Wei Zhou

Wei Zhou
Nanyang Technological University | ntu · School of Mechanical and Aerospace Engineering

BEng (Tsinghua, 1985); PhD (Cambridge, 1991)

About

276
Publications
54,264
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
6,158
Citations
Introduction
Additive manufacturing, including selective laser melting, laser direct energy deposition, and cold spray coating.
Additional affiliations
December 2013 - June 2014
University of Cambridge
Position
  • Visiting By-Fellow
April 1992 - present
Nanyang Technological University
Position
  • Professor (Associate)

Publications

Publications (276)
Article
Full-text available
In article 2100664, Zhou, Nai, and co‐workers show that 304L and 316L have similar compositions. However, a selective laser melted 304L and 316L show a significant difference in grain size and morphology. Their microstructures and mechanical properties are compared using a scanning electron microscope, electron backscattered diffraction, nanohardne...
Article
The current research represents the first systematic study on high temperature oxidation and oxychlorination behaviors of cold sprayed Inconel 718. Tests were carried out at 700 ℃ and cold sprayed Inconel 718 was shown to possess excellent oxidation resistance comparable to that of the bulk Inconel 718. In the oxychlorination condition, a single-la...
Article
Full-text available
Cold spray is an emerging additive manufacturing process that allows particles to be coated onto the surface of a base material without melting. It is suitable to repair components made from temperature-sensitive materials, such as grey cast iron, which cannot be easily restored using conventional methods like welding or thermal spray. In this stud...
Article
Additive manufacturing (AM) is a transformative approach to fabricating metal components in the industry. However, it is challenging for fusion-based AM to fabricate metallic materials, particularly austenitic stainless steels, which have fine equiaxed grains without the formation of undesirable intermetallic phases due to its intrinsic high therma...
Article
Full-text available
There has been limited research on Ni-based oxide dispersion strengthened (ODS) alloys. To alleviate the drawbacks of the traditional ODS alloy manufacturing method, selective laser melting technology was chosen in this study to successfully manufacture ODS Inconel 718-Y2O3 alloys. Y2O3 nanoparticles were mixed with Inconel 718 powder at different...
Article
Full-text available
Cold spray is a solid-state additive manufacturing process that has been increasingly used for restoration of damaged parts. Due to the nature of powder solid-state bonding, cold spray coatings usually possess pores in the microstructures. Heat treatment has been widely used as a post-processing method to reduce the porosity of cold sprayed coating...
Article
Among various types of stainless steels, 304L and 316L have the most engineering applications. In this work, 304L and 316L powders with similar size distributions and morphologies are used as raw materials for selective laser melting (SLM) using the same parameters. It is found that SLM 304L has two phases, γ‐austenite (∽95%) and δ‐ferrite (∽5%) ph...
Article
Full-text available
Wire arc additive manufacturing (WAAM) is suitable to fabricate large components because of its high deposition rate. In this study, a metal-cored low-alloy high-strength welding filler metal was used as feedstock. Single wall structures were prepared using the WAAM process with different interpass temperatures (150 °C, 350 °C, and 600 °C). No obvi...
Article
Full-text available
In this work, strengthening of 316L stainless steel was achieved through addition of 1 and 3 wt% TiC nanoparticles. The TiC nanoparticles and 316L powders were mixed using low energy ball milling and then processed by selective laser melting. The grains are significantly refined from 16.8 μm to 6.9 μm with the addition of 3 wt% TiC nanoparticles. A...
Article
Fe50Mn30Co10Cr10 high-entropy alloys were prepared by laser cladding technology. The microstructure and phase structure of the cladding layer were analyzed. The effects of laser cladding parameters on mechanical property of the cladding layer were studied. The results show that, the Fe50Mn30Co10Cr10 high entropy alloy cladding layer is composed of...
Article
Full-text available
Cold spray technology using micron-sized particles to produce coatings is increasingly used for reparative tasks in various industries. In a cold spray setup, the gun is usually connected to a robotic arm to deposit coatings on components with complex geometries. For these components, the standoff distance used in the cold spray process has to be l...
Chapter
Cold spray is an additive manufacturing process increasingly used for repair and restoration of damaged components. A common problem with the technology is the high level of porosity in the as-sprayed coatings. Effort has been made in the past to reduce the porosity level by post-processing methods such as heat treatment in vacuum furnace. However,...
Chapter
Cold spray is an emerging additive manufacturing technology that is promising to be used for surface repair and enhancement. In this study, Inconel 713 coating was successfully deposited on Inconel 718 substrate using a high-pressure cold spray process. The microstructure and hardness of the coating were studied. The cold sprayed Inconel 713 coatin...
Chapter
Cold spray is an emerging additive manufacturing process allowing particles to be coated onto surface of base material without melting. In this study, Diamalloy 1005 was successfully coated onto GJL-250 cast iron using a cold spray process, and extensive experiments were carried out to observe the effects of diffusion after heat treatment at 400, 7...
Chapter
Cold spray is a solid-state powder deposition technique suitable for repair of parts. Use of nominally the same powders from different manufacturers is known to lead to very different porosity levels in the cold spray coatings, so it is important to find an effective method for the powder evaluation. A comparative study was carried out of Ti6Al4V p...
Article
Full-text available
316L stainless steel has a wide range of engineering applications. However, its relatively low yield strength limits its applications. In this work, strengthened 316L stainless steel was fabricated via selective laser melting (SLM) with the addition of 3 wt% micronsized TiC particles. The grains of 316L are significantly refined to approximately 3...
Article
Full-text available
Inconel 713C is a nickel-based superalloy usually considered as a material of poor weldability due to its susceptibility to hot cracking in the heat-affected zones. Cold spray, a solid-state deposition technology that does not involve melting, can be proposed as a methodology to deposit Inconel 713C for surface enhancement of other target component...
Article
Full-text available
Laser surface hardening is an attractive heat treatment solution used to selectively enhance the surface properties of components by phase transformation. A quantitative parameter to measure the efficacy of hardening processes is still lacking, which hinders its application in industries. In this paper, we propose a simple approach to assess the ef...
Article
Varying degrees of strain was imposed to AZ31 hot-extrusion bars by ambient extrusion. Mechanical properties were tested along different loading direction to reveal the effect of working hardening on deformation mechanisms and strain hardening behavior. The results showed that, with the increase of extrusion strain, yield strength increased gradual...
Article
In this study, micron-TiC particles were added into an Inconel 718 matrix to fabricate a metal matrix composite by selective laser melting. The interactions between the micron-TiC particles and the precipitates in the matrix were studied through solutionization treatment. Four holding temperatures 975, 1075, 1175, and 1275 oC were chosen while the...
Article
Conventionally, the main goal of process optimization in selective laser melting (SLM) is to achieve the highest relative density. However, for Inconel 718 (IN718), this study has demonstrated that the highest relative density does not correspond to the best mechanical properties. Moreover, similar relative densities can result in significant diffe...
Article
In this study, Inconel 625 coatings were successfully deposited on 6061 aluminum alloy using a high-pressure cold spray process. The microstructure, mechanical and tribological properties of the coatings were systematically studied. The cold sprayed Inconel 625 coatings had a low porosity level due to the severe plastic deformation of the splats. E...
Article
Full-text available
Considerable research has been carried out to study the laser welding of magnesium alloys. However, the studies are mainly devoted to butt welding, and there has been limited information in the published literature concerning the bead-on-plate laser welding of AZ91D, even though bead-on-plate welding is required for the repair of cast AZ91D parts w...
Article
Full-text available
Vacuum furnace has been used for brazing repair of aerospace components, but it is a slow process which typically takes a few hours. The prolonged heating and cooling cycles could cause some adverse effects on the components such as excessive grain growth. A rapid brazing technique using induction coil was studied to evaluate its suitability for lo...
Article
In this study, we have fabricated a TiC particle strengthened 316L stainless steel metal matrix composite using selective laser melting and characterized the microstructure with a particular focus on the TiC carbides in terms of their crystallography and orientation relationship with the austenitic matrix. Two families of TiC carbides are found to...
Article
Full-text available
Cold spray is an emerging additive manufacturing technology used in the aerospace industry to repair damaged components made of expensive metal alloys. The cold sprayed layer is prone to surface integrity issues such as high porosity and inadequate bonding at the substrate-coating interface, which may cause premature failure of the repaired compone...
Article
To systematically investigate the texture induced anisotropy for magnesium, the microstructure, texture and mechanical properties were tested on samples cut along different orientations from an AZ31 extrusion bar. It shows that microstructure, texture and mechanical properties varied with the angle β between the sample direction and transverse dire...
Article
The local microstructural heterogeneities in a single layer of laser clad hypereutectic Al-50Si alloy over Al7075 substrate has been studied over different applied laser powers. The general microstructure of the laser clad layer, irrespective of the applied laser power, could be described by three distinctive regions from the deposited bead/substra...
