Fabrication of ultrafine and nanocrystalline WC–Co mixtures by planetary milling and subsequent consolidations

Abstract

In this work ultrafine and nanocrystalline WC–Co mixtures were obtained by low energy milling in planetary ball mill. The effect of the processing conditions on the reduction and distribution of the grain sizes and the internal strains level were studied. The characterisation of the powder mixtures was performed by means of scanning and transmission electron microscopy and X-ray diffraction analysis. Observations through SEM and TEM images showed a particle size below 100 nm, after milling. The X-ray diffraction profile analysis revealed a WC phase refined to a crystallite size of 19 nm.

The mixtures obtained have been consolidated and mechanical and microstructurally characterised. The results show improvements in resistant behaviour of the material consolidated from nanocrystalline powders, in spite of the grain growth experienced during the sintering. The best results were found for the material obtained by wet milling during 100 h, which presents values of hardness higher than 1800 HV.     

Synthesis of TiC–TiB–TiB2 composite powders by solid reaction of powders

In the present work, TiC–TiB–TiB₂ diffusion-layer-coated B₄C composite powders were synthesised via a powder immersion method using Ti and B₄C powders as reactants. The phase compositions and microstructure of the treated powders were characterised by employing X-ray diffraction and scanning electron microscopy. No significant reaction between B₄C and Ti could be detected at 800°C. After treatment at 900°C, the products generated were composed of TiC and TiB. After treatment at 1000°C, the products generated were primarily composed of TiC and TiB, with a small amount of TiB₂. The composition and proportions of the produced phases varied with process temperatures and the composition of the initial powders used. Powder mixtures with a Ti/B₄C molar ratio of 3.5:1 and treated at 1000°C for 14?h were more suitable for synthesis of TiC–TiB–TiB₂-coated B₄C composite powders.     

Development of Ti–Nb and Ti–Nb–Fe beta alloys from TiH2 powders

Ti–Nb β alloys are a promising alternative as an implant material due to their good properties and low Young’s modulus, compared to other Ti-alloys currently employed as biomaterials. In this study, three materials of the Ti–Nb and Ti–Nb–Fe systems were produced by powder metallurgy techniques starting from TiH₂ (TH) powder. Several sintering cycles were employed to evaluate the H₂ elimination and the effect of sintering temperature on densification and fraction of β-Ti phase. Also, the influence of alloying element size using two kinds of Fe powder was evaluated. The highest loss of H₂ was achieved by decreasing heating rate at the temperature range of hydride decomposition. SEM images and XRD results show mainly a β-Ti phase for TH–40Nb and TH–5Fe–25Nb samples. The TH–12Nb sample shows (α?+?β) microstructure. Fe addition with smaller particle size seems to improve the diffusion of Nb into Ti which promotes a higher β-phase fraction and sample homogeneity.     

On selection of milling atmosphere for production of Al–10%Ti powders

Abstract

A mixture of aluminium and 10 wt-% titanium powders was attrition milled for 10 h under air, nitrogen and vacuum atmospheres; pure aluminium powders were also prepared in a like manner. Particle size distribution, morphology and microstructure of the powders were studied by laser diffraction, scanning electron microscopy (SEM) and X-ray diffraction (XRD); special attention was paid to the influence of the milling atmosphere. There were differences in powder particle size obtained from pure Al powders that were not observed for Ti containing powders, however the same homogeneous morphology and microstructure was attained for the different milling atmospheres. The effect of milled powder annealing on microstructure was studied by differential scanning calorimetry (DSC) and XRD. New phases and their crystallite size were characterised as a function of annealing temperature, milling atmosphere, and powder microhardness. In short, the studied milling atmospheres for the production of Al–10%Ti powders do not affect the properties of the obtained powders, and in general, low cost atmospheres could be used.     

