Editorial

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Open AccessEditorial

by Patrice Peyre

Metals 2017, 7(10), 409; https://doi.org/10.3390/met7100409 - 01 Oct 2017

Cited by 3 | Viewed by 2664

Since its invention in the late 1960s, and the pioneering work on metal strengthening in USA during the late 1970s, laser shock processing (LSP) has become a reliable surface treatment for improving the mechanical or corrosion resistance of metallic materials.[...] Full article

(This article belongs to the Special Issue Laser Shock Processing on Metal)

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1503 KiB

Open AccessFeature PaperArticle

Laser-Driven Ramp Compression to Investigate and Model Dynamic Response of Iron at High Strain Rates

by Nourou Amadou, Erik Brambrink, Thibaut De Rességuier, Adamou Ousmane Manga, Almoustapha Aboubacar, Björn Borm and Anaïs Molineri

Metals 2016, 6(12), 320; https://doi.org/10.3390/met6120320 - 18 Dec 2016

Cited by 13 | Viewed by 4613

Abstract

Efficient laser shock processing of materials requires a good characterization of their dynamic response to pulsed compression, and predictive numerical models to simulate the thermomechanical processes governing this response. Due to the extremely high strain rates involved, the kinetics of these processes should [...] Read more.

Efficient laser shock processing of materials requires a good characterization of their dynamic response to pulsed compression, and predictive numerical models to simulate the thermomechanical processes governing this response. Due to the extremely high strain rates involved, the kinetics of these processes should be accounted for. In this paper, we present an experimental investigation of the dynamic behavior of iron under laser driven ramp loading, then we compare the results to the predictions of a constitutive model including viscoplasticity and a thermodynamically consistent description of the bcc to hcp phase transformation expected near 13 GPa. Both processes are shown to affect wave propagation and pressure decay, and the influence of the kinetics of the phase transformation on the velocity records is discussed in details. Full article

(This article belongs to the Special Issue Laser Shock Processing on Metal)

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2905 KiB

Open AccessFeature PaperArticle

Nanocrystallization in the Duplex Ti-6Al-4V Alloy Processed by Multiple Laser Shock Peening

by Wangfan Zhou, Xudong Ren, Fanfan Liu, Yunpeng Ren and Lin Li

Metals 2016, 6(12), 297; https://doi.org/10.3390/met6120297 - 24 Nov 2016

Cited by 22 | Viewed by 6107

Abstract

Laser shock peening of titanium alloys has been widely applied in the aerospace industry. However, little is known of the nanocrystalline formation characteristics and mechanisms. In this investigation, a nanocrystalline layer was formed in the duplex Ti-6Al-4V titanium alloy surface region by means [...] Read more.

Laser shock peening of titanium alloys has been widely applied in the aerospace industry. However, little is known of the nanocrystalline formation characteristics and mechanisms. In this investigation, a nanocrystalline layer was formed in the duplex Ti-6Al-4V titanium alloy surface region by means of multiple pulsed laser shock peening (LSP). The phase transition and residual stress characteristics of LSP samples were analyzed with X-ray diffraction (XRD) and scanning electron microscopy (SEM). Transmission electron microscopy (TEM) was used to characterize the microstructure and morphologies. As the number of laser pulses increased for each location, higher grain refinement was observed. Micro-hardness testing showed that hardness increased with the number of pulses delivered to each location due to the formation of nanocrystalline layers and high dislocation density in the samples, and a gradient variation of the micro-hardness was obtained. In addition, mechanical twins and different dislocation configurations were formed in the α phase region while only dense dislocation tangles were observed in the β phase region after multiple laser pulse impacts. Full article

(This article belongs to the Special Issue Laser Shock Processing on Metal)

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Open AccessArticle

Residual Stress Distribution and Microstructure Evolution of AA 6061-T6 Treated by Warm Laser Peening

by Shu Huang, Zuowei Wang, Jie Sheng, Emmanuel Agyenim-Boateng, Muxi Liu, Xiaole Yang and Jianzhong Zhou

Metals 2016, 6(11), 292; https://doi.org/10.3390/met6110292 - 22 Nov 2016

Cited by 9 | Viewed by 5048

Abstract

The aim of this paper is to study the effects of laser peening (LP) on the residual stress distribution and microstructure evolution of AA 6061-T6 under different temperatures. A laser peening experiment was conducted on the square-shape samples by using single spot and [...] Read more.

The aim of this paper is to study the effects of laser peening (LP) on the residual stress distribution and microstructure evolution of AA 6061-T6 under different temperatures. A laser peening experiment was conducted on the square-shape samples by using single spot and 50% overlap shock. Three-dimensional surface morphologies of treated samples were observed. The influence of peening temperature on the distribution of compressive residual stress was analyzed. An optical microscope (OM) and a transmission electron microscope (TEM) were employed to observe the microstructure evolution of the samples before and after LP. The results indicate that, as the peening temperature increases, the micro-hardness increases first and then decreases. The LP process induces high-amplitude compressive residual stress on the surface at different temperatures even if the compressive residual stress slightly reduces with increases in temperature. The maximum compressive residual stress affected layer depth is about 0.67 mm, appearing at a temperature of 160 °C. The OM test revealed that the grain size was significantly decreased after warm laser peening (WLP) and that the average value of grain size was reduced by 50%. The TEM test shows that more dislocation tangles were produced in AA 6061-T6 after WLP; compared to the LP process, the precipitate-dislocation interaction can benefit both strength and ductility for AA 6061-T6, thus enhancing the mechanical properties of the material. Full article

(This article belongs to the Special Issue Laser Shock Processing on Metal)

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Open AccessArticle

Water Droplet Erosion Performance of Laser Shock Peened Ti-6Al-4V

by Abdullahi K. Gujba, Lloyd Hackel and Mamoun Medraj

Metals 2016, 6(11), 262; https://doi.org/10.3390/met6110262 - 03 Nov 2016

Cited by 15 | Viewed by 4977

Abstract

The water droplet erosion (WDE) performance of laser shock peened (LSP) Ti-6Al-4V was investigated. LSP condition using two or three peening impacts per unit area induced compressive residual stresses. However, LSP treatment showed a mild increase in microhardness and no observable changes in [...] Read more.

