In situ (α-Al2O3+ZrB2)/Al composites with network distribution fabricated by reaction hot pressing

Abstract

In situ (α-Al 2 O 3 +ZrB 2 )/Al composites with network distribution were fabricated using low-energy ball milling and reaction hot pressing. Differential thermal analysis (DTA) was used to study the reaction mechanisms in the Al-ZrO 2 -B system. X-ray diffraction (XRD) and scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDX) were used to investigate the composite phases, morphology, and microstructure of the composites. The effect of matrix network size on the microstructure and mechanical properties was investigated. The results show that the optimum sintering parameters to complete reactions in the Al-ZrO 2 -B system are 850°C and 60 min. In situ-synthesized α-Al 2 O 3 and ZrB 2 particles are dispersed uniformly around Al particles, forming a network microstructure; the diameters of the α-Al 2 O 3 and ZrB 2 particles are approximately 1-3 μm. When the size of Al powder increases from 60-110 μm to 150-300 μm, the overall surface contact between Al powders and reactants decreases, thereby increasing the local volume fraction of reinforcements from 12% to 21%. This increase of the local volume leads to a significant increase in microhardness of the in situ (α-Al 2 O 3 -ZrB 2 )/Al composites from Hv 163 to Hv 251.

Design of In Situ Metal Matrix Composites Produced by Powder Metallurgy—A Critical Review

“…Figures in the "examples" column are meant to illustrate microstructural features listed in the summary. Microstructural evolution relies on the stability of BC [16].…”

“…Ti + B 4 C → Ti + TiC + TiB [43] Metals 2022, AB and AC form near BC reinforcements, so a cluster of nuclei forms at former BC particles. Microstructural evolution relies on the stability of BC [16]. Coherent and semi-coherent interfaces are possible.…”

“…AB forms near BC reinforcements, usually as clusters. Microstructural evolution relies on the stability of BC [16]. Coherent and semi-coherent interfaces are possible.…”

“…When interface bonding is adequate, it is possible to transfer load from matrix to reinforcement, and composites do not fail prematurely by intergranular fracture caused by poor interfacial strength. Such advantage implies that reinforcement particles can effectively generate and resist the movement of dislocations, as well as inhibit matrix grain growth [16]. Additionally, in situ techniques allow for raw materials saving, as they do not require the use of nanopowders to obtain nanosized reinforcements.…”