A system for locking blades to a rotor of a turbomachine including adjacent pairs of generally axially extending grooves for receiving blades inserted in an axial direction. A circumferential slot is disposed around the periphery of the rotor and a locking device assembly is located in the circumferential slot between an adjacent pair of grooves. The assembly includes a last locking device, a spacer and key member formed of a shape memory alloy. The key member is located in a gap between the last locking device and the spacer. The shape memory alloy key member is heated to cause a transition from a martensite to an austenite phase to cause the key member to engage and press against opposing faces of the last locking device and the spacer to increase a force applied to a respective pair of blades in the adjacent pair of grooves.