Material Selection for High Pressure (HP) Turbine Blade of Conventional Turbojet Engines

Abstract

Turbojet engine can be divided into three major sections including the compressor, combustion chamber and the gas turbine section. The relatively high temperature gas that passes through the high pressure turbine stages of a turbojet engine from the combustion chamber has a direct effect on the performance and efficiency of the gas turbine, which may hamper its longevity in the long run, particularly the turbine blades. The turbine blades extract energy from the high temperature gas and transfer the kinetic energy of the flowing gas to the compressor stages where it provides forward thrust and rotates the turbine shaft which drives the high pressure and low Pressure compressor fan blades. However, the ability of materials to withstand this high temperature is based on properties of such materials which can be attributed to advances in material selection, improvement techniques in terms of surface protection and cooling as well as manufacturing processes which this paper is based on. Material indices were derived for High Pressure (HP) turbine blades to determine materials that can resist yielding and creep condition when exposed to high temperature above 700°C in a turbojet engine gas turbine. Based on the material indices derived, CES software 2014 was used to generate graphs showing materials with adequate fracture toughness, fatigue strength, stiffness and yield strength property that can withstand the in-service condition of HP turbine blade. Considering all these properties in terms of relatively high temperature, Nickel based super alloys dominated the graphs but in terms of density, titanium alloys dominated as CES software gave the minimum density of nickel alloy (8150 kg/m3) as twice that of titanium alloy (4410 kg/m3). Although both alloys are very expensive, nickel based alloy particularly Nickel-Cr-Co-Mo Super alloy also known as Rene 41 was chosen because of its excellent corrosion property and high strength at elevated temperature (About 1000°C) which makes it suitable for conventional HP turbine blade application.