Background:
Nickel-based superalloys have good high-temperature properties and oxidation resistance, and are often used in the manufacture of parts in aero engines and industrial gas turbines that serve in high-temperature working environments. Additive manufacturing is a rapid manufacturing technology whose main feature is to build the desired three-dimensional structure by stacking materials layer by layer. Its advantage is that it can manufacture complex structural parts, save materials, manufacture small batches or personalized products, and manufacture multi-material assemblies, which brings new opportunities for the development of high-end manufacturing. In addition, additive manufacturing has a unique microstructure that can improve product performance, making it one of the main methods for preparing complex parts of superalloys. In this paper, the preparation methods, common grades, and microstructure and properties of additively manufactured nickel-based superalloys are reviewed, the existing problems are summarized, and the research areas worth exploring in the future are proposed.
Additive manufacturing methods
Additive manufacturing, also known as 3D printing, is a manufacturing technology that uses laser beams, electron beams, arcs, and more as energy sources to integrate raw materials into dense parts. Metal additive technology manufacturing can be divided into powder bed, powder feeding and wire feeding system according to the feeding system. Table 1 mainly describes the basic processes and advantages and disadvantages of different additive manufacturing methods.
Table 1 Comparison of different additive manufacturing methods
Additive manufacturing of nickel-based alloys
· Additive manufacturing of nickel-based superalloys is commonly used
Nickel-based superalloys are strengthened by the Ni-Cr binary system and by the addition of solution strengthening, precipitation strengthening and grain boundary strengthening elements. Table 2 focuses on the chemical composition of nickel-base superalloys that are widely used in additive manufacturing, including IN625, IN718, Hastelloy X, CM247LC, and IN738LC. Among them, Hastelloy X and IN625 are solution-strengthened nickel-based superalloys, which mainly rely on the addition of solution elements and the formation of carbides to enhance their strength. IN718 is the most widely used precipitation-strengthened nickel-based superalloy, accounting for more than 35% of the output of all superalloys, mainly through the common precipitate phases including γʹ and γ" to enhance its strength, IN718 alloy Al and Ti total content is still low, showing good weldability and printability. The aluminum-titanium content in CM247LC and IN738LC alloys exceeds 5%, which is often referred to as refractory nickel-based superalloys, and the high aluminium-titanium content makes it easy to form a high volume fraction γʹ strengthening phase in the alloy.
Table 2 Composition of common nickel-based superalloys for additive manufacturing (mass fraction/%)
· Room temperature tensile properties of additively manufactured nickel-base superalloys
Tables 3~6 show the tensile properties of different nickel-base superalloys at room temperature. It is concluded that the tensile properties of superalloys are affected by many factors. First of all, the tensile properties of additively manufactured nickel-based superalloys are closely related to the types of nickel-based superalloys. The solution-strengthened Hastelloy X and IN625 alloys had lower tensile properties at room temperature and better plasticity. The plasticity of IN718 alloy is not as good as that of IN625 alloy, but its strength can be achieved to a higher degree with suitable additive manufacturing and post-processing; The strength of the refractory superalloy CM247LC and IN738LC is generally high due to the large number of γʹ reinforcing phases, but it is prone to cracks and poor plasticity during the printing process.
Secondly, the tensile properties of superalloys at room temperature are affected by the processing method. In general, the tensile properties of additive manufacturing alloys at room temperature are higher than those of parts prepared by conventional casting. In different additive manufacturing methods, the alloy strength prepared by WAAM is low, sometimes even lower than the level of casting; The tensile properties of the alloy prepared by PBF at room temperature are highly dispersed, and its properties are extremely unstable. However, the tensile properties of the alloy prepared by DED at room temperature are higher than those of WAAM, and the dispersion of the tensile properties at room temperature is lower than that of PBF.
Finally, the tensile properties of additively manufactured superalloys are affected by heat treatment, and different types of superalloys have slightly different tensile properties after heat treatment. For solution-strengthened nickel-based superalloys, such as IN625 and Hastelly X, the strength of the alloy decreases and the plasticity increases after heat treatment. After HIP treatment, the tensile strength and elongation of the IN738LC alloy were improved at room temperature. The yield strength of the printed CM247LC is not much different from that of the printed CM247LC after standard heat treatment, and the strength does not change much after HIP treatment, but the ductility is improved. With the right heat treatment, additively manufactured superalloys can achieve significant performance improvements.
