Aijun Huang

• Doctor of Philosophy
• Professor (Full) at Monash University (Australia)

In-situ rolling in directed energy deposition has shown improvements in deposited part quality. These improvements are driven by high-temperature material deformation. Experimentally capturing high-temperature deformation aspects is challenging. The modelling approach requires simultaneous consideration of rolling and deposition aspects. Therefore,...

The design freedom of Laser Powder Bed Fusion (LPBF) components has been confined by the minimum allowable overhang angle of 45°. It remains unclear how to achieve multiple layers of overhang at zero-degree overhang angle, which is the fundamental basis of overhang. Here, we have confirmed the possibility of manufacturing three layers of support-fr...

The structural evolution of oxides in dispersion-strengthened superalloys during laser-powder bed fusion is considered in detail. Alloy chemistry and process parameter effects on oxide structure are assessed through a parameter study on the model alloy Ni-20Cr, doped with varying concentrations of Y2O3 and Al. A scaling analysis of mass and momentu...

For SLMed Ti–6Al–4V-xO (x = 0.11, 0.16, 0.21, and 0.25 wt%) alloys, both microstructure and mechanical properties are sensitive to oxygen content. The α′ martensites in as-built state transform to a ‘bimodal’ microstructure containing α lamellae interspersed with β transformed regions after 2 h annealing at 800 °C, 850 °C, 900 °C, and 950 °C follow...

Strict control of powder properties, especially particle size distribution (PSD), is critical in the laser powder bed fusion (LPBF) process to ensure the quality of the fabricated parts. This work shows that reducing the powder size could improve the ductility of LPBF fabricated AlSi10Mg. The tensile elongation increased from 4.1% to 8.8% when AlSi...

Oxide dispersion strengthened (ODS) nickel (Ni)‐based superalloys are advanced materials known for their outstanding tensile and creep performance at temperatures exceeding 1000 °C. Nevertheless, their conventional synthesis presents a longstanding challenge in cost‐effectively producing intricate components for critical applications. In this work,...

Platform heating is one of the effective strategies used in laser powder bed fusion (LPBF) to avoid cracking during manufacturing, especially when building relatively large-size components, as it removes significant process-induced residual strains. In this work, we propose a novel and simple method to spare the elaborate post-processing heat treat...

Laser powder bed fusion (LPBF) is an outstanding additive manufacturing (AM) technology that can enable both complicated geometries and desired mechanical properties in high-value components. However, the process reliability and cost have been the obstacles to the extensive industrial adoptions of LPBF. This work aims to develop a powder recycling...

A Laser Powder Bed Fusion Inconel 718 produced with intentionally non-optimized parameters is investigated to understand the role of defects and microstructure on the high-cycle fatigue life. Samples from three built directions and three heat treatments were used for fatigue tests at room and 650°C under R = 0.1. Printing orientation has a minor ef...

The reuse of recycled powder in laser powder bed fusion (LPBF) has significant economic and practical value. While numerous investigations have proposed the negative effects of recycled powder in LPBF, further research is still needed to develop effective schemes for powder reuse, which plays a critical role in sustainable development of additive m...

One of the most revolutionary aspects of Laser Powder Bed Fusion (LPBF) is to be able to lift the design constraints from conventional manufacturing. However, as a rule of thumb, any surfaces lower than 45° with respect to the horizontal plane would still require sacrificial supports in order to complete the printing. Fundamentally, it is unclear w...

Volume 24A provides a comprehensive review of additive manufacturing (AM) design fundamentals and applications. The primary focus of the Volume is on metallic systems with limited emphasis on polymers and ceramics where applicable. The first five divisions provide an in-depth review of each of the key aspects of the entire AM value chain. The mater...

The tensile properties at both room temperature and 550 °C are investigated in Ti–6.5Al–2Sn–4Zr–4Mo–1W–0.2Si with three typical microstructures, which are lamellar, bimodal, and equiaxed microstructures. The results show that the yield and ultimate tensile strengths decrease while the ductility increases as the volume fraction of primary α phase in...

The particle size distribution (PSD) often changes as powders are cycled for recycled and different powder batches are used, challenging a critical aspect of quality assurance in the Laser Powder Bed Fusion (LPBF) process. It is therefore important to understand how powder PSD affects the processability of powder in the context of LPBF. In this wor...

Post heat treatment is essential for additively manufactured alloys to eliminate residual stress and in some cases further improve mechanical performance. This study systematically investigated the hardening response of a Ti-6Al-2Sn-4Zr-6Mo alloy processed by laser powder bed fusion (LPBF) to a one-step heat treatment. The results revealed signific...

