On the threshold stress in mechanically alloyed NiAl
- Illinois Inst. of Technology, Chicago, IL (United States). Metallurgical and Materials Engineering Dept.
Intermetallic compounds, such as nickel, iron and titanium aluminides, have emerged as a new class of potential structural materials for high temperature applications such as gas turbine engines. However, before this material can be of practical use a number of technical problems must be overcome including lack of ductility at room temperature and poor strength at high temperatures. The authors approach has been to use mechanical alloying (MA) followed by hot extrusion to produce dispersion strengthened, fine-grained NiAl-based materials, to address both the ambient temperature brittleness and high temperature strength problems. Recently, they examined creep behavior of mechanically alloyed (MA) NiAl and demonstrated its potential for high temperature structural applications. Minimum creep rates in MA NiAl were on average three orders of magnitude lower than that in their cast counterparts. Improved creep resistance of MA NiAl was found to result above all from the presence of dispersoids. Virtually all modern theories for dislocation creep in metals and alloys assume the dislocation motion is opposed by back stresses which result from interactions between the moving dislocations and the substructure and that the creep rate is determined by a net stress, equal to the difference between an applied stress and a back stress. The final application of the net stress concept is in the area of dispersion strengthened (DS) materials, which creep behavior is best described in terms of the threshold stress below which creep rate is negligible and which must be overcome in order for dislocations to pass particles. In this article, threshold behavior in MA NiAl is reported and the physical origin of the threshold stress is discussed. Similarities and differences between creep behavior of MA NiAl and conventional'' DS materials are outlined.
- OSTI ID:
- 6989490
- Journal Information:
- Scripta Metallurgica et Materialia; (United States), Journal Name: Scripta Metallurgica et Materialia; (United States) Vol. 31:12; ISSN SCRMEX; ISSN 0956-716X
- Country of Publication:
- United States
- Language:
- English
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