Chunlei Qiu

• PhD
• Professor at Beihang University

In this study, a high‐strength eutectic high‐entropy alloy, AlCoCrFeNi2.1, is selected to produce lattice structures by selective laser melting to achieve high strength, good damage tolerance, and strong energy absorption capacity. The as‐printed lattice struts are found to contain numerous colonies of nanosized eutectic lamellar structures which a...

High-entropy alloys (HEAs) usually exhibit high strengths at ambient and low temperatures but rapidly degraded tensile properties with increased temperature. In this study, a high-strength HEA, (CoCrNi)94(TiAl)6, is selected and subjected to laser powder bed fusion (L-PBF) and ageing treatment. The microstructural evolution and mechanical property...

Continuous grain boundary α (CGB-α) usually causes degradation of mechanical properties in titanium alloys. Here, we propose to employ dislocation network in an additively manufactured titanium alloy for GB engineering to suppress CGB-α. A C-bearing titanium alloy was selectively laser melted to produce homogeneously distributed TiC flakes and a di...

In this study, the microstructure and mechanical properties of a laser powder bed fusion processed eutectic high-entropy alloy, AlCoCrFeNi2.1, and the influence of aging temperature have been investigated. The as-printed material consists of a hierarchical cellular eutectic microstructure with gamma cells and a B2 network along the cell boundaries....

In recent years, atomic clusters and composition undulation have been observed in a number of concentrated solid-solution alloys and were found to be beneficial for strength-ductility synergy. Some reports are also available on the observation of atomic clusters in body-centred cubic metastable beta titanium alloys but the role of these atomic clus...

In this study, a near-eutectic high entropy alloy Al1.8CrCuFeNi2 was processed by hot isostatic pressing (HIP). It is shown that the as-HIPed alloy demonstrates excellent formability and shows uniform and refined B2 grains. Large Cr0.7Fe0.3 precipitates were found at the grain boundaries while nano-sized Cu, Cu3Ni and Fe–Cr particles were uniformly...

Additive manufacturing of titanium alloys usually ends up with large columnar grains due to the steep thermal gradients within melt pools during solidification. In this study, ZrN particles were added into a beta titanium alloy, Ti-10V-2Fe-3Al, with the aim of promoting columnar-to-equiaxed grain transition during laser bed powder fusion (L-PBF). I...

A series of heat treatments with varying temperatures and holding times have been performed on a nickel-based disc superalloy, GH4065A. It is shown that, at the sub-solvus temperature, the grain size remained unchanged while the primary γ′ particles dissolved slowly and finally stopped decreasing. At super-solvus temperatures, however, rapid grain...

In this study, the influence of cooling strategy after solution treatment on microstructure and mechanical properties of a novel cast and wrought nickel-based superalloy is studied. It was found that continuous oil cooling (CC) from the solution temperature led to formation of large primary γ' and ultrafine tertiary γ'. Interrupted cooling (IC), wh...

In this study, TiAl and Cr3C2 particles were added to a high-entropy CrMnFeCoNi alloy through powder mixing and selective laser melting (SLM) with the aim of acquiring both high SLM processibility and an excellent combination of high strength and ductility with a post-process aging treatment. By only adding 4 at.% TiAl particles into CrMnFeCoNi, a...

Direct hot forging of heavily-alloyed nickel-based superalloy castings usually ends up with severe cracking due to serious macro-segregation. To address this issue, we propose to use hot extrusion as the replacement technology to process this kind of superalloys. An advanced cast and wrought nickel-based superalloy, GH4151, was thus subjected to ho...

Selective laser melting of Ti-48Al-2Cr-2Nb usually ends up with serious cracking. The cracking mechanism, however, remains elusive. In this study, both bulk samples and samples containing only several layers were prepared and investigated. It is shown that a freshly built layer is dominated by single alpha2 phase. Gamma started to form from alpha2...

In this study, a selectively laser melted (SLM) and hot isostatically pressed (HIPed) high entropy alloy (HEA), (CoCrFeMnNi)96(TiAl)4, was aged at different temperatures to investigate the microstructural evolution and mechanical property development with the aim of identifying the optimum aging condition that can produce the best combination of te...

