Milled Powder Mixture Research Articles

Formation and characterization of solid-solution (V,W,Ti)CN composite powder

We report on the synthesis of a mixture of vanadium (V), tungsten (W), titanium (Ti) and carbon (C) mixture using ball milling in argon atmosphere. Thermal analysis of the milled powder showed an exothermic reaction at approximately 700 °C in nitrogen atmosphere. As a result, the milled powder mixture was subjected to annealing in nitrogen atmosphere at 700 °C. The crystal structure of the milled and nitrided powders was analysed using X-ray diffraction technique. Our findings showed that the crystal structure of nitrided powder was comprised of the tetragonal and orthorhombic structures. Scanning electron microscopy was used to analyse the powder morphology, while the atomic force microscopy was used to validate the topography and surface textures.

A novel approach to in situ synthesis of WC-Al2O3 composite by high energy reactive milling

In-situ synthesis of WC-Al2O3 composite by milling and its subsequent heat treatment were investigated. Mixtures of Al, W, and C with stoichiometric ratio of W3AlC2 were ball milled up to 20h. Then, the 20-hour ball milled powder was heat treated at different temperatures of 900 and 1200°C. The reaction path was investigated by X-ray diffractometry (XRD). The particle size and microstructure of powders after milling was investigated by field emission scanning electron microscope (FESEM) equipped with energy-dispersive spectroscopy (EDS). Also, in order to analyze the heating behavior of 20h ball milled powder mixture during heat treatment, simultaneous thermal analysis (STA) was used. The results showed that after milling for 20h, the reactants reacted together and new phases including W2C and (W,Al)C1−x were formed. After heat treatment, the semi-stable compounds synthesized at the milling stage, were transferred to more stable compounds including WC and Al2O3.

Densification and alloying of ball milled Silicon-Germanium powder mixture during spark plasma sintering

In this research, the influence of process parameters such as sintering temperature and current during alloying and densification of silicon-germanium (Si80-Ge20) powder mixture using spark plasma sintering (SPS) was reported. Si80-Ge20 powder mixture was consolidated at the temperature range 900–1200°C with 40MPa pressure for 5min. soaking. X-ray diffraction (XRD) study was made on sintered compacts to confirm the Si(Ge) alloy formation. Scanning electron microscope (SEM) was used to understand the morphology, particle size and distribution of un-milled and milled Si80-Ge20 powder mixture. Transmission electron microscope (TEM) study was made on milled Si80-Ge20 powder mixture and bulk SiGe alloy to confirm the nano-crystallinity and alloy formation. Fracture toughness of sintered bulk SiGe alloy was determined from Palmqvist cracks geometry model using Vickers hardness testing. It is understood that, during spark plasma sintering nano-structured Si80-Ge20 powder simultaneously increases the densification and reaction kinetics. It helps to achieve homogenous nanostructured SiGe alloy of near theoretical density. The superior hardness and benchmarked fracture toughness (KIC) values of 630VHN and 2.19MPa√m was achieved for SiGe alloy sintered at 1200°C, respectively.

Carbon nanotube and in-situ titanium carbide reinforced titanium diboride matrix composites synthesized by reactive spark plasma sintering

Mechanically milled powder mixtures of Titanium and Boron containing 1, 2, 4 and 6vol% multi-walled carbon nanotubes (CNT) were consolidated by reactive spark plasma sintering resulting in TiB2-TiC-CNT hybrid composites. Addition of CNT was found to affect the reaction rate for TiB2 formation which results in sudden volume shrinkage. Rod shaped TiC were formed due to reaction between Ti and CNT. TiB2-TiC-CNT hybrid composites having more than 96% relative density with nanosized TiB2 grains were obtained. XRD results revealed TiB2 and TiC as major and minor phases respectively. Unreacted CNT were observed in SEM and TEM. TiB2-TiC-CNT composites showed nanohardness of above 25GPa and elastic modulus of 520GPa. Indentation fracture toughness was improved by 55% (3.3±0.1 to 5.11±0.6) by the addition of 4vol% of CNT. The effect of CNT addition on oxidation and co-efficient of thermal expansion is also presented.

