Viscous flow during sintering of attrition milled nanocrystalline titanium powders

Nanocrystalline powders are expected to exhibit viscous flow during sintering due to presence of substantial amount of quasi-amorphous layers at the grain boundaries. The present investigation attempts to determine the contribution of viscous flow during sintering of nanocrystalline titanium powders. Model equations originally suggested by Frenkel are applied on the shrinkage data to determine the activation energy for viscous flow, frequency factor and the coefficient of viscosity. Nanocrystalline titanium powders were found to exhibit lower activation energy for viscous flow, higher frequency factor and higher coefficient of viscosity as compared to micron sized titanium powders. (C) 200

Synthesis of nanosized titanium powder by high energy milling

Titanium powders of about 2 mu particle size were subjected to high energy attrition milling in an argon atmosphere. Selecting suitable milling parameters, nanosize (< 100 nm) titanium powders were prepared after 15 h of milling. An average particle size of 35 nm was obtained at 30 h of milling after which the particle size stabilized with continuation of milling to 75 h. The powders after milling for various durations were characterized by TEM, ICP and XRD, and these results are reported and discussed. (C) 2001 Elsevier Science B.V. All rights reserved

Dilatometric sintering study of titanium-titanium nitride nano/nanocomposite powders

The sintering behaviour of titanium-titanium nitride nano/nanocomposite powders has been investigated by dilatometry. The nanosized titanium powders (40 nm) were produced by the attrition milling of micron sized titanium powders (12 mu m) in Ar atmosphere while the nanosized titanium nitride powders (50 nm) were as procured. Two compositions of the nano/nanocomposite powders, i.e. Ti-8TiN and Ti-15TiN (wt-%) were produced by physical mixing and ultrasonification. Dilatometry was carried out at a constant rate of 10 K min(-1) heating to various temperatures in the range of 450-1250 degrees C followed by holding for 1 h. The effect of nanoTiN reinforcement on the sintering onset temperature, linear shrinkage, shrinkage rate, activation energy for sintering, microstructure and grain growth has been reported and discussed

Sintering behavior of titanium-titanium nitride nanocomposite powders

The sintering behavior of titanium-titanium nitride nanocomposite powders has been investigated by dilatometry. Micron-sized titanium powders of average particle size of similar to 12 mu m and nano sized titanium nitride powders of average particle size of similar to 50 nm were used to produce two compositions of Ti-8 wt%TiN and Ti-15 wt%TiN by physical mixing and ultrasonification. Dilatometry was carried out by constant rate of heating (10 degrees C/min) to various temperatures in the range of 650-1250 degrees C followed by isothermal holding for I h. The effect of nano TiN dispersion on the sintering onset temperature, linear shrinkage, shrinkage rate, activation energy, and microstructure of titanium was investigated. The sintering of titanium-titanium nitride nanocomposites was found to be influenced by the sintering between the Ti-Ti contacts (self diffusion), Ti-TiN contacts (diffusion of N into Ti), TiN-TiN contacts, the role of oxygen as well as the alpha-beta transformation in titanium. (C) 200

Nanocrystalline titanium powders by high energy attrition milling

The present investigation deals with the synthesis of nanocrystalline titanium powders by the high energy attrition milling of micron sized titanium powder in an inert atmosphere. Titanium powders of about 12 pm particle size were subjected to high energy attrition milling in an argon atmosphere. Selecting suitable milling parameters, nanosize (< 100 nm) titanium powders were obtained after 15 h of milling. An average particle size of 35 nm was obtained at 30 It of milling after which the particle size stabilized with continuation of milling to 75 h. The powders after milling for various durations were characterized by XRD, SEM, TEM, ICP-AES and DTA and these results are reported and discussed. (c) 200

Initial sintering kinetics of titanium-titanium nitride nano/nanocomposite powders

The present investigation deals with the mass transport mechanisms operating during the initial sintering of titanium-titanium nitride nano/nanocomposite powders. Two compositions of the nano/nanocomposite powders, i.e. nano Ti-8 wt-% nano TiN and nano Ti-15 wt-% nano TiN along with nano Ti were used in the present study. Sintering studies have been carried out by dilatometry of the powder compacts using a constant rate of heating (CRH) and employing model equations to the initial sintering portion. The shrinkage values obtained were analysed using Young and Cutlers equations and a model proposed by Johnson and Berrin. Based on the analysis of experimental data the effect of second phase TiN on the mass transport mechanisms of nano Ti was determined

The effect of extent of nitridation on the consolidation of mechanically alloyed Ti-TiN nano-composite powders

Titanium - titanium nitride nano-composite powders were prepared by attrition milling of elemental titanium in nitrogen atmosphere. The milling process was carried out at a speed of 450 rpm for 75 hours and interrupted at regular intervals of 15 hours to characterize the powders. The powders milled for various durations were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray fluorescence spectroscopy (XRF) for the determination of formation of phases, particle shape and size, impurity pickup and the extent of nitridation. The nano-composite powders of varying extent of nitridation were then uniaxially cold compacted and sintered in argon atmosphere to find out the effect of extent of nitridation on the compaction and sintering behaviour of the Ti-TiN nano-composite powders

Dilatometry of attrition milled nanocrystalline titanium powders

The sintering behavior of nanosized titanium powders was investigated by ditatometry. The nanosized Ti powders (40 nm) were produced by the attrition milling of micron sized Ti powders (12 mu m) in Ar atmosphere. Sintering was carried out in Ar atmosphere in the temperature range of 450-1250 degrees C for nanosized Ti and 650-1250 degrees C for micron sized Ti by heating at 10 degrees C/min, up to the sintering temperature followed by isothermal holding for I It. The nanosized Ti powders exhibited a lower sintering onset temperature, larger shrinkage, larger shrinkage rate, and lower activation energy for sintering as compared to the micron sized Ti powders. The sintered micron sized Ti specimens exhibited both intraagglomerate and interagglomerate porosity while the nanosized Ti specimens exhibited well densified agglomerates (almost no interagglomerate porosity) and large intraagglomerate porosity. In nanosized Ti grain growth was found to take place beyond 700 degrees C and reached a maximum of 66 nm in samples sintered at 1100 degrees C. (c) 200

Sintering mechanisms of attrition milled titanium nano powder

Detailed sintering Studies have been carried out on attrition milled nanocrystalline titanium powder through isothermal dilatometry over a temperature range of 300-1250 degrees C along with microstructural and x-ray diffraction studies. The sintering behavior of attrition milled nanocrystalline titanium appears to be characterized by: (i) very low activation energies, (ii) high shrinkage anisotropy, (iii) very rapid grain growth in the beta range, and (iv) two kinds of densification processes, namely, intra-agglomerate and inter-agglomerate. Analysis of the kinetic data through sintering diagram approach indicates the operation of particle sliding and grain boundary rotation, type of mechanism in addition to the grain-boundary diffusion, and lattice diffusion as the dominant mass transport mechanisms