CHARACTERIZATION OF THE CONSOLIDATION BEHAVIOR OF FABRICATED NANOCRYSTALLINE-NANOPOWDERS OF TiC/AL-2124 COMPOSITE

摘要

Nanoscale materials have been the subject of major interest in recent years due to the anticipated ultrahigh strength and toughness combination anticipated in contrast to materials with conventional meso and micro-scale structures. The key issue lays in the optimization of the processing parameters suitable for the production of bulk nanostructured materials (BNSM) with superior properties suitable for elevated and cryogenic temperature applications. In the current research, a top down approach was employed for the refinement of a micron scale Al-2124 alloy powder about 45 μm in average size using high energy ball milling up to 24 hours. Reinforcement of the refined Al-2124 nanocrystalline powders with 1 μm nanostructured powder of TiC with internal structure <100 nm was performed to investigate the compaction and consolidation behavior of the produced nanocomposites. X-ray diffraction was employed to determine the crystallite size as a function of milling time (MT). microhardness of the milled powders was characterized for the hot compacts. Microstructural evolution of the green compacts was investigated by a 1nm resolution field emission scanning electron microscope (SEM), while the hot compacts were investigated using optical microscopy. Nanocrystalline-nanopowders <300nm in particle size and 20nm internal structural size were fabricated successfully at 24hr of MT from a 45μm particle sized 2124-Al powder with internal structure of 78nm in average size. The green compact densities of the nanoscale powder decreased to 92% compared to 97% for the microscale as-received powder due to the resistance of the strain hardened agglomerates to the applied pressure used for compaction. The microscale as-received powder was severely deformed during compaction, which resulted in higher densities. The degree by which the density decreased with the addition of 5-wt% TiC to the matrix was much lower for the nanoscale powder compared to the microscale one due to the low RPS ratio between the matrix and the reinforcement which promoted uniform distribution of the TiC particles within the matrix agglomerates. Increasing TiC content up to 10 wt% resulted in the formation of large voids and cavities. Refinement of the microscale powder to the nanoscale size resulted in 22.5% increase in hardness in the un-reinforced condition. Moreover, significant increase in hardness was also achieved with increasing TiC-content up to 10%.