Abstract
Titanium alloys containing beta stabilizing and eutectoid forming elements are known to exhibit embrittlement after thermal exposures up to the eutectoid temperature. This phenomenon in the commercial titanium alloy Ti-5Al-2Cr-1Fe was investigated by the room-temperature tensile test, impact test, electrical resistance measurement, light and electron microscopy and X-ray diffraction after thermal exposures in the temperature range of 300 to 500°C for various times up to 5000 hr under both stressed and unstressed conditions.
The results obtained are as follows:
(1) The embrittlement in this alloy is accelerated by raising the temperature of thermal exposure and by stressed conditions.
(2) Analysis of data of mechanical properties, electrical resistance, microstructure and X-ray diffraction defines the embrittlement is attributed to the intermetallic compound TiCr2 phase which forms during thermal exposure. The activation energy for thermal exposure reaction approximates that for diffusion of chromium in the beta phase.
(3) As the embrittlement is found to be closely related to the thermal exposure reaction, the time-temperature relationship for the embrittlement can be given by the following equation:
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