Aging and thermal expansion behavior of Si₃N_4p/2024Al composite fabricated by pressure infiltration method

CHEN Guo-qing¹, YANG Wen-shu^{1, 2}, MA Kang¹, Murid HUSSAIN ², JIANG Long-tao¹, WU Gao-hui¹

(1. School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China;
2. Department of Materials Science and Chemical Engineering, Politecnico di Torino, Turin 10129, Italy)

Abstract:The aging and thermal expansion behaviors of Si₃N_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 Si₃N_4p/2024Al composite. The calculated activation energies of s′ (precursors of the Al₂MgCu) phase indicate that the precipitation of s′ phase in Si₃N_4p/2024Al composite occurs easily than in 2024Al alloy. The presence of Si₃N₄ particles does not alter precipitation sequence, but accelerates the process of aging precipitation in Si₃N_4p/2024Al composite. The experimental coefficient of thermal expansion (CTE) of Si₃N_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 Si₃N_4p/2024Al composite presents the best dimensional stability due to low internal stress and strong pining effect on dislocations from fine dispersed precipitates (Al₂MgCu) and high density tangled dislocations. The good mechanical properties, compatible CTE with steel and high dimensional stability make Si₃N_4p/2024Al composite very competitive for application in the inertial guidance field.

Key words:Si₃N₄; Al matrix composite; aging; thermal expansion