Study of a nanostructured Cr/CrN coating and dwell effect influence on the fatigue behavior of Ti-6Al-4V alloy at a temperature of 350°C

• Grant number: 19/25360-6
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate (Direct)
• Start date: January 11, 2022
• End date: January 10, 2023
• Field of knowledge: Engineering - Aerospace Engineering
• Principal Investigator: Herman Jacobus Cornelis Voorwald
• Grantee: Martin Ferreira Fernandes
• Supervisor: Patrick Villechaise
• Host Institution: Faculdade de Engenharia (FEG). Universidade Estadual Paulista (UNESP). Campus de Guaratinguetá. Guaratinguetá , SP, Brazil
• Institution abroad: Institut Pprime, France
• Associated to the scholarship: 19/02125-1 - Study of a nanostructured Cr/CrN coating and dwell effect influence on the fatigue behavior of Ti-6Al-4V alloy at a temperature of 350°C, BP.DD

Abstract

The Ti-6Al-4V titanium alloy is applied in the aeronautical industry in fan blades and disks of the first stage of gas turbine engines that operate in the temperature range from 20°C to (250 - 450)°C. Although the alloy has high specific mechanical strength, the material has a high friction coefficient, low wear resistance, and reduced high-temperature oxidation resistance. CrN is a hard coating with outstanding wear, corrosion, and oxidation resistance, while metallic Cr has ductile behavior, which hinders the cracks nucleated at the brittle layers of CrN in Cr/CrN based coatings. Gas turbine engines operate at a steady state after reaching the maximum stress, causing a phenomenon called dwell effect, which is responsible for fatigue life debits when load holds are applied even at ambient temperatures. In the present work, the fatigue behavior of the lamellar microstructure Ti-6Al-4V alloy with a Cr/CrN multilayer coating will be evaluated through fatigue and dwell-fatigue tests at room temperature and 350 ºC. In situ tensile tests will be performed in a scanning electron microscope (SEM) to precisely identify the activation of deformation and damage mechanisms in the coatings at the microstructure scale. The EBSD technique will be performed to analyze crack initiation processes operating in fatigue and dwell-fatigue tested specimens, and the fracture surfaces will be investigated through SEM. The mechanisms involved in the fatigue behavior of the alloy will be studied under the perspective of surface modifications provided by the multilayer Cr/CrN coating, the application temperature influence on time-dependent phenomena, and the combination of dynamic and constant loadings. (AU)