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Electron backscatter diffraction (EBSD) data collected on the SS specimen with a step size of 0.1 µm, the indexing rate before cleaning was 95% and after cleaning 96%. The surface that underwent the Surface Mechanical Attrition Treatment (SMAT) is on the right. a: Inverse pole figure (IPF) map showing the individual crystallographic orientation according to the color scheme represented on the right of the map (for the rest of the paper, the same color scheme is used for all IPF maps). b: Misorientation map showing local misorientations within the grains according to the color scheme represented on the right of the map.
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Austenitic 316L stainless steel can be used for orthopedic implants due to its biocompatibility and high corrosion resistance. Its range of applications in this field could be broadened by improving its wear and friction properties. Surface properties can be modified through surface hardening treatments. The effects of such treatments on the micros...
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... first scan was run at a step size of 0.1 μm and covered an area of 220 μm in length from the treated surface. The inverse pole figure (IPF) map and the misorientation map can been seen in Figure 1. The area close to the treated surface (on the right in both maps) cannot be studied thoroughly with this field of view and step size; however, other information is available regarding the area modified by the treatment. ...
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... from the treated surface. The inverse pole figure (IPF) map and the misorientation map can been seen in Figure 1. The area close to the treated surface (on the right in both maps) cannot be studied thoroughly with this field of view and step size; however, other information is available regarding the area modified by the treatment. In the IPF map (Fig. 1a), the grain boundaries are plotted using a critical misoriention angle between two adjacent points equal to 10° (which is the critical angle used for all other figures in this work). It can be observed that the grains closer to the treated surface present gradients of crystallographic orientations while ...
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... away from that surface the grains have a more homogenous crystallographic orientation. To better represent this, Figure 1b presents the misorientation map that shows misorientations from 0 to 5° between adjacent points. Here again higher misorientations are observed in grains closer to the SMATed surface. ...
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... data obtained in Figure 1 was then further analyzed using Channel 5 Tango software and the information regarding UFG thickness obtained from Figure 2. Grains in the scan from Figure 1 were determined using a critical angle of 10° and the grain completion parameter was set to 2° Inverse pole figure (IPF) map of the SS specimen, data collected using electron backscatter diffraction (EBSD) with a step size of 20 nm, the indexing rate before cleaning was 81% and after cleaning 85%. The SMATed surface is on the right of the figure. ...
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... data obtained in Figure 1 was then further analyzed using Channel 5 Tango software and the information regarding UFG thickness obtained from Figure 2. Grains in the scan from Figure 1 were determined using a critical angle of 10° and the grain completion parameter was set to 2° Inverse pole figure (IPF) map of the SS specimen, data collected using electron backscatter diffraction (EBSD) with a step size of 20 nm, the indexing rate before cleaning was 81% and after cleaning 85%. The SMATed surface is on the right of the figure. ...
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Citations
... The preliminary impact through severe surface plastic deformation reduces the intensity of the S-phase but increases the intensity of the ε-phase and leads to the appearance of a new (also hard) phase: stabilized nitrogen-bearing martensite. • This conclusion is generally supported by Proust et al. [47], who, for 316L steel, found that the average depth of the nitrogen-rich layer is 24.8 µm (425 • C/20 h plasma nitriding), but after preliminary surface mechanical attrition treatment, it is only 5 µm. Figure 5 shows the microstructure near the surface layer after hardening DB and subsequent LTGN. ...
... The preliminary impact through severe surface plastic deformation reduces the intensity of the S-phase but increases the intensity of the ε-phase and leads to the appearance of a new (also hard) phase: stabilized nitrogen-bearing martensite. • This conclusion is generally supported by Proust et al. [47], who, for 316L steel, found that the average depth of the nitrogen-rich layer is 24.8 µm (425 °C/20 h plasma nitriding), but after preliminary surface mechanical attrition treatment, it is only 5 µm. Figure 6a shows the microhardness profiles before LTGN. ...
