Development of a Small Punch Test to Evaluate Liquid Metal Embrittlement Susceptibility of 316L Stainless Steel in Liquid Sodium

Liquid sodium is proposed as a heat transfer fluid for solar thermal power receiver designs. It has a long history of use for heat transfer in various industries, with extensive knowledge of its impact on the structural integrity of materials at temperatures ranging from 300 ℃ to 800 ℃. However, the effects at lower temperatures are more poorly understood, which is crucial to studying solar thermal power plant systems. These systems experience diurnal cyclic temperature variation, which causes significant fluctuations in the operating temperature of liquid sodium. Several studies have demonstrated that the susceptibility of metals to Liquid Metal Embrittlement (LME) is highest at temperatures close to the melting point of the liquid metal. Therefore, this study investigates the susceptibility of 316L stainless steel, a common construction material, to sodium induced LME at temperatures between 100 ℃ to 300 ℃ using the Small Punch Test (SPT) method. The test apparatus was validated by using a known embrittling pair of Brass-Galinstan between 10 ℃ to 43 ℃, where the test revealed the expected LME susceptibility of brass. However, no evidence of LME was found in the 316L-sodium pair at temperatures up to 300 ℃.