研究目的

To investigate the influences of phase transition temperature and preheating on the residual stress of multi-layer and multi-pass laser metal deposition (LMD).

研究成果

The solid phase transition at a lower temperature has a significant effect on tensile stress relaxation and leads even to compressive stress zones. The tensile stress relaxation effect decreases with the increase of phase transition temperature. When the solid phase transition temperature is high, the preheating can increase the lowest temperature of the heat cycle beyond the solid phase transition temperature, thereby increasing the tensile stress relaxation effect of the solid phase transition. However, when the solid phase transition temperature is lower, the preheating can only to some extent increase the stress distribution uniformity.

研究不足

The interaction between stress and solid phase transition is complex and the relationship between TRIP and stress levels still needs to be further investigated. The kinetics of austenite phase transition need to be further studied. The material may be always at a higher temperature, which could result in some physical and chemical changes, altering the physical properties of the material. The physical parameters of the actual mixed phase do not strictly conform to the assumption of multiplying the volume ratio of the individual phases. The study on TRIP is based on uniaxial stress tests, however in actual LMD the stress field is very complex. The measurement error of thermophysical properties could also result in differences between the computational and the experimental results.