The tensile and compressive properties at room temperature of powder metallurgy Ni3Al synthesized using rapidly solidified powder particles, which were milled for up to 20h, were investigated. Furthermore, the mechanical behaviour at high temperatures was studied by strain rate change tests in compression at strain rates ranging from 5 x 10-6 to 2 x 10-3/s and from 1073 to 1373K. For comparative purposes, tensile tests at room temperature were carried out on materials consolidated from particles in both the as rapidly solidified condition and after 2h of milling time. Both materials showed a very similar microstructure composed of equiaxed grains. However, an increase in the yield strength of close to 40% was exhibited by the 2h milled particle material. The intermetallic made of 20h milled particles presented a bimodal microstructure and exhibited a dramatic increase in yield strength at room temperature to 740MPa; more than twice the value reached by the material consolidated with rapidly solidified particles. Analysis of the stress-strain rate data of tests performed at elevated temperatures revealed a transition from a stress exponent n ≈ 5 to an exponent n ≈ 3.5 at low stresses and/or high temperatures of testing. An activation energy for plastic flow of 370kJ/mol was deduced in the low stress regime.

Mechanical Behaviour of a Bimodal Microstructured Powder Metallurgy Ni3Al. Pérez, P., Jiménez, J.A., Borrego, A., Adeva, P.: Materials Science and Technology, 1999, 15[7], 833-9