High temperature fatigue crack propagation in MAR-M247 superalloy

• Grant number: 10/19948-6
• Support Opportunities: Scholarships abroad - Research
• Start date: July 01, 2011
• End date: June 30, 2012
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
• Principal Investigator: Cassius Olivio Figueiredo Terra Ruchert
• Grantee: Cassius Olivio Figueiredo Terra Ruchert
• Host Investigator: Paul Bowen
• Host Institution: Escola de Engenharia de São Carlos (EESC). Universidade de São Paulo (USP). São Carlos , SP, Brazil
• Institution abroad: University of Birmingham, England

Abstract

Nowadays, in the worldwide production of gas turbines for the aerospace industry there is a strong effort to reduce components weight and fuel consumption. The thermodynamic efficiency of a turbine is governed by the operating temperatures. Thus, there is sufficient motivation to develop new alloys of Ni and Ti presenting higher mechanical strengths that could allow higher gas temperature input to the compressor and turbine sections. Inevitably, these alloys require an improved resistance to high temperatures. The nickel-based superalloy MAR-M247 was designed for applications requiring excellent resistance to creep and oxidation at elevated temperatures and has been widely used in the manufacture of turbine blades. Therefore, this project intend to explore the basic fatigue crack growth behavior in MAR-M247 alloy superalloy produced by advanced processing techniques of microfusion and directed solidification, as well as the effect of the substitution of Ta by Nb in the of tensile and fatigue crack growth behavior at high temperatures. Also, it will be investigated the influence of material's intrinsic factors, as the microstructure, as well as extrinsic factors, such as the waveform, frequency, environment in air and vacuum, and testing temperature. Thus, the aim of this project is to establish relationships between the microstructure and the behavior of fatigue crack growth in such materials. Specimens to be used in fatigue crack growth testing will present square geometry and corner crack. The use of this specimen geometry and loading is because the restriction of plastic flow which is developed in front of the crack (constrain effect) would be the closest to a crack developed in a turbine in use. The influence of oxygen is also expected to be observed in fatigue crack growth testing because oxygen permeates the front of the crack, facilitating the formation of a brittle structure and promoting intergranular fracture in the material, with consequent increase in crack propagation rate. This study certainly will provide the adequacy of NEMAF (Materials Testing and Failure Analyses Laboratory) for mechanical testing in vacuum at ambient and high temperatures with detailed understanding of the relationship microstructure/fatigue properties. (AU)