In this paper, we discuss the optimization of chemical composition, processing (forging and rolling) and heat treatment parameters to obtain the best combination of mechanical properties in case of a Fe-15Cr-5Ni-4Cu precipitation hardenable stainless steel. The ε-copper precipitates that form during aging are spherical in shape and coherent with the matrix and principally provide strengthening in this alloy. The orientation relationship is found to be Kurdjumov-Sachs (K-S), which is common in fcc-bcc systems. Results obtained from metallurgical evaluation (mechanical property and metallography) on 15-5 PH alloy during type certification on 3 different melts were used for the optimization, attempted in this study. The mechanical properties following strain deformation has been carried out using optical microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM). In the aged conditions, the 15-5 PH alloy exhibited brittle failure with extensive cleavage and/or quasicleavage fracture. This paper reports all results and also factually shows that indigenously developed and produced 15-5 PH stainless steel matches in its properties with the equivalent aeronautical grade precipitation hardening stainless steels globally produced by internationally renowned manufactures.

A twin spool low bypass turbofan engine under development and its combustor in full-scale were tested independently at altitude conditions to establish the relight envelope of the engine. Demonstration of relight capability and defining its boundary are mandatory for military gas turbine engines and for single engine application in particular. The engine was first subjected to windmill to establish its windmilling characteristics. The full engine was then tested for light-off in an altitude test facility simulating windmilling conditions from 4 to 12 km altitude with flight Mach numbers from 0.2 to 1.0. The relight boundary is defined based on the successful light-off points achieved from engine tests. Similar tests were carried out on the full-scale combustion chamber in a stand-alone mode simulating altitude conditions at engine flame-out. The combustor test has defined the light-off and lean blow out limits of the at each point on the relight boundary. The information of fuel-air ratio at light-off and blow-out is very useful in setting the engine fuel schedule for altitude operation and relight. In this paper an attempt is made to highlight various tests carried out on engine and its combustor to define the relight boundary of the engine. The paper also emphasizes the experience of combustor development and associated problems in meeting the relight challenges of military engines. These problems include the necessity of higher fuel-air ratio at high altitudes, the role of additional localized fuel injection through start-up atomizers, and effect of single igniter on relight characteristics. The relight envelope demonstrated by the engine is very satisfactory to meet the first flight requirement where the flight mission generally concentrate in the zone of 0.6 to 0.8 Mach and altitude does not exceed 10 to 12 km. Combustor and atomizer modification is needed to improve relight performance and to shift the boundary to further left.

No abstract

No abstract

No abstract