Yu Zou

University of Toronto | U of T · Department of Materials Science and Engineering

Metals with nanometer scale grains, or nanocrystalline metals, exhibit high strengths at ambient conditions, yet their strengths substantially decrease with increasing temperature, rendering them unsuitable for usage at high temperatures. Here, we show that a nanocrystalline high entropy alloy (HEA) retains an extraordinarily high yield strength ov...

The discovery of quasicrystals three decades ago unveiled a class of matter that exhibits long-range order but lacks translational periodicity. Owing to their unique structures, quasicrystals possess many unusual properties. However, a well-known bottleneck that impedes their widespread application is their intrinsic brittleness: plastic deformatio...

Refractory high-entropy alloys (HEAs) are a class of emerging multi-component alloys, showing superior mechanical properties at elevated temperatures and being technologically interesting. However, they are generally brittle at room temperature, fail by cracking at low compressive strains and suffer from limited formability. Here we report a strate...

High-entropy alloys (HEAs) are evolving multi-component intermetallic systems, wherein multiple principal elements tend to form single solid-solution-like phases with a strong tendency to solid solution strengthening. In this study, an Nb25Mo25Ta25W25 refractory HEA was synthesized by arc melting and well homogenized at 1800 °C. Single-crystalline...

Electron Backscatter diffraction was used to investigate the microstructural evolution of nickel powder particles during the high-velocity impact in the cold spray process. Ultrafine grains in the scale of 100–200 nm were observed in the particle bonding region. The formation of these nanometer-sized grains is interpreted in terms of dynamic recrys...

Materials-by-design has been historically challenging due to complex process-microstructure-property relations. Conventional analytical or simulation-based approaches suffer from low accuracy or long computational time and poor transferability, further limiting their applications in solving the inverse material design problem. Here, we establish a...

AlSi10Mg components produced by laser powder bed fusion (LPBF) typically exhibit higher strength but lower ductility than those made by conventional mature processing technologies. The effects of melt pool boundaries on the ductility and fracture behavior of the LPBF-produced AlSi10Mg have not been systematically studied. The focus of this work is...

The in situ X-ray imaging method has attracted significant attention in the metal additive manufacturing community for characterizing keyhole dynamics and defect generation during laser-material interaction processes, particularly for laser powder bed fusion. Due to a high temporal and spatial resolution in this method, a vast volume of data are ge...

The laser powder bed fusion (LPBF) of aluminium alloys is associated with numerous challenges when compared to other commonly used alloys (e.g., steels and titanium alloys) due to their higher reflectivity and thermal conductivity. This leads to a higher defect density in the final parts, commonly related to melt pool instabilities in the transitio...

Herein, the influences of solution-aging treatments on the corrosion behavior of wrought Ti-6Al-3Nb-2Zr-1Mo alloy are investigated. The solution-aging treated alloys exhibit a much better corrosion performance than the wrought alloy, stemming from the alleviated galvanic corrosion. In artificial seawater, all alloys display a spontaneous passivatio...

Refractory high entropy alloys (RHEAs) are typically sensitive to oxygen, suffering from their poor oxidation resistance at elevated temperatures. Here we dope a NbMoTaW alloy with boron (B) and carbon (C) by 0.5 at.% and 2 at.% and then compare their oxidation behavior with that of pure tungsten (W) at 800 ℃ in air. We show that the NbMoTaW alloy...

Herein, we employ electron beam surface melting (EBSM) technology to process Ti-6Al-3Nb-2Zr-1Mo alloys and compare their microstructure and corrosion performance with wrought counterparts. The mechanism of microstructural evolution has been illustrated. The EBSM sample presents a better corrosion resistance than the wrought one, which can be ascrib...

The laser powder bed fusion (LPBF) of aluminium alloys is associated with numerous challenges when compared to other commonly used alloys due to their higher reflectivity and thermal conductivity. In this work, processing diagrams, temperature prediction models, X-ray computed tomography, and metallography are used for establishing criteria in proc...

Laser-based directed energy deposition (LDED) enables rapid near-net-shape fabrication of large-scale titanium components for aerospace applications. However, the poor tensile ductility of most as-deposited titanium alloys, particularly near-α alloys, hinders their wide usage for critical load-bearing structures. Here we report that a high density...

Here we show that the hot‐stamped steel exhibits high hardenability with a critical cooling rate of about 0.7 °C/s due to its unique chemical composition. The microstructure of the annealed sheet consists of ferrite, spherical carbides and intergranular martensite. Thereinto, the generation of intergranular martensite can eliminate the yield point...

Refractory high-entropy alloys (RHEAs) that consist of multiple principal refractory elements have attracted significant attention due to their many interesting and useful properties for structural applications. However, so far, a vast majority of reports on RHEAs focused on a few well-known compositions such as NbMoTaW, NbMoTaWV, and TiZrHfNbTa. T...

Herein, the microstructure and corrosion behavior of Ti-6Al-3Nb-2Zr-1Mo alloy manufactured by the electron beam freeform fabrication (EBF3) have been thoroughly investigated. The evident prior-β grain boundary, the inside of which is composed of predominant α-lath and slight β-phase, is achieved. The EBF3-manufactured alloy displays a significantly...

