Field-activated combustion synthesis of titanium aluminides

Abstract

The feasibility of synthesizing the titanium aluminides Ti 3 Al and TiAl through field-activated, selfpropagating combustion synthesis is demonstrated. A self-sustaining combustion wave can be initiated only when the imposed field is above a threshold value for each of these two aluminides. At the threshold values, wave propagation resulted in an incomplete reaction between the metals and the products, which contained several phases in addition to the desired one. As the field strength was increased, the reaction approached completion and the amounts of the secondary phases decreased. At a sufficiently high field, a single-phase product was obtained in the case of Ti 3 Al, but, in the case of TiAl, the product contained Ti 3 Al as a secondary phase even with the highest imposed field. The effect of reactant compact density was investigated for the case of Ti 3 Al synthesis. At a fixed value of imposed field, the degree of reaction completion and the conversion to the desired phase increased as the relative density decreased. These observations are discussed in light of the role of the electric field in activating the self-propagating combustion synthesis reactions and the effect of relative density on this activation. The results show that the synthesis by self-propagating high-temperature synthesis (SHS) can be optimized by the combination of field strength and relative density.

Mechanistic investigation of electric field-activated self-propagating reactions: experimental and modeling studies

“…During the second combustion step these intermediate phases interact with unreacted titanium and finally forming Ti 3 Al. This conclusion was also supported by the results obtained during the FACS of Ti 3 Al (Orrù et al, 1999b), where the field-assisted combustion wave propagates throughout the entire sample. The corresponding temperature profiles associated with the passage of the wave showed two peaks.…”

“…The final goal will be the possibility to predict the microstructure of final products so that to synthesize materials with tailored properties using the FACS method, whose advantages over conventional techniques are reported in the literature (cf. Feng and Munir, 1995a;Xue and Munir, 1996a;Xue and Munir, 1996b;Xue and Munir, 1997;Gedevanishvili and Munir, 1998;Orrù et al, 1999b). …”

“…Through this method, referred to in the literature as FACS (Field-Assisted Combustion Synthesis), the synthesis of materials heretofore not possible by normal SHS (e.g., SiC, SiC-AlN, TaC, B 4 C-TiB 2 , MoSi 2 -SiC, and Ti 3 Al) was successfully demonstrated (cf. Feng and Munir, 1995a;Xue and Munir, 1996a;Xue and Munir, 1996b;Xue and Munir, 1997;Gedevanishvili and Munir, 1998;Orrù et al, 1999b). SHS and FACS processes are typically characterized by high temperatures (up to about 3500 K), reaction waves which propagate at relatively high speeds (up to 25 cm/s), and low energy requirements, etc.…”

Historical perspective and contribution of US researchers into the field of self-propagating high-temperature synthesis (SHS)/combustion synthesis (CS): Personal reflections

“…His research activities at University of California at Davis resulted in education of large number of excellent scientists who are working in many countries. His selected major research contributions are listed below [92][93][94][95][96][97][98][99][100][101][102][103][104][105]:…”

“…In this review only few selected papers are mentioned [92][93][94][95][96][97][98][99][100][101][102][103][104][105]. He has also made very important contribution to the SHS community by reviewing articles on SHS for many journals, including the Ceramic Bulletin, and Materials Science Reports , which are cited by thou- [118][119][120][121][122][123][124][125][126].…”