Article
Full-text available
The magnet-assisted laser hole-cutting in magnesium alloys was explored systematically with and without using water immersion, including femtosecond laser multilayer center-oriented hole-cutting and millisecond laser helical hole-cutting of both blind holes and through holes. The effect of the magnetic field and water immersion on laser hole-cuttin...
Article
γ-TiAl-based alloys have been studied for decades due to their attractive properties. However, the applications are limited because of their poor formability. Electron beam melting (EBM) is advanced in fabricating components with high complexity. Studies have shown that γ-TiAl alloys can be successfully fabricated using EBM. To further explore the...
Article
Full-text available
With the development of Industry 4.0, additive manufacturing will be widely used to produce customized components. However, it is rather time-consuming and expensive to produce components with sound structure and good mechanical properties using additive manufacturing by a trial-and-error approach. To obtain optimal process conditions, numerous exp...
Article
Full-text available
A novel femtosecond laser layered ring trepanning (LLRT) technology assisted by external transverse magnetic fields is reported for improving laser trepanning efficiency and quality while reducing hole defects. The influence of key operating parameters on blind-hole geometry trepanned by altering magnetic flux density was discussed. The element com...
Article
Constrained groove pressing (CGP), as a novel severe plastic deformation method, is applied to a two‐phase Mg‐Li alloy at room temperature, 373 K, 423 K and 473 K. The microstructural evolution and mechanical properties of Mg‐Li alloy sheets during CGP are investigated. The optimum mechanical properties are achieved at 373 K after two passes. The t...
Article
Full-text available
316L austenitic stainless steel has a wide range of industrial applications. However, one of the major drawbacks is its low yield strength (170-300 MPa in annealed state). We report a method to strengthen 316L by adding 1 wt% and 3 wt% micron-sized TiC particles using low energy ball milling for the powder feedstock preparation followed by selectiv...
Article
Tungsten/steel joints are desired for fusion reactors and militarily applications, as it could combine the unique properties of these two dissimilar metals. In view of the large differences of physical and chemical properties between W and steel, diffusion bonding is considered to be the proper technique for joining of W to steel. In this paper, di...
Article
Diffusion bonding is an effective method for joining dissimilar materials. In this study, dissimilar metals of MA956 steel and tungsten (W) were diffusion bonded with Ni/Nb composite interlayer. The experiments were carried out at [Formula: see text], 20 MPa for 20 min in vacuum by spark plasma sintering (SPS) technique. The microstructure and mech...
Article
Full-text available
Two different sized SiC particles (~ 60 nm and ~ 1 μm) were mixed into AZ31 alloy by multi-pass friction stir processing (FSP). The microstructure and mechanical properties of the processed material were investigated by optical microscope, scanning electron microscope, and uniaxial tensile tests. After FSP without SiC addition, the grains were refi...
Article
Laser hardening is usually performed in air. Use of a controlled gas atmosphere might produce a direct reaction of the gas with surface and thus provide an opportunity to engineer the surface microstructures. However, few studies are reported on direct gas-assisted laser hardening process. In this paper, a direct gas-assisted laser hardening is dem...
Article
Brazing experiments between tungsten and MA956 ODS steel were conducted at [Formula: see text] with different holding time to investigate the interface microstructure evolution and mechanical properties of the brazed joints. The interface microstructures were analyzed by the scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) a...
Article
Full-text available
Pre-compression was conducted on AZ31 magnesium alloy bars to prepare different volume fraction of {101¯2} twins. The effect of twins and related crystal orientation on the corrosion properties of the AZ31 magnesium alloy was studied. With the increase of compression strain which induce more twins, corrosion resistance showed different tendency dur...
Article
Nanoparticles reinforced steels have many advantaged mechanical properties. Additive manufacturing offers a new method for fabricating nanoparticles reinforced high performance metal components. In this work, we report the application of low energy ball milling in mixing nanoparticles and micron 316 L powder. With this method, 0.3 and 1.0 wt% Y2O3...
Article
Full-text available
The numerical simulation on laser trepanning of square-slotted hole and hole array in stainless steel sheets with and without ultrasonic assistance was reported for analyzing the stress fields on the workpieces trepanned. Based on reasonable modification and verification for the established models using corresponding experimental results, the trans...
Article
Full-text available
A novel helical laser hole-cutting (HLHC) technology based on coupled assistance of water-based ultrasonic vibrations and external longitudinal/transverse magnetic fields is reported for cutting holes in nickel super-alloy GH4049 sheets. Effects of external unidirectional transverse and longitudinal magnetic fields on HLHC performance were correspo...