Numerical modelling is an effective tool to investigate the rapid temperature cycling in laser powder bed fusion. However, the high computational cost limits the modelling of part-scale components due to the significantly different scales between the highly local energy input region and the global field response region. This study presents a macros...

This work investigates the viability of fabricating Ti-3Al-8V-6Cr-4Mo-4Zr (Beta-CTM) using laser-based and powder-fed directed energy deposition. To determine an appropriate ageing strategy, heat treatments were conducted at 440 °C and 480 °C over different periods of time and their effectiveness were determined through hardness testing. After iden...

In this work, we presented an investigation into the deformation behavior of laser powder bed fusion (LPBF) Ti-6Al-4V (Ti64), particularly how microstructure characteristics determined the grain deformation behavior by using in-situ SEM tensile characterization. Results demonstrated that α laths with their elongation directions 45° to the tensile l...

A thermally induced hexagonal close-packed (HCP) to face-centered cubic (FCC) phase transition was investigated in an α-type Ti35 alloy with twinned structure by in situ heating transmission electron microscopy (TEM) and ab initio calculations. TEM observations indicated that the HCP to FCC phase transition occurred both within matrix/twin and at t...

Heat treatment (HT) is an effective way to attain the desired microstructure and mechanical properties in laser powder bed fusion (LPBF) Ti–6.5Al–2Zr–1Mo–1V (TA15). However, previous studies only obtained the high tensile ductility of LPBF TA15 but were accompanied by a large loss of strength, which was unable to achieve balanced mechanical propert...

The recently-developed Al-Mn-Sc based alloys fabricated by laser-powder bed fusion (L-PBF) have achieved a yield strength of 560 MPa and a ductility of 18%. However, these high strength Al alloys normally exhibit severely non-uniform plasticity due to the strain incompatibility of bimodal grain structure, which hinders their practical application....

Post-heat treatment is a necessary and important step for additive-manufactured products to relieve residual stress and to further improve mechanical performance. In this work, the heat treatment strategy for Inconel 718 superalloy fabricated by rolling-assisted laser-directed energy deposition (L-DED) has been designed and systematically investiga...

The defects remain a significant issue for additive manufactured titanium alloys, which hinders their further market penetration. In this work, we proposed a new understanding of the inhomogeneous microstructure formation affected by defects with detailed EBSD characterization, and how the defects and inhomogeneous microstructures determined the st...

In addition to the common stable and metastable phases in titanium alloys, the face-centered cubic phase was recently observed under various conditions; however, its formation remains largely unclarified. In this work, the effect of nonmetallic interstitial atoms O, N, C and B on the formation of the face-centered cubic phase of titanium was invest...

Titanium alloys, widely used in the aerospace, automotive and energy sectors, require complex casting and thermomechanical processing to achieve the high strengths required for load-bearing applications. Here we reveal that additive manufacturing can exploit thermal cycling and rapid solidification to create ultrastrong and thermally stable titaniu...

Metal powder characteristics can affect the build quality of laser powder bed fusion produced (LPBF) parts. In this study, two batches of Hastelloy X powder with different powder characteristics including powder chemical compositions, morphologies, amounts of inclusions, and size distributions were compared in terms of the subsequent flowability, p...

Grain boundary α-phase (GB-α) in titanium alloys is the vulnerable site for failure, while the correlation between deformation behavior and local dislocation motion is still ambiguous. In this study, we made a detailed investigation into the deformation behavior of GB-α with different morphologies in a laser powder bed fusion (LPBF) fabricated Ti-6...

The application of Inconel 718 (IN718) alloy parts at elevated-temperature under loading leads to creep failure. To date, the creep performance of additively manufactured IN718 is usually inferior to the conventionally fabricated counterparts. In this work, post heat treatment schemes were designed and applied to the LPBF-built IN718 to achieve enh...

This study investigates the effect of microstructure on short-term and long-term oxidation behaviours of GH3536 superalloy fabricated by laser powder bed fusion (LPBF), in which the superalloy is isothermally oxidised at 950 °C for 6 h and 500 h in air. The LPBF sample exhibits improved oxidation resistance compared with a wrought counterpart after...

Numerous studies have been conducted in the recent past to assess different nickel-based superalloys fabricated using laser-based powder bed fusion (PBF-LB). Most of these works focused on the processability, microstructural evolution, post-fabrication treatments and the mechanical behaviour of components manufactured by PBF-LB under static loading...

An Al-Mn-Mg-Sc-Zr alloy was additively manufactured and deformed by rotary swaging to investigate the effect of high defect densities on the precipitation behavior, work hardening capability and ductility. For this, the LPBF-fabricated alloy was deformed by rotary swaging up to a true strain of 2.5 subsequent to a laser powder bed fusion (LPBF) pro...

The influence of heat treatment holding temperatures from 600 to 1300 °C on the microstructure, mechanical properties and corrosion resistance in selective laser melted (SLMed) 304L stainless steel is investigated in this work. The results reveal that there is no remarkable microstructure change after holding at 600 °C for 2 h, while recrystallizat...

Ti-23Nb-0.7Ta-(0, 2)Zr-(1.2, 4, 6, 10)O alloys were prepared using a non-consumable arc-melting method. The tensile property of Ti-23Nb-0.7Ta-2Zr-1.2O alloys was tested at temperatures from −196 °C to 750 °C. The influence of O and Zr contents on thermal forgeability, room-temperature hardness and tensile property at 750 °C was investigated. For Ti...

Laser powder bed fusion (LPBF) is an emerging additive manufacturing technique that is currently adopted by a number of industries for its ability to directly fabricate complex near-net-shaped components with minimal material wastage. Two major limitations of LPBF, however, are that the process inherently produces components containing some amount...

In this study a novel micro-rolling set-up was installed on a directed energy deposition additive manufacturing system to achieve in-situ grain refinement and porosity closure. A 316 L stainless steel was investigated and it was found that even low micro-rolling loads were capable of increasing the part density from 99.7% to 99.98%. Martensitic tra...

A major problem of additively manufactured parts using laser powder bed fusion (LPBF) is the as-built high surface roughness. The poor surface finishing is detrimental to the mechanical and electrochemical properties of the parts. In this work, we present systematic investigations on surface roughness reduction of LPBF produced nickel-based superal...

Laser powder bed fusion (LPBF) is one of the major additive manufacturing techniques that industries have adopted to produce complex metal components. The scientific and industrial literature from the past few years reveals that there is a growing demand for the development of high-strength aluminium alloys for LPBF. However, some major challenges...

This study investigates the formation of defects and their impact on oxidation behaviour of GH3536 superalloys fabricated by laser powder bed fusion (LPBF). Defects of six series of samples manufactured by different parameters is dominated by pores, micro-cracks, and lack of fusion, respectively. The superalloy is isothermally oxidised in 950°C dry...

In this study, the influence that porosities play on the mechanical properties of Ti-6Al-4V parts fabricated by laser powder bed fusion (LPBF) was investigated with the aim of improving process efficiency of the LPBF process by establishing the resulting trade-offs to component quality. It was found that build times can be substantially reduced by...

Effective thermal conductivities (ETCs) of five commonly used metal powders in additive manufacturing have been measured at temperatures up to 750 °C. The ETCs of Al-Mn-Sc and Ti-6Al-4 V powders with different particle sizes are also investigated. When the temperature is lower than 300 °C, the ETC of metal powders is insensitive to the temperature...

In this work, a multiphysics process model is utilized to explain an observed correlation between cracking and anisotropic texture weakening of a Ni-based superalloy additively produced by laser powder bed fusion (LPBF). Six LPBF scanning strategies were implemented on the IN738LC superalloy, revealing significant variations in crack densities and...

The abundancy of defect sinks in the microstructure of laser powder bed fusion (LPBF) processed austenitic stainless steels was found to be beneficial for helium resistance. In the current study, the influence of the novel microstructure in LPBF processed 304L on the helium bubble growth behaviour was investigated using transmission electron micros...

Additive manufacturing of 25Cr super duplex stainless steel (SDSS) has been successfully demonstrated using laser powder bed fusion (L-PBF) in recent years. The as-built L-PBF 25Cr SDSS exhibits a microstructure that is close to 100% ferritic (due to the fast cooling in L-PBF) and requires a high temperature thermal treatment to obtain the desired...

Grain boundary α-phase (GB-α) precipitation and coarsening behavior in Ti-6Al-4V (Ti-64) processed by laser powder bed fusion (LPBF) were investigated and compared with those in as-cast Ti-64. GB-α in LPBF processed Ti-64 tended to precipitate at the triple junctions (TJs) of the β-phase grain boundaries during the subsequent annealing process. Kin...

The recently-developed Al-Mn-Sc based alloys specific for laser powder bed fusion (LPBF) have shown excellent mechanical performance. However, the complicated intermetallic particles in the microstructure remain to be identified, hindering the deep understanding of their effects on mechanical properties and further property improvement. In this wor...

Nickel-based superalloy IN738LC produced by selective laser melting (SLM) exhibits inferior high-temperature creep properties than its cast counterparts due to relatively smaller grain size, particularly for the plane normal to the building direction. This work studied effects of post heating strategy on the microstructure and especially the grain...

