Effect of Ti, Al and Cu Addition on Structural Evolution and Phase Constitution of FeCoNi System Equimolar Alloys

Abstract

FeCoNi system equimolar alloys were fabricated by a vacuum arc melting. The phase constitution of FeCoNi system alloys was determined by XRD analysis and the microstructure was observed by OM. The comprehensive atomic radius δ, the mixing enthalpy ΔHmix and the mixing entropy ΔSmix of alloys were also calculated according to relevant equations. The results show that the addition of Ti, Al and Cu has an obvious influence on the microstructure and phase constitution of FeCoNi system equimolar alloys. Single Ti addition resulted in almost entire solid solution with a typical dendrite growth character and a little unknown phase. However, further addition of Al, Cu or Al+Cu into the FeCoNiTi equimolar alloys led to the occurrence of an entire solution phase with dendrite, coarse dendrite, and rosette dendrite respectively. Such a phenomena suggested that the mixing entropy caused by the increase of components number rather than the comprehensive atomic radius between the elements or the mixing enthalpy of the alloy systems might be responsible for the formation of almost entire solid solution in FeCoNi system equimolar alloys.

Thermodynamic assessment and experimental investigation of the systems Al–Fe–Mn and Al–Fe–Mn–Ni

“…Addition of Ti alone led to almost entire solid solution with a typical dendrite growth character plus some unknown phase. Further addition of Al, Cu or Al+Cu to FeCoNiTi equimolar alloys led to the appearance of a complete solution phase with dendrites, coarse dendrites and rosette dendrites, respectively 52 . This suggested that the mixing entropy caused by the increase in the number of components, rather than the atomic radius difference or the mixing enthalpy, was responsible for the formation of almost complete solid solutions.…”