Surface Mechanical Attrition Treatment Process Research Articles

Investigation of Mechanical Properties and Microstructural Evolution in Pure Copper with Dual Heterostructures Produced by Surface Mechanical Attrition Treatment

Heterostructured materials consist of heterogeneous zones with dramatic variations in mechanical properties, and have attracted extensive attention due to their superior performance. Various heterostructured materials have been widely investigated in recent years. In the present study, a combination of two different types of heterogeneous structures, a surface bimodal structure and gradient structure, was designed using the traditional surface mechanical attrition treatment (SMAT) method in pure copper, and the mechanical properties and microstructural evolution of dual-heterostructure Cu were studied in depth. In total, 100 stainless steel balls with a diameter of 6 mm were utilized to impact the specimen surface at room temperature for a short period of time. In this work, the sample surface was divided into hard areas and soft areas, along with a roughly 90 μm gradient structure in the cross-sectional direction after 30 s of SMAT processing. After the partial SMAT processing, lasting 30 s, the strength increased to 158.0 MPa and a considerable ductility of 25.7% was sustained, which overcomes the strength–ductility trade-off. The loading–unloading–reloading (LUR) test was utilized to measure the HDI stress, and the result showed that the HDI stress of the partial SMAT sample was much higher than the annealed one, especially for the Cu-SMAT-30S specimen, the strength of which increased from 80.4 MPa to 153.8 MPa during the tensile test. An in situ digital image correlation (DIC) investigation demonstrated that the strain developed stably in the Cu-SMAT-10S specimen. Furthermore, electron backscatter diffraction (EBSD) was carried out to study the microstructural evolution after partial SMAT processing; the KAM value increased to 0.34 for the Cu-SMAT-10S specimen. This research provides insights for the effective combination of superior strength and good ductility in dual-heterostructure materials.

Enhancing wear resistance, anti-corrosion property and surface bioactivity of a beta-titanium alloy by adopting surface mechanical attrition treatment followed by phosphorus ion implantation

A two-step method of surface mechanical attrition treatment (SMAT) followed by phosphorous (P) ion-implantation was adopted to treat Ti-25Nb-3Mo-2Sn-3Zr (named as TLM) alloy. The initial SMAT process refined the grains from micrometer-scale to about 10–30 nm, and begot the TLM surface much rougher with apparently improved hydrophilicity. The subsequent P ion-implantation led to the formation of a hybrid structure of the TiP, β-Ti nanograins and P-interstitial amorphous in the surface layer of the TLM alloy, and resulted in a slight decrease of the surface roughness and wettability of the SMAT-processed alloy. The indentation, tribology and potentiodynamic polarization tests indicated that the SMAT procedure concurrently enhanced the microhardness, wear-resisting property and corrosion resistance of the TLM alloy, and the followed P-ion implantation could further improve these tested properties. Moreover, the P-ion implanted TLM alloy was verified to exhibit much better surface bioactivity (including biomineralization in the simulated body fluid (SBF) and in-vitro cell adhesion) as compared to the original TLM alloy. With the remarkable improvements of the wear resistance and anti-corrosion property as well as the surface bioactivity of the P ion-implanted TLM alloy, our study provides an alternative avenue to fabricating new-type Ti-based orthopedic implants with superior comprehensive performance.

Influence of Surface Mechanical Attrition Treatment (SMAT) on Microstructure, Tensile and Low-Cycle Fatigue Behavior of Additively Manufactured Stainless Steel 316L

Direct Energy Deposition (DED), as one common type of additive manufacturing, is capable of fabricating metallic components close to net-shape with complex geometry. Surface mechanical attrition treatment (SMAT) is an advanced surface treatment technology which is able to yield a nanostructured surface layer characterized by compressive residual stresses and work hardening, thereby improving the fatigue performances of metallic specimens. In the present study, stainless steel 316L specimens were fabricated by DED and subsequently surface treated by SMAT. Both uniaxial tensile tests and uniaxial tension-compression low-cycle fatigue tests were conducted for as-built and SMAT processed specimens. The microstructure of both conditions was characterized by roughness and hardness measurements, scanning electron microscopy and transmission electron microscopy. After SMAT, nanocrystallites and microtwins were found in the top surface layer. These microstructural features contribute to superior properties of the treated surfaces. Finally, it can be concluded that the mechanical performance of additively manufactured steel under static and fatigue loading can be improved by the SMAT process.

