An in-situ TEM nanowelding process via Joule heating was used to achieve superstrong CNT-carbide-metal contacts, in which all shells of a multiwalled CNT contact the tungsten wire through the intermediate tungsten carbide layer. A remarkably high tensile strength (5-15GPa) and ultralow resistance(<1 k Omega) were documented for the heterojunctions, which were also sufficiently robust in CNT fiel-demission applications.