No abstract

Thermal barrier coatings (TBCs) are widely used for industrial and aero turbines. The use of residual fuel oil is well known due to economic reasons, which causes hot corrosion. Hot corrosion over extended exposures reduces durability. Therefore, there is a requirement to develop new design approaches for TBCs in order to operate under hot corrosion environment. In this paper, the effect of bond coat thickness on the hot corrosion resistance was studied. Hot corrosion test were carried out in 50 wt.% Na2So4 + 50 wt.% V2O5 molten salt at 950• C for 50 hours. The characterizations of the coatings included X-ray diffraction analysis, scanning electron microscopy and optical microscope. Results indicated that TBCs with thick bond coat exhibited superior hot corrosion resistance to the TBCs with conventional bond coat.

No abstract

An engine bearing was failed during service. During inspection, ball and races of rear bearing were found with wear marks. The bearing was subjected to metallurgical failure analysis. Inclusion level in the balls of bearing was observed higher; these inclusions were rich in Mo and V. The inclusions being the potential sites of the stress concentration caused the subsurface fatigue cracks in the bearing balls. The bearing was failed due to the severe spalling produced under subsurface fatigue leading to the subsequent wear of the raceways.

A tripod jack collapsed when hoisting an aircraft being overhauled. The load capacity of the jack was 30 ton, and the cause of failure was corrosion in the weld region of a leg extension. During breakdown, a spacer in the tripod jack assembly also failed as the result of secondary damage. The failed spacer joins six braces in the assembly of jack. Material of the spacer was mild steel (AISI 1005). Failure of the leg extension imparted an imbalance on the underload structure of the jack. The spacer initially deformed and fractured partly by dimpled rupture and finally failed in a brittle, transgranular manner due to change in loading condition as the jack collapsed catastrophically.