Metastable  titanium alloys usually suffer from relatively low yield strengths, which restricts their applications as a structural material. Additive manufacturing (AM), due to its extremely high cooling rates, can generate a refined microstructure that is beneficial to yield strength. However, the intrinsic steep thermal gradients within melt poo...

Quasi-crystal (QC) Al65Cu20Fe10Cr5 powder particles were added into CoCrFeMnNi high entropy alloy (HEA) and processed by selective laser melting (SLM) under different conditions with the aim of enhancing their strengths. It is shown that increased energy density leads to increased grain size and texture in the SLMed HEA but does not cause significa...

The demand for increased aircraft engine efficiency requires the continual development of high performance heavily-alloyed nickel-based superalloys. However, nickel-based superalloy castings with heavy alloying usually suffer from severe macro-segregation that results in poor hot workability or cracking during hot forging. To address this issue, ho...

The 5 at% Cr3C2 particles were mixed with AlCoCrFeNi high entropy alloy powder particles and then selectively laser melted. The addition caused full columnar-to-equiaxed grain transition (CET) and significant grain refinement. The inter-dendritic regions and grain boundaries (GBs) of the as-fabricated sample were segregated with Cr and C, which led...

Invar 36 exhibits extremely low thermal expansion coefficients at low temperatures but also low yield strength which greatly restricts its application as a structural material. In this study, a small fraction of pure titanium powder particles was added into Invar 36 by powder mixing and selective laser melting (SLM) with the aim of further improvin...

3 wt% Nb particles were added to Al7075 alloy powder and processed by laser powder bed fusion (L-PBF) with the aim of improving the processability of the alloy and promoting grain refinement. It was found that with the addition of Nb, the grain structure changed from large columnar grains into ultrafine equiaxed grains and the hot tearing was compl...

Metastable beta titanium alloys are known for excellent ductility and corrosion resistance but relatively low yield strength (YS) which restricts their application. In this study, a novel high strength metastable beta titanium alloy, Ti-6Mo-5.5Cr-1Co-0.1C (wt%) was developed based on laser powder bed fusion (L-PBF). It is shown that the as-fabricat...

In this study, 4 at.% Ti-48Al-2Cr-2Nb (TiAl) powder particles were added into CoCrFeMnNi high entropy alloy (HEA) and processed by selective laser melting (SLM) followed by hot isostatic pressing and ageing with the aim of enhancing its strengths. It was found that the as-developed HEA-TiAl sample shows a complex microstructure which is composed of...

Invar 36 is well known for its extremely low thermal expansion coefficients at low temperatures. However, its relatively low strengths limit its application as a load-bearing structural material. In this study, powder particles of a titanium aluminide (Ti-48Al-2Cr-2Nb) were mixed with Invar 36 powder particles which were then processed by laser pow...

316 L stainless steel is well known for its excellent corrosion resistance and ductility. However, its relatively low strengths restrict its application in many load-bearing fields. In this study, Ti–48Al–2Cr–2Nb powder particles were mixed with 316 L powder and then processed by selective laser melting (SLM) with the aim of developing intermetalli...

Ti-6Al-2Sn-4Zr-6Mo is one of the most important titanium alloys characterised by its high strength, fatigue, and toughness properties, making it a popular material for aerospace and biomedical applications. However, no studies have been reported on processing this alloy using laser powder bed fusion. In this paper, a deep learning neural network (D...

A titanium alloy, Ti-10V-2Fe-3Al, was processed by pulsed selective laser melting. The as-fabricated sample was dominated by fibre-like columnar grains and cellular structures which were embedded with a high density of nano-sized precipitates and dislocations. The samples demonstrated extraordinarily high yield strength (920-950 MPa) and high elong...

In the present work, an innovative high-throughput method was developed to fabricate a Ti-6Al-4V alloy via pulsed laser melting with water-cooled copper mold. Moreover, a three-dimensional transient model was established via numerical simulation to reveal the dynamic mechanism of heat transfer and fluid flow of the molten pool during high-throughpu...

