Wenshu Yang

Effect of volume fraction on microstructure and mechanical properties of Si3N4/Al composites

Abstract Si3N4 particles reinforced aluminium matrix composites (Si3N4/Al) with different particle volume fractions (45%, 50%, and 55%) were fabricated by pressure infiltration method. The effects of Si3N4 volume fraction and T6 treatment on microstructure and mechanical properties of Si3N4/Al composite were investigated. The results show that Si3N4/Al composites are well infiltrated with good particles dispersion and no apparent porosity or significant casting defects are observed. High density of dislocations in Al matrix around Si3N4 particles is observed. The bending strength of Si3N4/Al composites decreases with an increase in Si3N4 volume fraction, and can be greatly improved by T6 treatment. Elastic modulus of composites increases linearly with Si3N4 volume fraction. At a lower Si3N4 volume fraction, more tearing ridge and dimples with elongation are observed. T6 heat treatment shows minor effect on the fracture surface of composite.

Aging and thermal expansion behavior of Si3N4p/2024Al composite fabricated by pressure infiltration method

Abstract The aging and thermal expansion behaviors of Si 3 N 4p /2024Al composite fabricated by pressure infiltration method were investigated. The peak-aging time and peak hardness both decrease with the increase of aging temperature for both the 2024Al alloy and Si 3 N 4p /2024Al composite. The calculated activation energies of s ′ (precursors of the Al 2 MgCu) phase indicate that the precipitation of s ′ phase in Si 3 N 4p /2024Al composite occurs easily than in 2024Al alloy. The presence of Si 3 N 4 particles does not alter precipitation sequence, but accelerates the process of aging precipitation in Si 3 N 4p /2024Al composite. The experimental coefficient of thermal expansion (CTE) of Si 3 N 4p /2024Al composite bellow 100°C is more close to the average value of the Kerner model (upper bound Schapery model) and lower bound Schapery model. Aging treated Si 3 N 4p /2024Al composite presents the best dimensional stability due to low internal stress and strong pining effect on dislocations from fine dispersed precipitates (Al 2 MgCu) and high density tangled dislocations. The good mechanical properties, compatible CTE with steel and high dimensional stability make Si 3 N 4p /2024Al composite very competitive for application in the inertial guidance field.