Ultrafine-grained Al composites reinforced with in-situ Al3Ti filaments

Abstract

Ultrafine-grained (UFG) Al matrix composites reinforced with 15 and 30vol% in-situ Al3Ti filaments were fabricated by extrusion of Al-Ti powder mixtures followed by solid-state reactive diffusion. Fine Al powder particles (1.3μm) heavily deformed the coarser Ti particles (24.5μm) into filaments during extrusion. Upon a subsequent operation of hot isostatic pressing (HIP), the micrometric Al3Ti filaments elongated along the extrusion direction and formed in situ in the UFG Al matrix. Fabricated composites are free of pores and voids with perfect bonding created at the Al-Al3Ti interfaces. In parallel, a small portion (2.4vol%) of nanoscale γ-Al2O3 particles, which originate from native amorphous films on fine Al powders, formed in situ and were homogenously dispersed in the Al matrix. The microstructures of as-extruded and after HIP composites were analyzed by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS) and electron back-scattered diffraction (EBSD). Owing to the presence of nanometric γ-Al2O3 particles with Al high angle grain boundaries (HAGBs), the UFG Al matrix remained stable even after HIP at 600°C for 9h. The mechanical properties and creep performance of composites at testing temperatures of up to 600°C were systematically studied. The Al-Al3Ti composites exhibited a combination of increased strength and Young's modulus in addition to excellent creep performance and structural stability, which indicates that the studied composites are potential structural materials capable of service at elevated temperatures.