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(a) A representative load-displacement curve showing pop-in event in nanoindentation test of the HE alloy. The distribution of maximum shear stress calculated based on elastic contact theory in the cases of (b) nanoindentation and (c) nanoscratch. The blue circles denote the positions of highest stress under only normal force applied, and the blue plus symbol corresponds to the one under normal loading plus sliding. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
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In this study, friction and wear of a body-centered cubic equiatomic TiZrHfNb high-entropy (HE) alloy were investigated using a nanoscratch method. Scratch tests, under both ramping and constant load modes, were conducted to evaluate the coefficient of friction (COF) and wear rate of the alloy. The effects of scratch rate on the friction and wear w...
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... This new class of alloys has high configurational entropy and favors the formation of simple solution-like structures, such as face-centered cubic (FCC) [26][27][28][29][30][31] and body-centered cubic (BCC) [32][33][34][35][36], rather than complex ordered intermetallics. These HEAs have demonstrated some unusual mechanical and physical properties, such as excellent combination of strength and ductility [37,38], good resistance to hightemperature softening [33] and fracture [26], attractive tribological properties [39], and outstanding magnetic properties [40,41]. Therefore, the formation and damage mechanisms of conventional irradiation defects and other functionalities are not yet fully understood and controlled, although several developments for practical application have been developed. ...
... HEAps have drawn much interest as unique multiprincipal element metal alloys because of their excellent wear resistance, which makes them a promising material that can serve as a suitable reinforcement in Al-based composites. [135,136] The fabrication technique has been employed to increase the wear resistance of Al/HEAp composites further. Yang et al. [104] conducted a wear test on AlCoCrFeNi HEAp-reinforced A5083 AMCs fabricated via underwater friction stir processing. ...
... This study examines the effect of annealing treatment on the microstructure evolution of gradient nanostructured M50 steel, as well as the thermal stability of the material post-annealing. Nanoscratch technology has become a valuable tool for analyzing the friction and wear behavior of various materials under dry wear conditions [48,49]. It helps establish a better connection between scratch resistance and the original microstructural characteristics of materials. ...
The M50 steel is a common material for main shaft bearings in aerospace applications. The thermal stability of gradient ultrafine grains/nanograins steels is of critical importance for engineering applications. Here, we fabricated gradient nanostructured M50 steel using ultrasonic shot peening and subsequent annealing. This study investigated the effect of annealing treatment on the microstructure evolution of gradient nanostructured M50 steel and the thermal stability of the USPed sample post-annealing. Furthermore, the friction behavior of gradient nanostructured M50 steel was also examined. After annealing at 350 °C for 30 min, ferrite phase at the depth span of 0–100 μm has better thermal stability, and formed a high-density dislocation network and cells at the top surface of the gradient layer. When annealed samples were continued annealed at 350 °C for 100 h, the average ferrite phase size at the depth span of 0–100 μm reduced to a fixed value (~434 nm). High-density dislocation cells with smaller and more dispersed ordered B2 phases have a stronger pinning effect of dislocation. Hetero-deformation induced hardening by a dislocation network of grain interior and dislocation wall (~200 nm thick) and precipitation hardening of dislocation cells with more dispersed ordered B2 phase is the main reason for the high microhardness of the samples annealing at 350 and 450 °C for 30 min. The USPed sample within the 100–200 μm depth span exhibits better friction properties attributed to the strengthened martensitic matrix, partial decomposition of spherical carbides, and the presence of high-density dislocations, which reduce the cracking of carbides and matrix, and carbide spalling. Although heat treatment results in a slight decrease in the friction properties of the USPed sample, they still surpass those of the tempered sample. This reduction in friction properties post-annealing primarily arises from the annihilation of high-density dislocations.
... In nearly two decades, high entropy alloys (HEAs) have attracted great scientific attention due to their huge alloy design space and outstanding mechanical properties, such as excellent strength and ductility combinations [1][2][3], high fracture toughness under cryogenic conditions [4], high corrosion and wear resistances [5]. Unlike the traditional alloying strategy by adding relatively small amounts of secondary elements to improve mechanical properties (e.g., aluminum alloy, titanium alloy, nickel alloy) [6], HEAs are defined as a new class of alloys composed of five or more elements in equiatomic or near equiatomic concentrations (ranging in 5-35%), as proposed by Yeh [7] and Cantor et al. [8] in 2004. ...
... To evaluate the mechanical properties of the newly designed TiZrNbHf 1.6 Ni x RHEA films, the relation of H 3 /E 2 and H/E (particularly predicting the wear resistance than the H alone [66]) of the films and the other bulk RHEAs [5,[20][21][22]25,[67][68][69], RHEA films [70] and pure elements [20] are plotted in Fig. 9. The value of H/E denotes an elastic deformation factor, reflecting the ability of the film to resist elastic strain [66]. ...
