What manufacturing process involves atoms diffusing across particle boundaries, fusing them together?

The manufacturing process that involves atoms diffusing across particle boundaries to fuse materials together is sintering. This technique typically involves powdered materials that are heated to a temperature below their melting point. As the temperature rises, particles within the powder start to bond at their contact points through diffusion, resulting in a solid mass without reaching a fully molten state. This process enhances the density and integrity of the material.

In contrast to sintering, quenching is a rapid cooling process involving materials, particularly metals, that have been heated. Welding combines the edges of materials through melting and then solidifying them; while it also involves atomic bonding, it does not specifically focus on diffusion across particle boundaries in the same way. Molding involves shaping materials in a cavity or form but does not include the atomic diffusion process described in sintering. Thus, the context of atomic diffusion across particle boundaries distinctly identifies sintering as the correct answer.