Fatigue of the Near-Alpha Ti-Alloy Ti6242 |
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Authors: | T K Heckel A Guerrero Tovar H-J Christ |
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Institution: | 1.Universit?t Siegen,Siegen,Germany;2.Universidad Simón Bolívar,Materials Science Department,Caracas,Venezuela |
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Abstract: | Ti6242 is the workhorse of high-temperature Ti-alloys in the high pressure compressor of aero engines. In this study the influence
on isothermal fatigue of different load controls, i.e. stress, total strain and plastic strain control at different temperatures
and environments was investigated. The alloy had a bi-modal microstructure (some 30 vol.% primary alpha), which yields a good
balance between fatigue and creep properties. In addition thermomechanical fatigue (TMF) tests were also performed. Modelling
lifetime on the basis of a Basquin–Coffin–Manson relationship revealed only marginal scattering in the temperature range between
350°C and 650°C. Increasing the temperature led to a decrease in lifetime. This can be attributed to increased oxidation and
creep. The latter one is clearly seen in isothermal tests under stress control. Tests in vacuum resulted in longer lifetimes.
In-phase TMF tests exhibited a longer lifetime than out-of-phase tests, with a factor of about 4. Lifetime and stress response
of in-phase tests are similar to the corresponding lifetime of an isothermal test at the maximum temperature. This similarity
can be considered as a starting point for modelling TMF behaviour on the basis of isothermal fatigue. |
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