High Temperature Deformation and Fracture Resistance of Single Crystals of NiAl and NiAl-Based Intermetallic Alloys
Final rept. 1 Feb 95-31 Jan 98
STANFORD UNIV CA DEPT OF MATERIALS SCIENCE AND ENGINEERING
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The main objective of this research has been to develop a fundamental understanding of the high temperature deformation, fracture, and fatigue crack growth resistance of single crystals of NiAl and NiAl-based intermetallic alloys. The approach we have taken involves high resolution mechanical property studies of well-characterized and well-oriented single crystals of NiAl containing various alloying elements Ti, Fe, Zr in the form of both solid solutions and two phase alloys. Our studies of the high temperature deformation of the solid-solution alloy Ni-AlTi revealed a significant solute strengthening effect which we studied, characterized and modeled. The creep rates for these alloys were observed to be independent of crystal orientation and were as much as three to four orders of magnitude lower than for unalloyed NiAl. We have also studied the unusual creep properties of Ni3Al, a related intermetallic alloy, at intermediate temperatures. We have also conducted the first-ever studies of the cyclic fatigue crack-growth behavior of NiAl single crystals at both room temperature and 800 deg C. Room temperature crack growths ranged over two orders of magnitude from 10-8 to 10-10 mcycle with a fatigue threshold value DKTH of approximately 2.3 MPaOem. Similar crack growths at 800 deg C required DK of about 8 MPaOem.
- Properties of Metals and Alloys