increase the hardness of the metal,
whereas dissolved hydrogen reduces toughness
and reduces notch sensitivity. Therefore, zirconium
and zirconium alloys must be welded in a
shield of high-purity inert gas or in a vacuum.
Furthermore, zirconium should be free of oil,
grease, and dirt to avoid the dissolving of carbon-
and oxygen-containing materials, which
can embrittle the metal or create porosity and