Single crystal seed

1. A seed for casting a single crystal article, consisting essentially of, in weight %, greater than 15.0% to about 40.0% Mo, up to 0.1% C, up to 0.1% B and balance essentially Ni and having hardening precipitates of Mo and Ni in the seed.

2. The seed of claim 1 consisting essentially of, in weight %, greater than 15% to about 30% Mo, up to about 0.053 C, and balance essentially Ni.

3. A single crystal casting mold, comprising a grain starter cavity connected to an article mold cavity by a connector passage and a seed as set forth in claim 1 in said starter cavity wherein the seed includes the hardening precipitates therein.

4. A single crystal casting mold, comprising a grain starter cavity connected to an article mold cavity by a connector passage and a heat treated seed in said starter cavity, said seed consisting essentially of, in weight %, greater than 15% to about 40.0% Mo, up to 0.1% C and balance selected from the group consisting of Ni and Co wherein the heat treated seed has hardening precipitates of Mo and Ni therein.

5. The mold of claim 4 wherein said seed consists essentially of, in weight %, greater than 15% to about 30% Mo, up to about 0.05% C, and balance essentially Ni.

6. A method of casting a single crystal article, comprising disposing a seed as set forth in claim 1 having the hardening precipitates therein in a grain starter cavity communicated to an article mold cavity, introducing molten superalloy in the mold cavity, and epitaxially nucleating and growing a single crystal grain in said molten superalloy.

7. The method of claim 6 wherein the seed is heat treated to form the hardening precipitates therein before being disposed in the mold cavity.