Papers by Keyword: SMAT

Abstract: Surface mechanical attrition treatment enhances the mechanical properties of metallic materials by inducing high strength layer on the top surface. In this study, multiple-shot impact behavior was modeled for the 7075-T6 aluminum alloy to achieve maximum magnitudes of equivalent stress, plastic strain, residual stress depth, and residual stress. Finite element simulations have been carried out to investigate the effect of selected framework on stress and strains in constituent. The plastic deformation process during SMAT was analyzed using ANSYS/AUTODYN explicit dynamic solver according to shot velocity and diameter with a dynamic explicit finite element method (FEM). Deformation behavior was evaluated after multiple-shot impact.

Abstract: Surface mechanical attrition treatment is a pre-stressing process that enhances the lifespan of mechanical parts. The experimental evaluation of SMAT parameters is not only very complex but also costly. In this study, the single impact behavior of commercially pure titanium and Ti6Al4V alloys is analyzed using the finite element method. For simulating the single-shot impact process, a rigid sphere on a rectangular component is modeled using ANSYS/AUTODYN explicit dynamic solver. The effects of single-shot impact on the induced compressive residual stress and plastic deformation were investigated. Besides, the change in shot velocity after a single shot was revealed by calculating the restitution coefficient, and its relation to plastic deformation was investigated.

Abstract: Surface mechanical attrition treatment (SMAT) has been recognized as a potential surface treatment for improving the strength and the wear resistance of magnesium (Mg) and its alloy. However, this treatment potentially increases the degradation rate of these particular materials. Therefore, additional treatments might be needed to overcome such limitation of the SMAT. In this research, the influence of polishing on the degradation of the SMAT-processed AZ31B Mg alloy was investigated. Weight losses measurement and pH monitoring were carried out to determine degradation behavior of the Mg alloy during an immersion test in 3.5 wt.% NaCl solution. The results showed that the degradability of the Mg alloy decreased with the application of polishing to remove the rough surface layer and the Fe contaminant on the material surface generated by the SMAT. Based on all the findings in this work, it can be concluded that the SMAT is indeed a promising technique for lowering the degradability of AZ31B Mg alloy, but such an advantage was masked by the increased roughness and contamination of the alloy surface with this treatment.

Abstract: Surface mechanical attrition treatment (SMAT) has so far been used as a technique for improving mechanical and tribological properties of magnesium and its alloys. However, the effects of the SMAT on corrosion and degradability of these materials are still rarely reported in open literature. In this research, the degradation behavior of AZ31B magnesium alloy after receiving the SMAT was characterized. The degradation behavior of the Mg alloy was determined from the weight losses after an immersion test for 24 h in 3.5 wt.% NaCl solution. During the test, the pH of the solution was also monitored. The results obviously showed higher corrosion rates of the Mg alloy that had been treated by using the SMAT. Interestingly, the degradation rate of the Mg alloy decreased once a longer duration of SMAT was applied. Meanwhile, the pH of NaCl solution increased up to 12 and 13.9 once the non-treated and the SMAT specimens were immersed into the solution, respectively. In addition, the energy dispersive X-ray spectroscopy (EDS) analysis confirmed the presence of corrosion products in all the Mg samples that were similar to those revealed in the literature.

Abstract: A pollution-free nanocrystalline layer was prepared on the surface of Ti6Al4V by surface mechanical attrition treatment (SMAT). The nanocrystalline samples were vacuum annealed at various temperatures and for different periods of time. The microstructure and thermal stability were characterized by X-ray (XRD), scanning electron microscopy (SEM) and, transmission electron microscopy (TEM). The results showed that the nanocrystalline Ti6Al4V presented a satisfactory thermal stability with the annealed temperature below 650°C. The critical growth temperature for nanocrystalline Ti6Al4V is 100°C higher than that for pure titanium.

