Thermal expansion behaviour of nanocrystalline titanium powder compacts

This investigation is an attempt to understand the expansion behaviour of compacts of nanocrystalline titanium powder during thermal treatments. Entrapped gases cause excessive expansion in the green compacts. The dilatometric study reveals that there is no significant difference in the expansion coefficient of sintered nanocrystalline titanium samples, compared to their micron-size counterpart. (c) 2005 Elsevier BX

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