Influence of molten-pool cooling rate on solidification structure and mechanical property of laser additive manufactured Inconel 718

Abstract

The relationship between solidification structure and cooling rate is critical for optimizing processing parameters to achieve desired mechanical property of additive manufactured parts. However, the establishment of the above relationship during laser additive manufacturing (LAM) is still challenging. In the present work, the molten-pool temperature was experimentally measured using a two-color pyrometer during LAM of Inconel 718. The relationship among laser processing parameters, molten-pool cooling parameters, solidification structure and mechanical property was investigated. The results showed that the Nb segregation ratio decreases from 9.30 to 4.26 and the volume fraction of Laves-phase particles decreases from 14.5% to 4.8% as the cooling rate increases from 480 °C/s to 2630 °C/s. The quantitative relationship between primary dendritic arm spacing λ1 and cooling rate ε was determined as λ1=438.5∗ε−0.5773. The laser processing parameter that creats the high cooling rate and rational molten-pool lifetime is recommend to achieve a good combination of tensile strength and plasticity, as it reduces the Nb segregation, the Laves volume fraction and the metallurgical defect. This work establishes the quantitative relationship between solidification structure and cooling rate, and provides the potential method for online evaluation of solidification structure and mechanical property.

Keywords

• Laser additive manufacturing
• Cooling rate
• Microstructure
• Mechanical property