Calcium hydride synthesis of Ti–Nb-based alloy powders

The metallothermic (calcium hydride) synthesis of Ti–Nb alloy powders alloyed with tantalum and zirconium is experimentally studied under various conditions. Chemical, X-ray diffraction, and metallographic analyses of the synthesized products show that initial oxides are completely reduced and a homogeneous β-Ti-based alloy powder forms under the optimum synthesis conditions at a temperature of 1200°C. At a lower synthesis temperature, the end products have a high oxygen content. The experimental results are used to plot the thermokinetic dependences o formation of a bcc solid solution at various times of isothermal holding of Ti–22Nb–6Ta and Ti–22Nb–6Zr (at %) alloys. The physicochemical and technological properties of the Ti–22Nb–6Ta and Ti–22Nb–6Zr alloy powders synthesized by calcium hydride reduction under the optimum conditions are determined.     

Synthesis and Characterization of Ti/(TiB + TiC) Hybrid in-situ Composites by Spark Plasma Sintering

Since Ti alloys exhibit inferior wear resistance and suffer considerable loss in mechanical strength at high temperature, it is aimed at synthesis an in-situ Ti/(TiB + TiC) hybrid composite. In order to synthesis Ti/(TiB + TiC) in-situ composite, B₄C particulate was mixed with titanium powder and sintered at 1400 °C at different time intervals by spark plasma sintering. Sintering parameters were optimized according to the complete in-situ reactions. Density of the sintered compacts was measured by Archimedes principle. Energy dispersive spectroscope and optical microscope observations of the sintered samples revealed that with increasing sintering time TiB and TiC particulates were gradually transforming into needle like structure and near equiaxed structure, respectively.     

Synthesis and Structural Characterization of V–4Ti–4Cr Alloy

V–(4–10)Ti–(4–5)Cr alloys are the potential candidate materials for the high performance structural applications in fusion power systems due to their favorable mechanical and physical properties. In the present study, the alloy design has been attempted through model based approach for pre mentioned composition range. Thermodynamic calculations have been carried out through Miedema model for this alloy system. The enthalpy difference—composition plot for the ternary V–Ti–Cr system indicate the stability of the solid solution phase in this composition range, which is also in agreement with the atomic size variation which is well within the 15 % size variation limit. Based on these plots, an alloy with a composition of V–4Ti–4Cr is considered as the reference composition for our study. The alloys have been prepared by melting the desired compositions of highly pure metals in a water cooled vacuum arc melting unit. For structural information, X-ray diffraction experiment has been carried out. The XRD pattern does not contain any signature for the secondary phase formation. The structure is bcc structure with small variation in lattice parameter from that of pure vanadium. Transmission electron microscopy characterization has also been carried out, which confirms the absence of fine secondary phases and the crystal structure as b.c.c.     

Effect of separate and combined milling of Cu and TiB2 powders on the electrical and mechanical properties of Cu–TiB2 composites

The present work compares the properties of the Cu–TiB₂ composites prepared by varying the mechanical milling conditions. The Cu–TiB₂ composites were processed using Cu–TiB₂ powders combined milling, a powder mixture consisting of separately milled Cu & TiB₂ and a powder mixture prepared by the combination of separate and combined milling. The hardness and flexural strength of the combined milled powders were found to be maximum, despite of their lower sintered density. The separately milled powders achieved excellent electrical properties combined with moderate hardness and flexural strength. The properties of composites processed using the combination of separate and combined milling laid in between the two conditions of combined and separate milling.     

Volume Combustion Synthesis in Fe–Ti–C and Fe–Ti Systems

Metallurgical and Materials Transactions A - In situ formation of TiC particles in Fe matrix from Fe + Ti + C (FTC) powder mixtures via volume combustion synthesis (VCS) was...     

Thermal Properties of Ultra- and Nanodispersed Core–Shell Structures of Ti(Mo)C and Ti(Mo)C-Co Obtained During Plasma-Chemical Synthesis by Plasma Recondensation Scheme

Metallurgical and Materials Transactions B - In this work, the thermal studies of ultrafine and nanocrystalline core–shell structures of Ti(Mo)C and Ti(Mo)C-Co formed in the process of plasma...     

