Showing papers on "Peening published in 2014"

Laser Peening Process and Its Impact on Materials Properties in Comparison with Shot Peening and Ultrasonic Impact Peening

Abstract: The laser shock peening (LSP) process using a Q-switched pulsed laser beam for surface modification has been reviewed. The development of the LSP technique and its numerous advantages over the conventional shot peening (SP) such as better surface finish, higher depths of residual stress and uniform distribution of intensity were discussed. Similar comparison with ultrasonic impact peening (UIP)/ultrasonic shot peening (USP) was incorporated, when possible. The generation of shock waves, processing parameters, and characterization of LSP treated specimens were described. Special attention was given to the influence of LSP process parameters on residual stress profiles, material properties and structures. Based on the studies so far, more fundamental understanding is still needed when selecting optimized LSP processing parameters and substrate conditions. A summary of the parametric studies of LSP on different materials has been presented. Furthermore, enhancements in the surface micro and nanohardness, elastic modulus, tensile yield strength and refinement of microstructure which translates to increased fatigue life, fretting fatigue life, stress corrosion cracking (SCC) and corrosion resistance were addressed. However, research gaps related to the inconsistencies in the literature were identified. Current status, developments and challenges of the LSP technique were discussed.

Experiment investigation of laser shock peening on TC6 titanium alloy to improve high cycle fatigue performance

Abstract: Laser shock peening (LSP) is an innovative surface treatment technique, and can significantly improve the fatigue performance of metallic components. In this paper, the objective of this work was to improve the fatigue resistance of TC6 titanium alloy by laser shock peening. Firstly, the effects on the microstructure and mechanical properties with different LSP impacts were investigated, which were observed and measured by X-ray diffraction (XRD), transmission electron microscope (TEM), residual stress tester and microhardness tester. Specially, nanostructure was detected in the laser-peened surface layer with multiple LSP impacts. Whereafter, a better parameter was chosen to be applied on the standard vibration fatigue specimens. Via the high-cycle vibration fatigue tests, the high cycle fatigue limits of the specimens without and with LSP were obtained and compared. The fatigue results demonstrate that LSP can effectively improve the fatigue limit of TC6 titanium alloy. The strengthening mechanism was indicated by analyzing the effects on the microstructure and mechanical properties comprehensively.

Effect study and application to improve high cycle fatigue resistance of TC11 titanium alloy by laser shock peening with multiple impacts

Abstract: Laser shock peening (LSP) is an effective surface treatment for improving fatigue resistance of metallic materials, in which high-amplitude beneficial residual stresses and structure changes can be produced. In aero-engines, the compressor blade made of TC11 titanium alloy was prone to result in high cycle fatigue (HCF) failure. The aim of this paper was to utilize LSP with befitting parameters to improve the HCF performance of TC11 titanium alloy. Firstly, the microstructure and mechanical properties of TC11 titanium alloy with different LSP impacts were observed and measured via transmission electron microscope (TEM), residual stress tester and microhardness tester. High-density dislocations and nanostructure were observed in the surface layer. High-amplitude compressive residual stresses were induced and microhardness was remarkably improved. According to the effects, a set of LSP parameters with three LSP impacts was confirmed and applied on standard vibration specimens. Vibration fatigue tests were conducted to validate the strengthening effect on HCF strength. The fracture mechanism was analyzed by fracture analysis. The strengthening mechanism of LSP was indicated by establishing the relationship between fatigue characteristics and effects on residual stress and microstructural changes.

Ultrahigh dense and gradient nano-precipitates generated by warm laser shock peening for combination of high strength and ductility

Abstract: Nanocrystalline materials generated by severe plastic deformation often come with high strength but low ductility due to the inability to accumulate dislocations and thus the low work hardening rate. In this study, a unique high strain rate deformation process – warm laser shock peening (WLSP) – is studied to generate extremely high-density nano-precipitates in precipitation hardenable alloy. Aluminum alloy (AA) 7075 was selected to evaluate the generation of ultra-high-density precipitates by WLSP and the effects on the strength and ductility. WLSP integrates the advantages of laser shock peening (LSP), dynamic strain aging (DSA) and dynamic precipitation (DP). The nanoscale precipitate particles generated by WLSP effectively block dislocations and thus increase the material strength. The precipitate–dislocation interaction has been observed by high resolution TEM (HR-TEM) and modeled by the multiscale discrete dislocation dynamic (MDDD) model. It has been demonstrated that compared with room temperature LSP, WLSP can improve material strength by 32.3% without compromising the ductility, in that elongation remains 20%. These ultra-high-density nano-precipitates greatly improve dislocation accumulation capacity and thus effectively increase ductility.

Investigating the effects of bulk and surface severe plastic deformation on the fatigue, corrosion behaviour and corrosion fatigue of AA5083

Abstract: This is a comparative study on the effects of bulk plastic deformation and surface-induced plastic deformation on the fatigue, corrosion behaviour and corrosion fatigue of AA5083. Bulk severe plastic deformation was performed through rotary swaging, whereas surface-induced plastic deformation was conducted by applying shot peening and ball-burnishing. Surface and near-surface properties such as surface topography, microhardness and residual compressive stresses were documented. In comparison to the as-received reference condition, results of potentiodyanmic polarization referred to a better corrosion resistance of the rotary swaged material, while both shot peening and ball-burnishing led to deterioration in corrosion resistance. It was found that, pitting corrosion occurred around Fe-rich intermetallic particles. Ball-burnishing led to superior fatigue performance in air and under corrosive environment in comparison to other investigated conditions.

