Casting densification method

In a hot isostatic pressure (HIP) method for densification of a metal casting which includes surface-connected discontinuities, wherein a coating is applied to a surface of the casting to bridge surface openings associated with the discontinuities and then the casting is subjected to a combination of a selected processing temperature and isostatic pressure to densify the casting, the improvement comprising:

• applying the coating in the form of a ceramic material selected to provide, at a glazing temperature less than the selected processing temperature in the HIP densification, a non-metallic amorphous, substantially gas impervious ceramic coating having a coefficient of thermal expansion matched in the temperature range of from ambient temperature to the selected densification processing temperature with the coefficient of thermal expansion of the casting surface to which it is applied, the coating having the property of being viscous at the selected densification processing temperature and having its bond with the casting surface degrade during the HIP densification;
• heating the casting surface and ceramic material at the glazing temperature to vitrify the ceramic material into the ceramic coating without providing a significantly strong bond with the casting surface;
• cooling the coated casing;
• subjecting the coated casting surfaces to the combination of the selected processing temperature and isostatic pressure to densify the coated portion of the casting and to degrade the bond between the ceramic coating and the casting surface;
• cooling the casting;
• and then
• removing the coating from the casting surface.