Multiple part cores for investment casting

Composite casting core for a hollow product having a portion with a small cavity size relative to that of another product portion, the core comprising:

• a first core part determinative of the cavity size and shape of the small cavity product:
• portion and formed from a first ceramic material;
• a second core part determinative of the cavity size and shape of the other product portion formed from a second ceramic material and joined to said first core part,
• wherein said second ceramic material has at least one characteristic selected from the group consisting of thermal expansion coefficient, leachability, flowability and reactivity with the casting metal, which selected characteristic is different from than that of said first ceramic material.

Composite casting core for a hollow product having a portion with a small cavity size relative to that of another product portion, the core comprising:

• a first core part determinative of the cavity size and shape of the small cavity product portion and formed from a first ceramic material;
• a second core part determinative of the cavity size and shape of the other product portion, formed from a second ceramic material;
• and
• means for mechanically Joining said first and second core parts,
• wherein the product is a hollow, gas-cooled gas engine turbine blade having a trailing edge portion and a body portion, and wherein said first core part is determinative of the cavity size and shape of said trailing edge portion, and the second core part is determinative of the cavity size and shape of said body portion.

Method for forming a casting core for a hollow product having a portion with a small cavity size relative to that of another product portion, the method comprising the steps of:

• a) forming a first core part determinative of the cavity size of the small cavity product portion from a first ceramic material having a characteristic grain size;
• b) forming a second core part determinative of the cavity size of the other product portions from a second ceramic material having a characteristic grain size greater than that of the first ceramic material;
• and
• c) joining the first and second core parts to provide a composite casting core.

Method for forming a casting core for a hollow gas turbine engine blade, the blade having a trailing edge portion with a small cavity size relative to that of the blade body portion, the method comprising the steps of:

• a) forming a first core part determinative of the cavity size and shape of the trailing edge portion from a first ceramic material;
• b) forming a second core part determinative of the cavity size of the body portion from a second ceramic material;
• and
• c) mechanically joining the first and second core parts to provide a composite casting core.