Small punch testing of heat resistant ultrafine-grained Al composites stabilized by nano-metric Al2O3 (HITEMAL©) in a broad temperature range

Highlights: • Mechanical properties of ultrafine-grained Al-Al₂O₃ composites were tested by small punch test (SPT) from 23 to 500 °C. • Four specific materials with different Al grain structure, morphology and distribution of Al₂O₃ dispersoids were used. • Mutual correlation of tensile test and SPT results strongly depends on the particular testing temperature. • Considering the temperature as a parameter, the precision of yield strength calculation from SPT results improves. -- Abstract: The mechanical properties of thermally stable ultrafine-grained Al metal matrix composites dispersion strengthened and stabilized by nano-metric in-situ Al₂O₃ (named HITEMAL©) fabricated by powder metallurgy (PM) were tested by small punch testing (SPT) in a broad temperature range from a room temperature (RT) to 500 °C. By changes to PM approach and applied processing parameters four specific HITEMAL© materials with different Al grain structure, and different morphology and distribution of Al₂O₃ dispersoids were fabricated and characterized by transmission electron microscopy and energy-dispersive X-ray spectroscopy. The effect of microstructural features on the mechanical properties of HITEMAL© materials was pursued by SPT. The SPT results were compared and correlated with the results obtained by conventional tensile testing. It was confirmed that a mutual correlation of tensile test and SPT results strongly depended on the particular testing temperature. As a result of microstructural differences between HITEMAL© materials the correlation between tensile test and SPT results changed quite significantly for each studied material. The analysis of fractured SPT discs by scanning electron microscopy (SEM) revealed the transformation in fracture mechanism during SPT from ductile to brittle behavior as the testing temperature increased from RT to elevated temperatures. If the testing temperature was considered as a parameter, the precision of yield strength calculation from SPT results improved significantly in whole temperature range.