Mechanical Properties and Strengthening Mechanisms of Al-15 Pct B4C Composites with Sc and Zr at Elevated Temperatures

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 47; no. 9; pp. 4694 - 4708
• Main Authors: Qin, Jian, Zhang, Zhan, Chen, X.-Grant
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.09.2016; Springer Nature B.V
• Subjects: Aluminum boron carbide; Ambient temperature; Annealing; Characterization and Evaluation of Materials; Chemical precipitation; Chemistry and Materials Science; Coarsening; Composite materials; Dislocation mobility; High temperature; Materials Science; Mechanical properties; Metallic Materials; Nanotechnology; Precipitates; Scandium; Shearing; Structural Materials; Surfaces and Interfaces; Thermal stability; Thin Films; Yield strength; Zirconium; Al3Sc; Precipitate Size; Dislocation Climb; Strength Increment; Peak Aging Condition
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-016-3606-4

The mechanical properties at ambient and elevated temperatures of two Al-15 vol pct B 4 C composites, S40 with 0.4 wt pct Sc and SZ40 with 0.4 wt pct Sc and 0.24 wt pct Zr, are investigated during long-term thermal annealing. The presence of large B 4 C particles in the microscale has a moderate but stable strengthening effect on Al-B 4 C composites at ambient and elevated temperatures, while the precipitation of nanoscale Al 3 Sc and Al 3 (Sc, Zr) in the composite matrix provides a predominate contribution to the composite strength, which is varied by tested temperatures. The Al 3 Sc precipitates in S40 remain coarsening resistant at 523 K (250 °C), whereas the Al 3 (Sc, Zr) precipitates in SZ40 are thermally stable at 573 K (300 °C) over 2000 hours of annealing. At higher annealing temperatures (573 K (300 °C) for S40 and 623 K (350 °C) for SZ40), both Al 3 Sc and Al 3 (Sc, Zr) precipitates become coarsening with prolonged annealing time. The yield strength of S40 and SZ40 at ambient temperature decreases with the increasing precipitate size, which can be explained by the classical precipitate shearing and Orowan bypass mechanisms. At elevated temperatures [523 K to 623 K (250 °C to 350 °C)], considerably lower yield stresses are observed compared to those at ambient temperature, which invokes a dislocation climb mechanism. The predicted yield strengths at elevated temperatures by the combination of dislocation climb and Orowan models are in good agreement with the experimental data.