Fretting fatigue of laser shock peened Ti–6Al–4V

doi:10.1016/j.triboint.2009.04.014

Tribology International

Volume 42, Issue 9, September 2009, Pages 1324-1329

https://doi.org/10.1016/j.triboint.2009.04.014 Get rights and content

Abstract

The objective of this paper is to examine fretting fatigue of laser shock peened (LSP) titanium to quantify the influence of LSP on fretting fatigue life. Contact conditions such as loads and pad geometry are chosen to generate fretting fatigue stresses similar to those occurring in blade/disk contacts in gas turbine engines. LSP treated specimens attained 5-, 10- and 25-fold increase in lives compared to untreated specimens. Metallography of the contact area and fractographic analysis of worn pads detail the fretting behavior of LSP treated specimens.

Introduction

Laser shock peening is a surface treatment method in which a high power, pulsed laser beam is used to impart compressive residual stresses on the surface. For application on metals, an absorbent coating followed by a transparent overlay (transparent to laser energy) is applied to the surface to be treated. Upon irradiating the surface with a pulsed laser, the absorbent coating rapidly vaporizes to a plasma layer and then expands, resulting in a high amplitude short duration pressure pulse; a portion of the energy propagates as a shock wave into the metal, and the use of transparent overlay significantly increase the shock wave intensity. When the pressure of the shock wave exceeds the dynamic yield strength of the metal plastic deformation occurs, imparting residual stresses to the surface. Detailed description of the LSP process [1], [2] and its effect on metal properties and microstructure [1] is available in the literature. The following describes experiments aimed at quantifying the effect of LSP on fretting fatigue behavior of Ti–6Al–4V subjected to contact loading that generates stresses similar to those occurring in gas turbine blade/disk contacts.

Section snippets

Experimental details

The specimen and pads are machined from a forged plate of alpha plus beta ( $α + β$ ) processed Ti–6Al–4V alloy with 60 $%$ primary alpha and a 40 $%$ lamellar transformed beta microstructure. Fig. 1 shows the microstructure of Ti–6Al–4V alloy identifying the alpha and beta grains [3]; material properties of the alloy are listed in Table 1 [4].

The fretting contact consisted of a nominally flat specimen in contact with a flat indenter with rounded edges. Both the flat length and radius of the rounded edges

Results and discussion

Load conditions for the experiments were chosen based on available test data for untreated Ti–6Al–4V [7] that could be used as a baseline to estimate the improvement in fretting fatigue lives due to LSP. The contact and fracture surfaces were examined using optical microscopy and SEM to understand the fretting behavior of LSP treated specimens. These observations are discussed in the context of mechanics based life prediction.

Conclusions

Fretting fatigue experiments were conducted using LSP treated Ti–6Al–4V. At the stress levels studied 5-, 10- and 25-fold increase in lives for LSP treated specimens were observed when compared to untreated specimens. While LSP treatment increases fatigue life it does not mitigate the formation of fretting cracks. Metallography of the LSP treated pad surface revealed the existence of an array of contact spots and the fretting damage was distributed throughout the contact surface. Contact

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Fracture mechanics based fretting fatigue life predictions in Ti–6Al–4V
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D.B. Garcia et al.
Fractographic investigation of fretting fatigue cracks in Ti–6Al–4V
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Preventing fatigue failures with laser peening
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There are more references available in the full text version of this article.

Cited by (50)

