Effects Of Laser Peening Research Articles

Effect of laser peening and shot peening on fatigue striations during FCGR study of Ti6Al4V

The fatigue life of steam turbine blades is enhanced by subjecting its fir tree blade root section to mechanical treatments like shot peening and laser peening to introduce compressive stresses in the surface layers. In the case of higher power rated steam turbines, light alloys such as Ti6Al4V are now being adopted in the last stage blades since their exit diameters are very large and hence it is not technically possible to use steels for these machines due to the enormous stresses that would be experienced at the blade roots. This paper studies the effect of shot peening and laser peening on the fatigue crack growth of Ti6Al4V alloy at a stress ratio R of 0.1 and the changes observed in the fracture microstructure during the fatigue crack growth (FCGR). In specific, study of the striations developed during the FCGR on the fracture surface at regular intervals of crack movement have been recorded; an attempt has been made to correlate the striation spacing with crack front growth. It is observed that the fatigue life in the initial stages of FCGR testing is affected by the shot peening effect whereas it is more affected by laser peening effect at higher values of delta K (ΔK). The effect of closure is seen in both the shot peened and laser peened samples to different degrees.

Effects of Warm Laser Peening on Thermal Stability and High Temperature Mechanical Properties of A356 Alloy

To study the effects of warm laser peening (WLP) on the thermal stability and mechanical properties of A356 alloy, the samples were treated by WLP using a Nd:YAG solid-state laser and temperature control device. The residual stress, micro-hardness and microstructures of samples treated by WLP were observed. The result shows that the temperature significantly affects the strengthening effect of laser peening (LP). The residual stress induced by WLP decreases with the increasing temperature. The micro-hardness and dislocation density increase first, and then decrease with the increases of temperature. The grain refinement degree of the samples treated by WLP is much higher than that of LP. In addition, after aging for 100 min at 220 °C, the samples treated by LP and WLP were comparatively investigated in thermal stability. Obviously, the residual compressive stress, micro-hardness and microstructure induced by WLP present a better thermal stability property than that of LP. The residual stress and micro-hardness of WLP samples are obviously improved, and the increasing degrees are 23.31% and 19.70%, respectively. The dislocation density remains at a high level, while the grains are still in fine crystalline state.

Effect of Laser Peening on Improving Fatigue Strength of Welded Rib of High-Strength Steel

Effect of Laser Peening on Improving Fatigue Strength of Welded Rib of High-Strength Steel

Verification of Effect of Laser Peening for Fatigue Crack Propagation in Friction Stir Welded Joints by Laminography

Verification of Effect of Laser Peening for Fatigue Crack Propagation in Friction Stir Welded Joints by Laminography

Effect of laser peening with different energies on fatigue fracture evolution of 6061-T6 aluminum alloy

To deeply understand the effect of laser peening (LP) with different laser pulse energies on 6061-T6 aluminum alloy, the fatigue fracture morphologies evolution process at various fatigue crack growth (FCG) stages and the corresponding strengthen mechanism were investigated. At the initial stage of FCG, more fatigue micro-cliffs were found after LP, while the fatigue striation spacing simultaneously reduced. A “stop-continue” phenomenon of crack propagation was discovered for laser peened samples. The fatigue striation spacing at the middle stage of FCG increased significantly while compared with that at the initial stage, in addition, the fatigue striation spacing decreased with an increase in laser pulse energy. Fracture morphologies in transition region of laser peened samples exhibit a mixing fracture characteristic of striations and dimples. The laser peened sample with laser pulse energy of 7J presents more circuitous growing paths. Due to the complex stress state induced by LP, dimples with different sizes appeared in the final fracture region.

