Failure of a lithium-filled target and some implications for fusion components

•Unexpected rapid failure of a small 1018 mild steel vessel preheated to ~200 °C and under vacuum occurred when lithium at ~400 °C and ~1 atm. flowed into the vessel.•Fractography confirms failure enabled by liquid metal embrittlement. In preparation for testing a lithium-helium heat exchanger at Sandia, unexpected rapid failure of the mild steel lithium preheater due to liquid metal embrittlement occurred when lithium at ~400 °C flowed into the preheater then at ~200 °C. This happened before the helium system was pressurized or heating with electron beams began. The paper presents an analysis of the preheater plus a discussion of some implications for fusion.