The age-strengthening by ordered particles of γ′-Ni3(Al,Ti) was studied by means of transmission electron microscopy and room-temperature tensile tests of aged specimens. The samples were aged at 525 to 650C for up to 104h. Two groups of samples having differing Ti/Al ratios were investigated in order to obtain more reliable information on the role played by the alloying elements on the age-hardening behaviour. The γ′ linear dimension increased as t1/3, and an activation energy of 70.0kcal/mol was derived from the temperature dependence of the coarsening rate. The particle volume-fraction, as measured by electron microscopy, was found to remain constant upon aging at 525 to 600C. The increase in the critical shear stress due to the γ′ particles was found to agree quantitatively with the equations of Brown and Ham which described hardening

by ordered particles. Antiphase boundary energies of 227 and 279mJ/m2, respectively, were measured for the two groups of samples.

γ′ Particle Coarsening and Yield in Alloy 800. M.Vittori: Journal of Materials Science, 1981, 16[12], 3461-9