Effects of laser shock peening on microstructure and residual stress evolution in Ti–45Al–2Cr–2Nb–0.2B alloy

Laser peening is a novel surface treatment technique for improving the mechanical properties of metal parts' surface. To investigate and evaluate the effect of laser peening on the microstructural changes, texture evolution, and residual stress distribution changes, laser peening experiment was undertaken using Nd:YAG laser system with the pulse–width of 20ns and max pulse–energy of 9J. Micro-hardness measurements of the untreated and treated specimens were carried out with Vickers indenter. Depth-resolved characterization of the residual stresses and strains was achieved using X-ray diffraction. The structure–texture–phase–stress combined analysis was performed based on the X-ray diffraction patterns using the whole pattern fitting method. The relationship between laser peening processing parameters, microstructure, texture, residual stress distribution and hardness are presented and discussed. The results showed that laser peening could improve microstructures and properties of TiAl alloy.

Effect of Laser Peening without Coating on 316L austenitic stainless steel

Laser Peening without Coating (LPwC) is an innovative surface modification technique used for the in-suit preventive maintenance of nuclear reactor components using frequency doubled (green) laser. The advantage of LPwC is that the laser required for this technique is in milli joule range and the processes can perform in aqueous environment. This paper discussed the effect of LPwC on 316L austenitic stainless steel using low energy Nd: YAG laser with various laser pulse density. The base specimen and laser peened specimen were subjected to surface residual stress, surface morphology, micro hardness and potentiodynamic polarization studies. The laser peened surface exhibit significant improvement in surface compressive residual stress. The depth profile of micro hardness revealed higher strain hardening on laser peened specimens. Though corrosion potential reported an anodic shift,current density is found to be increased after LPwC for the specimen peened with higher pulse density.

Study of Laser Peening on TiAl Alloy Properties with Different Parameters

Laser peening is a novel surface treatment process that generates deep compressive residual stresses and microstructural changes and thereby dramatically improves fatigue strength of critical metal aircraft engine parts. In order to study the effects of laser peening on properties of TiAl alloy, Surface micro-hardness, microstructural, residual stress and pole figures before and after laser peening were tested. The experimental results showed that surface micro-hardness increased by 23%. The compressive residual stress increased 20 times. The texture in the normal direction of 8J peened sample showed a strong fiber texture components 10o away. In conclusion, the laser peening could improve properties of TiAl alloy.

激光冲击强化对6082铝合金机械性能的影响

激光冲击强化对6082铝合金机械性能的影响

激光冲击强化对TiAl合金组织和性能的影响

To study the effect of laser peening on microstructures and properties of TiAl alloy,TiAl alloy samples were treated by a Nd:YAG laser system with a wavelength of 1 064nm,apulse-width of 20ns,and a pulse-energy of range 0-22J.The surface micro-hardness,roughness,and microstructural characteristics of the samples before and after laser peening were tested with a microhardness tester,a roughness tester and a Scanning Electron Microscope(SEM).The residual stress and pole figures of TiAl alloy were tested with X-ray Diffraction(XRD)and their high-temperature stabilities were analyzed.The experimental results show that the surface micro-hardness increases up to 33.4%,the roughness increases from 0.042μm to 0.285μm,the compress residual stress increases from 20MPa to 297MPa with the pulse energy up to 9J,and the local textures and typical lamellar microstructures are generated.When the samples are heated for 4hat 650℃,the residual stress value and micro hardness values have droped from 297 MPa to 230 MPa,and 377 HV0.2 to 345 HV0.2 respectively,and the(002)poles shift back to the center slightly.It concludes that the laser peening improves microstructures and properties of TiAl alloy significantly.

Effect of Laser Peening on Residual Stress and Micro-Hardness of TC4 Titanium Alloy

Laser peening offers potential advantages over conventional peen technologies in terms of the depth of the residual stresses that can be induced, and improvements in surface micro-hardness. The present study was undertaken to understand the effect of laser penning on the properties of titanium alloy, a TC4 titanium alloy work-piece was processed with ND: YAG laser with the wavelength of 1064 nm, pulse energy of 0-10J and pulse width of 12ns, and micro-hardness and residual stress for different laser peening parameters were examined and analyzed by micro-hardness tester and X-ray diffraction. Results are presented and discussed of the residual stress profiles and the micro-hardness profiles, The experimental results show that the satisfying laser peening appearance can be achieved when the pulse energy was 6J, water tamping layer thickness was 1.8mm and ablative layer thickness was 100μm, surface micro-hardness increased by up to 33% and the compressive residual stress on the surface of laser shocked area reached up to-327.8MPa, laser peening improved hardness and residual stress of titanium alloy significantly. The experiment results show that the effect of laser peening was evidently.