Formation of SrTiO3 in mechanically activated SrCO3–TiO2 system

In this study, mechanical activation process was used for intimate mixing as well as producing finely ground particles, increased surface area and improved chemical reactivity of milled materials for producing SrTiO3 from commercially pure strontium carbonate and TiO2 as a contributive process. Characterization of milled powder mixture by X-ray diffraction analysis showed that disappearing, decreasing and/or shifting of the patterns occurred with mechanical activation that means amorphization was taken place. Amorphization was also demonstrated by FT-IR analysis where shift of band centers as well as the decrement of transmittance related to CO3 was observed. Advantage of amorphization was established with high-temperature XRD analysis which showed 1300 °C was not enough for non-activated mixture to form SrTiO3, whereas structure only composed of SrTiO3 at 1000 °C for activated ones. The reason for this phenomenon was investigated by DTA-TG analysis, and it was based on energy accumulation originated from mechanical activation that corresponds to peak temperature shifting to the lower temperatures and CO2 liberation at mechanical activation step arising from local temperature rising at the vial during high-energy milling that was understood from peak temperature, and area decrement of endothermic peak corresponds to decomposition of SrCO3.

Producing dense zirconium diboride components by room-temperature injection molding of aqueous ceramic suspensions

Aqueous suspensions of zirconium diboride (ZrB2), boron carbide (B4C) and tungsten carbide (WC) with dispersant and water-soluble polyvinylpyrrolidone (PVP) were investigated for processing by room-temperature injection molding, a novel, environmentally benign ceramic processing method. B4C and WC were used as sintering aids, and the as-received powders were attrition milled to reduce particle size to promote full densification of ZrB2 specimens by pressureless sintering. Zeta potential measurements of individual ZrB2, B4C and WC powders and of powder mixtures revealed that maximum stability was achieved in aqueous solutions of attrition milled powder mixtures dispersed using an ammonium polyacrylate dispersant. A maximum powder loading of 49vol% with ≤5vol% PVP was attained for ZrB2/B4C/WC suspensions with dispersant. Although exhibiting a time-dependent rheological response determined by parallel-plate rheometry, suspensions containing 49vol% powders and ≤3vol% PVP, as well as suspensions of 46vol% powders and ≤4vol% PVP, were flowable under the conditions of the process. ZrB2 rings prepared by room-temperature injection molding were machinable prior to binder removal and exhibited maximum brown densities of 56% true density (TD). Sintered densities were >98%TD with ~20% linear shrinkage. Scanning electron microscopy revealed an average grain size of 7.3±2.8µm, and chemical analysis confirmed that no undesirable oxide phases remained in the sintered ZrB2 specimens. Aqueous ZrB2-based suspensions containing B4C and WC sintering aids and PVP were effectively processed via room-temperature injection molding to yield dense ZrB2 rings after binder burnout and pressureless sintering.

Role of Process Control Agent in the Synthesis of Multi‐Walled Carbon Nanotubes Reinforced Titanium Metal Matrix Powder Mixtures

The present study investigates the influence of process control agent (PCA), i.e., stearic acid (SA) on the dispersion of multi‐walled carbon nanotubes (MWCNT) into the titanium (Ti) matrix during mechanical alloying. A planetary ball mill was used in dispersing 0.5 wt.% MWCNT into the Ti matrix. The powder mixtures were prepared in two batches: without and with the addition of 0.5 wt.% SA. Green compacts of high energy ball milled powder mixtures were consolidated by using a uniaxial hydraulic press. Raman spectroscopy combined with X‐ray diffraction (XRD) and transmission electron microscopy (TEM) techniques were used to characterize the powder mixtures and green compacts. The evolution of MWCNT has been discussed in conjunction with the formation of nano crystalline TiC in the ball milled powder mixtures.