Effect of laser shock peening on the mechanical properties of a near-α titanium alloy

Abstract: Laser shock peening (LSP) or Laser shock processing is a novel surface treatment technique for strengthening metal materials. In this work, several investigations were performed to evaluate the effect of LSP on some mechanical properties of a near-α titanium alloy Ti834. Micro-hardness measurements of the untreated and LSP treated specimens were carried out by using a Vickers indenter. The depth profiles of subsurface micro-hardness of the shocked region were determined through the electro-polishing material removal in steps of 0.1 mm. It is observed that the micro-hardness of Ti834 alloy can be improved by LSP, and repeated shocks have a very beneficial effect on surface hardening. Residual stress distribution as a function of depth was determined by X-ray diffraction (XRD) with the sin 2 ψ method. The high-cycle fatigue performance of the alloy was investigated and the fractographs of fatigue specimens were observed by SEM. Results reveal that the high-cycle fatigue life of Ti834 alloy increases after laser shock peening due to the introduction of compressive stress which can delay the initiation and growth of the fatigue crack.

Laser shock peening and mechanical shot peening processes applicable for the surface treatment of technical grade ceramics: A review:

Abstract: Laser shock peening and conventional mechanical shot peening are both comparable processes generally applicable to surface treat various metals and alloys. Commercial advantages offered by the laser systems such as flexibility, deep penetration of laser-induced shocks with precise control of the thermal pulses, shorter process times, high speeds, accuracy and aesthetics are attractive in comparison with the mechanical shot peening technique. Laser shock peening in the recent years has proved to be successful with steels, aluminium and titanium surfaces and metallic alloys in general. Nevertheless, minimal research has been conducted on laser shock peening and mechanical shot peening of technical grade ceramics. This article presents an update of the theory and to-date relevant literature within the two subject areas, as well as a comparison and a contrast between the mechanical and laser shock peening techniques. In addition, various gaps in knowledge are identified to propose further research for the development of both the techniques applicable to the surface treatment of technical grade ceramics.

Review of Residual Stress Modification Techniques for Extending the Fatigue Life of Metallic Aircraft Components

Abstract: A major challenge for the aircraft industry in the future will be the development of effective strategies for maintaining and extending the service life of aging aircraft fleet. In this context, residual-stress-based approaches for extending the fatigue life of aircraft components are believed to have great potential for providing cost-effective solutions. This paper reviews residual-stress-based life extension techniques and published work on the use of these techniques in aerospace applications. The techniques reviewed include cold expansion, shot peening, laser shock peening, deep rolling, and heating. Comparisons of the various techniques with regard to current applications and limitations are given.

Effect of Ultrasonic Shot Peening on Microstructure and Mechanical Properties of High-Nitrogen Austenitic Stainless Steel

Abstract: The effect of ultrasonic shot peening (USSP) was studied on microstructural modification and mechanical properties such as microhardness, yield strength, tensile strength, and low cycle fatigue (LCF) life of a nitrogen stabilized austenitic stainless steel, at room temperature. There was grain refinement up to nano scale in surface region of the shot peened specimens and the microhardness was increased markedly up to the depth of approximately 100 µm. There was insignificant increase in yield and tensile strength, but drastic reduction in LCF life, particularly at low strain amplitude, from USSP. The nominal increase in yield and tensile strength was due to grain refinement in the surface region and drastic fall in LCF life was due to surface cracking resulting from USSP.

Influence of Surface Anomalies Following Hole Making Operations on the Fatigue Performance for a Nickel-Based Superalloy

Abstract: Aero-engine manufacturers are continuously striving to improve component performance and reliability while seeking to increase the efficiency of manufacturing to reduce costs. Efficiency gains by using higher rates of material removal, however, can be counterproductive if they give rise to surface anomalies that distort the material microstructure and reduce the resistance of the material to fatigue crack nucleation. This paper investigates the effect of hole making processes and parameters on surface integrity and the initiation of cracks from low-cycle fatigue (LCF). It reports the dependence of elevated temperature (600 degrees C) low-cycle fatigue performance of nickel alloy RR1000 from surfaces produced from hole making and subsequent surface conditioning. As-machined surfaces include a reference "damage-free" surface, and two distorted microstructures: (i) a white layer, produced to a depth of 5 and 10 mu m and (ii) a distorted gamma prime (gamma') structure, produced to a depth of 10 and 15 mu m. The effect of shot peening damage-free and 10 mu m deep white layer surfaces was also evaluated. It was found that the presence of white layer significantly reduced fatigue performance compared with that shown by the damage-free surface, regardless of whether the white layer was subsequently shot peened or not. In contrast, surfaces showing distorted gamma' structures produced much less debit in fatigue life and only from a depth of 15 mu m. These results have been rationalized from an examination of fracture surfaces and from measurement of residual stresses before and after fatigue testing. This research is of particular importance as it is among the few reports that quantify the effect of different levels of work piece surface integrity on the fatigue life of a nickel-based superalloy that has been developed for critical rotating components in aero-engine applications.

Influence of severe shot peening on wear behaviour of an aluminium alloy

Abstract: Recent developments in shot peening demonstrate that it can be applied using unconventional parameters in order to obtain nanocrystals on a thin surface layer of the treated material. These microstructural modifications have shown to be able to induce superior fatigue and corrosion properties, but still few data are available about their effect on wear behaviour of the materials. In this study, four series of Al 6063 alloy specimens, as-received, conventionally shot peened, severely shot peened and severely shot peened followed by a slight mechanical grinding are subjected to block on ring wear tests with lubrication, according to ASTM G77 standard. The results evidence the significant role played by the applied shot peening treatments on wear behaviour of the 6063 aluminium alloy with respect to the as-received not peened material. The important effect of the surface roughness is also highlighted. The data are discussed on the basis of roughness, surface layer microstructure, microhardness trends and the wear marks observed by means of scanning electron microscopy.