Laser rapid prototyping (LRP) of the Stellite12-B 4 C-Y 2 O 3 mixed powders produced a bottom layer; then the Stellite12-B 4 C-Cu-Y 2 O 3 mixed powders were deposited on this bottom-layer to form the microlaminates. This upper-layer showed higher wear resistance and micro-hardness than those of the bottom layer due to an action of Cu; Cu-added led lots of the AlCu 2 Ti intermetallics ultrafine nanocrystals (UNs) to be produced, which distributed uniformly in some location of the upper-layer matrix. UNs may destroy the atomic equilibrium state, increasing the potential/free energy and the strength/hardness of such microlaminates. The temperature of the laser induced molten pool (laser-pool) was very high, favoring the defects to be formed; UNs did not need the long waiting time to change from the normal lattice point to the interstitial particles; also the AlCu 2 Ti UNs had a high interface energy, which became the driving force of the atomic motions, favoring a compact fine microstructure to be formed. The AlCu 2 Ti UNs in laser-treated composites provides essential theoretical and experimental basis to promote the development of the laser 3D printing nano technologies.