J Mater Sci(2007)42:763-771 This value is 39% lower than the value measured for the thermal diffusivity values after 700-900C heat treat as-received material ments all show lower values than the as-received A more detailed set of thermal diffusivity results materials with the ranking order of greatest change after 10 h heat treatments are shown in Fig. 4. The shown after annealing at 700C, 800C and 900oC 1, 200C treatment shows a slight enhancement of thermal diffusivity, as does the 1,100C, whereas heat Microstructural studies treatment at 1000oC shows similar values to the values of the as-received material. all the other heat SEm studies treatments at temperatures lower than 1,000C show lower thermal diffusivities than the as-received mate- Limited SEM studies were carried out on samples heat rial. However, the 700C heat-treated sample again treated at temperatures between 700C and 1, 200C. shows the lowest thermal diffusivity values The most noteworthy observation was that a gap These trends are also maintained for the 30-h heat between fibre and matrix was noted at low tempera treatments for which thermal diffusivity results are ture. This is illustrated in Fig. 6 for a sample heat shown in Fig. 5. Again the heat treatment at 1, 200 treated at 700oC for 30 h. The shows higher thermal diffusivity values than those for residual stresses exist in the samples heated at lowe the as-received material, whereas data for samples temperatures. Residual glassy phases would tend to heated at 1,000C and 1, 100C are very close to that fow through any gaps in the matrix but the extent to of the as-received composite. On the other hand, the which this occurs depends on temperature of the heat Fig. 4 Measurement of 000 thermal diffusivity of BMAS/ Sic CMC after heat treatment in air for 10 h 0008 900°C 0D07 0006 日As recelved △△ 0004 0003 01002003040050060070080090010001100 Temperature rCl Fig 5 Measurement of 0.009 thermal diffusivity of BMAS/ 700°C 末 Sic CMC after heat treatment in air for 30 h 0.008 1100°c 0,006 x1200℃C 0.005 0.003 10020030040050060070080090010001100 Temperature rcThis value is 39% lower than the value measured for the as-received material. A more detailed set of thermal diffusivity results after 10 h heat treatments are shown in Fig. 4. The 1,200 C treatment shows a slight enhancement of thermal diffusivity, as does the 1,100 C, whereas heat treatment at 1,000 C shows similar values to the values of the as-received material. All the other heat treatments at temperatures lower than 1,000 C show lower thermal diffusivities than the as-received mate￾rial. However, the 700 C heat-treated sample again shows the lowest thermal diffusivity values. These trends are also maintained for the 30-h heat treatments for which thermal diffusivity results are shown in Fig. 5. Again the heat treatment at 1,200 C shows higher thermal diffusivity values than those for the as-received material, whereas data for samples heated at 1,000 C and 1,100 C are very close to that of the as-received composite. On the other hand, the thermal diffusivity values after 700–900 C heat treat￾ments all show lower values than the as-received materials with the ranking order of greatest change shown after annealing at 700 C, 800 C and 900 C. Microstructural studies SEM studies Limited SEM studies were carried out on samples heat treated at temperatures between 700 C and 1,200 C. The most noteworthy observation was that a gap between fibre and matrix was noted at low tempera￾ture. This is illustrated in Fig. 6 for a sample heat treated at 700 C for 30 h. These may indicate that residual stresses exist in the samples heated at lower temperatures. Residual glassy phases would tend to flow through any gaps in the matrix but the extent to which this occurs depends on temperature of the heat Fig. 4 Measurement of thermal diffusivity of BMAS/ SiC CMC after heat treatment in air for 10 h Fig. 5 Measurement of thermal diffusivity of BMAS/ SiC CMC after heat treatment in air for 30 h 123 J Mater Sci (2007) 42:763–771 767