Effects of laser peening on residual stresses and fatigue crack growth properties of Ti–6Al–4V titanium alloy

The effects of laser peening (LP) with different laser peening coverage rates on residual stresses and fatigue crack growth (FCG) properties of Ti–6Al–4V titanium alloy were investigated. Residual stresses after LP and micro-structure with different fatigue striation patterns on fracture cross-sections were analyzed. Compressive residual stresses and dense dislocation arrangements can be obtained in the superficial layer after LP. The influence of compressive residual stresses induced under different LP coverage rates on FCG properties was revealed. LP coverage rate had an apparent influence on FCG properties as confirmed by the fatigue striation spacing on fracture cross-sections. Moreover, FCG rate decreased with the increase of compressive residual stresses perpendicular to the crack growth direction, which indicated that LP had an obvious inhibitory effects on FCG.

Effect of Laser Peening on Residual Stress and Micro-Hardness of TC4 Titanium Alloy

Laser peening offers potential advantages over conventional peen technologies in terms of the depth of the residual stresses that can be induced, and improvements in surface micro-hardness. The present study was undertaken to understand the effect of laser penning on the properties of titanium alloy, a TC4 titanium alloy work-piece was processed with ND: YAG laser with the wavelength of 1064 nm, pulse energy of 0-10J and pulse width of 12ns, and micro-hardness and residual stress for different laser peening parameters were examined and analyzed by micro-hardness tester and X-ray diffraction. Results are presented and discussed of the residual stress profiles and the micro-hardness profiles, The experimental results show that the satisfying laser peening appearance can be achieved when the pulse energy was 6J, water tamping layer thickness was 1.8mm and ablative layer thickness was 100μm, surface micro-hardness increased by up to 33% and the compressive residual stress on the surface of laser shocked area reached up to-327.8MPa, laser peening improved hardness and residual stress of titanium alloy significantly. The experiment results show that the effect of laser peening was evidently.

TC4钛合金激光冲击强化参数及性能分析

TC4钛合金激光冲击强化参数及性能分析

Ti-6Al-4V合金の回転曲げ疲労特性に及ぼすレーザピーニング処理の影響

In order to investigate the effects of laser peening on high cycle fatigue properties of (α+β) type Ti-6Al-4V alloy, rotating bending fatigue tests were carried out. The laser peening conditions were a spot size of 0.8mm in diameter, a pulse energy of 200mJ and an irradiation pulse density of 38 pulse/mm2. The fatigue properties were not improved with these conditions of laser peening ; even though the material was hardened to some extent and high level compressive residual stresses were induced in the near-surface layer. Because the reason that the fatigue properties were not improved was considered the notch effect of surface roughness introduced by laser peening, further fatigue tests were performed with laser-peened specimens followed by surface polishing. However, the fatigue lives of polished specimens were shorter than those of unpolished specimens, unexpectedly. Considering the peening effects such as surface roughness, hardness and residual stress, the reasons for arriving at the unexpected results would be the influence of the strain-induced transformation of β phase into α' martensite and a larger yield strength in tension than that in compression due to the HCP structure of α phase of titanium alloy.

