טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAmouyal Yaron
SubjectThe Correlation between Grain Boundary Energy,
Crystallography and Chemical Composition in the
Intermetallic Compound NiAl
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Eugen Rabkin


Abstract

Severe intergranular brittleness at low temperatures hinders engineering applications of NiAl, which otherwise exhibits an excellent combination of low density, high strength, and high corrosion resistance at elevated temperatures. The physical parameter that determines the grain boundary (GB) strength in brittle materials is GB energy. It depends on the alloy composition as well as on the geometry of GB. The latter can be described by five macroscopic degrees of freedom (DOFs). The goal of this research is to establish the correlation between the GB geometry and energy in the intermetallic compound NiAl. For this purpose the energies of 43 different GBs were determined with the aid of atomic force microscopy (AFM) analysis of GB thermal grooves. The geometrical DOFs of the same GBs were determined by the combination of electron back-scatter diffraction (EBSD) and the serial sectioning technique.  The measured relative energies were scattered in a wide range of 0.2-1. It was found that twist GBs are generally more energetic than their tilt counterparts. Moreover, general GBs with approximately equal tilt and twist components did not exhibit high energies. These two findings were explained using the Read-Shockley dislocation model. The GBs that are parallel to {h,k,0} in one of two grains exhibited high energies. In addition, it was found that high- and low- energy GBs exhibit {211}{100} and {211}{110} plane matching, respectively. Both findings have been discussed in terms of atomic matching at the GB plane.