Journal of Alloys and Compounds 436 (2007) 181–186

Investigation of the SHS mechanisms of titanium nitride by in situ time-resolved diffraction and infrared thermography D. Carole a , N. Fr´ety a,∗ , S. Paris b , D. Vrel c , F. Bernard b , R.-M. Marin-Ayral a a

Universit´e de Montpellier II, LPMC, UMR CNRS 5617, 34090 Montpellier Cedex 5, France b Universit´ e de Bourgogne, LRRS, UMR CNRS 5613, 21078 Dijon, France c Universit´ e Paris XIII, LIMHP, UPR 1311, 93430 Villetaneuse, France Received 17 February 2006; received in revised form 30 June 2006; accepted 1 July 2006 Available online 15 September 2006

Abstract The self-propagating high-temperature synthesis (SHS) or combustion synthesis is a promising process to produce advanced ceramics due to the high purity of the elaborated materials and the very short synthesis time. Titanium nitride has been synthesised from pressed titanium powder and a nitrogen gas flow under a 0.1 MPa pressure. The influence of the addition of a TiN diluent was investigated. For the first time, SHS reaction mechanisms were determined from in situ time-resolved X-ray diffraction (TRXRD) experiments using the synchrotron radiation. These experiments were coupled with infrared thermography to study the propagation of the combustion reaction. It appeared that the initiation of the combustion reaction is due to the ␣-Ti to ␤-Ti phase transformation. A single ␦-TiN phase was then produced from pressed titanium powder. The addition of a TiN diluent resulted in the synthesis of a multiphase material with the presence of the ␣-Ti, Ti2 N and TiN phases. The combustion reaction propagates in a surface mode at a velocity ranging from 6.4 to 7.4 mm/s. © 2006 Elsevier B.V. All rights reserved. Keywords: Nitride materials; Gas–solid reactions; X-ray diffraction; Synchrotron radiation

1. Introduction The self-propagating high-temperature synthesis (SHS) or combustion synthesis has become an attractive process to produce advanced ceramic materials [1–4]. Compared to the conventional methods, this process presents numerous advantages such as low durations of synthesis, low costs in energy and high purity products [5,6]. A great variety of materials, including carbides, borides, nitrides and oxides, have been synthesised using the SHS process [3,5]. Among nitride ceramic materials, titanium nitride is of particular interest due to its high hardness and good thermal stability associated to a high wear and corrosion resistance [7]. The combustion synthesis of titanium nitride is based on a solid–gas reaction between cold-pressed titanium powder and nitrogen gas, which is ignited at one end of the sample by an external heat source. The exothermicity of the reaction is sufficient to generate a self-sustained combustion wave, which propagates

from 1 to 100 mm/s through the sample without requiring any additional energy. The parameters to take into account during the SHS process are the powder particle size, the initial nitrogen pressure, the formation heat, the content of reaction diluent as well as the heat losses occurring in a non-adiabatic system by convection and radiation [2,8–11]. In this study titanium nitride was produced using the SHS process with a nitrogen gas flow under a 0.1 MPa pressure, the aim being to understand the mechanisms of the combustion reaction. Time-resolved X-ray diffraction (TRXRD) experiments were then investigated in order to determine the phases which were formed in situ. If this diffraction technique was already used to study solid–solid and solid–liquid SHS reactions [12–14], it was applied for the first time in this work to a solid–gas one. The TRXRD experiments were coupled with infrared thermography to study the propagation of the combustion front and to determine the temperatures involved as well as the combustion front velocity. 2. Experimental procedure

∗

Corresponding author. Tel.: +33 4 67 14 33 88; fax: +33 4 67 14 42 90. E-mail address: [email protected] (N. Fr´ety).

0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.07.010

The SHS reaction was performed using a reaction chamber with a nitrogen gas flow under a 0.1 MPa pressure. The reactants were constituted either of tita-