Selective laser melting（SLM）, one of powder bed fusion（PBF）-type additive manufacturing（AM）processes, is a promising technology that enables high accuracy production of arbitrary structures; therefore, it had been utilized in aerospace and medical fields. However, there are many un-elucidated phenomena which will largely affect the quality of products. Spatter generation, in particular, has been reported to adversely affect the stability of fabrication, resulting in impaired performance of the products. The suppression of spatter generation is indispensable for acquiring high quality products. However, there are many unknown controlling factors about the basis of spatter generation. In this article, we aimed to elucidate the influence of atmosphere gas on spatter generation during laser irradiation on Ti-6Al-4V powder, in particular, the effect of oxygen concentration in inert gas. The amount of spatter generation increased with the oxygen concentration in the atmosphere, and the oxygen content in the spatter particles also increased. The diameter of spatter particles increases remarkably compared with the raw powder particles, which lead to not only inhomogeneous powder bed when the spatter particles fall down on the fabricating products, but also to an unexpected increase in the oxygen concentration of products closely relating to the mechanical property. Impurity oxygen in the atmosphere gas should be eliminated during SLM process.
The demand for the improved efficiency of industrial gas turbine engines has led to the increase in turbine inlet temperature (TIT), and hence the operating environment temperature of turbine blades has been increasingly higher. For this reason, techniques to control anisotropic crystallographic texture have been developed such as directional solidification (DS) and single crystallization (SC), together with complex internal cooling designs for efficient metal cooling. However, with regard to precision casting methods for turbine blade production, it is difficult to achieve both high accuracy of complex internal shapes and anisotropic crystallographic texture.
To overcome this challenge, we have focused on selective laser melting (SLM), a technique suitable for creating elaborate internal shapes. In addition, the material properties are greatly influenced by various factors such as fabricating conditions, including laser power, scanning speed, atmosphere during molding, etc., as well as alloy composition. Research on the microstructure control of additive manufacturing materials has been actively conducted in recent years, but no systematic study on the control of anisotropic crystallographic texture has been made.
In this article, we demonstrate the control of anisotropic crystallographic texture using the IN718 nickel-based superalloy manufactured by SLM, and report the results on the improvement of creep properties.