Chromium–nickel austenitic stainless steels are widely used due to their high corrosion resistance, good weldability and deformability. To some extent, their application is limited by their mechanical characteristics. As a result of their austenitic structure, increasing the static and dynamic strength of the components can be achieved by surface cold work. Due to the tendency of these steels to undergo intercrystalline corrosion, another approach to improving their mechanical characteristics is the use of low-temperature thermo-chemical diffusion processes. This article proposes a new combined process based on sequentially applied diamond burnishing (DB) and low-temperature gas nitriding (LTGN) to optimally improve the fatigue strength of 304 steel. The essence of the proposed approach is to combine the advantages of the two processes (DB and LTGN) to create a zone of residual compressive stresses in the surface and subsurface layers—the enormous surface residual stresses (axial and hoop) introduced by LTGN, with the significant depth of the compressive zone characteristic of static surface cold working processes. DB (both smoothing and single-pass hardening), in combination with LTGN, achieves a fatigue limit of 600 MPa, an improvement of 36.4% compared to untreated specimens. Individually, smoothing DB, single-pass DB and LTGN achieve 540 MPa, 580 MPa and 580 MPa, respectively. It was found that as the degree of plastic deformation of the surface layer introduced by DB increases, the content of the S-phase in the nitrogen-rich layer formed by LTGN decreases, with a resultant increased content of the ε-phase and a new (also hard) phase: stabilized nitrogen-bearing martensite.
... Microstructure near the surface layer after LTGN and hardening DB: a. affected layer; b. EDX outcomes This conclusion is generally supported by Proust et al.[47] who, for 316L steel, found that the average depth of the nitrogen-rich layer is 24.8 m (425°C/20 h plasma nitriding), but after preliminary surface mechanical a rition treatment is only 5 m. Ignoring the negligible amount of -phase in the first two samples, the ALs of all three samples contain hard phases in different proportions. ...
Chromium-nickel austenitic stainless steels are widely used due to their high corrosion resistance, good weldability and deformability. To some extent, their application is limited by their mechanical characteristics. As a result of their austenitic structure, increasing the static and dynamic strength of the components can be achieved by surface cold work. Due to the tendency of these steels to undergo intercrystalline corrosion, another approach to improve their mechanical characteristics is the use of low-temperature thermo-chemical diffusion processes. This article proposes a new combined process based on sequentially applied diamond burnishing (DB) and low-temperature gas nitriding (LTGN) to optimally improve the fatigue strength of 304 steel. The essence of the proposed approach is to combine the advantages of the two processes (DB and LTGN) to create a zone of residual compressive stresses in the surface and subsurface layers–the enormous surface residual stresses (axial and hoop) introduced by LTGN, with the significant depth of the compressive zone characteristic of static surface cold working processes. DB (both smoothing and single-pass hardening), in combination with LTGN, achieves a fatigue limit of 600 MPa, an improvement of 36.4% compared to untreated specimens. Individually, smoothing DB, single-pass DB and LTGN achieve 540 MPa, 580 MPa and 580 MPa, respectively. It was found that as the degree of plastic deformation of the surface layer introduced by DB increases, the content of the S-phase in the nitrogen-rich layer formed by LTGN decreases, with resultant increased content of -phase, and a new (also hard) phase: stabilized nitrogen-bearing martensite.
... Taking into account the structure of the grains and their misorientation, as quantitatively observed by EBSD [266] coupled with TKD (transmission Kikuchi diffraction) [267] or with TEM [268], the microstructure in the gradient layer is generally depicted as the succession of three different zones: (i) an 'UFG zone', which also contains a nanostructured zone present at the extreme top surface -containing randomly oriented grains separated by high-angle grain boundaries; (ii) a 'transition zone', where grains have been fragmented under heavy deformation; and finally, (iii) a 'deformed zone', where initial grains are simply deformed. Using the SMAT-type Figure 19. ...
... The surface contamination also has a significant effect on the tribological properties as wear is affected by the exact nature of the oxide formed during processing and subsequent rubbing [305]. Finally, although SMAT is sometimes performed under vacuum, chemical etching [306] or mechanical polishing [267,307,308] was used as an intermediate stage during SMAT and nitriding duplex treatment process to reduce the surface contamination and, thereby, further improve the quality and thickness of the nitrided layers. ...
