As temperature decreases a ductile material can become brittle - ductile-to-brittle transition
Alloying usually increases the ductile-to-brittle transition temperature. For ceramics, this type of transition occurs at much higher temperatures than for metals.
The ductile-to-brittle transition can be measured by impact testing: the impact energy needed for fracture drops suddenly over a relatively narrow temperature range – temperature of the ductile-to-brittle transition.