... A lot of defects (stacking faults and dislocations) are dectected in the deformed region as indicated in the inverse FFT image (Fig. 11e). Generally, there are no stable stacking faults in Fig. 9. Relationship between the H/E and H 3 /E 2 of the designed TiZrNbHf 1.6-Ni x RHEA films and other bulk RHEAs (TiZrHfNb [5], TiZrHfNbTa [20], TiZrNbTaHf 0.6 Al 0.4 [25], TiZrHfNbTaMo [67], TiZrNbAlMo 0.5 Ta 0.5 [25], TiZrNbCrMo 0.5 Ta 0.5 [21], TiZrNbVCr [22], TiZrNb [68], TiZrHf [69]), HEA film (TiZrNbHfTa [70]) and pure metal elements (Ti, Zr, Nb, Hf) [20]. ...
... Scratch testing is a common mechanical characterization method for materials, and it is widely used for characterizing the film adhesion strength [1][2][3] as well as the damage mechanism of bulk materials [4][5][6]. Specially, the in-situ scratch testing allows direct observation of the interaction region between the indenter and the sample, which can provide additional information such as the process of plastic flow and crack propagation. Some commercial scratch testers can achieve in-situ scratch testing, which are integrated into the scanning electron microscope (SEM) and transmission electron microscope (TEM), as listed in Table 1. ...
For in-situ scratch tests, real time and high resolution observation is the ultimate goal. In-situ scratch tests inside the scanning electron microscope (SEM) or transmission electron microscope (TEM) could provide a relatively high imaging resolution but require a low refresh rate, and in-situ scratch tests under the ordinary optical microscope could employ a relatively high refresh rate but the imaging resolution is low. Alternatively, the confocal laser scanning microscope (CLSM) can provide a balanced performance in both the imaging resolution and refresh rate. Accordingly, a miniaturization scratch tester with dimensions of 170 mm × 80 mm × 80 mm was developed for performing in-situ scratch testing under a commercial CLSM. Its structure and working principle were discussed, followed by characterizing the performance by experiments. In-situ scratch tests of three typical materials, fused silica, ITO thin film deposited on glass, and polymethylmethacrylate (PMMA) were conducted to demonstrate the feasibility of the proposed scratch tester. The dynamic cracking process of fused silica and ITO thin film deposited on glass, and the ductile deformation behavior of PMMA were analyzed according to the in-situ observed results. This study provides a new experimental tool for investigating the deformation and damage processes of transparent materials.
... The challenge of designing and developing a novel HEA with superior mechanical properties compared with currently available HEAs has been a significant undertaking. Several atomic distortion parameters, such as the root-mean-square atomic displacement (RMSAD), 6 the atomic volume difference, [20][21][22] and the local atomic strain, 23,24 have recently been proposed to be linearly related to the critical resolved shear stress (CRSS), with experimental support. In this study, our primary objective is to investigate the effects of edge dislocation and GBs on the mechanical properties of an FCC equiatomic CoCrCuFeNi HEA. ...
This study uses molecular dynamics simulations to explore the mechanical behavior of a CoCrCuFeNi high-entropy alloy (HEA) with Σ5 and Σ13 grain boundaries (GBs) as well as without GBs and dislocation. The analysis focused on understanding the influence mechanisms of these grain boundaries on the mechanical behavior of the HEA. Our findings reveal that the atomic size disparity among the constituent elements induces lattice distortion, leading to deformation in HEAs. The determined elastic constants met Born stability requirements, ensuring mechanical stability across both the examined GBs. Higher elastic moduli were associated with increased strength and stiffness, particularly evident in HEAs with Σ5 GB, surpassing those of non-GB structures. Notably, GB Σ5 demonstrated enhanced strength and hardness, indicated by larger elastic moduli compared with those of non-GB structures. Conversely, GB Σ13 exhibited increased Cauchy pressure and Poisson and Pugh's ratios. The ductility of face-centered cubic HEAs was found to be significantly influenced by the GBs, affecting mechanical properties. The Kleinman parameter highlighted a bending-type bonding with reduced strength at the GBs. Machinability indices indicated high machinability of the CoCrCuFeNi alloy, further enhanced by the presence of the GBs. Direction-dependent parameters underscored the anisotropic nature of the HEA, mitigated by the GBs. Overall, this study elucidates the nuanced influence of different GBs on the mechanical properties of HEAs, offering valuable insights for materials design and applications. The results of this investigation shed light on HEAs with improved mechanical properties via GB engineering.
... A number of nanoscratch systems inside SEM have been developed by companies, including Bruker, Alemnis, and Nanomechanics [3][4][5][6]. The 3D topography imaging of nanoscratch residual imprint enables the nanoscratch data analysis [7][8][9][10][11][12][13], which are benefit for the study of the deformation mechanism of coating with micro-and nanoscale thickness. Due to the lacking capability of depth measurement of SEM image, the coating-after-nanoscratch needs to be transferred to atomic force microscope (AFM) to 3D topography imaging of nanoscratch residual imprint. ...
