# Plastic Behavior of Laser-Deposited Inconel 718 Superalloy at High Strain Rate and Temperature
## 1 Introduction  
Nickel-based superalloys show an excellent combination of properties. Among these, the most important property is to retain high strength at high temperatures. This characteristic makes this class of material suitable for applications in which the components could be exposed to temperatures even higher than 800 \({}^{\circ}\)C [1] during services. Thus, nickel-based superalloys are well suited to the aerospace, aviation, marine, nuclear, chemical, and power generation industries. Focusing on the aerospace field, nickel-based alloys are widely used to manufacture aerogening parts [2], for which the resistance to impact loads also needs to be evaluated. In the case of impact, high deformation of components, or even their failure, occurs in a short time. This loading condition underlines that for the safe design and realization of high-performance engine parts, it is mandatory to understand the plastic behavior in case of combined high temperature and high strain rate conditions.  
Additive manufacturing (AM) technology represents a good alternative for the manufacturing of components made of nickel-based superalloys. When conventional machining methods are employed, processes with high costs, long delivery times, and a high wasting ratio for material can emerge [3, 4, 5]. Conversely, AM limits these aspects and introduces the important advantages of having the possibility to repair the components or to renovate their geometry. The main disadvantage of the AM technique is represented by the need for a specific heat treatment to improve the poor mechanical properties that characterize the as-deposited (aD) condition. In fact, the resulting microstructure is completely different from that obtained with traditional manufacturing methods.  
In this study, the plastic flow behavior of Inconel 718 superalloy produced by laser metal deposition (LMD) is investigated in tension. Different loading conditions were explored in terms of both the strain rate and temperature: the experimental testing campaign covered a wide range of temperatures at a high strain rate, whereas in the quasi-static condition, only tests at room temperature were performed. In addition, the influence of the heat treatment, and consequently, that of the material microstructure, was investigated. The final aim of the present study was to define a strength material model that can correctly predict the material response.  
In the scientific literature, many studies have investigated the mechanical response of the as-cast Inconel 718 alloy as a function of several parameters, such as the type of loading (e.g., [6; 7]), temperature, and strain rate (e.g., [8; 9; 10; 11]). In some cases, the aim of the studies was the calibration or proposal of a strength model suitable for the prediction of the material response (e.g., [12; 13]). Conversely, to the authors' knowledge, only a few studies have been performed on the investigation of the mechanical response for additively manufactured Inconel 718, especially in the case of combined high strain rate and high-temperature tensile loading conditions and for heat-treated materials. Some examples of similar studies are listed below, but none of these works completely cover all the mentioned aspects. In [14], quasi-static compression tests were performed at high temperatures. In [15], the quasi-static tensile behavior was investigated between 20 \({}^{\circ}\)C and 650 \({}^{\circ}\)C. In [16], the influence of the heat treatment on the quasi-static response was investigated in tension. In [17], the strain rate sensitivity was evaluated in compression for as-deposited and heat-treated conditions. Finally, in [18], the combined high strain rate and medium-high temperature conditions were explored in tension on aD materials by varying the printing parameters.