. The crystallite size of the milled powder decreased significantly while lattice strain, lattice parameter, and dislocation density increased with milling time. Dynamic recrystallization was evident after 4 h of milling; as a result, a slight increase in crystallite size and a slight decrease in lattice strain and dislocation density were observed. The 8 h MA powders were further filled into a mild steel can and placed in a tubular furnace to carry out the loose sintering at 1150 °C after which they were hot forged. The forged slab exhibited almost full density, near isotropic properties, ultrafine equiaxed grained structure and minimised prior particles boundaries (PPB). This suggests that powder forging has a potential to be an alternative processing method to hot isostatic pressing (HIP), hot powder extrusion and additive manufacturing (AM) for the processing of powder metallurgy nickel based alloys.

Synthesis of Equiatomic CoCrFeMnTiNi Multicomponent Alloy by Sequential Alloying Using Mechanical Alloying and Vacuum Arc Melting

Synthesis of Equiatomic CoCrFeMnTiNi Multicomponent Alloy by Sequential Alloying Using Mechanical Alloying and Vacuum Arc Melting

Microstructures and Antioxidation of W Self-Passivating Alloys: Synergistic Effect of Yttrium and Milling Time

Tungsten and its alloys are widely recognized as key components in high-temperature environments. In this study, self-passivating W-Si-xY alloys with varying Y content were prepared using mechanical alloying (MA) and spark plasma sintering (SPS). The synergistic effects of Y content and milling time on the microstructures and oxidation resistance of the alloys were revealed. This study found that the oxidation resistance of the alloys increased as the Y content increased. However, the effect of milling time on oxidation resistance was complex. For W-Si-xY alloys with low Y content (0Y and 2Y), the oxidation resistance decreased with increasing milling time. In contrast, for W-Si-xY alloys with high Y content (4Y and 6Y), the oxidation resistance increased with increasing milling time. This enhanced oxidation resistance is due to the microstructural changes in the protective composite layer, including the size and distribution of W5Si3, Y2Si2O7 aggregates, and W-Y-O melt. The thickness of the oxide layer on the W-Si-6Y alloy after being oxidized at 1000 °C for 2 h was only 70.7 μm, demonstrating its superior oxidation resistance.

The effect of chemical composition and heat parameter on Nano-sized precipitate dispersion characterization in ODS steels

Oxide dispersion strengthened (ODS) supersaturated solid solution alloy powders with different Y/Ti atomic ratios were formed by mechanical alloying (MA) method and then heat treated under different conditions. The morphology, phase composition, and particle size distribution were researched. The precipitate distribution densities and hardness values of alloy powders after heat treatment were measured at the same time by the SAXS method and hard tester. The results show that the morphology of MA alloy powders is irregular in shape and only a small amount of MA alloy powders is bigger than 30 μm. During the MA process, alloy elements are solid solutions in the matrix. The work-harden effect of alloy powders formed in the MA process would be eliminated during the heat treatment process. The chemical composition and heat treatment parameters are crucial effects on nano-sized precipitate distribution characterization in ODS steels. The ODS sample with a Y/Ti atomic ratio of 0.99 has the highest distribution density of oxide precipitates at 1.89×1022/m3 resulting in the highest hardness value during the heat treatment process. The sample with a Y/Ti atomic ratio of 0.42 has the highest distribution density of nanoclusters 7.32×1023/m3.

Investigation of Cu-diamond/Cu-diamond-high-entropy alloys bi-layer coating via mechanical alloying

In this work, Cu-diamond/Cu-diamond-Cu2NiAlAgZn bi-layer coatings were prepared via mechanical alloying on copper substrate, in which Cu-diamond was the inner layer and Cu-diamond-Cu2NiAlAgZn was the outer layer. The results revealed that the quinary alloy Cu2NiAlAgZn HEAs has simple FCC solid solution structure and the interface of bi-layer coating is identifiable. The inner gray area consisted of a Cu-diamond composite, while the outer gray area was a Cu2NiAlAgZn HEAs reinforced Cu matrix composite. However, there were some defects in the microstructure and the compactness was not satisfactory. Therefore, recrystallization annealing treatment was performed on the bi-layer coatings. The microhardness distribution from the substrate to the coating showed the characteristics of ‘increase-drop-increase’ before and after heat treatment. Although the microhardness slightly decreased, heat treatment resulted in a denser coating and eliminated defects. Moreover, the thermal and electrical conductivity of the sample that have undergone heat treatment significantly increased.

Effects of process parameters on microstructure and properties of Ni–Ti coatings synthesized by mechanical alloying method

Effects of process parameters on microstructure and properties of Ni–Ti coatings synthesized by mechanical alloying method