Jet engines/Turbine blades – Ti superalloys

When it comes to designing improved materials for components and structures of aerospace engines, most of the attention is focused on how to reduce the fuel consumption of the engine for both environmental and economical reasons.

Figure 1:  Cross-sectionnal view of Rolls-Royce AE3007C engine. The primary air flow path is highlighted. Source:“Materials Selection in Gas Turbine Engine Design and the Role of Low Thermal Expansion Materials “ Benjamin W. Lagow

There are two main approaches to decrease the fuel consumption of an aerospace engine:

1st: Decreasing the mass of the structure.

The lighter the structure is, the less energy is required to move it. In order to decrease the mass of the structure, we aim for materials with low density such as Titanium and Nickel alloys (4 – 8 g/cm3) which are widely used in aerospace for their very good combination of mechanical properties and low densities. We can also aim to improve the mechanical properties of the materials used (Yield strength and ductility, fatigue resistance…), which then allows us to build more mater-efficient engine parts.

2nd: Improving the engine efficiency.

The efficiency of an aerospace engine can be assimilated to a thermal engine efficiency, since the amounts of heat & work generated are directly linked to the amount of fuel consumed. The maximum Carnot efficiency achievable is given by the following relationship:

Where Tc and Th are respectively the temperatures of the cold and hot sources. This equation shows that in order to maximise the engine efficiency ηcmax, we need to increase Th, the working temperature of the engine.

The critical part of the engine, undergoing the maximum amount of heat and stress are the gas turbines (figure 1). It is this part of the engine that currently limits the operating temperature, as the materials used are pushed to their limit in terms of creep strength, melting point and high temperature mechanical performance.

– Alloys studied –

Our work focuses on novel Beta-titanium ‘bcc-superalloys’, to unlock the high melting point refractory metals Mo and Nb, paired with the low-density of Ti. Inspired by the widely used Nickel fcc-superalloys, these bcc-superalloys exploit a combination of a β matrix with ordered-bcc β’ precipitates. Our work designs & develops new alloys to achieve an optimum property balance in this new class of alloys, between high temperature mechanical performance, ductility and environmental resistance.