A turbine rotor blade of the spar and shell construction, the spar including a tip end with a dovetail shaped groove extending from the top, and a tip cap includes a dovetail shaped slot that engages with the spar groove to retain the tip cap in place. A shell made from a high temperature resistant material is secured in place between the platform and the tip cap. The platform includes a core extending into a hollow space formed by the shell and discharges impingement cooling air against the backside wall of the shell. The spar and the platform include fir tree configurations so that an assembled blade can be inserted into a slot of a rotor disk.