Application of Disorder-Induced Melting Concept to Fracture

185 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2000.The second set of experiments performed in this thesis is designed to apply the disorder-induced melting concept to an existing fracture problem: segregation-induced intergranular embrittlement. This is accomplished in the nickel-sulfur system by a comparison of the composition dependencies for polymorphous melting and intergranular fracture. The composition dependence for polymorphous melting is determined by sulfur implantation into nickel; Rutherford backscattering spectrometry is used to determine the implantation profile in thin-film specimens, and it is also used to monitor the C → A transformation in single-crystal specimens. The composition dependence for intergranular embrittlement is determined by fracture experiments in a dilute nickel-sulfur alloy; Auger electron spectroscopy is used to measure grain-boundary segregation in notched impact specimens, and slow strain-rate tests are used to monitor intergranular embrittlement in tensile specimens. The results of these experiments reveal that the critical sulfur concentrations for polymorphous melting and intergranular embrittlement at 300 K are 14.2 +/- 3.3 at.% S and 15.5 +/- 3.4 at.% S respectively in nickel. These values, derived from experimental fits to the data using kinetic models based on Poisson statistics, are equivalent within experimental error. This equivalence strongly supports the description of segregation-induced intergranular embrittlement as a low-temperature polymorphous melting process.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD