The influence of Laves phases on the room temperature tensile properties of Inconel 718 fabricated by powder feeding laser additive manufacturing

Powder Bed Fusion (PBF) techniques constitute a family of Additive Manufacturing (AM) processes, which are characterised by high design flexibility and no tooling requirement. This makes PBF techniques attractive to many modern manufacturing sectors (e.g. aerospace, defence, energy and automotive) where some materials, such as Nickel-based superalloys, cannot be easily processed using conventional subtractive techniques. Nickel-based superalloys are crucial materials in modern engineering and underpin the performance of many advanced mechanical systems. Their physical properties (high mechanical integrity at high temperature) make them difficult to process via traditional techniques. Consequently, manufacture of nickel-based superalloys using PBF platforms has attracted significant attention. To permit a wider application, a deep understanding of their mechanical behaviour and relation to process needs to be achieved. The motivation for this paper is to provide a comprehensive review of the mechanical properties of PBF nickel-based superalloys and how process parameters affect these, and to aid practitioners in identifying the shortcomings and the opportunities in this field. Therefore, this paper aims to review research contributions regarding the microstructure and mechanical properties of nickel-based superalloys, manufactured using the two principle PBF techniques: Laser Powder Bed Fusion (LPBF) and Electron Beam Melting (EBM). The ‘target’ microstructures are introduced alongside the characteristics of those produced by PBF process, followed by an overview of the most used building processes, as well as build quality inspection techniques. A comprehensive evaluation of the mechanical properties, including tensile strength, hardness, shear strength, fatigue resistance, creep resistance and fracture toughness of PBF nickel-based superalloys are analysed. This work concludes with summary tables for data published on these properties serving as a quick reference to scholars. Characteristic process factors influencing functional performance are also discussed and compared throughout for the purpose of identifying research opportunities and directing the research community toward the end goal of achieving part integrity that extends beyond static components only.

Powder Bed Fusion of nickel-based superalloys: A review

Effect of heat treatment on microstructure evolution of Inconel 718 alloy fabricated by selective laser melting

Unique crystallographic texture formation in Inconel 718 by laser powder bed fusion and its effect on mechanical anisotropy

Aerospace is a key market driver for the advancement of additive manufacturing (AM) due to the huge demands in high-mix low-volume production of high-value parts, integrated complex part geometries and simplified fabrication workflow. Rapid and significant progress has been made in the laser additive manufacturing (LAM) of aeroengine materials, including the advanced high-strength steels, nickel-based superalloys and titanium-based alloys. Despite the extensive investigation of these three families of materials by the research community, there is a lack of comprehensive review on LAM of high strength steels, and existing gaps in published reviews on Ti-based alloys and Ni-based superalloys. Furthermore, although emerging materials such as high/medium entropy alloys and heterostructured materials exhibit promising mechanical performance, rigorous characterization, testing, qualification, and certification are still required before actual application in engine parts. Thus, it is still important and relevant to have a deep understanding on the relationship between process parameters – microstructures – mechanical properties in these widely used aeroengine materials, to drive the development of superior high-value alloys. This review aims to provide a critical and in-depth evaluation of laser powder bed fusion (LPBF) and laser directed energy deposition (LDED) technologies of the mentioned aeroengine materials. The review will summarize the material properties, performance envelops and outlines the research gaps of these aeroengine materials. Furthermore, perspectives on research opportunities, materials development, and new R&D approaches of LAM for the aeroengine materials are also highlighted.

Progress and perspectives in laser additive manufacturing of key aeroengine materials

The paper comparatively investigates the microstructures and mechanical properties of Inconel 718 superalloy manufactured by selective laser melting (SLM) and casting. The finite element analysis (FEA) method is used to simulate the temperature fields during SLM and casting processes. Driven by ultra-high temperature gradient and ultra-fast cooling rate during SLM process, the fine grains (average grain size of 48 µm) and dispersed fine precipitation in SLM-ed sample even after HSA (homogenization + solution + aging) and HA (homogenization + aging) heat treatment significantly enhance its mechanical properties, which far exceeds that of casting with average grain size of 1300 µm, and is comparable to that of forging. The microstructure of casting with coarse irregular Laves phases, acicular δ precipitates and globular carbides in the interdendritic zones after HSA heat treatment and some defects existed possibly result in premature failure of tensile samples. The microstructure without δ phases but only some globular carbides in the grain boundary of SLM-ed sample after HA heat treatment possesses higher mechanical properties than that after HSA heat treatment, in which there is only some finer needle-like δ phase and few carbides are precipitated in the grain boundaries. The analysis shows the large amounts of δ phase precipitated in the matrix will deteriorate the plasticity of SLM-ed IN718 superalloy, the appropriate reduction of the δ phase will improve the strength and plasticity of material simultaneously.

