Examples for refining the microstructure of metallic materials used for additive manufacturing are described herein. An example can involve generating a first layer of an integral object by heating a metallic material to a molten state such that the metallic material includes a solid-liquid interface. The example can further involve applying an electromagnetic field or vibrations to the metallic material of the first layer. In some instances, the electromagnetic fields or vibrations perturb the first layer of metallic material causing nucleation sites to form at the solid-liquid interface of the metallic material in the molten state. The example also includes generating a second layer coupled to the first layer of the integral object. Generating the second layer increases a number of nucleation sites at the solid-liquid interface of the metallic material in the molten state. Each nucleation site can grows a crystal at a spatially-random orientation.