Metallic materials with heterogeneous microstructures are reported to exhibit an excellent combination of high strength and ductility. Although a vast majority of studies have been focused on their local microstructure evolution before and after plastic deformation, the change of their local mechanical properties, rather than global mechanical prop...

Inhibiting the diffusion and aggregation of hydrogen atoms can effectively improve the resistance to hydrogen embrittlement (HE) of high strength hot-stamped steel. Here we investigate the interaction between dislocations, precipitates and hydrogen atoms in a 2000 MPa grade hot-stamped steel through a combination of microstructure characterization...

Additive manufacturing (AM) has been widely used to produce AlSi10MgAlSi10Mg samples, which have heterogeneous structuresHeterogenous structure. They have coarse cellular dendrites along the melting pools, fine cellular dendrites inside the melting pools, and heat-affected zone with broken Si networks beneath the melting pools. The role of the hete...

In a selective laser melting (SLM) process, the fluctuation of as-produced part quality remains a problem that hinders its broader industrial applications. In situ monitoring that identifies the variations of melt pool characteristics is promising to improve part quality and control the SLM process. So far, such monitoring approaches have been impe...

Herein, we systematically investigate the corrosion behaviour of a wrought Ti-6Al-3Nb-2Zr-1Mo (Ti80) alloy in artificial seawater with various fluoride ion (F−) concentrations and pH values using electrochemical, static immersion measurements and surface characterizations. Results of electrochemical tests manifest that increasing the F− concentrati...

The development of steels with a combination of high strength, ductility, and toughness has been highly desirable for structural applications. Here we achieve high fracture toughness (129 MPa•m½) in a high-strength (∼1.5 GPa yield strength) and ductile (∼37% uniform elongation) austenitic stainless steel. Through cold rolling, flash annealing, and...

High-entropy alloy (HEA) catalysts have recently attracted worldwide research interest due to their promising catalytic performance. Most current studies focus on designing HEA catalysts through trial-and-error methods. This produces scattered data and is not conducive to obtaining a fundamental understanding of the structure-property-performance r...

For decades, enhancing both strength and thermal stability in nanocrystalline materials for structural applications has been a significant challenge. Recently, entropy-based stabilization strategies for nanostructured materials have gained traction in the high-entropy alloy (HEA) community, however, such studies typically focus on synthesis techniq...

Most metal additive manufacturing (AM) methods involve the melting or sintering of feedstock powder or wire using an energy source (laser, electron beam, or electric arc). Solid-state AM, sometimes also known as non-beam-based AM, is a process in which the deposited material does not melt and is built up layer-by-layer, typically through severe pla...

The combustion behavior and mechanism of Ti2AlNb alloy are revealed by Promoted Ignition Combustion (PIC) tests and compared with Ti-6.5Al-3.5Mo-1.5Zr-0.3Si (TC11) alloy. Although the ignition temperatures of two alloys show little difference, however, the burning velocity of Ti2AlNb is faster than TC11. Such difference is attributed to different l...

Increasing the yield strength of austenitic steel without significantly sacrificing ductility has been a long-standing technical challenge. Here, we obtained an ultrahigh yield strength (∼1.4 GPa) and ductile (∼37% uniform elongation) austenitic steel through innovatively combining cold rolling, flash annealing, and tempering (CFT) processes. Such...

Additive manufacturing (AM) is a transformative technology to many industries that enables the fabrication of parts with complex geometries. A vast majority of powder-bed metal AM techniques use powder as feedstock. The powder packing behavior and flowability significantly influence the defect density of as-built parts and, eventually, affect their...

The identification of process windows in additive manufacturing (AM) out of a vast parameter space is a daunting task, especially for a large variety of feedstock powders used in selective laser melting (SLM). Despite many numerical simulations of the SLM process, the process window for each type of metal powder is typically determined through a se...

Refractory high-entropy alloys (HEAs) possess many useful properties such as high strength and high-temperature stability. So far, most studies on refractory HEAs have been limited to a few well-known compositions and on their coarse-grain bulk forms. Here we fabricate nanocrystalline (TiZrHf)x(NbTa)1−x HEA thin films with a large range of composit...

The flowability of metal powders is critical to many additive manufacturing (AM) processes, particularly for laser or electron-beam powder bed fusion. Many poewder features may simultaneously influence its powder flow behavior, yet how particle size distribution (PSD) individually affects its flowability has not been comprehensively evaluated. The...

ABSTRACT Quasicrystalline materials possess a unique structure that is ordered yet not periodic. Despite their special configuration and many useful properties, they are typically very brittle at temperatures below ∼75% of their melting points, rendering them difficult to process and often unsuitable for practical implementations. Micro-compression...

Titanium alloys are expensive and difficult to process into large complex components for aerospace applications. Directed energy deposition (DED), one of the additive manufacturing (AM) technologies, offers a high deposition rate, being suitable for fabricating large metallic components. So far, most review articles on the AM of titanium discuss th...

