Abstract: A diaphragm assembly for use in highly corrosive industrial applications includes a metal body subject to corrosion and a diaphragm formed of a corrosion resistant metal. The metal of the diaphragm is metallurgically incompatible with the body metal. The diaphragm is nevertheless hermetically sealed to the body with the aid of a transition member having a first portion of metal which is metallurgically compatible with the body and a second portion of another metal metallurgically compatible with the diaphragm. Both portions are joined together by a sound, molecular bond, as for example, by using explosive bonding techniques. The first portion of the transition member is fusion welded to the body and the diaphragm is similarly welded to the second portion, thereby presenting at the process fluid interface a barrier that consists solely of corrosion resistant metal.