Article
Full-text available
A systematic investigation was reported for observing and analyzing the process and performance of millisecond laser drilling with and without magnetic assistance and/or assist gas using a self-developed real-time monitoring system based on high-speed photography. The systematic and corresponding comparisons between the effects of longitudinal magn...
Article
Water can act as an effective cooling agent during processing of materials. This can be beneficial especially for surface hardening of steels whereby a rapid quenching rate is desired to generate a hard martensitic surface layer. In this study, the underwater laser hardening of bearing steels is experimentally investigated using a fiber laser. The...
Article
In this work, the effect of multipass friction stir processing (FSP) on the microstructure and impact toughness of an as-cast Al–20Si alloy was investigated. FSP resulted in the breakage of coarse primary Si particles and acicular eutectic Si particles, elimination of porosity, and better homogeneity of Si particles. The average size and aspect rat...
Article
Surface laser treatments are often used on metals and metal alloys to improve the material's hardness and corrosion resistance. Investigating the reasons for this property enhancement is not trivial because the resulting microstructure changes gradually from the surface to the bulk. Here we report a simple serial-sectioning technique to assess the...
Article
Diffusion bonding is an effective technique for joining dissimilar metals. In this paper, tungsten and MA956 steel were diffusion-bonded by Spark Plasma Sintering (SPS) technique with titanium (Ti) foil as an interlayer. The bonded joints were evaluated by metallographic analysis and mechanical tests, and the results reveal that all W/Ti/MA956 join...
Article
Friction stir processing (FSP) and surface mechanical attrition treatment (SMAT) were performed on an AZ31 magnesium alloy to improve the mechanical properties. The microstructure, macro-texture, as well as mechanical properties were investigated by optical microscopy, transmission electron microscopy, X-ray diffractometer and uniaxial tensile test...
Article
A steady magnetic field perpendicular to a laser beam is widely used to improve the rate and quality of laser ablation. Recently, we reported a 69-fold enhancement of laser ablation of silicon using a magnetic field parallel to a laser beam. To understand the fundamental mechanisms of that phenomenon, multipulse magnetic-field-enhanced ablation of...
Article
Underwater laser hardening might produce better surface mechanical properties than conventional laser hardening in air due to additional cooling effect by water. However, it has not been studied in detail. This study investigates the effect of water layer on laser surface hardening of AISI 1055 steel. It is found that laser surface hardening is fea...
Article
Laser surface hardening, used to achieve hardened surface without affecting bulk properties of steels, generally employs continuous-wave laser to do the job. The purpose of this paper is to systematically investigate the use of different pulsed lasers for surface hardening of 50CrMo4 steel. A continuous-wave laser and various pulsed lasers with pul...
Article
Brazing is an effective technique for joining tungsten and steel. However, the high residual stresses are produced due to the different coefficients of thermal expansions between tungsten and steel. Compared with the direct brazing with BNi-2 foil filler, BNi-2/Cu/ BNi-2 multiple interlayer was used as filler to minimize the residual stresses betwe...
Article
A millisecond-pulsed percussion laser drilling technique using water-based ultrasonic assistance is reported for drilling nickel super-alloy GH4037 sheets with 12-mm-thickness. Influence of ultrasonic vibration on drilling quality including hole taper angle, hole sidewall quality, recast layer microstructure, and hardness distribution of hole heat...
Article
In this study, oxide dispersion strengthened (ODS) layers with different Y2O3 addition were cladded on China Low Activation Martensitic (CLAM) steel to improve its mechanical strength, micro-hardness and high-temperature behavior. The results show that fine surface morphologies can be observed in cladding zones. In cladding layers, the Fe, Cr, W, Y...
Article
Full-text available
Unwanted removal of carbon from surface may occur during laser surface processing of steels despite the short interaction time and thermal cycle. However, no attention is paid in literature to investigate this phenomenon systematically. This paper presents two different scenarios during laser surface processing of steels: complete absence of decarb...
Article
The ultrasonic vibration-assisted laser drilling is a recently emerging/growing new technique, especially in laser drilling. Differently from the previous work reported, this paper proposed to use the ultrasonic vibration (25 kHz) for assisting the millisecond pulsed Nd:YAG laser percussion drilling process to improve the drilling performance. Thro...
Article
Laser ablation is a rapid-material removal technique with potential application in remanufacturing of bearings to clean damaged surfaces. This study reports the ablation morphology and change in surface composition of 52100 bearing steel irradiated with a femtosecond laser. A smooth ablated surface was achieved by operating the laser at fluence jus...