Properties of Transition Metal Borides Ceramics

Transition metal borides are mainly explored for their mechanical properties. Since they exhibit metallic transport properties such as high electric and thermal conductivity with a negative temperature coefficient they are also of interest as electrode materials, for heating elements and sensors. 

The electric resistivity in the solid solution system TiB2-ZrB2 was studied by Rahman et al. [273]. Billehaug and 0ye [274] present a study of several transition metal diborides for cathode materials in Hall-Herould cells and come to the conclusion that TiB2 should be an excellent candidate because of its stability against the 

High-temperature reinforcement by in situ precipitation of TiC and TiB2 from supersaturated solid solutions has already been used with interesting results. In the TiC-TiB2 system, either TiC or TiB2 can be the host crystal for the corresponding minority phase or the precipitate [278-280]. The addition of a small fraction of boron to TiC can increase the critical resolved shear stress at 1600°C by a factor of six if TiB2 precipitates are formed at the (111) slip plane of TiC. 

Reinforcement of TiB2 by dispersed SiC particles is generally possible since both materials are chemically compatible. As a result, crack impediment is obtained but the increase in strength and toughness is small [282], This composite material has, however, not yet been studied extensively. 

Combinations of diborides of different transition metal borides have been studied, especially in the TiB2/CrB2 and TiB2/W2B5 systems, for wear applications and to a minor extent for eleetrodes in Hall-Herould cells [135,139,140,293-295], Since the transition metal diborides crystallize in the same structure type, namely the AIB2 

---