Abstract: Boronizing is a surface thermochemical treatment in which boron atoms are made to diffuse into a metallic surface at high temperatures. A nano-crystalline surface with larger defect density assists in enhancing the diffusion rate even at low temperatures. In the present work Ni-Cr-Mo steel is subjected to a surface mechanical attrition treatment (SMAT) to activate the surface with nanocrystalline structures and crystal defects. Subsequently the samples were boronized at low temperature regime (400°C - 600°C) for 5 hours using a pack boronizing technique. The microstructure, chemical analysis and hardness of borided layers were investigated using optical microscope, SEM – EDX and Microvicker’s Hardness Tester. The SMAT treated samples showed severe plastic deformation of the surface, nano-structured grains (10-30 nm) and larger defect density illustrating mechanically activated surface for diffusion. The boronizing had clearly demonstrated the diffusion of boron even at 400°C. The thickness of diffused layer was found to be about 20 µm at 400°C and 50 µm at 600°C for SMAT samples while the untreated samples showed practically no diffusion at 400°C and 12 µm at 600°C. The SEM-EDX results had confirmed the presence of boron at the diffused layer; however the hardness was found to be low. A maximum of 650 HV_0.3 was achieved by low temperature boronizing of SMAT treated samples.

Abstract: Hydroxyapatite (HAP) and 58S Bioactive Glasses (BG) coatings are successfully synthesized by Electrophoretic Deposition (EPD) on Ti6Al4V alloy subjected to Surface Mechanical Attrition Treatment (SMAT). This process uses steel balls impacts on the Ti6Al4V surface to improve its mechanical properties. However when the Ti6Al4V substrate is treated by SMAT the industrial plasma spray technique is not efficient to obtain adherent HAP coatings. This problem is mainly related to the modifications of the Ti6Al4V surface topography due to the SMAT process. Therefore, in this work we demonstrate that EPD offers an efficient solution to solve this technical problem. Indeed we obtain a homogeneous and adherent HAP coating on the SMATed Ti6Al4V surface from a suspension of nanoparticles in ethanol. Moreover EPD is successfully employed to produce a 58S BG coating on the SMATed Ti6Al4V surface. Scanning Electron Microscopy (SEM) associated to Energy Dispersive X-Ray Spectroscopy (EDXS) reveals that the coatings obtained by EPD are adherent and compact without alteration of their chemical composition.

Abstract: Surface mechanical attrition treatment (SMAT) is an excellent method to get nanocrystalline and nanotwinned ultrafine crystalline steels from coarse-grained AISI 304 stainless steel. Due to their outstanding mechanical properties, they both appear to be relevant candidates for ballistic protection of marine engineering. Comparing their ballistic performance against coarse-grained steel, as well as identifying the effect of the hybridization with a carbon fiber–epoxy composite layer have been done by Jaime Frontan et al. Hybridization is proposed as a way to improve the nanocrystalline brittle properties in a similar way as is done with ceramics in other protection systems. Dur to the limit of experimental equipment, there are many results which are hardly got. In this paper, a numerical method with Johnson–Cook flow stress model, user material subroutine VUMAT and surface-based cohesive behaviour is presented.

Abstract: In this paper, the effects of Surface Mechanical Attrition Treatment on the high-temperature oxidation of AISI 316L austenitic stainless steel are investigated. Samples treated with different conditions were oxidized at 650°C in order to study the effect of this type of nanocrystallisation on the oxidation resistance of the alloy concerned. X-ray diffraction and in-situ Raman spectroscopy were used to identify the oxides formed at the surface. The results indicate the presence of hematite and chromium oxides. Experimental results obtained by Raman spectroscopy were also used to study the stress evolution in Cr₂O₃ films during isothermal conditions.

Abstract: In this paper the residual stress states induced by conventional shot peening (SP) and surface mechanical attrition treatment (SMAT) are compared. The treated part correspond to plates made of a titanium alloy. Different intensities of these two mechanical treatments are first considered: their influence on the surface characteristics (roughness, hardness...) is studied. These experimental data are then used to develop a model for the residual stress profiles with dimensional analysis, Experimental and analytical approaches are then discussed.