Metallic additive manufacturing, particularly selective laser melting (SLM), usually involves rapid heating and cooling and steep thermal gradients within melt pools, making it extremely difficult to achieve effective control over microstructure. In this study, we propose a new in-situ approach which involves laser reheating/re-melting of SLM-proce...

316L stainless steel lattice structures with several designs were prepared by selective laser melting at different laser powers. The surface structure, internal porosity distribution and microstructure of the lattice structures were investigated using a range of characterisation techniques and their properties evaluated by compressive testing. It w...

316L stainless steel samples were built vertically (VB) and horizontally (HB) by selective pulsed laser melting. The microstructure of the as-fabricated samples was investigated using a range of characterisation techniques and the properties evaluated by tensile testing. It was found that at a relatively low laser power (200 W) pores evolved from l...

A β titanium alloy was fabricated horizontally and vertically at two different energy densities by selective laser melting. The microstructures of the as-fabricated samples were examined using a range of characterization techniques and the properties evaluated by tensile testing. It was found that the samples that were horizontally built at the low...

A stainless steel 316L was fabricated by selective laser melting at different laser powers/energy densities. The as-fabricated samples were investigated using both optical and electron microscopy and the properties evaluated by tensile testing and electrochemical testing. It was found that within the energy density range investigated, porosity decr...

A powder nickel-based superalloy, FGH4096, was hot isostatically pressed at a super-solvus temperature. The microstructure of the as-fabricated sample was investigated by using a range of characterisation techniques and the properties evaluated by tensile testing. Prior particle boundaries (PPBs) decorated by near-continuous precipitates were obser...

A β titanium alloy, Ti-10V-2Fe-3Al, was selectively laser melted under a modulated pulsed laser mode with different processing conditions. The as-fabricated samples were examined using a range of characterization techniques and properties evaluated through tensile testing. It is shown that with a small powder layer thickness (30 μm), a low laser po...

316L samples were fabricated by selective laser melting (SLM) with different laser powers and scanning strategies/patterns. The porosity distribution and surface structures of the as-fabricated samples were characterized using optical microscopy and scanning electron microscopy. This combined with a mathematical modeling of the SLM process aims to...

High oxygen content is usually harmful for metals and alloys. However, in this study, we propose a new approach, which involves direct additive manufacturing of a powder alloy that contains a high oxygen level, to synthesise nano-oxide dispersion strengthened (ODS) alloys. Thus, by selectively laser melting a Fe–]Ni alloy powder with an oxygen leve...

316L stainless steel samples have been prepared by selective laser melting (SLM) using a pulsed laser mode and different laser powers and scanning patterns. The as-fabricated samples were found to be dominated by clusters of nano-sized γ needles or cells. TEM imaging shows that these needles contain a high population of dislocations while TEM-EDX a...

A multiscale model is developed to investigate the evolution mechanisms of site-specific grain structures during additive manufacturing (AM) of metallic alloys, using the selective electron beam melting (SEBM) fabrication of Ti-6Al-4V as an example. Specifically, finite-element method is utilized to predict the thermal response at macroscale during...

A method of remanufacturing a cylinder head comprises the steps of removing material from the cylinder head around at least a portion of a crack in the cylinder head to form a slot, and applying a compound material using direct laser deposition to fill the slot. The direct laser deposition includes performing a pre-scanning operation at a first las...

Purpose The purpose of this study is to develop a manufacturing technology using hybrid selective laser melting/hot isostatic pressing (SLM/HIP) process to produce full density net-shape components more rapidly and at lower cost than processing by SLM alone. Design/methodology/approach Ti-6Al-4V powder was encapsulated in situ by the production of...

In this study, titanium borides reinforced Ti-6Al-4V composites have been successfully prepared by hot isostatic pressing (HIPing). The microstructure of the as-fabricated samples was investigated using X-ray diffraction technique, secondary electron microscopy and electron backscatter diffraction and the mechanical properties evaluated through mic...

Pd was evenly distributed among Ti-6Al-4V particles using a new mixing technique. • Pd has dissolved completely into Ti-6Al-4V matrix after selective laser melting. • With the addition of Pd, the corrosion resistance of the Ti alloy has been improved. • Coarser grain structure also improves corrosion resistance of the Ti alloy in 2 M HCl. A new pow...

