Overheating Damage Analysis On Turbo-disk And Turbo-blades Used In Locomotive Turbocharger Heated By High-temperature And Short-time

Morphology development of K418 and GH2036 high-temperature alloys during high-temperature and short-time aging was investigated by SEM,OPM and XRD to evaluate the overheating damage microstructure features.The failure analysis was conducted on the overheating-damaged turbo-blades and turbo-disk used in locomotive turbocharger.The main results were concluded as follows:(1) High-temperature and short-time aging process:â‘ The phases constitutes of K418 alloy have no changes during aging,which are still composed ofγ-austenite,γ′-Ni₃(Al,Ti) and MC-carbide.However,the lattice parameter ofγ′phase increases slightly with aging temperature.②γ′phase would aggregated gradually and grew-up with aging temperature. Re-solution ofγ′phase would take place and the amount ofγ′phase would decrease when aging temperature attained to the solvus temperature ofγ′-phase.The burn-off microstructure,such as re-melting eutectic phases(γ+γ′),re-meting boundary and degraded carbide would appear in the located region when aging at 1200℃.The hardness of K418 alloy increases slightly with aging temperature.â‘¢The area of carbide precipitation zone of GH2036 alloy decreases gradually with aging temperature and intergranular carbide grow-up obviously.The micro-hardness in carbide precipitation zone is higher than one in no-carbide precipitation zone.And the micro-hardness decreases in two zones with aging temperature.(2) Overheat damage analysis on the failed turbo-blade and turbo-disk:â‘ Melting of the boundary,degraded interdendritic carbides and re-melting of eutectic phases(γ+γ′),typical of overheat damage occurred on the mid-airfoil of blades, which decrease fatigue strength of the blade.The multiple-origins fatigue fracture took place on the blades.The fractured blades have similar microstructure to the specimen aged at 1200℃,and the hardness of the fractured blade corresponds to the hardness of the specimen aged at 1200℃. â‘¡Overheating during the operation of turbo-disk resulting from the intense friction between the air-seal and the back face of disk was found,which was reflected by microstructure features.The yield strength and fracture strength of the rubbed disk surface decreased resulting from overheating.The microstructure of disk surface intensely worn has similar features to the specimen aged at 1150℃,and the hardness of failed blades corresponds to the specimen aged at 1150℃.