Hip and Sinter-Hip of Ternary NiAl-X Alloys

Prealloyed powders of NiAl, NiAl-5Ti and NiAl-5Nb (at.-%) were gas atomized with an average particle size of 90 μm and attritor milled under Ar atmosphere reducing the average particle size to 1.5 μm. Sintering CIP compacts developed microstructure and density disributions, which allowed subsequent containerless HIPing to near full density (>98.5%) and a final grain size < 8 μm. Alloying of NiAl with 5at% Nb or Ti increased its hardness, Young’s modulus, toughness and creep resistance. The room temperature fracture path changed from primarily intergranular (NiAl) to primarily transgranular (Nb, Ti alloyed), increasing the KIC values from 3.8 to 14.4 and 15.3 MPa\( \sqrt m \), respectively. For comparison, HIPed materials from the as-atomized powders were also tested.