Analysis of Microstructure and Mechanical Properties in As-Built/As-Cast and Heat-Treated Conditions for IN718 Alloy Obtained by Selective Laser Melting and Investment Casting Processes

Abstract

In this work, new customized heat treatments for selective laser melted (SLM) parts in IN718 alloy were analyzed. This was done through the evaluation of the mechanical properties and advanced characterization of the phases and microstructure obtained in as-built condition and after the application of standard and tailored heat treatments. The microstructure and mechanical properties were compared and discussed with results reported in the literature. Finally, strengthening mechanisms of IN718 alloy processed by SLM and its differences with mechanisms that occur in investment casting were analyzed. Both processes generate quite different microstructures, investment casting is composed mainly by a dendritic structure, and SLM is characterized by columnar and cellular structures with very thin cells. Due to the fine and homogeneous microstructure obtained from SLM processing and its specific strengthening mechanisms, it is not necessary to apply homogenization and solution stages as in standard heat treatment used for this type of alloy in casting or wrought. The pre-heating and process parameters selected, in combination with a direct stepped aging (at 720 °C/620 °C), provide the material with its best mechanical properties, which are superior to those obtained by standard heat treatment (AMS 5383F) applied to investment casting of IN718 alloy.

Grain Refinement of Inconel 718 Superalloy—The Effect of Rotating Magnetic Field

“…As characteristic of cast IN718 [ 14 ], extensive segregation is observed in the microstructures of the castings produced, mainly in the interdendritic space but also in the dendritic (γ) region. This segregation is intensified due to the large section size of the cast parts since longer solidification process occurs [ 13 ].…”

“…Nickel-based superalloys can also be hardened by solid-solution strengthening or precipitation of intermetallic compounds in the metal matrix. IN718, in particular, is frequently strengthened by precipitating γ’ (Ni 3 (Al, Ti)) and γ’’ (Ni 3 Nb) phases in the γ matrix [ 9 , 10 , 11 , 12 , 13 , 14 ].…”

“…Typically, the needle-like δ phase forms in the vicinity of or is attached to the Laves phase, mainly in the Nb-rich areas of the interdendritic regions [ 13 ]. Laves phases have low ductility and their greater incidence causes a decrease in castings’ mechanical and corrosion properties [ 13 , 14 , 15 , 16 ].…”

“…Usually, Inconel 718 components are fabricated using conventional melting and investment casting techniques. Nevertheless, other processes that allow one to obtain components with complex shape and highly precise dimensions, such as selective laser melting (SLM), are also applied to produce these parts [ 10 , 11 , 14 ].…”

Investigations of Model Multilayer Ceramic Casting Molds in a Raw State by Nondestructive Methods

“…The aim of the research presented in publications is to change the general approach to the problem of special processes, in particular the production of multilayer ceramic casting molds. Despite the fact that this process is known and subject to constant research and analysis, as evidenced by recent publications [39][40][41][42][43][44][45][46], it has not been possible to define all the causes of defects, despite detailed monitoring of the manufacturing processes. This issue is extremely important because it concerns the large-scale industrial production of investment castings of aircraft engine parts, which are decisive for flight safety and therefore cannot be burdened with defects.…”