On the Change in Lattice Parameter in the Matrix of Cu-Ti Alloys during Ageing Process

Abstract

The lattice parameter of the specimens quenched from the region of a homogenious solid solution was measured for various Cu-Ti alloys containing about 0.2, 0.3, 0.6, 1.1, 1.7, 2.5 and 5.1 at%Ti. The ageing characteristics of the alloys aged at 450°C were studied by X-ray diffraction analysis, optical and electron microscope observations.
The following conclusions are obtained.
(1) The lattice parameter of the quenched specimens increases at a rate of 0.00055 nm/at%Ti with increasing Ti concentration up to 1.7 at%Ti. For more than 1.7 at%Ti, however, the increasing rate of lattice parameter becomes smaller than for less than 1.7 at%Ti.
By transmission electron microscope observation, the decomposition of the solid solution during quenching is confirmed to occur in the alloys containing more than 1.7 at%Ti. So, it seemes that such a decomposition decreases the increasing rate of the lattice parameter for the alloys of less than 1.7 at%Ti.
(2) The lattice parameter of each alloy decreases continuously to a constant value during ageing. The decrease of the lattice parameter corresponds to the decreases of the Ti concentration in the matrix of the alloys in the ageing process: solid solution—3-phase structure (model of G.P.zone)—2-phase structure.