Growth Kinetics Of Columnar Grains In Alumina Composite Ceramics By Microwave Sintering

Al2O3 composite ceramics materials have been widely used due to its excellent properties. However, it is greatly restricted because of its low fracture toughness.During the sintering process of in-situ toughening Al2O3 composite ceramics Al2O3 grains grow preferentially forming some lamellae grains and columnar grains. These have significantly enhanced toughness of Al2O3 composites ceramics. As sintering ceramics was a thermally activated process, we can determine the which of the diffusion mechanism or interface reaction mechanism plays a dominant role for sintering process by calculating the activation energy of the grain size. In this paper,Al2O3 composite ceramics were fabricated by microwave sintering. By means of XRD, SEM+EDS, TEM, the micro-structure were analyzed and by means of growth kinetics to calculate the Al2O3 columnar grain growth kinetics and activation energy index for further preparation Al2O3 columnar crystals change of Al2O3 composite ceramics provide a theoretical basis.The influence of different Nb2O5 content and different preparation processing on the Al2O3 columnar grains in Al2O3 matrix composite ceramics were investigated.Results showed that the grain size and number of Al2O3 columnar grains increased gradually with increasing Nb2O5 content, sintering temperature and holding time.The growth kinetic index n of Al2O3 columnar grains decreased with the increasing Nb2O5 content, and the grain growth activation energy Q increased and then decreased with the increasing Nb2O5 content, and in 10Nb2O5-7.5La2O3-82.5Al2O3 composite ceramics the grain growth activation energy are the minimum, the Q were361.19 k J/mol in the minor axis and 609.29kJ/mol in the minor one. The value of n and Q of the major axis was smaller than the minor one. The activation energy of10Nb2O5-7.5La2O3-82.5Al2O3 reached the minimum value. In this paper, the wetting effect of grain boundaries by the LaNbO4+Nb2O5 phases on Al2O3 grains promote the Al2O3 columnar grains. sintering temperature of Al2O3 ceramics was high, and the interfacial reaction mechanism in liquid phase sintering was the control mechanism of Al2O3 columnar crystal formation. The influence of different sintering process on 10Nb2O5-7.5La2O3-82.5Al2O3 composite ceramics on grain growth kinetics parameters was investigated. Results showed that: growth kinetic index n ofAl2O3 columnar grains decreased with increasing sintering temperature, and the major ones were smaller than the minor ones; the growth activation energy decreased with increasing sintering time, and the major ones were also smaller than the minor ones. With the comparison of growth kinetics by microwave sintering and conventional sintering, the value of n by microwave sintering decreased from 4.46 to2.50 in major axis, and 5.56 to 4.84 in minor ones. Microwave sintering technology is better than conventional sintering in terms of promoting Al2O3 columnar grain growth. The growth mechanism of microwave sintering columnar grains was two-dimensional nucleation growth mechanism. When the sintering time was shorter and temperature was lower, the growth mechanism of the conventional sintering grains was screw dislocation growth mechanism; with the increasing temperature or time, the solid phase sintering mechanism played a leading role.