  Tungsten usually exhibits poor weldability and marked brittleness at room
temperature. This cause tungsten welds to be affected by the evolution of
cracks along the weld bead, which can be eliminated by using a pre-heating step
to reduce thermal straining. In this study, based on the tungsten inert gas
welding process, a working envelope, focussed on varying welding speed and five
different shielding gas mixtures of argon and helium, has been defined with the
view of producing crack-free autogenous welds. The bead appearance and the
microstructure of the different welds were correlated to the welding
parameters, whose main effects have been analysed. Welding defects such as
humping occurred when using gas mixtures with relatively low content of helium,
and when using relatively high welding speeds. Crack-free autogenous welds have
been produced without pre-heating when using a high content of helium and
relatively low welding speeds. Thus, this study has demonstrated that a
helium-rich shielding gas is required for welding thick tungsten plates.
Moreover, the low thermal shock induced by the process, coupled with the purity
of the tungsten plates used, strongly contributed to avoid the occurrence of
any crack.
