Formation of defects in selective laser melted Inconel 718 and its correlation with mechanical properties through dimensionless numbers

This paper presents a profound study on the formation of three typical types of defects (i.e., lack of fusion, keyholes, and gas pores) observed in selective laser melting (SLM) printed Inconel 718 samples, along with their correlations with mechanical properties of the samples. Computed tomography, scanning electron microscopy, and mechanical property tests revealed that the three types of defects fall into three stages of porosity evolution classified by recently-proposed dimensionless numbers eta(m) (melting efficiency) and eta(v) (vaporization efficiency). Meanwhile, experimental tests verified that the mechanical properties of products, such as strength and elongation, are remarkably sensitive to lack of fusion. However, these properties are slightly affected by the keyholes and gas pores. An optimal process window characterized by dimensionless numbers is realized by adjusting the processing parameters and employing different powders. This process window allows products to have relatively low defects and high mechanical performances. A quantitative relation between processing parameters, dimensionless numbers, defects, and mechanical properties is established based on these observations. This relation, along with the optimal process window, is believed to enhance the quality of SLM products of Inconel 718 alloy and can be further extended to SLM with other metal materials.