Investigation into the effect of build direction on fatigue and fracture properties of SLM Nickel-based super alloys used for the manufacture of high speed gas turbine blades
A turbine blade is the individual component that makes up the turbine section of a gas turbine engine. The blades are responsible for extracting energy from the high temperature, high pressure gas produced by the combustor. The turbine blades as well as their maximum operating temperature are often the limiting components of gas turbine engines. To survive in this difficult environment, where the temperatures and stresses are both high, turbine blades often use exotic materials such as super-alloys, for example, the nickel-based super-alloy Inconel 713LC or Inconel 718.
For high speed gas turbines, the blades and rotor disk are typically incorporated into a single component which is known as the blisk. The blisk has a complex design and is typically produced through investment casting. The CSIR has designed a novel stator blisk which is proving very difficult to manufacture. For this reason they are interested in using additive manufacturing techniques to manufacture the blisks. Since the creep resistance properties are critical to turbines and rotors, the build direction of the additive manufacturing technique relative to the rotational axis of each blade may be critical.
This project focuses on selective laser melted nickel-based super alloy parts (an additive manufacturing process in powder metallurgy) for the blisk assembly. In order to determine the effect of build direction on mechanical properties it is necessary to perform fatigue tests to investigate how the build direction affects the fracture toughness and fatigue crack growth rates of the parts. Compact tension samples will be built and testing will cover a combination of fracture toughness and fatigue crack propagation tests of samples with different build directions. This project also involves investigating the effect of heat treatments for the removal of residual stress and homogenisation, and the effect of these heat treatments on the mechanical and fatigue properties. Fractography and microstructure analysis would be performed to investigate the effect of the as-built and heat treated microstructures on the crack path during fatigue crack propagation.