抄録
Structural changes during ageing of Cu-Ni-Al alloys containing various amounts of Ni and Al were investigated by means of transmission electron microscopy. The characteristic features of their deformations were also investigated on single crystals.
The results obtained are as follows.
(1) In Cu-5at%Ni-2.5at%Al (A), Cu-5at%Ni-5at%Al (B) and Cu-7.5at%Ni-2.5at%Al (E) spherical precipitates α1 (Ni3Al) nucleated within grains. Lump-like precipitates with the same crystal structure as α1 existed at the grain boundaries of(A) and (E) alloys.
(2) In Cu-5at%Ni-10at%Al (C) and Cu-5at%Ni-15%Al (D), plate-like β2 (NiAl) precipitated by ageing at high temperatures. At intermediate and low temperatures α1+β2 and α1 precipitated, respectively.
(3) The relation between CRSS (critical resolved shear stress) and ageing time at 500°C was studied on each alloy. CRSS increased as ageing proceeded and had a peak at ageing of∼500hr.
(4) Lüders type deformation occurred in (A) (B) (C) and (E) alloys during ageing before CRSS had the peak. The characteristics in the slip mode and deformation structure indicated that dislocation would pass through the coherent precipitates α1.
(5) The characteristics in the deformation of (D) and over-aged (C) alloys indicated that dislocation would by-pass or cross slip to avoid incoherent precipitates β2.
