Investigation and characterization of sintering behavior of Al2O3 and ZrO2 doped silicon carbide

Silicon Carbide (SiC) is a covalent bond, low density, low atomic weight basic components, high corrosion resistance, extremely hard and strong materials that fully meet the high melting point and thermal stability refractory criteria. Silicon carbide based materials can be obtained by methods such as cold isostatic press, hot press, reactive sintering and solid/liquid phase sintering. Refractory carbides divided into interstitial carbide sand covalent carbides as structurally. SiC is in the class of covalently bonded carbides. Due to its strong covalent bond sand high melting point, it is a very difficult material to be sintered monolithically by conventional methods. For this reason, a composition should be created by adding additive so ambient conditions such as temperature sand pressure should be changed in order to reach the desired density as a result of sintering and to accelerate the liquid/solid phase sintering. In this study, the effect of Al2O3 and ZrO2 additives on SiC material under different sintering conditions were investigated by applying the sintering process in atmospheric environment at different temperatures and for three different times to SiC-based samples obtained with the addition of Al2O3 and ZrO2 in different compositions. Compositions were prepared by adding Al2O3 and ZrO2 powders separately, at % 1-3-5 by weight, to the SiC powder supplied in high purity. After the mixtures obtained are shaped by manual mechanical press and then with cold isostatic press, each composition at 1400 °C, 1450 °C and 1500 °C temperatures for half an hour, 1 hour and 2 hours in atmospheric environment is sintered at a heating rate of 5 °C/min and the same cooling rate. Relative densities according to Archimet principle and mechanical behaviors such as Vickers hardness and compressive strength of the compositions prepared at different rates by using Al2O3 and ZrO2 powders as additives on the samples obtained at different temperatures and sintering times were investigated. XRD and SEM characterizations of products formed after the sintering process were made and different sintering conditions were compared with each other. It seems that relative densities of both composites which prepared by adding Al2O3 and ZrO2 powders increased with sintering time to 60 min at all temperatures and with sintering time increased to from 60 to 120 min, relative densities of both composites decreased. An increasing trend in relative density was observed with addition of Al2O3 and ZrO2 in the composites based SiC from % 1 to % 5. It was observed that the relative density decreased significantly with the sintering time increased to 120 min at 1450 °C and 1500 °C. If it was observed that amount of Al2O3 and ZrO2 in the composites mixture increase, sintering amount is increase. Likewise sintering increased with increasing time and temperature. While both of composites Vickers hardness values increase with sintering time increase to from 30 min to 60 min generally, a decrease was observed with sintering time increase from 60 min to 120 min. In addition to amount of Al2O3 and ZrO2 increased, the hardness value decreased. However, as Al2O3 and ZrO2 additives increased, the hardness value increased. As sintering temperatures increased, the hardness value decreased. It was observed that as sintering time increased, the hardness value decreased especially at 1500 °C. Results of compression strength test are in agreement with the hardness value graphs, it was observed that increasing the sintering time has a negative effect on the compressive strength according to compressive strength graphs of Al2O3 and ZrO2 doped silicon carbide material which sintered at 1400 °C, 1450°C and 1500 °C.