FORMATION ENTHALPY OF NI3AL-BASED ALLOYS WITH COBALT ADDITIONS VS THEIR MECHANICAL-PROPERTIES

The formation enthalpy of ternary Ni3Al-based alloys with cobalt addit ions was determined. The calorimetric method used was based on compari son of heat effect of the dissolution of the alloy and its components in the bath. In literature one can find controversial opinions as to w hether cobalt enhances the ductility of the studied compound. This pro perty is Important since embrittlement is the main obstacle in the app lication of Ni3Al as a material for high temperature use. In the discu ssion of the obtained formation enthalpy values from the aspect of pha se structure a sketch of main trends sygnalized in literature is prese nted. The dependence of formation enthalpy vs. ductility is analysed. The question is at the cost of which of the host elements /Ni or Al/ c obalt is introduced to the composition of the alloy. When cobalt is in troduced at the cost of nickel, no change of formation enthalpy and du ctility is observed. In the case of substitution at the cost of Al in the alloy composition substantial increase of heat of formation and pl asticity is noted, even for a small /2at.%/ Co content.