Phase-field models offer the possibility of simulating microstructure evolution under rapid solidification conditions without having to neglect the key physical mechanisms such as nucleation, growth kinetics and solute diffusion. However, until now the phase-field simulations are mostly restricted to binary alloys owing to the complexity of obtaining thermodynamic descriptions for technical alloy compositions. In this study, we employ 3-Dimensional multi-component and multi-phase-field simulations directly coupled to thermodynamic database to obtain the bulk free energies of individual phases. In addition, thermal boundary conditions of AM are implemented in such a way that the solver allows to model both melting and solidification (with latent heat release) simultaneously. The phase filed equations are implemented in openphase studio, a C++ based software package offered by OpenPhase Solutions. Through the 3-D simulations, microstructure evolution especially the dendrite morphology, primary dendrite arm spacing and solute segregation of full alloy composition of CMSX4 is studied in detail.