An additive manufacturing method of fabricating a 3D object on a build stage, the method comprising in the following order: a step of depositing onto a build stage positioned within a build chamber a first quantity of at least one reactive base material on a selective portion where the 3D object is to be built, wherein the at least one reactive base material has a surface capable of modification to a desired chemistry by a reactive gas (60, 60', 60") with or without the application of energy; a step of depositing onto the build stage positioned within a build chamber at least one base material having a surface that is non-reactive to said reactive gas (60, 60', 60") on a selective portion where the 3D object is to be built; a step of introducing at least one reactive gas (60, 60', 60") into said build chamber; a step of modifying the reactive base material to create a modified surface; a step of applying energy to said modified reactive base material and said non-reactive base material and fusing said modified reactive base material and said non-reactive base material creating a first layer or substrate; a step of forming at least one additional layer on said substrate by depositing a second quantity of said reactive base material and a step of depositing a second quantity of said non-reactive base material, followed by a step of introducing the at least one reactive gas, modifying the reactive base material to create a modified surface, and applying energy to said at least one additional layer deposited upon said substrate or said first layer so as to fuse said at least one additional layer to said first layer or said substrate; and continuing to form individual layers comprising said reactive base material and said non-reactive base material on said substrate until the fabrication of the object is complete. a step of depositing onto a build stage positioned within a build chamber a first quantity of at least one reactive base material on a selective portion where the 3D object is to be built, wherein the at least one reactive base material has a surface capable of modification to a desired chemistry by a reactive gas (60, 60', 60") with or without the application of energy; a step of depositing onto the build stage positioned within a build chamber at least one base material having a surface that is non-reactive to said reactive gas (60, 60', 60") on a selective portion where the 3D object is to be built; a step of introducing at least one reactive gas (60, 60', 60") into said build chamber; a step of modifying the reactive base material to create a modified surface; a step of applying energy to said modified reactive base material and said non-reactive base material and fusing said modified reactive base material and said non-reactive base material creating a first layer or substrate; a step of forming at least one additional layer on said substrate by depositing a second quantity of said reactive base material and a step of depositing a second quantity of said non-reactive base material, followed by a step of introducing the at least one reactive gas, modifying the reactive base material to create a modified surface, and applying energy to said at least one additional layer deposited upon said substrate or said first layer so as to fuse said at least one additional layer to said first layer or said substrate; and continuing to form individual layers comprising said reactive base material and said non-reactive base material on said substrate until the fabrication of the object is complete.