Diffusion bonding and advanced additive manufacturing produce parts applicable in a wide range of industries, extending from electronics and nuclear applications to the manufacturing of various engineering and aerospace components. Characteristics and homogenization of diffusion-bonded joints rely on many parameters of the process. 3D printing depends on particle sintering as one of the key process steps. However, the micromechanics of diffusion bonding and additive manufacturing is not well understood. The joining method produces residual stresses and defects in the joint so that the joint typically represents a weak link in applications. Sintering often results in parts that deviate from the intended shape, which is a major obstacle to realizing the potential of 3D printing technology. We address the mechanics and physical mechanisms, including the underlying driving forces, responsible for joint homogenization in diffusion bonding of ceramics and shape distortion in sintering. We consider diffusion bonding of ceramics with a metallic interlayer. The key process for joint homogenization is the diffusion of carbon from the carbide phase into the metallic interlayer, which when the critical carbon concentration is reached, initiates the phase transformation of the metallic interlayer to carbide structure. We show that the driving force for carbon diffusion is the interfacial energy dependence on the carbon concentration jump across the metal-ceramic interface.3D printing of nanoparticles is used to study shape distortion in nonhomogeneous sintering. Freestanding microstructures such as pillars and walls are considered. Experiments show that sintering-induced distortion produces no porosity gradients in distorted parts, revealing that a mass transport mechanism must exist. Two physical mechanisms for mass transport in nonhomogeneous are identified. A macroscopic continuum theory that accounts for mass transfer and applicable to both mechanisms is formulated. The model predicts transient and permanent deformation during nonhomogeneous sintering and exhibits numerical consistency with the experimental data.In addition to diffusion bonding and nonhomogeneous sintering, we develop the computational framework for diffusional creep of single grain crystals using the lattice continuum formulation. The model is tested and applied on various grain sizes, applied stresses, governing processes, and compared with the classical theory for diffusional creep