Ti-6Al-4V samples have been fabricated by direct laser deposition using different laser powers and two different laser processing modes, continuous wave (CW) mode and CW+PW (pulsed wave) mode. The as-fabricated microstructure was investigated using photography, optical microscopy and secondary electron microscopy. It was found that both laser mode...

The study of high temperature deformation of Ni-base superalloys finds a number of applications. In this study we consider how stress/strain resulting from directional solidification can be alleviated through phenomena such as relaxation and how this can be measured. Based on a modelling study, a range of stresses between 550 and 650 MPa were chose...

Invar 36 samples have been fabricated by selective laser melting at a constant laser power but with varied laser scanning speeds. Some samples were further heat treated or hot isostatically pressed (HIPed). The obtained microstructures were studied using optical and electron microscopes, X-ray diffraction and electron backscattered diffraction tech...

A concern associated with Direct Laser Deposition (DLD) is the difficulty in controlling microstructure due to rapid cooling rates after deposition, particularly in beta-Ti alloys. In these alloys, the beta-phase is likely to exist following DLD, instead of the desirable duplex alpha + beta microstructure that gives a good balance of properties. Th...

In this study, the development of surface structure and porosity of Ti–6Al–4V samples fabricated by selective laser melting under different laser scanning speeds and powder layer thicknesses has been studied and correlated with the melt flow behaviour through both experimental and modelling approaches. The as-fabricated samples were investigated us...

AlSi10Mg cellular lattice structures have been fabricated by selective laser melting (SLM) using a range of laser scanning speeds and powers. The as-fabricated strut size, morphology and internal porosity were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray microtomo-graphy (micro-CT) and correlated to the c...

Thermal fluid dynamics and experiments have been used to study the evolution of pores during selective laser melting of Ti-6Al-4V. Scanning electron micrographs show that the morphology of pores changed from near-spherical to elongated shape as the laser scan speed increased. Computational fluid dynamics suggests that this is caused by the change o...

Ti-6Al-4V samples have been prepared by direct laser deposition (DLD) using varied processing conditions. Some of the as-fabricated samples were stress-relieved or hot isostatically pressed (HIPed). The microstructures of all the samples were characterised using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD)...

AlSi10Mg cellular lattice structures have been fabricated by selective laser melting (SLM) using a range of laser scanning speeds and powers. The as-fabricated strut size, morphology and internal porosity were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray microtomography (micro-CT) and correlated to the co...

Ti–6Al–4V samples have been prepared by direct laser deposition (DLD) using varied processing conditions. Some of the as-fabricated samples were stress-relieved or hot isostatically pressed (HIPed). The microstructures of all the samples were characterised using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD)...

Powder of a nickel-based superalloy, RR1000, has been hot isostatically pressed (HIPped) at a supersolvus temperature and post-HIP heat treated to produce different microstructures. Microstructures were investigated using a scanning electron microscope together with an energy dispersive X-ray spectrometer and a wave-length dispersive X-ray spectrom...

a b s t r a c t A nickel-based superalloy powder RR1000 has been hot isostatically pressed (HIPed) and heat treated to produce different microstructures. Microstructures were investigated using a scanning electron micro-scope (SEM). Tensile testing was performed at room temperature and 700 °C and the deformed samples were examined using SEM and tra...

Ti-6Al-4V samples have been prepared by selective laser melting (SLM) with varied processing conditions. Some of the samples were stress-relieved or hot isostatically pressed (HIPed). The microstructures of all samples were characterised using optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) and the tensile pr...

A high strength high gamma' fraction nickel-based superalloy powder RR 1000 has been hot isotatically pressed (HIPed) at different temperatures. Microstructural analysis and assessment of the tensile properties were performed on these samples. It was found that HIP led to the formation of (Hf,Zr)O-2 particles on prior particle boundaries (PPBs) whi...

A nickel-based superalloy powder RR1000 has been hot isotatically pressed (HIPed) and heat treated to produce different microstructures. Microstructures were investigated using a scanning electron microscope (SEM). Tensile testing was performed at room temperature and 700ºC and the deformed samples were examined using SEM and transmission electron...

