Water droplet erosion mechanism of nearly fully-lamellar gamma TiAl alloy

Abstract

Water droplet erosion (WDE), is a known mechanical degradation and progressive damage for turbine blades in the power generation and aerospace industries. Hence, water droplet erosion study of TiAl as an important structural material in such industries would be very attractive. The current work is to investigate the erosion damage mechanism of nearly fully lamellar Ti45Al2Nb2Mn0.8TiB2 (45-2-2XD) alloy. This alloy was subjected to water droplet erosion using 460μm droplets and 350ms−1 impact speed. In order to track the erosion damage, WDE test was interrupted at different stages; incubation, maximum erosion rate and final steady state stages. The eroded specimens were characterized using optical microscope (OM), scanning electron microscope (SEM) and atomic force microscope (AFM). The qualitative and quantitative study reveals that the erosion damage of TiAl initiates by inhomogeneous and localized material flow followed by crack network generation on the surface. Such cracks mainly nucleate on the interlamellar slip bands and cause delamination of lamellae. Further droplet impacts result in the cracks coalescence and subsequent micro-pitting within the colonies. In the advanced stages, the erosion damage was governed by periodic water roughening and water polishing, which were observed on the bottom and the sidewalls of deep erosion craters.