Author: Seung-Joon Hwang
Title: The Microstructure and Mechanical Properties of Mechanically Alloyed NiAl Based Alloys
ABSTRACT
Nickel aluminide (NiAl) and NiAl based alloys containing alloying additions of Ti, Ta, and Mo have been produced by mechanical alloying in a Szegvari type attritor mill using elemental or prealloyed powder. The mechanically alloyed powders (MA) were consolidated by hot extrusion, resulting in material which was fully dense, with a homogeneous bimodal distribution of oxide particles with modes of 10 and 100 nm and a fine grain size of less than 1 mm. A NiAl cast ingot was also hot extruded and investigated for comparison with the MA materials. Mechanical properties have been studied by compression testing from room temperature to 1300K in air. Yield strengths of mechanically alloyed materials ranged from 1453 MPa to 32 MPa depending on material and test temperature. All MA alloys, except the alloy containing Ti and Ta, showed considerable compressive ductility at room temperature without any microcracking being observed. The cast material exhibited poor ductility to failure (2.3%) and microcracks at the grain boundaries after room temperature deformation. A ductility minimum was observed at 800K in the MA material which may be due to dynamic strain aging. Also, extruded MA materials showed strong <110> texture parallel to the extrusion direction while cast and extruded NiAl exhibited <111> texture. The effects of microstructure on the mechanical properties of MA materials are discussed.