Effect of Powder Particle Shape on the Properties of In Situ Ti–TiB Composite Materials Produced by Selective Laser Melting

This work studied the preparation of starting powder mixture influenced by milling time and its effect on the particle morphology (especially the shape) and, consequently, density and compression properties of in situ Ti–TiB composite materials produced by selective laser melting (SLM) technology. Starting powder composite system was prepared by mixing 95 wt% commercially pure titanium (CP-Ti) and 5 wt% titanium diboride (TiB2) powders and subsequently milled for two different times (i.e. 2 h and 4 h). The milled powder mixtures after 2 h and 4 h show nearly spherical and irregular shape, respectively. Subsequently, the resultant Ti–5 wt% TiB2 powder mixtures were used for SLM processing. Scanning electron microscopy image of the SLM-processed Ti–TiB composite samples show needle-shape TiB phase distributed across the Ti matrix, which is the product of an in-situ chemical reaction between Ti and TiB2 during SLM. The Ti–TiB composite samples prepared from 2 h and 4 h milled Ti–TiB2 powders show different relative densities of 99.5% and 95.1%, respectively. Also, the compression properties such as ultimate strength and compression strain for the 99.5% dense composite samples is 1421 MPa and 17.8%, respectively, which are superior to those (883 MPa and 5.5%, respectively) for the 95.1% dense sample. The results indicate that once Ti and TiB2 powders are connected firmly to each other and powder mixture of nearly spherical shape is obtained, there is no additional benefit in increasing the milling time and, instead, it has a negative effect on the density (i.e. increasing porosity level) of the Ti–TiB composite materials and their mechanical properties.

Pulsed current activated synthesis and rapid consolidation of a nanostructured Mg2Al4Si5O18 and its mechanical properties

Nanocrystalline materials have received much attention as advanced engineering materials, with improved mechanical properties. Attention has been directed to the application of nanomaterials, as they possess excellent mechanical properties (high strength, high hardness, excellent ductility and toughness). A singlestep synthesis and consolidation of nanostructured Mg2Al4Si5O18 was achieved by pulsed current heating, using the stoichiometric mixture of MgO, Al2O3 and SiO2 powders. Before sintering, the powder mixture was high-energy ball milled for 10 h. From the milled powder mixture, a highly dense nanostructured Mg2Al4Si5O18 compound could be obtained within one minute, under the simultaneous application of 80 MPa pressure, and a pulsed current. The advantage of this process is that it allows an instant densification to the near theoretical density, while sustaining the nanosized microstructure of raw powders. The sintering behavior, microstructure and mechanical properties of Mg2Al4Si5O18 were evaluated. The fracture toughness of a nanostructured Mg2Al4Si5O18 compound was higher than that of sub-micron Mg2Al4Si5O18 compound.

Effect of Ni addition on the preparation of Al2O3–TiB2 composites using high-energy ball milling

Al2O3–TiB2 composites were synthesized using high-energy ball milling from starting powders containing Al, TiO2, and B2O3. To explore the effect of the addition of another ductile metallic phase during milling, 15 wt.% Ni was added to a sample of the starting powders. The phase transformations and microstructure of the milled powder mixtures were investigated using X-ray diffraction and electron microscopy. The results showed that the Ni addition facilitated the mechanochemical reaction between the Al, TiO2, and B2O3. Before the appearance of the Al2O3–TiB2 composite, the intermediate product NiAl was formed by a gradual exothermic reaction. With continued milling, the final phases of Al2O3–TiB2 and Ni were obtained.

Synthesis and Characterization of Cu–TiC Nanocomposites by Ball Milling and Spark Plasma Sintering

In this study, Cu-TiC nanocomposites were fabricated from a mixture of Cu and 5÷15% wt. TiC powders by ball milling and subsequent spark-plasma sintering. The morphology of Cu-TiC nanocomposite powders were observed by field emission scanning electron microscopy. Only characteristic peaks of Cu and TiC phases were detected from X-ray diffraction patterns of milled powder mixture. Sintered compacts showed a highly densified compacts (∼95% relative density) while retaining fine grains in the matrix. The hardness, wear resistance, and fracture surface of the sintered specimens were also investigated.