Severe plastic deformation (SPD) is effective in producing bulk ultrafine-grained and nanostructured materials with large densities of lattice defects. This field, also known as NanoSPD, experienced a significant progress within the past two decades. Beside classic SPD methods such as high-pressure torsion, equal-channel angular pressing, accumulative roll-bonding, twist extrusion, and multi-directional forging, various continuous techniques were introduced to produce upscaled samples. Moreover, numerous alloys, glasses, semiconductors, ceramics, polymers, and their composites were processed. The SPD methods were used to synthesize new materials or to stabilize metastable phases with advanced mechanical and functional properties. High strength combined with high ductility, low/room-temperature superplasticity, creep resistance, hydrogen storage, photocatalytic hydrogen production, photocatalytic CO2 conversion, superconductivity, thermoelectric performance, radiation resistance, corrosion resistance, and biocompatibility are some highlighted properties of SPD-processed materials. This article reviews recent advances in the NanoSPD field and provides a brief history regarding its progress from the ancient times to modernity.
Abbreviations: ARB: Accumulative Roll-Bonding; BCC: Body-Centered Cubic; DAC: Diamond Anvil Cell; EBSD: Electron Backscatter Diffraction; ECAP: Equal-Channel Angular Pressing (Extrusion); FCC: Face-Centered Cubic; FEM: Finite Element Method; FSP: Friction Stir Processing; HCP: Hexagonal Close-Packed; HPT: High-Pressure Torsion; HPTT: High-Pressure Tube Twisting; MDF: Multi-Directional (-Axial) Forging; NanoSPD: Nanomaterials by Severe Plastic Deformation; SDAC: Shear (Rotational) Diamond Anvil Cell; SEM: Scanning Electron Microscopy; SMAT: Surface Mechanical Attrition Treatment; SPD: Severe Plastic Deformation; TE: Twist Extrusion; TEM: Transmission Electron Microscopy; UFG: Ultrafine Grained
... On the other hand in phase identification there is a great deal of uncertainty of phases present and a large database of crystalline compounds would need to be searched for a good match, which would be impractical" 2 . In particular, in austenitic steel structures containing colossal dissolution of nitrogen, EBSD technique is not accurate enough to characterize the lattice expansion neither the lattice distortion reported with XRD analysis as a basis [17][18][19] . Austenitic steel structures containing colossal dissolution of nitrogen could contain dispersion of nanometric nitrogen-rich compound phases 17 . ...
... Austenitic steel structures containing colossal dissolution of nitrogen could contain dispersion of nanometric nitrogen-rich compound phases 17 . A complete unambiguous characterization of the nitrogen-rich austenitic steel structure demands for the using of diverse complementary characterization techniques, like XRD or TEM, being not possible to fully identify the phases present by EBSD characterization [17][18][19] . ...
... We ascribed this to both surface roughening and residual stresses induced by lattice rotations 18 . Characterization via EBSD of cross-sectioned nitrided structures, in diverse types of steels, shows full indexability of Kikuchi diffraction patterns 19,39,40 . Thus, we can address to the The results in this contribution showed that the major role of the grinding stage was to accelerate the reduction of the relief between the highest hills and the deepest valleys in the intergranular regions. ...
Abstract This contribution reports on an experimental polishing procedure, that is comprised of early grinding in Al2O3 slurries and late polishing in colloidal silica, which is used for preparing the nitrided region of a plasma nitrided austenitic stainless steel, for crystallographic analysis via electron backscatter diffraction (EBSD). The suitability of the polished surfaces for conducting EBSD characterization was assessed through an analysis of both the surface roughness (appraised by atomic force microscopy) and the quality of the Kikuchi diffraction patterns. We observed that as-nitrided virgin surfaces were not suitable for EBSD characterization, due to intense surface roughening, which was induced by the nitriding process itself. At the subsurface region, exposed by on-top mechanical polishing, the flatter nature of the polished surfaces allowed the acquisition of EBSD patterns with enough quality for microtexture analysis. A resolution of 100 nm in the total removed layer was attainable via careful control of the polishing parameters. Close parallelism between the polished and original surfaces was verified.