The water droplet erosion (WDE) performance of laser shock peened (LSP) Ti-6Al-4V was investigated. LSP condition using two or three peening impacts per unit area induced compressive residual stresses. However, LSP treatment showed a mild increase in microhardness and no observable changes in the microstructure. The effect of LSP and its associated attributes on the WDE performance was studied according to the American Society for Testing and Materials Standard (ASTM G73). Influence of the impact speed between 150 and 350 m/s on the WDE performance was explored. Two sample geometries, T-shaped flat and airfoil, were used for the WDE tests. For the flat samples, LSP showed little or no beneficial effect in enhancing the WDE performances at all tested speeds. The peened and unpeened flat samples showed similar erosion initiation and maximum erosion rate (ER_max). The LSP airfoil samples showed mild improvement in the WDE performance at 300 m/s during the advanced erosion stage compared to the as-machined (As-M) condition. However, at 350 m/s, no improved WDE performance was observed for the LSP airfoil condition at all stages of the erosion. It was concluded that compressive residual stresses alone are not enough to mitigate WDE. Hence, the notion that the fatigue mechanism is dominating in WDE damage is unlikely. Full article

(This article belongs to the Special Issue Laser Shock Processing on Metal)

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6985 KiB

Open AccessArticle

Investigation on a Novel Laser Impact Spot Welding

by Huixia Liu, Shuai Gao, Zhang Yan, Liyin Li, Cong Li, Xianqing Sun, Chaofei Sha, Zongbao Shen, Youjuan Ma and Xiao Wang

Metals 2016, 6(8), 179; https://doi.org/10.3390/met6080179 - 03 Aug 2016

Cited by 23 | Viewed by 7236

Abstract

In this paper a novel laser impact spot welding (LISW) method is described, in which a hump was formed on the flyer plate on the intended welding spot location by local pre-forming. When the flyer and base plates were placed together to perform [...] Read more.

In this paper a novel laser impact spot welding (LISW) method is described, in which a hump was formed on the flyer plate on the intended welding spot location by local pre-forming. When the flyer and base plates were placed together to perform welding, the two plates kept in contact over their entire surfaces except at the hump, where a local air gap was enough to guarantee the impact velocity and collision angle to achieve spot welding using laser pulse energy. The presented approach was implemented to join thin titanium foils to copper foils under low laser energy system. Joints with regular shapes were obtained. The microstructure in the weld interface was studied with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It was found that the jetting occurred at the central region of the weld spots due to oblique impact. Wave features were observed in the weld interfaces. The impact energy was found to have significant influence on the wave’s characteristics. Moreover, SEM images and EDS analysis did not show apparent element diffusion across the weld interface. Besides, the lap shearing test was used to characterize the mechanical properties of the spot welded joints. Full article

(This article belongs to the Special Issue Laser Shock Processing on Metal)

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4297 KiB

Open AccessArticle

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

by Hansong Chen, Jianzhong Zhou, Jie Sheng, Xiankai Meng, Shu Huang and Xiaojiang Xie

Metals 2016, 6(6), 126; https://doi.org/10.3390/met6060126 - 24 May 2016

Cited by 8 | Viewed by 4303

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Laser Shock Processing on Metal)

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2762 KiB

Open AccessArticle

Picosecond Laser Shock Peening of Nimonic 263 at 1064 nm and 532 nm Wavelength

by Sanja Petronic, Tatjana Sibalija, Meri Burzic, Suzana Polic, Katarina Colic and Dubravka Milovanovic

Metals 2016, 6(3), 41; https://doi.org/10.3390/met6030041 - 23 Feb 2016

Cited by 14 | Viewed by 6106

Abstract

The paper presents a study on the surface modifications of nickel based superalloy Nimonic 263 induced by laser shock peening (LSP) process. The process was performed by Nd³⁺:Yttrium Aluminium Garnet (YAG) picosecond laser using the following parameters: pulse duration 170 ps; [...] Read more.

The paper presents a study on the surface modifications of nickel based superalloy Nimonic 263 induced by laser shock peening (LSP) process. The process was performed by Nd³⁺:Yttrium Aluminium Garnet (YAG) picosecond laser using the following parameters: pulse duration 170 ps; repetition rate 10 Hz; pulse numbers of 50, 100 and 200; and wavelength of 1064 nm (with pulse energy of 2 mJ, 10 mJ and 15 mJ) and 532 nm (with pulse energy of 25 mJ, 30 mJ and 35 mJ). The following response characteristics were analyzed: modified surface areas obtained by the laser/material interaction were observed by scanning electron microscopy; elemental composition of the modified surface was evaluated by energy-dispersive spectroscopy (EDS); and Vickers microhardness tests were performed. LSP processing at both 1064 nm and 532 nm wavelengths improved the surface structure and microhardness of a material. Surface morphology changes of the irradiated samples were determined and surface roughness was calculated. These investigations are intended to contribute to the study on the level of microstructure and mechanical properties improvements due to LSP process that operate in a picosecond regime. In particular, the effects of laser wavelength on the microstructural and mechanical changes of a material are studied in detail. Full article

(This article belongs to the Special Issue Laser Shock Processing on Metal)

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