Relation between combustion parameters and phase diagram for the systems Ti-Co and Ti-Ni

Abstract

In self-propagating high-temperature synthesis there are isothermal parts in the temperature profile of the reaction zone, which result in flat parts on the curve relating the maximum combustion temperature to the initial temperature. To define points on the phase diagram by combustion methods it is necessary to record the maximum temperature as a function of the initial temperature for various composition and determine the temperature that corresponds to a flat area, while examining the appearance and structure of the casting. This enables one to construct the liquidus curve, and thus, to describe the high-temperature part of the phase diagram. The authors have used the combustion method to construct the liquidus curves for Ti-Co and Ti-Ni systems. The study examines the maximum temperature, the combustion rate, and the phase composition of the final products as affected by the ratio of the components in the initial mixture for several initial temperatures. The concentration range in which a synthesis can be performed in a burning wave increases with the initial temperature. The burning rate increases with the initial temperature. Throughout the component concentration ranges, the phase compositions of the products as determined by x-ray phase and local spectral methods practically corresponded to themore » phase diagram. In most cases the products consisted of several phases, namely intermetallides known from the equilibrium phase diagram. The final products from a composition corresponding to the single-phase region contained small amounts of other phases, but the content of these fell as the initial temperature was raised.« less