Combustion synthesis of Fe–Al/TiC composite powders and effect of Al content on its characteristics

Abstract

In this work, combustion synthesis of ferrotitanium–Al–C powder mixtures with different compositions was carried out to synthesise Fe–Al/TiC composites. Differential thermal analysis was performed on the precursor powder from ambient temperature to 1673 K at a heating rate of 30 K min^?1. Phase development and structural changes were investigated by X-ray diffraction technique and scanning electron microscopy. The results showed that no trace of TiAl_x (x?=?1, 3) was formed in all samples, and the reaction of (Ti–Fe)–Al–C system took place in the following two steps: first, molten Al and Fe reacted exothermically to form Fe–Al intermetallic compound. Second, the produced heat melted the ferrotitanium with lower Fe content and resulted in a liquid containing Ti, Fe, Al and C. TiC formed in all samples, but depending on the Al content, different phases containing FeAl₂, FeAl, Fe₃Al, Fe₃AlC_x and α-Fe formed as phases of matrix. The mixture with the lower Al content gave out a higher combustion temperature.     

The influence of milling parameters on the characteristics of milled and spray-dried NiCoCrAlY–Al2O3 composite powders

Spray-drying process was selected to agglomerate ball milled NiCoCrAlY–Al₂O₃ composite powders. The effect of the starting alloy powder size on the morphology of composite powder was studied. The parameters of milling were optimised by orthogonal experiment to improve the powder’s flowability and apparent density. Then the optimised powder was sprayed by air plasma spray to prepare NiCoCrAlY–Al₂O₃ composite coating. The results showed that the size distribution of starting particles decided the deformation of alloy particles and the characteristics of agglomerated powders eventually. With the decreasing size range of the starting alloy particles, the sphericity of agglomerated powders increased. The optimised milling parameters were as follows: solid content, 60?wt-%; BPR, 4:1; the rotating speed, 350?rev?min^?1; and milling time, 5?h. And the contribution of solid content was the largest. The Al₂O₃ splats showed good adhesion with alloy matrix when the composite powder melted in good condition.     

Self-Propagating High-Temperature Synthesis of (Al–2% Mn)–10% TiC and (Al–5% Cu–2% Mn)–10% TiC Nanostructured Composite Alloys Doped with Manganese Powder

Russian Journal of Non-Ferrous Metals - The influence of alloying with powder manganese on the preparation of nanostructured (Al‒2% Mn)–10% TiC and (Al–5% Cu–2%...     

Microstructure of TiC–TiN–Ni–(B) cermet systems

Abstract

TiC-TiN-Ni-(B) systems were investigated to understand particle coarsening and morphology changes as a function of sintering time and compositions. In addition, the variations in the C/(C+N) ratios of Ti(C_1-xN_x) solid solutions formed in the system were studied. As expected, the particle size becomes larger with an increase in the duration of sintering. However, added boron significantly reduced the growth of particles. X-ray diffraction analysis shows that the binder phase consists largely of Ni₃B in TiC-TiN-20Ni-1B (in wt-%) system. The presence of boron in the liquid Ni seems to interfere with the dissolution of TiC and TiN and/or transport of Ti, C, and N. The effect of boron decreases as the amount of Ni binder increases. The particle morphology is found to change with variations in the C/(C+N) ratio.     

Synthesis of TiC–NiCrBSi Binder Alloy Composite Powders for Cladding and Deposition of Wear-Resistant Coatings

Russian Journal of Non-Ferrous Metals - TiC–NiCrBSi binder metal matrix composites are fabricated by self-propagating high-temperature synthesis (SHS) in reaction powder mixtures of titanium,...     

