The purpose of aging treatment of titanium and titanium alloy is to promote the decomposition of the metastable phase produced by solid solution treatment in a certain way and to cause strengthening.In general, this process can be represented by a c-shaped curve describing the time-temperature-transition relationship.The shape of the "C" curve varies according to the composition of the alloy.A "C" shape curve for a heat-treatable beta alloy and a binary alloy with a high content of beta stable elements.
The aging process of an alloy is generally determined according to the aging hardening curve.It describes the relationship between mechanical properties and aging time at different aging temperatures.Mechanical properties may be room temperature tensile properties, hardness or other properties.Aging temperature and time should be selected according to the best comprehensive performance. Generally, the aging temperature of a+ beta alloy is about 500 ~ 600℃ and the time is 4 ~ 12 hours.Heat-treatable beta alloys have a lower aging temperature and a longer aging time of about 450 ~ 500℃, 8 ~ 24 hours.All cooling methods are air cooling.
In order to control the size, shape and quantity of precipitated phase, some alloys can be treated by multistage aging.For example, TB1 alloy is aged again at 560 ° c and 15 minutes after aging for 35 hours at 450 ° c, so that the tiny dispersed a-phase generated during the first aging is gathered and the plasticity after aging is improved.
In order to require titanium alloy to have better thermal stability at the service temperature, aging above the service temperature is often used.In order to obtain better toughness and shear resistance, some titanium alloys also adopt aging at higher temperature.This aging is sometimes called stabilization.
It should be noted that both cold processing before aging and cold preaging greatly accelerated the decomposition rate of the metastable beta phase and enhanced the dispersion of phase a.In some special conditions, the tensile strength and elastic modulus of heat-treatable titanium alloy can be improved by aging treatment after cold deformation.