Effects of Sintering Conditions on the Mechanical Properties of Alumina Particle Dispersed Magnesium SPS Compacts

To enhance the mechanical properties of Mg alloys, 0-30vol% Al2O3/Mg powders were formed by ball milling powder mixtures of pure Mg and Al2O3 particles, and then Spark plasma sintering (SPS) compacts (Al2O3/Mg discs) were made by the Al2O3/Mg powders. The effect of the cooling conditions in the SPS process on the mechanical properties of the Al2O3/Mg discs was investigated. From the results of SEM, XRD and TEM-EDS, the microstructures of the Al2O3/Mg discs were identified to consist of α-Mg solid solution, Al2O3 particles, refined MgO particles and refined needle-like Mg17Al12 ( more than 20vol% Al2O3 content). The mechanical properties of the discs were able to control by the regulation of the cooling conditions (cooling rate (vc) and applied pressure in the cooling (pc)) in SPS process, and as a result, the SPS discs possessing the mechanical properties beyond HP compacts were obtained under the cooling conditions of “vc= 0.83K/sand pc = 20MPa”. Main factor that the cooling conditions in SPS process effect on the mechanical properties of the Al2O3/Mg discs are considered to be the compresive residual stress generated in the α - Mg solid solution by the thermal stress associated with deference of the coefficients of thermal expansion between the α - Mg and ceramics particles (Al2O3 and MgO) in the discs.

Simultaneously rapid synthesis and consolidation of nanostructured Mg0.3Al1.4Ti1.3O5 by high-frequency induction heating

A one-step synthesis and consolidation of nanostructured Mg0.3Al1.4Ti1.3O5 was achieved by high-frequency induction heating, using the stoichometric mixture of MgO, Al2O3 and TiO2 powders. Before sintering, the powder mixture was high-energy ball milled for 10 h. From the milled powder mixture, a highly dense nanostructured Mg0.3Al1.4Ti1.3O5 compound could be obtained within one minute, under the simultaneous application of 80 MPa pressure and an induced current. The advantage of this process is that it allows an instant densification to the near theoretical density, while sustaining the nanosized microstructure of raw powders. The sintering behavior, microstructure and mechanical properties of Mg0.3Al1.4Ti1.3O5 compound were evaluated.

Synthesis of Single-Phase Gd-Doped Ceria Nanopowders by Radio Frequency Thermal Plasma Treatment

Gd-doped ceria nanopowders were synthesized using Radio Frequency (RF) thermal plasma. The powders were prepared by ball-milling Gd2O3 and CeO2 powders of several tens of μm in size at the cation ratio of 8:2 and 9:1. The prepared precursors were treated by RF thermal plasma at a plate power level of ~140 kVA, and then, small-sized powders (~50 nm) were retrieved by filtration. Transmission Electron Microscopy, Electron Energy Loss Spectroscopy, and Selected-Area Electron-Diffraction images of the as-synthesized powders showed that Gd atoms were incorporated into the CeO2 particles. In addition, no crystalline peak for Gd2O3 appeared in the X-ray diffraction patterns of the as-synthesized powders, which is attributed to the solid solution of Gd3+ into the CeO2 lattices. Finally, Inductively Coupled Plasma-Optical Emission Spectrometry analysis data revealed relatively small changes within 3 at.% in the cation composition between the ball milled powder mixtures and the nanoscale powders prepared from these mixtures.

Enhanced mechanical properties of a nanostructured Mg2Al4Si5O18–MgAl2O4 composite

Single-step synthesis and consolidation of nanostructured Mg2Al4Si5O18–MgAl2O4 composite were achieved via pulsed-current-activated heating using a mixture of 3MgO, 3Al2O3 and 5SiO2 powders. Before sintering, the powder mixture was high-energy ball milled for 10h. From the milled powder mixture, a highly dense nanostructured Mg2Al4Si5O18–MgAl2O4 composite could be obtained within one minute by simultaneously applying 80MPa of pressure and a pulsed current. The advantage of this process is that it allows simultaneous synthesis and densification to near theoretical density while sustaining the nanosized microstructure of raw powders. The mechanical properties (hardness and fracture toughness) of Mg2Al4Si5O18 were improved by the addition of MgAl2O4.