Effect of various sintering methods on microstructures and mechanical properties of titanium and its alloy (Ti–Al–V–X): A review

Titanium having high demand in aircraft industries because of its mechanical properties like high strength to weight ratio, high temperature performance and it’s resistant to corrosion. Therefore, Titanium and its alloys are used in airplane and engine applications. One of the major usages of alloy in the aircraft industries are Titanium alloy. By using Powder Metallurgy, the powder materials are compacted and sintered in the furnace to achieve high densities for the further process of the samples. In this paper reviews the various research investigations of Titanium and its alloy (Ti–% Al–% V–% X alloy), to optimize the microstructure and mechanical properties by various sintering methods like Conventional, Spark plasma and Microwave sintering techniques. From this the major advantages in the Spark plasma sintering tend to reduce the sintering time with high temperatures, achieving higher densities and improved microstructures tends to improve the mechanical properties of the material.     

Synthesis of Co3W–Cu composite nanopowders by mechanical milling and hydrogen reduction process

Abstract

In this research, synthesis of Co₃W–Cu composite nanopowders based on Co₃W intermetallic compound by mechanical milling and hydrogen reduction process was investigated. Powder mixture of Co₃O₄, WC and CuO with Co₅₀W₄₀Cu₁₀ stoichiometry was first milled by high energy planetary ball mill and then reduced in a hydrogen reduction system. Crystallite structure of milled mixture and reduced powders was determined by X-ray diffraction. Particles size, morphology and cross-section of reduced samples were studied by SEM, TEM and SEM back scattered electron microscopy. Optimum condition of reduction under hydrogen atmosphere was found at 900°C. Particles have Cu coring structure surrounded with Co₃W intermetallic compound. Mean particle size was observed less than 50 nm with six fold hexagon morphology.     

Synthesis of CaWO4：Eu3＋ phosphor powders via ethylene glycol route and its optical properties

Eu3+ doped CaWO4 with tetragonal system were prepared at comparatively low temperature (125 ?C) in ethylene glycol medium. The phosphor was further investigated by X-ray diffractometer (XRD), photoluminescence spectrophotometer (PL), Fourier transform infra red (FT-IR) spectroscopy and transmission electron microscopy (TEM). XRD analysis indicated a decrease in the unit cell volume of CaWO4 with increasing Eu3+ ion concentration. It indicated the homogeneous substitution of Ca2+ ions in CaWO4 by the Eu3+ ions. TEM images showed that the particle size ranged from 20 to 200 nm and it could extend the application of the nanoparticles. The photoluminescence study showed that the intensity of electric dipole transition (5D0→7F2) at 614 nm dominated over the magnetic dipole transition (5D0→7F1) at 592 nm. The optimum concentration of Eu3+ for the highest luminescence was found to be 20 at.%. The as prepared samples were found to be dis-persible in water and methanol.     

Mechanical milling of gas-atomized Al−Ni−Mm (Mm=misch metal) alloy powders

Al−14Ni−14Mm (Mm=misch metal) alloy powders rapidly solidified by the gas atomization method were subjected to mechanical milling (MM). The microstructure, hardness, and thermal stability of the powders were investigated as a function of milling time using X-ray diffraction (XRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) methods. In the early stages of milling, a cold-welded layer with a fine microstructure formed along the edge of the milled powder (zone A). The interior of the powder remained unworked (zone B), resulting in a two-zone microstructure, reminiscent of the microstructures in rapidly solidified ribbons containing zones A and B. With increasing milling time, the crystallite size decreased gradually reaching a size of about 10 to 15 nm and the lattice strain increased reaching a maximum value of about 0.7 pct for a milling time of 200 hours. The microhardness of the mechanically milled powder was 132 kg/mm² after milling for 72 hours and it increased to 290 kg/mm² after milling for 200 hours. This increase in microhardness is attributed to a significant refinement of mcirostructure, presence of lattice strain, and presence of a mixture of phases in the alloy. Details of the microstructural development as a function of milling time and its effect on the microhardness of the alloy are discussed.