Table 3 Tensile properties of IN625 alloy at room temperature under different preparation methods
Table 4 Tensile properties of IN718 alloy at room temperature under different preparation methods
Table 5 Tensile properties of Hastelloy X alloy at room temperature under different preparation methods
Table 6 Tensile properties of CM247LC and IN738LC alloys at room temperature under different preparation methods
The problem exists
Although additive manufacturing has been widely used in the preparation of nickel-based superalloys, there are still a number of problems to be solved.
(1) There are obvious anisotropy in the microstructure and mechanical properties of additive manufacturing alloys. A columnar crystal structure with a distinct texture along the <00>1 direction was formed inside the additive manufacturing specimen, which led to the anisotropy of the alloy in terms of mechanical properties.
(2) The printing performance of high-performance nickel-based superalloys is poor and the sensitivity to cracking is high. The poor welding performance of high-performance nickel-based superalloys and crack susceptibility continue to be an important technical challenge in additive manufacturing.
(3) Lack of specifications and standards for additive manufacturing of nickel-based superalloys. Industry standards are critical to the consistency of final product quality, but the lack of comprehensive, uniform standards remains a prominent problem in the field of additive manufacturing. Planning and standards are essential to drive the mass production and industrial applications of additive manufacturing.
Areas of future research
The field of additive manufacturing of nickel-based superalloys is full of opportunities, and based on this review, the authors suggest some areas worth exploring. Future research areas for additive manufacturing of nickel-base superalloys include:
(1) Additive manufacturing of nickel-based superalloy heat treatment
Heat treatment can reduce metallurgical defects and manipulate the microstructure of additively manufactured nickel-base superalloys to optimize material properties. However, most of the current heat treatment methods are based on traditional experience, which is not fully applicable to parts in the additive manufacturing process, and there is an urgent need to establish heat treatment technologies suitable for additive manufacturing of nickel-based superalloys.
(2) Customization and development of new crack-free nickel-based superalloys for additive manufacturing
One of the opportunities in additive manufacturing is the development of new alloys. At present, most of the additive manufacturing nickel-based superalloys that have been applied are mainly designed for traditional manufacturing methods such as casting or forging, resulting in some high-performance superalloys that cannot be applied to additive manufacturing. The strong interaction between multiple elements in superalloys can accelerate the design and verification of superalloys by using a combination of machine learning, computational materials science, materials design software, and high-throughput methods, providing a fast, low-cost, and reliable path to alloy design and optimization.
(3) To explore the process-structure-performance relationship of nickel-based superalloy additive components with complex structures
While the relationship between nickel-base superalloy additive manufacturing processes, material cracking behavior, and mechanical properties is well understood, it is still challenging to apply these relationships directly to larger or finer real-world engineered parts with complex structures. Therefore, it is crucial to study the controllable preparation of fine features and large-scale lattice structures in additive manufacturing nickel-based superalloy components, as well as the residual stress distribution and evolution, cracking behavior and service performance of complex structural engineering components.
(4) Calculations and modeling are used to solve various problems in the additive manufacturing process
By integrating computing and modeling, artificial intelligence and additive manufacturing, stable production can be achieved more efficiently, accurately and sustainably. AI-based online monitoring systems and feedback systems play a key role in real-time process control and optimization. The computational and modeling field of additive manufacturing will rely more heavily on artificial intelligence, online monitoring systems, and the convergence of simulation and modeling to further accelerate the rapid development of the field.
Meet the team
Zhu Guoliang's research team is affiliated to the Institute of Coagulation Science and Technology, School of Materials Science and Engineering, Shanghai Jiao Tong University. The team mainly focuses on metal additive manufacturing technology and load-bearing function integration construction materials to carry out research work, including national defense high-level talents, youth Yangtze River, youth lifting including 1 senior high, 1 deputy senior and 3 intermediate, and has taken the lead in undertaking major basic research projects, major special projects, the National Natural Science Foundation of China, the Ministry of Education Joint Fund and other projects, published more than 100 SCI papers, and won 4 provincial and ministerial awards.
Original source:
ZHU Guoliang, LUO Hua, HE Jian, et al. Research Progress on Additive Manufacturing of Nickel-based Superalloys[J]. Journal of Materials Engineering, 2024, 52(2): 1-15
ZHU G L, LUO H, HE J, et al. Advances in additive manufacturing of nickel-based high-temperature alloys[J]. Journal of Materials Engineering, 2024, 52(2): 1-15