MAR-M-247 is a nickel-based casting alloy developed by the organization formerly known as Martin-Marietta. Information is available on this alloy in the Aerospace Structural Metals Handbook from CINDAS. You are lucky in that the chapter that covers MAR-M-247 is freely available as a sample from their website, so you do not have to find this book in a library or purchase your own copy. Use the following link for more info: