This paper mainly analyzes the typical thermodynamic response (thermal history, thermal strain and residual stress) in a conventional continuous-wave (CW) laser during Directed Energy Deposition (DED). The influence of process parameters (laser power and scanning speed) on the temperature gradient in the heat-affected zone, thermal strain and residual stress are studied, and the corresponding relationship are established. The results show that a reduction in residual stress can be obtained by decreasing the temperature gradient. However, the method of reducing the temperature gradient by changing process parameters leads to low forming quality and low density. A pulse-wave laser (PW) is proposed to actively control the residual stress of the deposited sample. This laser mode can reduce not only the temperature gradient in the process of DED but also the in situ release of thermal stress, correspondingly greatly reducing the residual stress.

Laser Additive Manufacturing (LAM) involves complex laser-matter interactions characterized by extreme non-equilibrium thermodynamic processes. During this process, localized high-energy heat input and rapid cooling establish a highly non-uniform temperature field within the material. The interplay between severe temperature gradients and the material's thermal expansion and contraction behavior inevitably leads to the accumulation of significant residual stresses within the fabricated component. The presence of these internal stresses not only induces component warping and compromises geometric precision but also acts as a driving force for micro-crack propagation. This severely degrades fatigue life, fracture toughness, and corrosion resistance, thereby posing potential risks to structural safety during service. Consequently, the effective mitigation of residual stress has become a critical bottleneck restricting the large-scale application of LAM technology in high-end manufacturing sectors such as aerospace and biomedicine. This paper first elucidates the fundamental nature, classification system, and thermo-mechanical coupling origins of residual stress. It then systematically reviews multi-dimensional characterization techniques and the effects of key process parameters. Finally, integrating recent research advancements, it provides an in-depth analysis of the mechanisms, merits, limitations, and future trends of existing control strategies.