Modelling residual stress and residual work hardening induced by surface mechanical attrition treatment

Shot peening induced residual stress is strongly related to residual work hardening which relies on both the process and the target material. In this work, residual stress and coupled residual work hardening are studied in a surface mechanical attrition treatment (SMAT) on a cylindrical structure by combining discrete element method (DEM) and finite element method (FEM). Shot, ultrasonic parameters, chamber structure, sonotrode surface, and cylindrical structure of the target are finely modeled in DEM simulation. On the basis of the DEM results, FEM simulation of the SMAT process is performed on a representative area considering the factual impact parameters and elastic-plastic behavior of the target material, and mechanism of residual stress generation is analyzed. It shows that isotropic hardening and kinematic hardening of the target material play a different role in residual stress generation. The obtained maximum compressive residual stress is mainly determined by residual yield stress, while the residual kinematic hardening is nearly unchanged when the coverage is increased. Further analyses indicate that the mechanisms of residual stress generation should be very different for the Johnson-Cook model and the model that includes kinematic hardening, even though these two kinds of models are reported to be able to well predict the shot peening induced residual stress. The gradient of the residual work hardening can be used for further evaluating mechanical properties of the SMATed cylindrical structure.

Strain hardening behavior and microstructure evolution of gradient-structured Cu-Al alloys with low stack fault energy

Nanocrystallization can significantly improve the strength and hardness of metallic materials, but usually sacrifice ductility due to low work hardening capability. Heterostructured materials are an emerging class of materials with superior performances, because of their outstanding work hardening capability. In this work, a type of heterostructured material, a gradient structured Cu-Al alloy, was produced by surface mechanical attrition treatment (SMAT) at liquid nitrogen temperature. After SMAT processing, the yield strength was increased to more than 1.5 times, and the ductility remained almost unchanged. In conjunction with hetero-deformation induced (HDI) hardening, stacking fault energy is another important factor to increase the strain hardening in the system. Low stacking fault energy increased the density of stacking fault, and led to a finer spacing of nano twins (∼5.4 nm) and higher dislocation storage (8 × 1013 m−2) in the SMATed Cu-Al alloy at the intermediate strain stage. A significant up-turn of strain-hardening rate was also induced by low stacking fault energy.

On the high cycle fatigue resistance of austenitic stainless steels with surface gradient microstructures: Effect of load ratio and associated residual stress modification

The effect of gradient microstructure generated by ultrasonic surface mechanical attrition treatment (SMAT) on the fatigue performance of an austenitic stainless steel has been evaluated in the context of localized and general plasticity by comparing two load ratios: fully reversed tension-compression (TC) RTC = -1 and tension-tension (TT) RTT = +0.1, respectively.After identical SMAT processing conditions, the fatigue limit was enhanced by +17% for RTC while it was reduced by -7% for RTT. Under RTC cyclic loading, self-heating of the specimens and sub-surface martensitic transformation occurred but not for RTT. The residual stress measurements have also revealed that while the stress gradient was smoothed after the RTC fatigue loading, it was completely reverted for the RTT one. In turns, the fatigue crack initiation sites and propagation were modified between the RTC and RTT loading conditions.Considering the stabilized surface residual stress after fatigue loading, the use of a Crossland criterion allowed to explain both the effects of load ratio and SMAT on the high cycle fatigue behavior of the stainless steel. It turns out that under the studied loading conditions the modifications of residual stress state can be considered as the primary factor governing the varying fatigue performances and the observed triggering at different initiation sites.

Dynamic Finite Element Analysis on Single Impact Plastic Deformation Behavior Induced by SMAT Process in 7075-T6 Aluminum Alloy

Surface mechanical attrition treatment (SMAT) is a method that enhances the mechanical properties of metallic materials by generating a thin nanostructured layer on the top surface. In this study, single-shot impact behavior was modeled for the 7075-T6 aluminum alloy to reach maximum values of equivalent stress, plastic strain, deformation depth, residual stress depth, and residual stress. Finite element simulations have been carried out to analyze the effect of selected parameters on stress and strains in the component. For simulating the SMAT process, a rigid sphere on a rectangular component is modeled using ANSYS/AUTODYN explicit dynamic solver. The plastic deformation process during SMAT was analyzed according to shot velocity and diameter with a dynamic explicit finite element method (FEM). The response surface methodology was used to evaluate the parametric results for the SMAT process. In addition, deformation behavior was evaluated after a single-shot impact according to the restitution coefficient.

