Provided is a method for forming a three-dimensional article through successively depositing individual layers of powder material that are fused together so as to form the article in a vacuum chamber, said method comprising the steps of: providing at least one electron beam source emitting an electron beam for at least one of heating or fusing said powder material in said vacuum chamber, applying a first set of beam parameters for formation of a fused bulk material of said three-dimensional article, where said bulk material has a predetermined microstructure, applying a second set of beam parameters for formation of a top portion of said three-dimensional article, wherein said second set of beam parameters is applied a predetermined number of layers prior to reaching a top surface of said three-dimensional article for encapsulating chimney porosities into said bulk material. Associated apparatus and computer program product are also provided.

A method of forming a retention structure including magnetic regions and non-magnetic regions includes positioning one or more magnetic materials over one or more magnets of a rotor assembly and positioning one or more non-magnetic materials over one or more spacers, the spacers being positioned between the one or more magnets. The method also includes forming a cylindrical retention structure sized to fit around the one or more magnetic materials and the one or more non-magnetic materials. Forming the cylindrical retention structure is implemented via a three-dimensional printing process.