Combustion synthesis of TiB2-based cermets: modeling and experimental results

Abstract

TiB 2 -based cermets are prepared by combustion synthesis followed by a pressing stage in a granulate medium. Products obtained by combustion synthesis are characterized by a large remaining porosity (typically 50%). To produce dense cermets, a subsequent densification step is performed after the combustion process and when the reacted material is still hot. To design the process, numerical simulations are carried out and compared to experimental results. In addition, physical and electrical properties of the products related to electrical contact applications are evaluated. IntroductionSelf-propagating high-temperature synthesis (SHS), also known as combustion synthesis or solid-flame combustion, is considered a gasless combustion process. It is a cost-effective method for producing high-purity refractory compounds and advanced ceramics [1]. Here, the application to functionally graded cermets and electrical contact materials is shown.The basis of the reaction synthesis relies on the ability of gasless and highly exothermic reactions to be selfsustaining. Ignition can be achieved by a laser beam, ohmic heating, induction, or spark. However, a sufficient amount of energy needs to be deposited for the reaction to become selfpropagating. SHS has assumed significance for the production of intermetallics, ceramics, and cermets because it is a very rapid processing technique without the need for complex furnaces [2], and can increase the productivity in comparison with conventional techniques. One of the drawbacks of this technique is the high porosity of the final product (typically 50%), due to: (1) initial porosity in the reactant mixture, and (2) the higher density of the reaction products with respect to starting materials. A subsequent densification stage is needed, which is often hard to achieve in ceramic composite materials because they are highly deformation-resistant. However, one may take advantage of the ductile behavior when reaction products are still hot and apply techniques such as hot u Fax: +31-15-2843997, E-mail: richard.bouma@tno.nl pressing, hot rolling, hot isostatic pressing, or shock waves to eliminate porosity. Combustion synthesis followed by quasiisostatic pressing (QIP) in a granulate medium is the technique for removal of porosity studied here.In the QIP technique, the particulate acts as a pressuretransmitting medium (PTM) and redistributes an initially applied axial load to create a stress profile similar to isostatic pressing [3][4][5][6][7]. The pressure distribution in the PTM has been discussed in a previous paper [8]. In addition, the PTM thermally isolates the sample, thereby minimizing cracking due to rapid cooling and keeping the temperature of the specimen for a longer time above the ductile-to-brittle transition temperature of the ceramic phase. In this study, numerical simulations of the heat flow from the reacted material to its surroundings are presented and will be compared with experimental results in order to know whether a sufficient time-window exists for th...

Численное Исследование Ударно-Волнового Нагружения Металлических Композитов На Базе W И WC

“…Аналогичные расчеты были выполнены для металлического композита, содержащего серебро, на примере элконита, содержащего WC и Ag. Исследованиям материалов такого типа посвящен ряд работ, в частности [29,30]. Результаты моделирования ударно-волнового нагружения для смеси серебра и карбида вольфрама (элконит G-12−WC(40)Ag(60)), показаны на рис.…”

Microstructure and wear resistance of solidified TiB2-based composites for cutting tools achieved by SHS in high-gravity field

“…Self-propagating high-temperature synthesis or briefly SHS, also known as combustion synthesis, is a facile processing to prepare many refractory ceramic materials. By this processing, TiB 2 and its composites have been also synthesized [6] . In comparison with conventional sintering processing, SHS has the advantage of time and energy-saving, and thus applicable for large-scale industrial production with low cost.…”

Infiltrated Cu8Al–Ti alumina composites

“…Pure or alloyed copper has thus been combined with ceramics as diverse as TiB 2 [1][2][3][4][5][6][7], Al 2 O 3 [1,[8][9][10][11], several forms of carbon [12][13][14][15][16] or various carbides [17][18][19][20][21]; Ref. [22] gives a review of their processing methods and mechanical properties.…”