Zeya Oo

Phase and thermal stability in Ti3SiC2 and Ti3SiC2/TiC/TiSi2 systems

It is known that Ti 3 SiC 2 is the only stable ternary compound in the Ti-Si-C system; however the preparation of pure Ti 3 SiC 2 is very difficult as there are always impurities. The properties of these Ti 3 SiC 2 composites can be enhanced or weakened by these impurities. In this chapter, the effect of argon and high vacuum annealing on the phase stability and phase transitions of highly-pure Ti 3 SiC 2 and Ti 3 SiC 2 /TiC x /TiSi 2 composites up to 1550°C has been studied using in situ neutron diffraction. The role of TiC x and/or TiSi 2 in the thermal stability of Ti 3 SiC 2 during argon or vacuum annealing has been discussed. The mechanism of Ti 3 SiC 2 decomposition in vacuum has also been proposed. The decomposition rate of Ti 3 SiC 2 was both dependent on temperature and dwell time, and exhibited a linear relationship with the dwell time and increased with temperature. Furthermore, the activation energy for the formation and decomposition of Ti 3 SiC 2 was determined using the Arrhenius equation. The kinetics of isothermal phase decomposition at 1500 °C was modelled using a modified Avrami equation.

Indentation Responses of Functionally-Graded Al2TiO5- Based Ceramics

Aluminium titanate, Al2TiO5 (AT) with the pseudobrookite structure is the only compound in the alumina-titania system. It is an excellent refractory and thermal shock resistant material due to its relatively low thermal expansion coefficient (1 ´10-6 °C –1) and high melting point (1860°C). However, its low mechanical strength, hardness and fracture resistance together with susceptibility to decomposition in the temperature range 900–1200°C has limited its wider application. In this paper, the innovative tailored design of functionally- graded Al2TiO5 – based ceramics system was presented. This involves the use of a vacuum heat-treatment or die-pressing to form hard graded layers of alumina on Al2TiO5. These hard outer layers will provide hardness and wear resistance to protect the softer but damage resistant underlayers. The results will also explore unresolved issues concerning the effect of graded interfaces on their physical and mechanical performance properties.

Effect of Grain Size and Controlled Atmospheres on the Thermal Stability of Aluminium Titanate

Aluminium titanate (Al2TiO5) is an excellent refractory and thermal shock resistant material due to 25 its relatively low thermal expansion coefficient and high melting point. However, Al2TiO5 is only 25 thermodynamically stable above 1280° C and undergoes a eutectoid‐like decomposition to α‐Al2O3 and TiO2 (rutile) at the temperature range of 900–1280° C. Hitherto, the effect of grain size and 2 atmosphere on the kinetics of decomposition is poorly understood but experimental evidences suggest a nucleation and growth controlled process. In this paper, we describe the role of grain size and controlled atmospheres on the thermal stability of Al2TiO5. In particular, the effects of grain size 25 and oxygen partial pressure on the rate of isothermal decomposition of Al2TiO at 1100° C have been 25 investigated. Results show that the thermal stability of Al0TiO5 increases as the grain size and 25 oxygen partial pressure increases. However, both the on‐set temperature nor the temperature range of Al2TiO5 thermal ...

Mapping of Composition, Phase Transitions and Properties in OxidizedTi3SiC2

The oxidation characteristics, composition profile and phase transition of Ti3SiC2 in the temperature range 20-1400°C have been investigated by in-situ neutron diffraction and secondary ion mass spectroscopy (SIMS). Anatase has been observed to form at ~600°C, rutile at ~750°C and cristobalite at ∼1300°C. Depth-profiling results by SIMS and Vickers indentation have revealed a distinct gradient in composition and microhardness within the surface oxide layers.