An overview of creep in tungsten and its alloys

TLDR: In this article, the authors provide an overview on the current understanding of creep in tungsten and its alloys, and discuss the role of different factors such as grain size and grain shape, rhenium concentration, potassium as dopant, dispersion strengthening with HfC, ThO2, La2O3 and effect of oxygen containing environment on the creep behaviour of tengsten.

Abstract: The objective of this short review is to provide an overview on the current understanding of creep in tungsten and its alloys. Tungsten is a high temperature material on account of its high melting point and has been historically used for light bulb filaments. In recent years it has been under active consideration for plasma facing liners; an application that demands high temperature strength and durability wherein creep performance becomes important. However, tungsten suffers from poor formability which causes difficulties in making complex parts and components from it. A lot of work has been conducted to improve the formability of tungsten and factors such as amount of cold work, alloying additions and grain size and shape were found to play an important role in improving formability of tungsten. Contrary to conventional metals, the ductility of tungsten is enhanced with increasing cold work. Since recrystallization leads to creation of strain-free grains, and recrystallization is a high temperature phenomena, the ductility of tungsten is intricately related to its ability to resist recrystallization to as high temperatures as possible. Since high temperatures invariably make the role of creep deformation important, a lot of work has been carried out to understand the influence of the ductility-enhancing factors on creep of tungsten and its alloys. The review discusses the role of different factors such as grain size and grain shape, rhenium concentration, potassium as dopant, dispersion strengthening with HfC, ThO2, La2O3 and effect of oxygen containing environment on the creep behaviour of tungsten. Wherever possible, data from literature was analyzed to extract important creep parameters such as stress exponent, grain size exponent, activation energy and Larson-Miller parameter to gain an understanding of the mechanism of creep deformation in tungsten and its alloys. It was observed that fine grain size, low rhenium concentration, high potassium content, addition of dispersions especially of HfC, low oxygen concentration and oblong shaped grains are all beneficial for high creep resistance of tungsten.