Sintering behavior and effect of ternary additions on the microstructure and mechanical properties of Ni–Fe-based alloy

ABSTRACT

The sintering behavior and effect of ternary additions on the microstructure and mechanical properties of Ni–Fe-based alloy were investigated, with the ternary additions Al, Co, Cr, Mo, Ta, and Ti. The effect of the different ternary additions was more obvious when comparing Ni40Fe10X (X = Al, Ti) and the rest of the alloys, with the former having better density and hardness than the latter. Sintered densities close to theoretical (≥98%), excluding Ni40Fe10Mo, were achieved. Interestingly, the visible porosity regions in all the samples were very small in agreement of the high sintered densities observed. The shrinkage rate was similar for all the alloys, and three peaks were observed, the first two peaks merged, and overall all the peaks were indicative of the phenomena responsible for good densification. The hardness measurement revealed that samples with poor homogeneity and those with clusters of ternary element addition in the microstructure had no hardness improvement compared to the base binary alloy. For alloys with Al, Cr, and Ti, fracture surface SEM morphology revealed the intergranular fracture of the grains and the ductile tearing of the binding phase, typical dimple structure of a ductile material; therefore, the mechanical properties of these samples are improved, while the rest of the alloys were characterized with peeling of very fine spherical particles and varying grain size and consequently compromising its mechanical properties.

KEYWORDS:

• Densification
• fracture
• hardness
• microstructure
• spark plasma sintering