Estimation of ductility of Fe–Al alloys by means of small punch test

Small punch test consists in a deformation of supported disk specimen by a penetrator with either constant rate of deflection or under constant force. In the present contribution, the ductility of three selected Fe–Al alloys with different content of aluminium was studied by the constant-rate variant of the test (all concentrations in atomic %): (i) 18% Al (A2 lattice), (ii) 31.5% Al (D03 lattice at lower temperatures and B2 lattice at higher temperatures) and (iii) 43% Al (B2 lattice). Small punch tests were performed at the deflection rate of 0.006 mm/s at temperatures from 20 to 800 °C. Fracture energy was determined by integrating the area under the load–deflection curve. The dependence of fracture energy on temperature differed significantly for different alloys. The fracture energy of the alloy (i) increased with the increasing temperature, attained a maximum value at about 400 °C and then rapidly fell down. The dependence for the alloy (ii) was qualitatively similar for temperatures up to 500 °C and then a new steep increase was observed with the maximum at about 550 °C. A rapid decrease of the fracture energy was finally recorded at temperatures above 550 °C. In the alloy (iii), the values of the fracture energy were low in the whole temperature range and the fracture appearance was brittle even at temperature of 800 °C. It is shown that the method can be used for an assessment of ductile-to-brittle transition temperature.