Samples of Hot Isostatically Pressed (HIPped) powder of TIMETAL 6-4 (Ti-6Al-4V, compositions in wt pct unless indicated), which was HIPped at 1203 K (930 °C), and of forged bar stock, which was slowly cooled from above the beta transus, were both subsequently held at 773 K (500 °C) for times up to 5 weeks and analyzed using scanning and transmissio...

Three Ni-free Zr-based BMGs with composition of Zr60Nb5Cu20Fe5Al10, Zr60Nb5Cu22.5Pd5Al7.5, Zr60Ti6Cu19Fe5Al10 were fabricated by suck copper-mould casting. All the BMGs prepared exhibit good glassy forming ability and wide supercooled liquid region ranging from 38 to 99K. These BMGs also show good mechanical properties under static compression with...

Two Ni-free bulk metallic glasses (BMGs) of Zr(60)Nb(5)Cu(22.5)Pd(5)Al(7.5) and Zr(60)Nb(5)Cu(20)Fe(5)Al(10) were successfully prepared by arc-melting and copper mold casting. The thermal stability and crystallization were studied using differential scanning calorimetry. It demonstrates that the two BMGs exhibit very good glass forming ability with...

A Ni-free bulk metallic glass (BMG) of Zr60Nb5Cu20Fe5Al10 with a diameter of 3 mm was successfully prepared by copper mold casting The structure and thermal stability of the BMG were studied by x-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). It is found that the BMG is apparently of a sin...

Bulk metallic glasses (BMGs) of Zr65−xNbxCu17.5Ni10Al7.5 (x = 0, 2, and 5 at.%) were prepared by copper mold casting. Room-temperature uniaxial compression tests revealed that the addition of a small amount of Nb could considerably enhance the compression plasticity of Zr-based BMGs. Electrochemical polarization measurements and ion release tests o...

Bulk metallic glasses (BMGs) of Zr65Cu17.5Ni10Al7.5, (Zr60Nb5)Cu17.5Ni10Al7.5 and (Zr60Nb5)Cu17.5(Ni5Pd5)Al7.5 were prepared by copper mold casting. The corrosion behavior of the BMGs in different types of artificial body fluids, including artificial salvia solution (ASS), phosphate buffered solution (PBS) and artificial blood plasma solution (ABP)...

A novel Ni-free bulk metallic glass (BMG) of Zr60Cu22.5Pd5Al7.5Nb5 was successfully prepared by copper mold casting. The BMG exhibited excellent mechanical properties, and superior corrosion resistance in an artificial body fluid and reasonably good biocompatibility, thus demonstrating its promise for biomedical application.

Zr65-xCu17.5Al7.5Ni10Nbx bulk metallic glasses (BMGs) with x = 0, 2 and 5 were prepared by water-cooled copper mold casting. X-ray diffraction and differential scanning calorimetry revealed that the addition of Nb changes crystallization pathway of the base alloy and promotes an initial formation of icosahedral quasicrystals. The mechanical propert...

Bulk metallic glasses (BMGs) of Zr(65 - x)Nb(x)- Cu(17.5)Ni(10)Al(7.5) with Nb = 0, 2, and 5 at % were prepared by copper mold casting. Compression tests reveal that the two BMGs containing Nb exhibited superior strength and plasticity to the base alloy. The corrosion behavior of the alloys obtained was investigated in artificial body fluid by elec...

Bulk metallic glasses of Zr65−xHfxCu17.5Ni10Al7.5 with Hf = 0 and 1 at.% and bulk metallic glass composite with Hf = 2 at.% were prepared by copper mould casting. The corrosion behavior of the alloys obtained were investigated in 3% NaCl, 1N H2SO4, and 1N HCl solutions, respectively, by electrochemical measurements. It is found that all three alloy...

(Cu47Zr11Ti34 Ni8)100-xCrx(x = 0, 0.5 and 1.0) bulk metallic glasses (BMGs) were obtained by water-cooled copper mold casting. The effect of Cr micro-addition on the glass-forming ability (GFA) of the alloys was investigated by means of XRD, DSC and DTA. It was found that Cr micro-addition can enhance the GFA. Electrochemical measurements were carr...