Relationship between segregation-induced intergranular fracture and melting in the nickel–sulfur system

• Published in: Applied physics letters 2000-06, Vol.76 (23), p.3403-3405
• Main Authors: Heuer, J. K., Okamoto, P. R., Lam, N. Q., Stubbins, J. F.
• Format: Article
• Language: English
• Subjects: AMORTIZATION; ANNEALING; AUGER ELECTRON SPECTROSCOPY; DUCTILE-BRITTLE TRANSITIONS; EXPERIMENTAL DATA; FRACTURE PROPERTIES; GRAIN BOUNDARIES; MATERIALS SCIENCE; MELTING; NICKEL; SULFUR
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.126660

The effect of S segregation to grain boundaries on the intergranular embrittlement of Ni has been studied at room temperature using Auger electron spectroscopy and slow strain rate tensile tests. The grain-boundary S concentration was varied by time-controlled annealing of dilute Ni–S alloy specimens at 625 °C. The ductile-to-brittle transition in Ni, as determined from percent integranular fracture and reduction-in-area measurements, occurred over a narrow range of S concentrations centered on 15.5±3.4 at. % S. This critical S concentration for 50% intergranular fracture of polycrystalline Ni is similar to the 14.2±3.3 at. % S required to induce 50% amorphization of single-crystal Ni by S+-ion implantation. This suggests that segregation-induced intergranular fracture, like implantation-induced amorphization, may be a disorder-induced polymorphous melting process. In agreement with experimental observations, the polymorphous melting curve for the Ni–S solid solution on the phase diagram drops rapidly to zero as the alloy composition approaches ∼18 at. % S. The critical grain-boundary concentration for intergranular fracture, while slightly less, is within experimental error of the concentration predicted for polymorphous melting as well as that measured for ion-implantation-induced amorphization.