Effect of Surface Mechanical Attrition Treatment on Micro-mechanical Properties of ZrCuAlNi Bulk Metallic Glass

In this work, surface mechanical attrition treatment (SMAT) was employed to rejuvenate ZrCuAlNi bulk metallic glass (BMG) plate. Differential scanning calorimetry (DSC), atomic force microscopy (AFM) and nanoindentation analyses were carried out to evaluate stored energy and micro-mechanical properties of treated BMGs. According to DSC results, 10 min SMAT process increased the stored energy of BMG plates up to 50%. AFM analysis showed that the structural rejuvenation occurred in the bulk of samples and just a slight rejuvenation gradient was detected from the front to the back side of BMG plates. Nanoindentation analysis indicated that the structural rejuvenation is consistent with anelastic strain induced under the SMAT process. It was also found that an optimum treatment time is needed for maximum rejuvenation in the BMGs. This event is due to the fact that the glassy structure is able to store a critical anelastic strain, which leads to a saturated condition in rejuvenation.

Effects of SMAT at cryogenic and room temperatures on the kink band and martensite formations with associated fatigue resistance in a β-metastable titanium alloy

Surface Mechanical Attrition Treatment (SMAT) has been carried out at cryogenic and room temperatures on a 5553 β-metastable Ti alloy to describe its effects on the modification of the microstructure and fatigue properties. The cryogenic temperature promoted the martensitic transformation and the width of the kink bands produced by SMAT. The kink bands formation was promoted by the high strain rates of the SMAT process. The samples SMATed at cryogenic temperature showed an increase in fatigue resistance, by about 8 % , compared to samples processed by SMAT at room temperature. This improvement was possibly due to a combination of several factors: compressive residual stresses, lower roughness, deeper formation of martensite and larger kink bands. On the contrary, the SMAT at room temperature did not provide any improvement in terms of fatigue compared to the polished condition. The large grain size provoked the appearance of subsurface crystallographic defects on which primary cracks initiated. This greatly limited the effectiveness of the reinforced surface layer produced by SMAT. • Kink bands generated by the high strain rates induced by SMAT. • A lower kink band density in the first μm of SMATed surfaces. • Deeper martensitic formation and lower roughness for cryogenic SMAT. • Increased fatigue resistance for SMAT at cryogenic temperature.

Investigations on the influence of surface mechanical attrition treatment on the corrosion behaviour of friction stir welded NiTi shape memory alloy

The surface mechanical attrition treatment (SMAT) was applied to friction stir welded NiTi shape memory alloy (SMA) as a post welding treatment to improve the corrosion properties of the weld. The influence of SMAT on corrosion behaviour of friction stir welded NiTi alloy was studied by employing electrochemical impedance spectroscopy and potentiodynamic polarization tests. The SMAT process has improved the corrosion properties of the welded NiTi alloy. Notably, the 1 h SMAT has shown the lowest corrosion rates and its oxide layer exhibited the highest resistance. The 1.15 h SMAT sample has exhibited a noblest breakdown potential of 1331 mV among other samples.

Effect of surface mechanical attrition treatment on the microstructure of cobalt-chromium-molybdenum biomedical alloy.

This research work describes the impact of the surface mechanical attrition treatment (SMAT) on the microstructure of cobalt-chromium-molybdenum (CoCrMo), a biomedical alloy commonly used for orthopedic applications. This surface treatment induces crystalline phases transformations characterized by X-ray diffraction (XRD) and selected area electron diffraction (SAED). The corresponding structural changes are observed from cross-section images obtained by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the SMAT process induces the martensitic transformation of the CoCrMo alloy (from γ-fcc phase to ε-hcp phase) related to an important grain refinement due to twinning and sliding.

Role of surface nanocrystallization on corrosion properties of low carbon steel during surface mechanical attrition treatment

Surface mechanical attrition treatment (SMAT) was carried out on low carbon steel (LCS) by varying ball size from 4 to 8 mm diameter. Present work studies the effect of ball size on the electrochemical behaviour of the LCS in 3.5 wt.% NaCl solution, using open circuit potential (OCP), impedance (EIS) and anodic polarization methods. The untreated LCS shows ~29 nm grain size, whereas after SMAT with 4 mm ball size exhibited remarkable reduction in grain size i.e., ~11 nm. Reduction in grain size was achieved due to the presence of highly densified mechanical twins after SMAT as well as the formation of dislocation tangles that rearrange themselves into nanocrystallites. These factors have a direct impact on the corrosion behaviour of SMATed LCS. The increase in corrosion potential (Ecorr) towards positive side and a reduction of 93% in corrosion current density (icorr) value were observed after SMAT using 4 mm balls as compared to the untreated LCS. Remarkable improvement in corrosion resistance was due to grain refinement after SMAT processing, hindrance of the corrosive ion, increase in the activity of charge carriers at the interface between solution and substrate, and reduction in surface roughness. Nanocrystalline surface after SMAT effectively hindered the chloride infiltration into the substrate and resisted pit formation, thus the corrosion performance is improved.

A superior strength-ductility combination in gradient structured Cu–Al–Zn alloys with proper stacking fault energy and processing time

This article aims to investigate the mechanical properties of the gradient structured (GS) Cu–Al–Zn alloys. To prepare the GS samples, three kinds of Cu–Al–Zn alloys with different stacking fault energies (SFEs) were processed by surface mechanical attrition treatment (SMAT) at cryogenic temperature. The results show that the Cu-5.5%Al-4.5%Zn alloy having the lowest SFE processed by SMAT for 5 min exhibits an optimized combination of strength and ductility. For both the initial annealed sample and the SMAT samples processed for the same processing time, uniform elongation (UE) and ultimate tensile strength (UTS) increase with decreasing SFE, whereas the yield strength (YS) is not sensitive to SFE. In the case of the same SFE, as the SMAT processing time increases, the YS and UTS of the GS alloy increase and the UE decrease. The optimized SMAT processing time can sufficiently refine the grains in the GS layer, which can increase the strength and maintain good ductility. Also, sufficient grain refinement promotes the better accumulation of geometrically necessary dislocations (GNDs), thus forming rather effective hetero-deformation induced (HDI) stress strengthening and HDI hardening to enhance strength while maintaining good ductility. The combination of low SFE and optimized SMAT processing time is beneficial to obtain an optimized combination of strength and ductility. Additionally, since the near-surface layer of the GS material is plastically deformed earlier than the sub-surface layer, the accumulation of GNDs at the interface between the two layers also contributes to HDI strengthening and HDI hardening to improve strength and ductility.

Literature review on the mechanical properties of materials after surface mechanical attrition treatment (SMAT)

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.

Effect of surface mechanical attrition on microstructure and mechanical properties of hypoeuctectoid steel

Effect of ultra-fine structure obtained by surface mechanical attrition treatment(SMAT) on microstructure, yield strength (YS), ultimate tensile strength (UTS) and microhardness of hypoeuctectoid steel have been studied in this paper. Surface alteration has been obtained by vibratory SMAT equipment with particular parameters for similar class of material. The SMAT has been carried out for different time periods such as 10, 20, 30 min. The pearlite and ferrite geometry present has been found intermixed after SMAT process. The microstructure shows a composite structure consisting of fiber/angular cementite particulates dispersed in a ferrite matrix. Thus, these structure obtained at 30 min of SMAT has significantly affected the mechanical properties. The SMAT affected layer has found to be 300μm which shows an increased Young’s modulus from 140 GPa to 246 GPa. The yield stress (YS) and ultimate tensile strength (UTS) has been increased about 6% and 22% , respectively. The surface microhardness of the material has been changed from 226±5 HV0.3 to 405±7 HV0.3 by SMAT, which is attributed to the grain refinement and dispersion of fine carbide particles within the matrix.

Surface mechanical attrition treatment of commercially cold rolled copper plate

Severe plastic deformation such as surface mechanical attrition treatment (SMAT) transfers surface layer of metallic material into ultra-fine-grain. In this work commercially cold rolled copper plate subjected to SMAT for different time 10, 20, 30, 60 and 120 min. Significant variation of crystallite size, lattice strain and stored energy along different crystallographic planes was estimated from X-ray diffraction (XRD) with initial orientation during the SMAT process. Through the SMAT process stored energy increased while lattice parameter decreases with treatment time. The corrosion behavior of SMAT copper were comparatively investigated by electrochemical methods in 5 wt% NaCl solution. Mechanical surface treatment processes have a great influence on the surface which increase surface activities consequently improve the corrosion resistance of metal. SMAT process enhance the corrosion resistance of copper surface resulting from oxide layer growth at the treated surface. Higher impedance and lower corrosion current were observed after SMAT. The hardness (Hv) increased with increasing SMAT time and tends to be stable after 30 min of treatment. The hardness and corrosion rate values were strongly related to the samples crystallographic planes orientation.

Experimental and Theoretical Investigation on Bistable Symmetric Shells Built by Locally Nanostructuring Isotropic Rectangular Plates

A new bistable shell with two symmetric configurations is proposed by using the nanotechnology, surface mechanical attrition treatment (SMAT), to locally treat a rectangular region. The impacts from randomly fast moving balls during the process induce nanotwins and mesh material grains into nanoscale on originally flat plates, which largely increase the material’s yield strength and elastic deformation capacity. Also, the plastic deformations accumulated from thousands of impacts may stretch the plate under the constraint from the untreated region, while inducing internal compressive forces in the processed region. The experiments show that, when the accumulated plastic deformations are large enough, the locally nanostructured plate may buckle transversely by the internal forces to hold two different stable configurations, resulting in the bistable feature. An analytical model is developed to predict the stable configurations, which is numerically verified and experimentally validated. The parameters, including the SMAT region, plate dimensions, and SMAT process, to design the stable configurations of the bistable shells are systematically studied experimentally, analytically, and numerically.

Discrete element simulation of surface mechanical attrition treatment with rough-surface sonotrode

Surface mechanical attrition treatment (SMAT) is a specialized cold working method that is used to induce compressive residual stresses and refine crystalline grains at the surface of metal components. This technique is increasingly employed in different industries, and the control and optimization of the method require fundamental understanding and accurate process modelling, in particularly detailed information regarding the shot-target interaction. This paper presents a Discrete Element Method (DEM) study of the shot dynamics with rough sonotrodes. These rough surfaces are created by grouping in a hexagonal packing of identical spheres. Different roughness values are obtained by varying the sphere diameter and spacing. The coefficient of restitution (CoR) between shot and target used in our DEM simulations was obtained from Finite Element Method (FEM) simulations of multiple shot-target impacts. The DEM results are analyzed after the SMAT process has reached the steady state. The relationships between surface roughness and the resulting impact angle and velocity distributions are investigated. Furthermore, based on a parametric study, we conducted correlation analyses between processing parameters and shot dynamics, and identified key conditions, using the mechanistic models. The proposed numerical method and findings of this study could be used to tailor the SMAT processes.

Improving mechanical properties for pure irons by local surface mechanical attrition treatment

ABSTRACTAfter a short-time surface mechanical attrition treatment process, a planar uneven structure was obtained on the surface of irons. The yield strength of the sample subjected to surface mechanical attrition treatment for 60 s is almost twice than that of the annealed sample, but the ductility is still well retained. The good combination of strength and ductility is mainly due to the extra strain hardening and the coexistence of soft and hard phases. The extra strain hardening delays the annihilation of dislocations and reduces the plastic instability, while the hard phase in the planar uneven structure suppresses the crack initiation, and the soft phase delays the crack propagation.

Effect of surface mechanical attrition treatment on corrosion fatigue behavior of AZ31B magnesium alloy

Surface mechanical attrition treatment (SMAT) is considered as an effective technology to influence fatigue and corrosion resistance as these properties are largely related to surface structure and property. Despite the increasing number of studies that report the effects of SMAT on separate fatigue or corrosion behaviors, the impact of SMAT on fatigue property under corrosive environment is left unexplored. In this paper, the corrosion fatigue properties of AZ31B magnesium alloy before and after SMAT process are investigated. Hydrogen evolution tests and potentiodynamic polarization tests are carried out to obtain the corrosion resistance, and it is found that SMAT promotes corrosion rate. The surface roughness of SMATed specimen also increases, which accelerates corrosion rate. In terms of fatigue properties, the fatigue life of SMATed specimen is found to be higher, in both air and 3% NaCl solution. And the larger the size of stainless steel balls used during processing SMAT specimens, the longer the fatigue life. Under 3% NaCl corrosive environment, the beneficial effects induced by SMAT process gradually emerge with increasing stress amplitude during fatigue tests. Reduced fatigue life of SMATed specimen under corrosive environment is attributed to roughened interface between deformed surface layer and bulk material. Nevertheless, the crack initiation sites for SMAT specimens are the same in both air and NaCl solution, all located at the subsurface area.