This paper presents a novel piezoelectric hybrid-driven nanopositioner using combined leaf-spring-shaped and C-shaped flexure hinge mechanism. The piezoelectric hybrid-driven nanopositioner combines the piezoelectric stick-slip-driven nanopositioner and piezoelectric scanner in a single and compact device. This advance can decrease the size of nanoscratch-AFM hybrid system and make nanoscratch-AFM hybrid system compatible with the limited space of SEM vacuum chamber. A flexure hinge combining leaf-spring-shaped mechanism and C-shaped mechanism is developed to improve the load capability of piezoelectric stick-slip-driven nanopositioner. Unlike existing methods of improving load-capability by decreasing kinetic friction force value, the proposed flexure hinge employs C-shaped structure to decrease the retraction motion time of kinetic friction force, which can achieve high-load and compact structure simultaneously. Finite element analysis is implemented to optimize the thickness of the leaf-spring-shaped mechanism and diameter of the C-shaped mechanism. A prototype is fabricated and its experimental system is established. The mechanical output experiments show that the piezoelectric scanner achieved a maximum travel range of 4.9 μm, and piezoelectric stick-slip-driven nanopositionerm achieves a maximum load of 2 Kg. Experimental results of the nanoscratch-AFM hybrid system inside a standard SEM HITACHI SU5000 demonstrate that the proposed piezoelectric hybrid-driven nanopositioner is capable of nanoscratch positioning.
... Generally, MPEAs consist of several main components in approximately equal proportions [3,4]. In recent years, excellent properties were reported for MPEAs, such as high strength [5,6], high hardness [7], good wear resistance [8,9], excellent corrosion resistance [10,11], good fatigue performance [12,13], excellent cryogenic-temperature mechanical properties [14] and high resistance to radiation [15], just to name a few. Due to their promising potential for applications as structural and functional materials, along with more degrees of freedom in the alloy design space, MPEAs provide an intriguing opportunity to develop novel materials and therefore have attracted much attention. ...
A R T I C L E I N F O Keywords: Multi-principal element alloy Rare-earth element Microstructure Mechanical properties Intermetallics A B S T R A C T Here, two multi-principal element alloys (MEPAs): CoCrFeNi and CoCrFeNiGd 0.05 are fabricated by high-energy ball milling and spark plasma sintering. The effect of Gd on microstructure and mechanical properties of the CoCrFeNi MPEA is investigated. The addition of Gd to the CoCrFeNi base alloy leads to precipitation of a GdNi 5-type phase with hexagonal structure (HS) and minor amounts of a Gd-rich oxide phase from the FCC matrix. Compared to the CoCrFeNi base alloy, the grain size of CoCrFeNiGd 0.05 is smaller, and the tensile yield strength of CoCrFeNiGd 0.05 significantly increases from 546 MPa to 859 MPa, along with minor sacrifices in plasticity where the elongation only slightly decreases from 20.8% to 19.4%. The enhanced strength of Gd-containing MPEA is mainly attributed to grain boundary strengthening from the ultrafine-grained microstructure and the precipitation strengthening contributed by the HS phase. Transmission electron microscopy (TEM) results demonstrate that the GdNi 5-type intermetallic phase is coherent with the FCC matrix and shows the following orientation relationship: {111}FCC//{2119}HS. The high plasticity of the composite-structured CoCrFeNiGd 0.05 alloy is attributed to the homogenous distribution of the ultrafine HS phase and the coherent HS-FCC interface facilitating dislocation slipping.
... Their specific properties by doping were, thereafter, further improved by the addition of small amounts of other elements. [3] In the combination of the four most common effects of the HEA (lattice torsion effect, high-entropy effect, cocktail effect, and sluggish diffusion effect), [4,5] the HEA was found to have many excellent properties (such as oxidation-resistance, [6,7] wear-resistance, [8,9] and corrosion-resistance). [10,11] Meanwhile, laser cladding technology, which has been frequently used to prepare HEA coatings in recent years, has a high energy density and cooling rate, which can effectively reduce the grain size, dilution rate, and heataffected zone of the base metal. ...
With the continuous development of the aviation and aerospace industries, there is an increasing demand for surface coatings that can enhance the wear‐resistance and lubricity of substrates. High‐entropy alloy (HEA) coatings and high‐entropy alloy‐based composite coatings (including ceramic and lubricating phases) have attracted large attention, which is due to their excellent properties. They have, therefore, developed rapidly in the past decade. This article reviews the current status of research on the tribological properties of the HEA coatings and HEA‐based composite coatings that have been prepared by laser cladding technology. The focus is then on the wear‐resistance and wear‐reduction mechanism of the coatings. Furthermore, the review analyzes the influence of element addition, atomic ratio change, and process parameters on the coating organization and properties. The problems that have to be solved in the development of tribology‐based HEAs coatings, and the expected future development of HEA the coatings, are also discussed.
... Among the bcc single phase RHEAs, TiZrHfNbTa alloy developed by Senkov et al. [8] has been well studied because of its excellent strength and ductility, meanwhile one of its derivative, TiZrHfNb alloy [9], is attracting increasing attentions [10][11][12][13][14][15][16][17][18]. It is well known that metallic materials can be strengthened by introducing lattice defects such as dislocations and grain boundaries [19] and forming dispersed precipitates [20]. ...
