ABSTRACT
SiC powder (D50=16 μm) and BN powder (D50 = 3.5 μm). La2O3 powder (D50 = 1 μm) and Al2O3 powder (D50 = 45 μm) were applied as sintering aids. The weight ratio of SiC and BN were 6:4. Al2O3 and La2O3 were chosen as sintered aids for fabrication of SiC/BN ceramics with molar ratio were 1:1. The total amount of the sinter additions was varied from 6wt% to 15wt% in the mixture. The aids content of hot-pressed specimens were 6wt%, 9wt%, 12wt% and 15wt%, which were
1 INTRODUCTION
Non-oxide ceramics, for example carbides and nitrides, had many advantageous mechanical properties under the room temperature and high temperatures condition owing to strong covalent bonding. In particular, Silicon Carbide (SiC) was a promising candidate for components in advanced gas turbines, piston engines, and heat exchangers thanks to their high strength and excellent creep resistance at elevated temperatures[1-3]. For multi-phase composites, either fibrous or particulate in nature, were employed to reduce probability of catastrophic failure. The mainly method to manage thermal stresses generated and simultaneously increase both crack initiation and propagation parameters was to use a high-low modulus composite. Generally, the addition of a low modulus phase to a strong, high modulus matrix decreases elastic modulus and flexure strength. Examples of these composites that use BN as the low modulus phase are Al2O3-BN[4],
designated as S6, S9, S12 and S15, respectively. The mixture powders were refined by a wet ball milling for 8 h using SiC balls in absolute ethanol. After milling, ethanol was cleared by applying a co-evaporating method to decrease segregation during the drying process. Then, the dried mixtures were put into a graphite mold with an inner diameter of 40 mm and an outer diameter of 100 mm, and then sintered by a vacuum hot-press furnace (Multi functioned 5000 type, in Japan), at 1900°C for 40 min under a pressure of 30 MPa in argon gas. The heating rate was executed with 15°C/min from room temperature to 1900°C. The specimens together with graphite mold were cooled to ambient temperature. The specific mass was determined according to Archimedes method. The phase constitution was identified by XRD and micro-structure was investigated by SEM. At least four bars were tested for each test condition. A minimum of fifteen indentation tests were performed for each condition of material and temperature. Vickers Hardness (HV) (in GPa) was calculated as:
HV P ae
= ⎛ ⎝⎜
⎞ ⎠⎟0 0018544.