Comparison of microstructures and mechanical properties of Inconel 718 alloy processed by selective laser melting and casting

A physical model coupled with heat transfer and fluid flow was developed to investigate the thermofluid field of molten pool and its effects on SLM process of Inconel 718 alloy, in which a heat source considering the porous properties of powder bed and its reflection to laser beam is used. The simulation results showed that surface tension caused by temperature gradient on the surface of molten pool drives to Marangoni convection, which makes fluid flow state mainly an outward convection during SLM process. Marangoni convection includes convective and conductive heat flux, both of them have effects of on molten pool shape, but the effect of convective heat flux is dominant because its magnitude is one order larger than that of conductive heat flux. The convective heat flux accelerates the flow rate of the molten metal, benefits to heat dissipation. The convective heat flux makes the molten pool wider, while the conductive heat flux makes comparably the molten pool deeper and wider. Furthermore, heat accumulation caused by multiple scanning increases convection and conduction heat flux resulting in the increase of the width and depth of the molten pool, but no change of dominant role of convective heat flux to the shape of the molten pool.

Thermofluid field of molten pool and its effects during selective laser melting (SLM) of Inconel 718 alloy

It is of great importance to thoroughly explore the evolving temperature fields of direct laser metal deposition (abbreviated as LMD) in vertical thin wall manufacturing. It is helpful to control the temperature gradient, and even to adjust to forming microstructures and accumulation of residual stress. In this paper, a comprehensive three-dimensional transient model is developed for evolving temperature fields. The manufactured material is DS superalloy Rene80. The laser-powder interaction during the powder flowing process is simulated first, and its possible effect on the temperature field of the melting pool is analyzed. Then a 3D numerical simulation for the evolving temperature field is carried out based on considering transport phenomena during LMD such as the change in phase, powder injection and liquid flow. The applied deposition parameters are derived from experimental investigation with optimized vertical wall manufacturing. The simulated results explain why a balance between heat input and dissipation could form inside the vertical thin wall. These reconstruct the instability at an early phase of the building process without any temperature control unit and exhibit the influence of parameters such as laser power, deposition velocity and laser beam deposition pattern. The simulation results of temperature evolution are consistent with experimental investigation.

Modeling of Temperature Field Evolution During Multilayered Direct Laser Metal Deposition

The invention relates to a surface polishing method for 3D printed metal parts. The surface polishing method includes the steps that through the water bath environment of SiO2 nano-scale micro-particles with antirust agents and lubricating agents added, a turbo type stirrer rotates and drives liquid with the polishing effect to flow and scour the surfaces of the metal parts, and therefore the metal structure parts can be polished; liquid polishing is utilized, the complex 3D printed metal structure parts can be polished, and the work-piece integrity and the polishing quality can be well guaranteed; clamps fixing the metal parts can be detached, and different clamps can be designed for the metal parts of different types; and a power system automatically controlled can provide different polishing power according to the surface requirements and the polishing time of the parts to be polished. According to the method, the operation is convenient, the production cost is low, and the practicability is high. The method can be mainly used for surface polishing of 3D printed parts and also can be used for polishing other devices with polishing problems.

Surface polishing method for 3D printed metal parts

The invention relates to a distal femur tumor accurate resection operation auxiliary instrument system manufactured by carrying out 3D printing. The system is characterized by containing a bone approaching and fixing part, a height adjusting threaded rod, a length adjusting threaded rod, a length adjusting threaded rod mating part, an osteotomy interposition mating part, an osteotomy outer side interposition part and an osteotomy inner side interposition part; computer assistance is adopted for accurately determining tumor resection limitation, CAD is adopted for designing adjustable distal femur tumor accurate resection operation instruments to accurately guide tumor resection and a postoperative reconstruction operation, the auxiliary instrument system is detachable and adjustable, an adjustable screw thread and an adjustable screw determine tumor resection length and tumor resection height, the advantages of a 3D printing technology in the medical field are analyzed, and the whole resection operation auxiliary instrument system parts are manufactured and processed by combining a 3D printing SLM technology.

Chengjie Wang

Papers

Comparison of microstructures and mechanical properties of Inconel 718 alloy processed by selective laser melting and casting

Thermofluid field of molten pool and its effects during selective laser melting (SLM) of Inconel 718 alloy

Modeling of Temperature Field Evolution During Multilayered Direct Laser Metal Deposition

Surface polishing method for 3D printed metal parts

Distal femur tumor accurate resection operation auxiliary instrument system manufactured by carrying out 3D printing