Improving Mechanical Properties of Ceramic Composites by Harmonic Microstructure Control

In this research, several ceramic composites such as SiC-ZrO2, Al2O3-ZrO2, and Si3N4-ZrO2 containing nominally equal ratio 1:1 were prepared through high energy mechanical milling and spark plasma sintering. The relationship of microstructure and mechanical properties were investigated. Harmonic microstructures consisting of fine and ultra-fine grains forming a network were obtained by the optimum milling time for 144ks with high mechanical properties. The non-milled powder mixtures and too long milling time powder mixtures have low mechanical properties sintered by spark plasma. The crack propagates through ultra-fine grains and deflected by larger fine grains were obtained on the harmonic microstructure sample resulting in high toughness. Thus, the harmonic microstructure can be considered a remarkable design tool for improving the mechanical properties of SiC-ZrO2, Al2O3-ZrO2, and Si3N4-ZrO2 as well as other ceramic composites.

Microstructure and mechanical properties of Al-7075/B4C composites fabricated by plasma activated sintering

In this work, we prepared Al-7075/B4C composites by milling powder mixtures using a shaker–mixer mill, sintering the milled mixtures using plasma activated sintering (PAS), and heat treating the sintered product. To characterize the microstructure of the composites, we used field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Al-7075/B4C composites can be prepared by PAS with high relative densities at low temperature. Increasing the B4C content increased the hardness, bending strength, and compressive yield strength of the composite. However, adding too much B4C caused B4C agglomerates to form, decreasing the hardness and bending strength of the composite. At 7.5 wt.% B4C, the Vickers hardness, bending strength, and compressive strength of the consolidated samples were 184.3HV, 813MPa, and 895MPa, respectively. We attributed these superior mechanical properties to good interfacial bonding between the matrix alloy and the reinforcement.

Development of Nano-Structure Cu-Ti Alloys by Mechanical Alloying Process

Cu-Ti system with a terminal solution in the Cu-rich portion of equilibrium Cu-Ti phase diagram with a decreasing trend with temperature shows a potential to develop age hardenable alloys with suitable strength and thermal and electrical conductivities. In the present study, the mechanical alloy process has been employed to increase solubility of Ti in Cu matrix to make age hardenable Cu alloys. Cu-Ti powder mixtures with different rations of 1 and 6 wt% of Ti were milled in planetary ball mill for different milling times of 4, 12, 48, 96 and 192 hours. The milled powder mixtures were investigated and characterised by X-ray diffraction (XRD) technique. The results show increasing in lattice parameter of Cu, which indicates that Ti atoms are dissolved in the Cu matrix. Cu crystal sizes showed decreasing trend which were more obvious in the mixture with higher Ti contents. The final crystal sizes were in the range of 17-23 nm after 192 hours of milling.

Simultaneous synthesis and rapid consolidation of a nanocrystalline Mg0.6Al0.8Ti1.6O5 by high-frequency induction heating and its mechanical properties

A single-step synthesis and consolidation of nanostructured Mg0.6Al0.8Ti1.6O5 was achieved by high-frequency induction heating using the stoichometric mixture of MgO, Al2O3 and TiO2 powders. Before sintering, the powder mixture was high-energy ball milled for 10h. From the milled powder mixture, a highly dense nanostructured Mg0.6Al0.8Ti1.6O5 compound could be obtained within one minute under the simultaneous application of 80MPa pressure and an induced current. The advantage of this process is that it allows an instant densification to the near theoretical density while sustaining the nanosized microstructure of raw powders. The sintering behavior, microstructure and mechanical properties of Mg0.6Al0.8Ti1.6O5 were evaluated.

Synthesis and characterization of nanocrystalline Al 2024–B4C composite powders by mechanical alloying

In the present work, the effect of milling parameters on the morphology and microstructure of nanostructure Al2024–B4C composite powders obtained by mechanical alloying (MA) was studied. The effects of milling time and B4C content on the morphology, microstructure and particle size of nanostructure Al2024–B4C composite powders have been investigated. Different amounts of B4C particles (0, 5, 10 and 20 wt.%) were mixed with Al2024 powders and milled in a planetary ball mill for 30, 60, 120, 300, 420 and 600 min. Al 2024–B4C composite powders were characterized using a scanning electron microscope (SEM), laser particle-size analyzer, X-ray diffraction analysis (XRD) and the Vickers microhardness test. The results showed that the nanostructure Al2024–B4C composite powders were produced when they were milled for 600 min. The size of composite powder in the milled powder mixture was affected by the milling time and content of B4C particles. Moreover, it was observed that when MA reached a steady state, the properties of composite powders were stabilized.