Method of applying a refractory coating to metal substrate

The method of obtaining an improved bond strength in shear at the interface between (1) a formed ferrous metal substrate having sections thereof of such small dimensions as to be readily heat deformable and (2) a refractory coating on said substrate, said method comprising the following steps:

• making available to said interface a constituent capable of diffusion bonding the interface surfaces at temperatures within a range above the plastic state temperatures but below the molten state temperatures of said substrate, and
• cyclicly applying inductive heating and cooling to said surfaces but substantially only to a depth equivalent to the thickness of said coating plus only several thousandths of an inch into said substrate to effect by said inductive heating a temperature at said surfaces in the order of 1600- 2000.degree. F. for a sufficient length of time to effect such diffusion bonding but at bulk temperatures of said substrate not exceeding about 500.degree. F. and without substantial distortion of any of said sections of said formed ferrous metal substrate.

The method of obtaining an improved bond strength in shear at the interface between (1) a shaped metal substrate of such small sectional dimensions as to be readily deformable by heat and (2) a hard tungsten-boron alloy refractory coating on said substrate, said method comprising the following steps:

• applying to a surface at the interface between said substrate and said coating an intermediate coating containing an available diffusion bonding constituent, and
• inductively heating said coatings to a temperature sufficiently high to effect a diffusion bonding at said interface without substantial distortion of said shaped metal substrate and to hereby obtain a bond strength in shear of at least 10,000 psi.