Diffusion bonding method
 A turbine blade spar wall surrounds a coolant plenum of the blade and is cast with an intermediate thickness exceeding its final or design thickness. The outer surface of the spar wall is machined to form a plurality of incomplete holes extending to bottoms located at the final thickness dimension of the spar wall. A pre-formed sheath of porous metal is fit closely around the spar wall outer surface with coolant pores in the sheath communicating with the incomplete holes. A high pressure inert gas is introduced into the coolant plenum concurrently with application of compressive forces to the sheath as both the sheath and the spar wall are raised to a high temperature whereby the sheath is diffusion bonded to the spar wall. The inert gas pressure in the coolant plenum reinforces the spar wall against the compressive forces. The inner surface of the spar wall is then chemically machined to an etch depth dimension which brings the spar wall to its design thickness and simultaneously removes the bottoms of the incomplete holes so that the incomplete holes become complete holes between the coolant plenum and the sheath of porous metal. 
General Motors Corporation
B B F Y Y B B
B23K B23P F01D Y10T Y10T B23K B23K
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Yu-Lin
Chen