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

In this work, a functionally graded material (FGM) part was fabricated by depositing a Cu-based alloy on top of a high strength low alloy (HSLA) steel by twin-wire and arc additive manufacturing (T-WAAM). Copper and steel parts are of interest in many industries since they can combine high thermal/electrical conductivity, wear resistance with excellent mechanical properties. However, mixing copper with steel is difficult due to mismatches in the coefficient of thermal expansion, in the melting temperature, and crystal structure. Moreover, the existence of a miscibility gap during solidification, when the melt is undercooled, causes serious phase separation and segregation during solidification which greatly affects the mechanical properties. Copper and steel control samples and the functionally graded material specimen were fabricated and investigated using optical microscopy, scanning electron microscopy, and high energy synchrotron X-ray diffraction. Retained δ-ferrite was found in a Cu matrix at the interface region due to regions with mixed composition. A smooth gradient of hardness and electric conductivity along the FGM sample height was obtained. An ultimate tensile strength of 690 MPa and an elongation at fracture of 16.6% were measured in the FGM part. 

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Steel-copper functionally graded material produced by twin-wire and arc additive manufacturing (T-WAAM)

Steel-copper functionally graded material produced by twin-wire and arc additive manufacturing

Considering the stringent regulations, manufacturing of aircraft parts is often quite complex and time consuming. The multi-million components, multi-tier manufacturing systems and the severe constraints surrounding the sector lead to heavy inventory investments to achieve the just-in-time supply of parts often needed to reduce the airplane ground times. Additive manufacturing evolved allowing for the direct production of complex parts based on digital data with no complex tooling or machinery, a messiah of true just in time production. Appropriate integration of additive manufacturing with the aircraft industry could resolve some of the supply chain and inventory hurdles. Significant progress is already evident in these lines, but the lack of quality assurance attributes and certification standards is hampering the progress. The state-of-the-art of the application of additive manufacturing in the aircraft industry is reviewed in this paper.

https://www.longdom.org/articles/additive-manufacturing-for-the-aircraft-industry-a-review.pdf

Additive Manufacturing for the Aircraft Industry: A Review.

Defect formation is a critical challenge for powder-based metal additive manufacturing (AM). Current understanding on the three important issues including formation mechanism, influence and control method of metal AM defects should be updated. In this review paper, multi-scale defects in AMed metals and alloys are identified and for the first time classified into three categories, including geometry related, surface integrity related and microstructural defects. In particular, the microstructural defects are further divided into internal cracks and pores, textured columnar grains, compositional defects and dislocation cells. The root causes of the multi-scale defects are discussed. The key factors that affect the defect formation are identified and analyzed. The detection methods and modeling of the multi-scale defects are briefly introduced. The effects of the multi-scale defects on the mechanical properties especially for tensile properties and fatigue performance of AMed metallic components are reviewed. Various control and mitigation methods for the corresponding defects, include process parameter control, post processing, alloy design and hybrid AM techniques, are summarized and discussed. From research aspect, current research gaps and future prospects from three important aspects of the multi-scale AM defects are identified and delineated. 

Multi-scale defects in powder-based additively manufactured metals and alloys

Additive manufacturing of steel–copper functionally graded material with ultrahigh bonding strength

Additive manufacturing (AM) enables the processing of heterogeneous materials with customised architectures to improve strength-ductility synergy. Herein, layerwise-heterostructured high-strength s...

https://www.tandfonline.com/doi/pdf/10.1080/21663831.2021.1904299

Additive manufacturing of multi-scale heterostructured high-strength steels

Improvement in high temperature material properties of aerospace alloys is critical to extend the performances of aeroengines. Apart from new alloy development, there is also great potential in optimizing the microstructure of laser directed energy deposited (Laser-DEDed) parts. This work reports a novel method of handling the undesirable and large-sized Laves phase particles in Laser-DEDed alloys. Experimental results demonstrate improvement in high temperature mechanical properties of IN718, by fully leveraging on the fast dissolution behaviors of the Laves phase in Laser-DEDed microstructure. The obtained Laser-DEDed IN718 contains about 1.55 vol % Laves phase with the dimension of 0.4–0.6 μm and aspect ratio of approximately 1.4. In particular, the high-temperature stress rupture (HTSR) performance of Laser-DEDed IN718 samples tested at 650 °C and 725 MPa (~130 h) exhibit a ~148% improvement in HRST life compared with the forged material (~51 h). It has been ascertained that the small and granular Laves phases have positive effects on the high-temperature mechanical properties of IN718. They can induce dynamic recrystallization to lower localized stress concentration and enhance high temperature performance.

Laves phase tuning for enhancing high temperature mechanical property improvement in laser directed energy deposited Inconel 718

Fabricating fine equiaxed grains without undesirable secondary phases is highly challenging for additively manufactured Ti−6Al−4V alloy. The reference amount of Ni addition, which can achieve grain...

Youxiang Chew

Papers

Progress and perspectives in laser additive manufacturing of key aeroengine materials

Additive manufacturing of steel–copper functionally graded material with ultrahigh bonding strength

Additive manufacturing of multi-scale heterostructured high-strength steels

Laves phase tuning for enhancing high temperature mechanical property improvement in laser directed energy deposited Inconel 718

Achieving grain refinement and ultrahigh yield strength in laser aided additive manufacturing of Ti−6Al−4V alloy by trace Ni addition