Al-Ti Particulate Composite: Processing and Studies on Particle Twinning, Microstructure, and Thermal Stability

The present investigation shows that alternate to the ceramic particles, hard metallic particles can be used as reinforcement in an aluminum matrix to achieve a good strength-ductility combination in a composite. Titanium particles were incorporated into aluminum by friction stir processing (FSP) to process an Al-Ti particulate composite. FSP led to uniform distribution of the particles in the stir zone without any particle-matrix reaction, thereby retaining the particles in their elemental state. Fracture and twinning of the Ti particles with different frequency of occurrence on the advancing and retreating sides of the stir zone was observed. Twinning of the particles was studied by focused ion beam-assisted transmission electron microscopy. The processed Al-Ti composite exhibited a significant improvement in strength and also retained appreciable amount of ductility. The thermal stability of the fine-grained structure against abnormal grain growth (AGG) was improved by the Ti particles. The AGG in the Al-Ti composite occurred at 713 K (440 A degrees C) compared to 673 K (400 A degrees C) in the unreinforced aluminum processed under the same conditions. On the other hand, the particle-matrix reaction occurred only at 823 K (550 A degrees C), and hence the Ti particles were thermally more stable compared to the matrix grain structure. (C) The Minerals, Metals & Materials Society and ASM International 2016