Effect of laser shock peening on fretting wear behaviour of AISI 304 stainless alloy
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Unlike many other surface treatment techniques, such as shot peening (SP), low plasticity burnishing (LPB), ultrasonic surface rolling process (USRP), ultrasonic nanocrystal surface modification (UNSM), laser shock peening (LSP) is a non-contact process. This means that LSP achieves surface modification without direct physical contact, thereby eliminating the risk of media contamination and undesired wear on the peening equipment. As a surface hardening technology, LSP tends to produce a hardened layer with a high gradient of residual stress (RS) in the near-surface, significantly enhancing wear resistance. The well-known wear theories applied for numerical prediction, whether Archard model or dissipated frictional-energy model, contain a multiplier for contact pressure and relative slip amplitude $(p \cdot ds)$ or shear stress and relative slip amplitude $(q \cdot ds)$ , respectively. These multipliers are sensitive to the mechanical properties near the surface. Additionally, the wear profile is governed not only by the wear effect but also by the deformation of materials. Therefore, to accurately evaluate the wear performance for surface-hardened materials, the influence of RS is hard to be overlooked. In this work, the finite element method (FEM) is utilised to construct a 3D numerical model, which ignores and considers RS, for both as-received and LSP-treated samples. Two distinct RS distributions induced by different scanning strategies (one- and five-time), are introduced in the finite element (FE) model. The numerical simulation results are then compared with the experimental data to verify the accuracy of the fretting wear model built in this study. On this basis, the impact of different RS distributions on fretting wear characteristics, including wear profile and volume, is extensively investigated. The findings reveal that higher amplitude RS can reduce the degree of fretting wear to a greater extent, highlighting the beneficial role of RS in enhancing wear resistance. Furthermore, the numerical models incorporating RS demonstrate superior predictive accuracy compared to those that omit RS. This naturally underscores the importance of integrating RS in numerical simulations of LSP and other surface-hardened materials.
Effect of laser shock peening without protective coating on surface integrity of titanium-based carbon-fibre/epoxy laminates
2023, Optics and Laser Technology
The failure of fibre metal laminates originates from the surface of outer metal layer while the multi-layer structure makes it difficult to achieve surface strengthening. This paper investigates the effect of laser shock peening without protective coating (LSPwC) on the surface integrity of titanium-based carbon-fibre/epoxy laminates (Ti-CF FMLs). The experimental results show that LSPwC produced a hardened layer and compressive residual stress layer in the Ti CF FMLs without interface damage. The numerical results indicate that the temperature rise of the interface between titanium and CFRP is less than 2 °C during LSPwC and the cooling rate of the layer affected by phase transition temperature exceeds 10⁶ °C/s. The microstructures on the topmost surface are characterized as ultra-fine martensite lamellar grains due to ultrafast solidification of liquid titanium. The in-depth microstructures in the Ti-CF FMLs after LSPwC are characterized as geometrically necessary dislocation interface structures, dislocation cells and multidirectional twins. This work demonstrates a promising method for the surface strengthening of fibre metal laminates.
Fretting fatigue life improvement of nickel-based superalloy GH4169 dovetail slots by deflecting abrasive waterjet peening process
2023, International Journal of Fatigue
The proposed deflecting abrasive waterjet peening (DAWJP) process can be used for surface strengthening of metallic parts with confined space features, which has great potential to improve the surface integrity and fretting fatigue (FF) life of dovetail slots in turbine discs. In this paper, the nickel-based superalloy GH4169 dovetail slot is strengthened by DAWJP and shot peening (SP), and the effects of DAWJP and SP on surface integrity and FF performance of the dovetail slot are investigated. First, the DAWJP with three different processes (water pressure of 205 MPa, traverse speed of 5 mm/s, standoff distance of 2 mm, and path interval of 0.05, 0.1, and 0.15 mm) and the SP with one process (peening intensity of 0.25 mmA with coverage of 100%) were conducted on the contour surface of the dovetail slot. The surface integrity of the dovetail slot before and after the DAWJP and SP treatment was investigated, including microstructure, surface roughness and microscopic morphology, microhardness, and residual stress. Results showed that the dovetail slot treated by the DAWJP with different path intervals formed a plastic deformation layer with a thickness of 22–43 μm and surface roughness Ra and Sa of 0.391–0.501 μm and 0.763–0.907 μm. The surface microhardness and CRS of the DAWJP-treated dovetail slot were approximately 541–591 HV and 1005–1169 MPa, 16%–27% and 178%–224% times higher than the as-received dovetail slot. The SP-treated dovetail slot produced relatively large surface roughness, slight plastic deformation, and low microhardness and CRS compared with the DAWJP-treated dovetail slot. Finally, FF tests were carried out to study the FF behavior of the dovetail slot before and after DAWJP and SP treatment. The FF lives of the dovetail slot treated by DAWJP were 4.82 and 3.91 times that of the as-received dovetail slot at room temperature and a high temperature of 650 °C. In contrast, the FF lives of the SP-treated dovetail slot were 2.96 and 1.96 times that of the as-received specimen at room temperature and a high temperature of 650 °C, which verified that DAWJP has a more significant effect on improving the FF life of dovetail slots than the SP treatment used for comparison. The FF fracture and fretting contact surface and its cross-sectional microstructure were examined, and the results showed that the extreme grain refinement, large CRS, and high work-hardening induced by DAWJP could be the key to greatly improving the FF life of dovetail slots. This work takes the lead in the surface treatment of dovetail slots through the proposed DAWJP process, which provides a feasible reference plan for effectively and economically improving the FF resistance of dovetail slots in turbine discs.
