A method for manufacturing a rotor shaft is provided. A rod is formed from a metal matrix composite material, the rod having an outer diameter. The rod is heated to attain a stiffness thereof that is greater than about 300 GPa. A machinable sleeve is formed from material having a stiffness that is less than the stiffness of the rod and that is different than the material of the rod, the sleeve having an inner diameter that is equal to or less than the rod outer diameter. The rod is inserted into the sleeve, after the rod is heated.