... Microhardness, resistances to wear, and corrosion of the nitrided/ aluminized/chromized SMAT sample have been investigated on commonly used industrial metals (AISI 321 SS [215]; 304 SS [216][217][218][219], 316 SS [220][221][222][223][224], 38CrMoAl steel [225]; low carbon steel [226][227][228]; Cu-Ag alloys [229], Mg-1Ca alloy [230], Co28Cr6Mo alloy [231], pure iron plate [232][233][234][235], titanium [236], in comparison with those of the nitrided/chromized coarse-grained counterpart and the as-annealed coarse-grained sample. It was demonstrated that the nitrided/chromized SMAT sample showed larger hardness and superior resistances to wear and corrosion. ...
Most of the challenges experienced by many engineering materials originate from the surface which later leads to total failure, hence affecting the resultant mechanical properties and service life. However, these challenges have been addressed thanks to the invention of a novel surface mechanical attrition treatment (SMAT) method which protects the material surface by generating a gradient-structured layer with improved strength and hardness without jeopardizing the ductility. The present work provides a comprehensive literature review on the mechanical properties of materials after SMAT including the hardness, tensile strength and elongation, and residual stress. Firstly, a brief introduction on the different forms of surface nanocrystallization is given to get a better understanding of the SMAT process and its advantages over other forms of surface treatments, and then the grain refinement mechanisms of materials by SMAT from the matrix region (base material) to the nanocrystallized layer are explained. The effects of fatigue, fracture, and wear of materials by the enhanced mechanical properties after SMAT are also discussed in detail. In addition, the various applications of SMAT ranging from automotive, photoelectric conversion, biomedical, diffusion, and 3D-printing of materials are extensively discussed. The prospects and recent research trends in terms of mechanical properties of materials affected by SMAT are then summarized.
... However, electron backscatter diffraction (EBSD) technique is not sufficient to obtain the detailed features of the UFG region. Therefore, Gwénaëlle Proust et al. 55) used the newly developed highresolution transmission Kikuchi diffraction (TKD) technique to better characterize the UFG region. On the whole, the microstructure in the GS layer can be better characterized by the combined use of the above three methods. ...
It is well known that the bulk nanostructured metallic materials generally exhibit high strength but poor ductility, which greatly hinders their applications. In most cases, material failures usually start from the surface. Therefore, the surface modification is crucial to improving the mechanical properties of metallic materials. The surface mechanical attrition treatment (SMAT) is one of the most effective surface modification methods. It can be used to manufacture gradient nanostructured materials that there is no interfaces between the surface and the coarse-grained matrix. Additionally, the gradient nanostructured metallic materials fabricated by SMAT exhibit a preferable combination of strength and ductility compared with conventional homogeneous materials. It is generally believed that the high strength of the SMAT-ed metallic materials is owing to the surface fine-grain strengthening. Whereas the improved ductility can be attributed to the coarse-grained matrix and the superior work hardening ability of the gradient structured (GS) materials.
In this overview, the research progress of the GS metallic materials fabricated by SMAT is summarized. It mainly introduces the microstructure characteristics of the GS layer and the mechanical properties of GS metallic materials. Finally, in order to find the optimal match between the strength and ductility in the GS materials, the several factors affecting the mechanical properties of GS materials are summarized.
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... Surface mechanical attrition treatment (SMAT) [9][10][11][12] , a simple, yet flexible and cost-effective method, has been widely used to improve mechanical properties of metals, such as 316 L stainless steel, which is a widely used alloy for biomedical applications [13][14][15][16] . This process generates a nanocrystalline layer at the surface of the treated material [17][18][19][20] , which, due to the large fraction of grain boundaries and compressive residual stresses, presents extraordinary strength, fatigue life and wear resistance [21][22][23][24][25] . During SMAT, a sonotrode generates ultrasonic vibrations, propelling shot particles inside the enclosed chamber to impact the surface of the target. ...
... (7) , (11) , (22) and (23) into Eq. (20) , and simplifying the expression of F d : ...
... Under their tested processing conditions -varying the amplitude of vibration and treatment duration -these authors have established that the UFG and transition zones were more significantly modified than the overall affected thickness for a 316L stainless steel. Because the spatial resolution of EBSD is not high enough to fully depict the NC structure in the UFG zone, such type of approach was coupled with Transmission Kikuchi Diffraction (TKD) analyses in the SEM 75) or with TEM. 76) However, in view of potential and reproducible industrial applications, a large amount of work remains to be done to establish quantitatively the effect of the comparative effect of each processing parameter. ...
