The failure analysis of gas turbine blades at high rotational speeds is accomplished considering metallurgical, structural and thermal aspects. One of the reasons for the failure is found to be due to metallurgical phase transformations of the alloy at high temperatures. The blade material A718 Inconel transforms into d- Phase and becomes susceptible to embrittlement at 6500 C. Further the stresses developed at high rotational speeds of 50000 rpm exceed the yield strength and hence the rotational speeds must not exceed 40,000 rpm. The one dimensional transient thermal analysis is carried out by carefully adopting the thermal boundary conditions both at tip of the blade and root of the blade. For thermal ambience of the gas medium and rotational speeds, the blade temperature shoots up to very high values within a short time interval of 120 seconds. Hence it is suggested that the operating gas temperatures must be less than 5000C and the rotational speeds must be in the range 30,000-40,000rpm for Inconel as the blade material to avoid failure.
gas turbine blades - A 718 inconel - d phase – transient thermal study – structural failure
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