Effects of loading variables on fatigue-crack growth in liquid-metal environments

Abstract

Liquid-metal-induced embrittlement (LMIE) refers to the loss of ductility in normally ductile metals and alloys when stressed while in contact with a liquid metal. In this study, the fatigue crack growth behaviour of brass in molten gallium is examined using standard LEFM testing procedures. The effects of environment, load ratio, cyclic frequency and load waveform on the rate of crack growth are investigated. At Delta K > Delta K-th, crack growth rates are approximately an order of magnitude faster in liquid metal than in air. However, at low AK values (low fatigue crack growth rates) and/or where the crack tip is exposed to the liquid metal for long periods of time, crack tip blunting by dissolution of the solid metal into the liquid metal occurs. This markedly decreases the rate of crack growth and results in apparent Delta K-th values in liquid metal that are significantly higher than the unembrittled threshold values.