EFFECT OF POROSITY ON THE COMBUSTION SYNTHESIS OF TITANIUM NITRIDE

The effect of porosity on the self‐propagating reaction between porous titanium and gaseous nitrogen was investigated. The relationship between total nitrogen uptake and porosity showed a maximum at about 44% porosity. High initial sample porosities lead to partial melting of the titanium and subsequently to a lower degree of conversion to the nitride. Low initial porosities limit the conversion through lower reaction interfacial areas and lower gas permeation. Wave velocity measurements, thermogravimetric determinations on the progression of the combustion front, and microstructural analyses demonstrated that the passage of the front is associated primarily with the formation of a surface layer of TiN1‐x with x being 0.10 and 0.06 for lowdensity (49%) and high‐density (59%) samples. The product of combustion contained titanium nitride and primary and β‐transformed α solid solutions. The relative abundance of the latter two phases was dependent on the initial relative density of the samples. Copyright © 1990, Wiley Blackwell. All rights reserved