Method for expelling entrapped air from reactive metallic layups prior to diffusion bonding

In a process for diffusion bonding of at least two metal workpieces of a reactive metal, particularly titanium, the improvement for expelling entrapped air from between surfaces of such workpieces prior to diffusion bonding, which comprises precoating the metal surfaces of the workpieces which are to be diffusion bonded with a substance capable of decomposing at a temperature above about 800 DEG F. and below the diffusion bonding temperature of the workpieces, e.g. of the order about 1300 DEG F., such substance being preferably polytetrafluoroethylene, to form an inert gas having a density greater than air, heating the workpieces to a temperature above about 800 DEG F. and causing decomposition or pyrolysis of such substance and forming an inert gas having a density greater than air, and flushing the inert gas together with the entrapped air out of contact with the surfaces of the workpieces, preferably by means of argon having a density greater than the pyrolysis products or the inert gas. The workpieces are further heated to cause diffusion bonding of the workpieces.