Abstract
Many urgently needed inconel superalloy parts with complex internal cavity geometry and high surface precision are difficult to prepare by traditional subtractive manufacturing methods because of its poor machinability. The additive manufacturing technology that has emerged in recent years became a research hotspot in the manufacture of refractory and difficult-to-process metals. In the present study, selective laser melting (SLM), a typical additive manufacture technology, was used to prepare Inconel 718 samples. The influences of input laser energy density ((E, J/mm3) on densification behavior, phases composition, microstructures, microhardness, and wear performance of the SLM as-built Inconel 718 samples were explored in detail. X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to examine the phase composition and microstructure evolutions. The results show that the formablity, microstructures and mechanical properties of the printed samples were all improved with the increase of E within the parameter setting range of this study. At a lower E, the poor surface morphology and balling effect occurred, the density, hardness, and wear resistance were all at a relatively lower level. When an E value of 190 J/mm was properly set, the surface open-pores and balling effect disappeared, the laser scanning tracks became smooth and continuous, the near-full dense (99.15%) and specimens with good metallurgical bonding and no critical defect were obtained, in which the average microhardness value reached 348 HV0.2 and wear rate was 5.67 × 10−4 mm3/N·m. The homogeneity of the superalloy Inconel 718 was also explored.
Highlights
In the past four decades, nickel-base superalloys have experienced rapid development and received widespread attention from experts in various fields [1,2,3]
At an even higher E of 171 J/mm3, as shown in Figure 3c, it was found that the size and number of metal balls distributed on the surface were significantly reduced, the open-holes were almost disappeared, the laser scanning tracks were clear and the density of the shaped sample increased to 98.67%
The analysis showed that for the selective laser melting (SLM) forming of Inconel 718 superalloy, with the increasing of input laser energy density E, the surface morphology became smooth, the scanning tracks tended to be clearly visible and tidy, and the density of the sample gradually increased within the scope of the present study
Summary
In the past four decades, nickel-base superalloys have experienced rapid development and received widespread attention from experts in various fields [1,2,3]. The unique dendritic microstructures of the SLM as-built samples can be dominated by the complex physical and chemical behaviors within the laser micro-melting pool because the SLM technology based on the nonequilibrium extremely rapid melting/solidification mechanism. Popovich et al [27] proved the ability of additive manufacturing to produce customized microstructures and mechanical properties Apart from these studies, many scholars focused on kinds of post heat-treatments such as solution treatment, annealing and hot isostatic pressing (HIP)) to improve the comprehensive performance of SLM-Inconel 718 parts. Amato et al [10] pointed out that the microstructure of the SLM-formed part exhibited columnar grains whether it was parallel to or perpendicular to the building direction, microindentation (Vickers) hardness of as-fabricated, HIP and annealed material were investigated. Few studies on the influence of laser parameters on the SLM-parts’ microstructure and mechanical properties have been reported [29]. Materials 2021, 14, 991 basis for selective laser melting of other materials or other laser powder processing methods such as laser engineered net shaping and laser metal deposition
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