Effects of curved geometry on residual stress in laser peening

Prevention of failure in materials has been extensively researched for centuries by people all over the world. Sustained or cyclic loading is a major cause of failure in many situations. There can be other contributing factors, such as manufacturing defects and the presence of unfavorable residual stresses. But residual stresses can also play a positive role and can enhance the life of the component, if applied properly. Laser peening (LP) is a surface enhancement technique that can impede crack initiation and propagation by inducing favorable compressive residual stresses in the peened components. Laser peening can generate deeper compressive stresses compared with other surface enhancement techniques, such as shot peening, and it has been used to improve the fatigue life of components in aerospace, automotive and medical applications. In this work, the effects of laser peening are studied by using two dimensional finite element simulation models created with ABAQUS©. Crack initiation often occurs along the curved regions or fillets of structural components because of the presence of high stress concentrations. These critical regions are modeled as a curved geometry to capture the curvature effects using simulation models. Concave and convex simulation models are created and compared with flat geometry to investigate the effects of curvature in a laser peening problem. A mechanism of residual stress generation in curved models is used to explain the residual stress results obtained from finite element models. The results predict that increasing the radius of curvature in a concave model decreases the compressive residual stress generated in the component while increasing the radius of curvature of a convex model increases the compressive residual stress induced in the material when compared with a flat component.

Effects of laser peening with different coverage areas on fatigue crack growth properties of 6061-T6 aluminum alloy

The effects of coverage area on fatigue crack growth (FCG) properties of 6061-T6 aluminum alloy subject to multiple laser peening (LP) impacts were investigated. Residual stress, micro-structure and fatigue striation pattern on fracture cross-sections were analyzed. Compressive residual stresses and dense dislocation arrangements can be found in the superficial layer after LP. LP coverage area has a direct influence on FCG properties as verified by different size of shell ridges and fatigue striation spacing on fracture cross-sections. Meanwhile, FCG rate decreases with the increase of compressive residual stresses distribution perpendicular to the crack growth direction in the initial FCG stage.

Laser peening without coating on aluminum alloy Al-6061-T6 using low energy Nd:YAG laser

The present study investigates the effect of laser peening without coating on aluminum alloy Al-6061-T6 with a 300mJ infrared laser. The surface topography, microstructure, surface topography, surface residual stress and micro-hardness of peened and unpeened surfaces were studied. The study shows that laser peening without coating can significantly improve surface compressive stress and micro-hardness with trivial increase in surface roughness. Microstructure evaluation confirmed there was no near surface solidification after LPwC.

일체형 원자로 안전주입 노즐 이종금속 용접부에 대한 레이저 피닝 적용의 수치 해석적 연구

일체형 원자로의 안전주입 노즐 이종금속 용접부의 잔류응력에 대한 레이저 피닝의 효과를 고찰하기 위해 상용 프로그램인 ABAQUS를 이용하여 implicit 동적 유한요소 해석을 통해 연구를 수행하였다. implicit 동적 유한요소 해석은 기존의 실험 결과와의 비교에 따르면 레이저 피닝을 통한 잔류응력 이완에 대해 타당하다고 확인된다. 한편 내부 보수용접이 수행된 이종금속 용접부에 대해 해석이 수행되며 그 결과는 축방향 및 원환 잔류응력 모두 내부 보수용접에 기인하여 노즐의 내표면에서 인장임을 나타낸다. 또한 용접 잔류응력 이완에 대한 최대 충격 압력, 압력 지속 시간, 스폿 직경 및 피닝 방향과 같은 여러 변수의 효과를 고찰하기 위해 변수 해석 또한 수행하였다. 결과적으로, 레이저 피닝은 내표면 근처 영역의 잔류응력을 주로 이완시키는 예방정비 효과가 있음을 확인하였다.

Effects of laser peening on stress corrosion cracking (SCC) of ANSI 304 austenitic stainless steel

The effects of massive laser peening (LP) impacts on surface residual stress, micro-structure, and stress corrosion cracking (SCC) behaviour of U-bend samples were investigated by X-ray diffraction (XRD) technology, optical microscope (OM) and transmission electron microscope (TEM) observations. Two important factors to influence SCC initiation, residual stress and grain refinement, were discussed in detail by using different types of treatment processes. Results showed massive LP impacts can induce both deep compressive residual stress and refined grains in the surface layer of ANSI 304 stainless steel, and the corrosion mechanism of massive LP impacts on SCC was also analysed and revealed.