... 121123) Further analysis has shown that this contamination, acting as a barrier to the nitrogen flux, could also result from the material transfer of fragments coming from different constitutive parts of the SMAT treating machine 103) and lead to discontinuous nitriding layers. Thus, chemical etching 124) or mechanical polishing 75,103,122,125) were used as an intermediary stage during such duplex treatment process to reduce the surface contamination and, thereby, improve further the quality and thickness of the nitrided layers. ...
After a short recall of various techniques that use shots to induce surface severe plastic deformation and a brief survey of the advantages of having a gradient structure for mechanical properties, this manuscript presents recent developments taking advantages of the “reactivity” of these modified surfaces in the fields of corrosion, “duplex” surface treatments as well as potential applications for an easier activation of H-storage materials. The importance of controlling the processing parameters (including temperature) to get the optimum gradient structure depending on the desired applications as well as the necessary requirements for a high quality microstructure and chemical characterizations are also highlighted.
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... It can lead to a progressive grain size refinement due to severe plastic deformation, whereas the bulk of the part is not mechanically deformed, so that its characteristics remain unchanged as well as its mechanical properties. A gradient microstructure is thus formed from the treated surface to the interior region of the material [10]- [13]. The particularity of SMAT with respect to conventional shot peening lies in the fact that it can transform the top surface layer of materials from coarse grains to nano-sized grains [8] [9]. ...
... The fatigue property can also be enhanced. SMAT treatment is able to induce high compression residual stress and grain refinement at the top surface of the treated sample, which are capable to resist crack initiation and propagation [10], [12]. As a nanostructured layer is formed at the top surface after SMAT, the volume fraction of grain boundaries of this layer has also been significantly increased. ...
... The increase in hardness due to GND is more pronounced when the indentation depth is small. This is because that in the case of small indentation depth, the strain gradient is relatively larger, as indicated by equation (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). With the increase of indentation depth, the influence of GND becomes smaller and smaller. ...
This work focuses on the local experimental characterization of the gradient microstructure of 316L steels treated by SMAT. The gradient microstructure could be roughly divided into a top surface nanostructured layer, a transition layer and the bulk region. Grain refinement, compressive residual stress and strain hardening are three major SMAT-induced parameters as a result of severe plastic deformation induced by SMAT. Consequently, the enhanced mechanical properties of the gradient microstructure are due to the combined effects of these SMAT-induced changes. However, emphasis was mainly placed on the global properties of the gradient microstructure in previous studies and little effort was devoted to the individual characterization of each layers. The aim of this work is thus to investigate individually the mechanical properties of each layer by means of various characterization techniques. Characteristics of the gradient microstructure are first highlighted by EBSD which reveals the formation of a top surface nanostructured layer. The grain size for this layer ranges from 50 to 300 nm. As for the mechanical properties, nanoindentation and micro-pillar compression tests were carried out for the individual characterization of each layer of the gradient microstructure. The local mechanical properties could be subsequently derived according to the corresponding mechanical reponse. Another part of this work consisted of using Finite element method for the simulation of the mechanical behaviour of nanocrystalline materials. A two-dimensional crystal plasticity model was thus used for the simulation.
... This nanocrystallisation process leads to different effects that have been successively studied on several metallic materials, such as increase in the surface hardness, enhancement of wear resistance and fatigue properties [3][4][5][6][7] or the coupling with nitriding process [8]. Recently, investigations have been performed on these effects; most of them mainly focus on the surface morphologies and tribological properties [9]. It can be expected that SMAT could affect the oxidation resistance. ...
... Except for the chemical composition provided by ACNIS International (Table 1), all the experiments were performed ourselves in our lab or with collaborative labs. The grain size was obtained in a previous work by TKD [9]. ...
... The observations of the two cross-sections reveal an evolution of the grain size as shown in Fig. 4. No nano-grain can be clearly distinguished at the top surface (a higher magnification and resolution would be required), but previous work showed that nanograins are actually present at the top surface of the SMATed samples (see [9]). By the way, high plastic deformation can be observed inside the grains near the impacted surface (see at the top of Fig. 4). ...
