High-temperature Synthesis Reaction Research Articles

Processing intermetallic composites by self-propagating, high-temperature synthesis

Initiated at the interface of dissimilar elemental metal foils, a self-propagating, high-temperature synthesis (SHS) reaction can be used to produce a fully dense, well-bonded metal-intermetallic layered composite. In the research described here, aluminum foils were sandwiched between metal foils (Fe, Ni, Ti) and heated in a hot press to approximately the melting point of aluminum. An SHS reaction occurred at the metal-aluminum interface, consuming all of the aluminum foil and part of the metal foil, resulting in a strongly bonded metal-aluminide interface. Tensile tests conducted at room temperature revealed that composites can be designed to behave in a high-strength and high-toughness manner by altering the thicknesses of the elemental foils.

Pore formation during reactive sintering of extruded titanium-aluminium powder mixtures: M. Dahms et al (GKSS-Forschungzentru, Geesthacht, Germany), Z. für Metallkunde, Vol 84, No 5, 1993, 351–357

Multilayered Ti-Al based intermetallic sheets were fabricated by sintering alternately layered titanium and aluminum foils. The microstructure and phase formation of the obtained sheets under different sintering conditions were evaluated by various techniques. The results reveal that when the sintering temperature is above the melting point of aluminum, the self-propagating high-temperature synthesis reaction occurs between Ti and Al, and forms various phases of Ti-based solid solutions including α-Ti Ti3Al, TiAl, TiAl2 and α-Ti including TiAl3, etc. When the sintering time increased, Ti-based solid solution, TiAl2 and TiAl3 disappeared gradually, and the sheet containing Ti3Al and TiAl phases in a multilayered structure formed finally. A lot of voids were also observed in the sintered structures, which were caused by the melting Al, Kirkendall effect and the difference of molar volumes between reactants and products. The voids were eliminated and a dense sample was obtained by the following hot press.

Amorphization of immiscible copper-vanadium by mechanical alloying in nitrogen: N. Kuroda et al (Nagoya University, Nagoya, Japan), J Japan Soc Power and Powder Metallurgy, Vol 40, No 11, 1993, 92–95. (In Japanese)

Multilayered Ti-Al based intermetallic sheets were fabricated by sintering alternately layered titanium and aluminum foils. The microstructure and phase formation of the obtained sheets under different sintering conditions were evaluated by various techniques. The results reveal that when the sintering temperature is above the melting point of aluminum, the self-propagating high-temperature synthesis reaction occurs between Ti and Al, and forms various phases of Ti-based solid solutions including α-Ti Ti3Al, TiAl, TiAl2 and α-Ti including TiAl3, etc. When the sintering time increased, Ti-based solid solution, TiAl2 and TiAl3 disappeared gradually, and the sheet containing Ti3Al and TiAl phases in a multilayered structure formed finally. A lot of voids were also observed in the sintered structures, which were caused by the melting Al, Kirkendall effect and the difference of molar volumes between reactants and products. The voids were eliminated and a dense sample was obtained by the following hot press.

A Theoretical Analysis of Combustive Synthesis of Titanium Carbide and a Comparison of Predictions with Measurements

Abstract –A numerical model is developed to predict the propagation speed of a Self-Propagating High-Temperature Synthesis (SHS) reaction wave along a vertical cylindrical reactant compact made from a mixture of titanium and carbon powders. A two-dimensional formulation along with convective + radiative heat loss from the peripheral surface to the surrounding inert gas atmosphere is used. The reaction kinetics employed are from the earlier work of Kanury. The model predicts the dependency of the wave propagation speed on various physical and geometric parameters of a titanium + carbon compact. It also predicts conditions at which the reaction wave does not propagate in a self-supporting manner. Effects of peripheral heat losses are also investigated. Some of the predictions are compared with experimentally measured propagation speeds to find excellent agreement.

Shock-induced and self-propagating high-temperature synthesis reactions in two powder mixtures: 5:3 Atomic ratio Ti/Si and 1:1 Atomic ratio Ni/Si

The conditions for initiation and propagation of the reaction forming the intermetallic compounds Ti5Si3 and NiSi from mixtures of elemental powders of varying porosity have been investigated using shock waves of different pressure and at atmospheric pressure using hot wire ignition in air and in an argon atmosphere. In each case, the reaction either went to completion or the powder remained essentially unreacted. The conditions for the initiation of the reaction in Ti/Si are sensitive to the presence of air. Two regimes of porosity and shock pressure are found for the Ti/Si mixture which cause complete reaction. A low-energy regime with a high initial porosity (producing a low shock pressure) with 0.1 torr of residual air triggers the reaction, while no reaction is observed with a 128 pct higher shock energy and a lower initial porosity (producing a higher shock pressure) when the residual air is replaced with argon. Hot wire ignition of porous Ti/Si powder at room temperature initiates a self-propagating high-temperature synthesis (SHS) reaction more easily in air than in an argon atmosphere, while the Ni/Si powder must be heated to allow the SHS reaction to propagate in high- or low-porosity mixtures in air. These observations are compared to published work on self-sustaining reactions in multilayer films. Reasons for the difference in behavior of the two powder mixtures are discussed.

An Experimental Investigation of Combustive Synthesis of Titanium Carbide

Abstract Described here is an experiment to determine the propagation speed of a self-propagating high-temperature synthesis (SHS) reaction wave along a vertical cylindrical reactant compact. The results obtained in this experiment pertain to the reaction between titanium and carbon to produce titanium carbide. They show the dependency of the steady propagation speed on: (i) the diameter of the reactant compact; (ii) the density of the compact; (iii) the reactant mixture composition; and (iv) dilution of the reactant mixture with the inert product TiC. The effects of these parameters on the density of the final product are also presented. Conditions at which the reaction wave ceases to propagate in a self-supporting manner are also identified.

High-speed diffractometer-reaction chamber using synchrotron radiation

A high-speed diffractometer capable of recording diffraction patterns in the time scale of a few milliseconds using a synchrotron x-ray source is described. This instrument is designed to monitor fast, self-propagating high-temperature solid-state synthesis reactions in an inert atmosphere. A vertical θ-2θ geometry is employed to collect maximum scattering from the horizontally polarized synchrotron beam. The detector system consists of two silicon photodiode arrays each of which can be integrated in as little time as 4 ms with shorter time frames possible if some pixels are skipped. Operation of the detectors, transfer and storage of data, and movement of the motors are controlled by an IBM-AT computer. The design, construction, and subsequent testing and performance at the Brookhaven National Synchrotron Light Source are discussed in detail.

Untersuchungen zum Mechanismus der Mechanochemischen Synthese von Verbindungen aus dem System SnS mit Hilfe des Mössbauer-Effektes

By means of Mössbauer and X-ray structural investigation it was shown that the compounds Sn 3S 4 and Sn 2S 3 can be synthesized mechanochemically. The influence of an inert additive on the explosive character of the mechanochemical synthesis of tin sulfides was investigated. A transition from the explosive way of synthesis to the nonexplosive one upon adding great quantities of inert material was observed. A mechanism explaining this phenomenon was suggested. The initiation of a high-temperature synthesis reaction by the heat effect of a mechanochemical explosive reaction was observed for the first time.

Initiation of self-propagating high-temperature synthesis reactions by pulsed laser radiation

Initiation of self-propagating high-temperature synthesis reactions by pulsed laser radiation