رسائل دكتوراة
English
2017
Development of Two-Phase Reinforced Alumina Nanocomposite for Cutting Tools Applications
خواجة محمد , صاحب نواري
كلية الهندسة-جامعة الملك فهد للبترول والمعادن · السعودية
The high stiffness and hardness of ceramic materials made them attractive for various applications. However, their low toughness limit their use in many structural applications such as cutting tools. Reinforcing ceramics by two nanoscale phases, having different morphologies, is a new methodology that has been adopted to develop hybrid nanostructure with improved mechanical properties. However, achieving a uniform distribution/dispersion of the nanosize reinforcements in the matrix and retaining nanostructure during consolidation process are major challenges in synthesizing these highly claimed materials.In this research work, an approach for the synthesis of homogenous Al2O3-SiC-CNTs hybrid nanocomposite powders via molecular level mixing was developed. In addition, Al2O3-SiC-CNTs nanocomposite powders was also synthesized using ball-milling technique. Synthesized powders were consolidated using spark plasma sintering technique. The influence of synthesis and sintering parameters, and reinforcements’ content on the microstructure, densification, hardness, fracture toughness, and bending strength of the composites was investigated.The prepared materials were characterized, wherever needed using FE-SEM, TEM, X-ray mapping, XRD, FT-IR, and TGA. The nanocomposite powders synthesised via molecular level mixing or ball milling as well as sintered samples showed uniform distribution of SiC and CNTs.The final microstructure of sintered samples comprised intergranular CNTs, along with inter- and intergranular SiC nanoparticles, which restricted grain growth. Fully dense monolithic alumina and almost fully dense hybrid nanocomposites were obtained (relative density higher than 98%). The mode of fracture changed from intergranular mode for the monolithic alumina to almost complete transgranular mode for the Al2O3-SiC-CNTs nanocomposites, which along with other toughening mechanisms improved the fracture toughness.The Al2O3-5SiC-1CNTs composite, synthesised using molecular level mixing and sintered at 1600°C for 10 min, possessed both high hardness and toughness values of 23.32GPa and 7.10 MPam1/2, respectively. This constitutes an increase in hardness and toughness of 25.6 and 96%, respectively, compared to alumina.As for the composites prepared using ball milling and sintered at 1500°C for 10 min, Al2O3-10SiC-2CNT possessed a high fracture toughness value of 6.98 MPam1/2, representing an increase of 94% compared to alumina. Al2O3-10SiC-1CNT possessed a high hardness value of 20.81GPa, representing an increase of 12 % compared to alumina.