Designing a gradient structure in a Ni-based superalloy to improve fretting fatigue resistance at elevated temperatures through an ultrasonic surface rolling process
2023, International Journal of Fatigue
In this study, a gradient nanostructured GH4169 superalloy was prepared by ultrasonic surface rolling process (USRP), and the fretting fatigue resistance was investigated at elevated temperatures. After USRP, a high density of deformation twins, stacking faults and dislocations as well as precipitates were observed in the surface of the gradient nanostructured GH4169 superalloy when examined using transmission electron microscopy. Factor separation analysis was carried out to determine the leading factor for the improvement of the fretting fatigue properties of GH4169 at elevated temperatures, and the compressive residual stress was found to be the leading factor. The mechanism was determined to be dislocation movement that can be pinned by deformation twins, stacking faults and precipitates and, thus, is able to stabilize the compressive residual stress at elevated temperatures. As a result, the USRP-treated GH4169 with gradient nanostructure was found to have the highest fretting fatigue resistance at elevated temperatures.
Analysis of the thermal stability of residual stresses induced in Ti-6Al-4 V by high density LSP treatments
2023, Journal of Alloys and Compounds
Laser Shock Processing (LSP) is increasingly applied as an effective technology for the improvement mechanical and surface properties of metallic materials for different types of components, mostly as a means of enhancement of their fatigue life behavior. As reported in previous contributions, a main effect resulting from the application of the LSP technique consists in the generation of relatively deep compression residual stresses fields allowing an improved mechanical behavior. In this paper, the special case of Ti-6Al-4 V alloy is considered with specific consideration of the microstructural changes and residual stresses fields justifying those macroscopic effects. In particular, the effect of the application of different typical LSP intensities on the microstructure and residual stresses fields introduced in this material and their possible correlation to the associated surface effects are analyzed. Emphasis is placed on the study of the thermal stability of these fields after an aging heat treatment at typical high temperature working conditions. The results show that, according to expectations, a certain level of residual stresses and dislocation density remains after in-work thermal aging. The combination of different material characterization techniques has made possible to obtain a correlated set of results highlighting the complementarity of different scale approaches from surface (X-ray) to bulk (neutrons) methods. A model based on the evolution of immobile dislocation density is proposed to rationalize the distribution of dislocation densities, pointing out that plastic deformation is retained. The results clearly show such material improvement stability under typical heavy-duty conditions, thus endorsing the use of the LSP for Ti-6Al-4 V as a suitable technology for industrial applications in relatively high temperature conditions.
The effect of laser shock peening on surface integrity and high and very high cycle fatigue properties of 2024-T351 aluminum alloy
2022, Optics and Laser Technology
Citation Excerpt :
The result showed that LSP treatment provides much greater fretting fatigue resistance than traditional shot peening (SP) alone due to the much deeper compressive zone. S. Srinivasan [22] also found that compared with untreated specimens, the LSP-treated specimens could increase fatigue life obviously. However, Kevin K. Liu's [23] research results showed that the fretting fatigue life improvements for LSP were less than SP, especially when the applied stress is low.
Laser shock peening (LSP) as an emerging surface peening technology that is widely used in aerospace manufacturing. The effect of laser shock peening on surface integrity and high cycle fatigue (HCF) and very high cycle fatigue (VHCF) properties of 2024-T351 aluminum alloy was investigated in this study. Accordingly, the surface roughness, surface topography, microstructural, microhardness and residual stress of specimens treated with two different LSP pulse energy levels (10 J and 20 J) were analyzed. Additionally, the HCF and VHCF test was performed by ultrasonic fatigue test system. The results showed that surface roughness R_a value and microhardness of LSP treated specimens increased by a maximum of 89.37% and 16.3% comparing to the untreated specimen, respectively. X-ray diffraction analysis also showed that subgrain sizes were refined to the nanoscale. Furthermore, high-level compressive residual stresses (the maximum value about −210 MPa with 700 μm thickness) were introduced to the surface layer of the specimens. The S-N curve results showed that LSP treatment reduced the fatigue life of specimens, and the higher the laser pulse energy, the more obvious the effect of reduction. The fatigue fracture of specimens was analyzed via scanning electron microscope and residual stress distribution map. It is observed that fatigue cracks are predominantly initiated at fractured secondary phase particle locations in a VHCF range for untreated specimens. However, for LSP specimens, surface and internal crack initiation mechanisms were both observed. Under low and intermediate stress levels, the tensile residual stresses (which coexists with the compressive residual stresses) initiated fatigue cracks from the interior of the specimens; under high-stress levels, fatigue cracks were initiated at the material surface.

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Fretting fatigue of laser shock peened Ti–6Al–4V

Abstract

Introduction

Section snippets

Experimental details

Results and discussion

Conclusions

International Journal of Fatigue

Engineering Fracture Mechanics

Engineering Failure Analysis

Preventing fatigue failures with laser peening

The AMPTIAC Quarterly