In this work, the effects of post-LPBF (laser powder bed fusion) heat treatments on microstructure evolution, tensile and Charpy properties of Ti-6Al-4V have been investigated. The results show that the original martensitic microstructure in the LPBF sample has converted to a lamellae mixture of α and β phases when post heat-treatment temperatures...

This study provides a novel methodology to evaluate fatigue life with the consideration of both confidence level and reliability for CFRP laminates by combining fracture fatigue entropy (FFE) theory and knowledge of statistics. After carrying out distribution analysis and statistical hypothesis testing, it is found that the FFEs obey well to log-no...

A high solute 7xxx series aluminium alloy, Al-14Zn-3Mg (in wt. %), was prepared using laser powder bed fusion (LPBF). To provide an insight into the correlation of second phase particles and mechanical properties, several heat treatment conditions were modelled with CALPHAD, and phase transformations were realised through in-situ characterisation t...

Creep fracture is a general failure mode for nickel-based superalloy components made by additive manufacturing (AM). However, the existing creep models originally built for conventional superalloys cannot explain the creep rate acceleration caused by fast cavitation, which relates to the AM-specific microstructural features, in particular the poros...

The unique thermal history of selective laser melting (SLM) can lead to high residual stress and a non-equilibrium state in as-fabricated titanium alloy components and hinders their extensive use. Post heat treatment, as a classical and effective way, could transform non-equilibrium α’ martensite and achieves desirable mechanical performance in SLM...

Additive manufacturing (AM) of nickel superalloys typically leads to large columnar grains forming along the build direction, resulting in poor and anisotropic tensile performance. In this work, a novel AM process involving directed energy deposition (DED) combined with in-situ rolling was applied to fabricate a typical nickel superalloy – Inconel...

Ethylene glycol-sodium chloride (NaCl) is an environmentally friendly electrolyte in the electropolishing of titanium. To better understand the effect of the alcohol on the electropolishing of titanium, the solubility of NaCl in different alcohols and the electropolishing of titanium with different mixtures have been systematically investigated. Th...

A high temperature compression and compression creep study was undertaken performed on Al–Mn–Mg–Sc–Zr alloy produced by selective laser melting (SLM). High temperature compression tests in the temperature range from 150 to 300 °C were conducted for the as-fabricated (AF) and aged (HT) SLM specimens. The 0.2% proof stress (σ0.2) showed comparable va...

There is increasing usage of high strength Beta Ti alloy in aerospace components. However, one of the major challenges is to obtain homogeneous refined microstructures via the thermo-mechanical processing. To overcome this issue, an understanding of the hot deformation conditions effect on the microstructure, prior to and after annealing, is needed...

Directed energy deposition (DED) is an additive manufacturing technique that employs laser melting to permit for the free form manufacturing of components from many input materials from powder or wire form of feedstock. The nature of DED processes and advancements thereof has led to research that has been aimed at leveraging this additive manufactu...

The Al-Mn-Sc-based alloys specific for additive manufacturing (AM) have been recently developed and can reach ultrahigh strength and adequate elongation. However, these alloys commonly exhibit non-uniform plasticity during tensile deformation, which is a critical issue hindering their wider application. In this work, the origin of this non-uniform...

Prior to the application of AM components for critical applications, it is necessary to have a better understanding of the effect of different post-fabrication treatments on the microstructure and mechanical properties of such parts. In this study, efforts were made to achieve an in-depth understanding of the effect of post-fabrication solution hea...

In this study, the tribological properties of an AlSi10Mg alloy that was fabricated using laser powder bed fusion, an additive manufacturing technique, was investigated in both the as-built (but stress-relieved) and T6-treated condition. The stress-relieved condition consists of elongated Al grains and a dendritically-arranged nano-crystalline Si-p...

An additively manufactured aluminium alloy with very high solute content, Al-14Zn-3Mg (wt. %), was studied herein. Compared to wrought AA7075-T6 as a benchmark, Al-14Zn-3Mg revealed a lower rate of corrosion, attributed to its microstructure and solute content. Specifically, the lack of coarse intermetallic particles in the Al-14Zn-3Mg led to reduc...

The competitive effect of microstructural features including primary α (αp), secondary α (αs), grain boundary α (αGB) and β grain size on mechanical properties of a near β Ti alloy were studied with two heat treatment processes. The relative effect of β grain size and STA (solution treatment and ageing) processing parameters on mechanical propertie...

The longstanding issue in additive manufacturing (AM) of titanium alloys is the large, columnar grains created by the intrinsic directional heat flow along the build direction. These long grains lead to strongly anisotropic mechanical properties that impede the qualification and applications of the final products. In this work, a novel in-situ roll...