Titanium alloys are widely used in additive manufacturing, but their complex microstructures and related micromechanical properties have not been fully explored. Here, we employ high-speed nanoindentation mapping, electron probe microanalysis, and electron backscatter diffraction to characterize as-deposited and heat-treated Ti–6Al–2Zr–Mo–V alloys....

Additive manufacturing (AM) is a transformative technology to the aerospace industry. As one of the AM techniques, laser metal deposition (LMD) enables the fabrication of engine blades and a disk, as a single component, known as blisk. In this study, we use the LMD technique to fabricate a γ-TiAl/Ti2AlNb graded metallic alloy by depositing γ-TiAl p...

Selective laser melting (SLM) is an additive manufacturing (AM) technique designed to use a high energy density laser to fuse metallic powders for producing three-dimensional parts. So far, most studies of SLM have been focused on using virgin metal powders. There are few comprehensive studies on the microstructure and mechanical properties of SLM-...

Joining multi-materials with complex geometries is a promising method to achieve multi-functional components that overcome traditional manufacturing limitations. Selective laser melting (SLM), also known as laser powder bed fusion (LPBF), is an additive manufacturing (AM) technique that enables the production of complex geometries, but it typically...

Multiprincipal element alloys, or medium‐ and high‐entropy alloys (MEAs and HEAs), hold great potential for numerous structural and functional applications, yet the synthesis of such alloys out of a vast composition space is a daunting task. Herein, a radio frequency inductively coupled plasma (RF‐ICP) method for preparing bulk MEAs and HEAs in a r...

The formation of “mud-cracking” networks in coatings and thin films is a widely observed phenomenon, particularly in Cr-containing electrodeposited materials. Here we have documented and described aspects of mud-cracking specific to Cr-containing electrodeposited alloys made from trivalent Cr electrolytes. In addition to describing the different cr...

Questions regarding bubble nucleation on an ideally smooth surface are seemingly endless, but it can not be adequately verified yet because of the scale limitation (microscopic scale). Hence, in this study, bubble nucleation on an ideally smooth substrate is explored using the molecular dynamics simulation method. An ideally smooth hydrophilic plat...

The classical heterogeneous nucleation theory explains that the groove in the substrate is a desirable place to breed a bubble nucleus. However, the existing research method cannot reproduce the nucleation process. Therefore, in the present study, the molecular dynamics simulation method is conducted to investigate the bubble nucleation on grooved...

Multi-principal element (MPE) alloys, sometimes also known as high entropy, complex concentration or multicomponent alloys, have attracted significant attention due to their remarkable mechanical properties, especially face-centered cubic (fcc) CrCoNi-based alloys. In this study, the size effect and strain rate dependence of the strength of equiato...

Cold spray processing is a solid-state coating technique and an emerging method for additive manufacturing, in which metal powder particles are bonded through high-velocity impact-induced deformation. However, the severe plastic deformation of powder particles at extremely high strain rates, high strain gradients, and localized elevated temperature...

In the present study, the molecular dynamics simulation method is conducted to study the bubble nucleation on a platinum substrate with non-uniform wettability. The central region of the substrate is strong hydrophilicity, and both sides are weak hydrophobicity. It is attractive that the bubble nucleation happens in the hydrophobic region when the...

High-entropy alloys (HEAs) are evolving multi-component metallic systems, wherein generally five or more principal elements tend to provide strong solid-solution strengthening. In contrast to typical metals and alloys, the deformation mechanisms in HEAs have not been well understood so far. Here, we employ strain rate jump micro-compression testing...

In the past decade, the emergence of high-entropy alloys (HEAs) and other high-entropy materials (HEMs) has brought about new opportunities in the development of novel materials for high-performance applications. In combining solid-solution (SS) strengthening with grain-boundary strengthening, new material systems-nanostructured or nanocrystalline...

To promote the engineering application of additive in enhancing nucleate boiling, the effect of foreign particles on bubble nucleation is investigated by the molecular dynamics simulation method. Some foreign atoms are added into the pure argon system with a proportion of 5%. The liquid is heated by a hydrophilic smooth platinum substrate to achiev...

It has been a long-standing challenge to obtain nanocrystalline pure aluminum with grain sizes below 10 nm by plastic deformation. Here, we studied the microstructure characteristics of two bonded pure aluminum powder particles after a cold spray process. In the particle–particle bonding region, nanometer-sized grains are revealed, about 30% of whi...

The effect of length scale on mechanical strength is a significant consideration for semiconductor materials. In III-V semiconductors, such as InSb, a transition from partial to perfect dislocations occurs at the brittle-to-ductile transition temperature (∼150 °C for InSb). High temperature micro-compression reveals InSb to show a small size effect...

Metal additive manufacturing (AM) techniques, particularly laser powder-bed methods, have shown tremendous advantages for producing high-value, complex, and customized components. However, precisely controlling the microstructure and defects of the products in the AM process has been a long-standing issue. Here, we have developed a coupled thermal-...