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A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (30 April 2018) | Viewed by 66544

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Prof. Dr. Frank A. Müller

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Friedrich Schiller University Jena, Otto Schott Institute of Materials Research (OSIM), Colloids, Surfaces, and Interfaces (CSI), Löbdergraben 32, 07743 Jena, Germany
Interests: bio-inspired materials; biomaterials; biomineralization; laser materials processing; additive manufacturing; surface modification; nanoparticles
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Dr. Stephan Gräf

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Friedrich Schiller University Jena, Otto Schott Institute of Materials Research (OSIM), Colloids, Surfaces, and Interfaces (CSI), Löbdergraben 32, 07743 Jena, Germany
Interests: bio-inspired materials; laser materials processing; functional surfaces; surface structuring; laser-induced periodic surface structures (LIPSS)
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Nowadays, industrial production processes are inconceivable without lasers. Lasers have been established in numerous areas of materials processing, like cutting, drilling and welding. A broad variety of available laser systems with different wavelengths, pulse durations, and intensities facilitate the processing of almost all types of materials, including metals, ceramics, semiconductors, polymers, and composites. The main advantages of laser-based technologies include their high flexibility and efficiency, the reproducible adjustability of processing parameters, and the excellent quality of processed products. The required amount of energy can be provided in a well-defined, locally limited volume with negligible heat transfer to surrounding components. These unique properties are continuously stimulating new applications of lasers as a tool in materials processing. Consequently, novel processing routes in surface engineering (micro- and nanostructuring; laser induced periodic surface structures), additive manufacturing (stereolithography; selective laser sintering), coating techniques (pulsed laser deposition; matrix assisted pulsed laser evaporation), and nanoparticle synthesis (laser ablation; laser vaporisation) are on their way from research to industrial application.

This Special Issue covers the whole spectrum of laser materials processing, ranging from novel trends in well-established industrial processing techniques like cutting and drilling, via the synthesis of functional nanoparticles and coatings, the fabrication of sub-wavelength surface structures up to additive manufacturing techniques for the preparation of 3D scaffolds. The performance and application of laser-processed materials in the fields of biomaterials, optics, energy and environmental technologies will be discussed. In addition, fundamental research concerning the interaction between laser radiation and matter, as well as simulations and modeling of formation processes and structure-property relations will be topics of specific interest.

It is our pleasure to invite you to submit a manuscript for this Special Issue. Full papers, short communications, as well as reviews, would be greatly appreciated.

Prof. Dr. Frank A. Müller
Dr. Stephan Gräf
Guest Editors

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Keywords

interaction between laser radiation and matter
novel trends in laser materials processing
micro- and nanoscale structures
laser induced periodic surface structures
selective laser sintering stereolithography
pulsed laser deposition
laser-based nanoparticle synthesis
strategies for the fabrication of bio-inspired materials
application of laser processed materials
simulation and modeling

Published Papers (13 papers)

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Research

13 pages, 9065 KiB

Open AccessArticle

Impact-Sliding Tribology Behavior of TC17 Alloy Treated by Laser Shock Peening

by Meigui Yin, Wenjian Wang, Weifeng He and Zhenbing Cai

Materials 2018, 11(7), 1229; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11071229 - 17 Jul 2018

Cited by 6 | Viewed by 3165

Abstract

Outer particle collision with certain dynamic objects is not a pure impact wear behavior; it is typically accompanied by sliding wear phenomena. This study is aimed at investigating the impact-sliding wear performance of three different TC17 titanium alloys. One was untreated, and the other two were subjected to laser shock peening (LSP) by 5 and 7 J pulse energy, respectively. The wear test was performed on a novel impact-sliding wear testing rig, which can realize multiple impact-sliding motions by changing motion parameters in the x and z directions. Present results showed that wear resistance of both treated samples improved compared with the untreated alloy. Given the increase in wear cycles, increment in wear rate of the untreated sample was constantly higher than those of the treated samples. All results can be attributed to the increase in surface hardness of the material and residual compressive stress, which was also introduced after LSP. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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14 pages, 8797 KiB

Open AccessArticle

Corrosion Behavior of Heat-Treated AlSi10Mg Manufactured by Laser Powder Bed Fusion

by Marina Cabrini, Flaviana Calignano, Paolo Fino, Sergio Lorenzi, Massimo Lorusso, Diego Manfredi, Cristian Testa and Tommaso Pastore

Materials 2018, 11(7), 1051; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11071051 - 21 Jun 2018

Cited by 56 | Viewed by 4600

Abstract

This experimental work is aimed at studying the effect of microstructural modifications induced by post-processing heat treatments on the corrosion behavior of silicon-aluminum alloys produced by means of laser powder bed fusion (LPBF). The manufacturing technique leads to microstructures characterized by the presence of melt pools, which are quite different compared to casting alloys. In this study, the behavior of an AlSi10Mg alloy was evaluated by means of intergranular corrosion tests according to ISO 11846 standard on heat-treated samples ranging from 200 to 500 °C as well as on untreated samples. We found that temperatures above 200 °C reduced microhardness of the alloy, and different corrosion morphologies occurred due to the modification of both size and distribution of silicon precipitates. Selective penetrating attacks occurred at melt pool borders. The intergranular corrosion phenomena were less intense for as-produced specimens without heat treatments compared to the heat-treated specimens at 200 and 300 °C. General corrosion morphologies were noticed for specimens heat treated at temperatures exceeding 400 °C. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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12 pages, 5000 KiB

Open AccessArticle

The Application of Globular Water-Atomized Iron Powders for Additive Manufacturing by a LENS Technique

by Tomasz Durejko, Justyna Aniszewska, Michał Ziętala, Anna Antolak-Dudka, Tomasz Czujko, Robert A. Varin and Vlad Paserin

Materials 2018, 11(5), 843; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11050843 - 18 May 2018

Cited by 10 | Viewed by 4156

Abstract

The water-atomized ATOMET 28, 1001, 4701, and 4801 powders, manufactured by Rio Tinto Metal Powders, were used for additive manufacturing by a laser engineered net shaping (LENS) technique. Their overall morphology was globular and rounded with a size distribution from about 20 to 200 µm. Only the ATOMET 28 powder was characterized by a strong inhomogeneity of particle size and irregular polyhedral shape of powder particles with sharp edges. The powders were pre-sieved to a size distribution from 40 to 150 µm before LENS processing. One particular sample—LENS-fabricated from the ATOMET 28 powder—was characterized by the largest cross-sectional (2D) porosity of 4.2% and bulk porosity of 3.9%, the latter determined by microtomography measurements. In contrast, the cross-sectional porosities of bulk, solid, nearly cubic LENS-fabricated samples from the other ATOMET powders exhibited very low porosities within the range 0.03–0.1%. Unexpectedly, the solid sample—LENS-fabricated from the reference, a purely spherical Fe 99.8 powder—exhibited a porosity of 1.1%, the second largest after that of the pre-sieved, nonspherical ATOMET 28 powder. Vibrations incorporated mechanically into the LENS powder feeding system substantially improved the flow rate vs. feeding rate dependence, making it completely linear with an excellent coefficient of fit, R² = 0.99. In comparison, the reference powder Fe 99.8 always exhibited a linear dependence of the powder flow rate vs. feeding rate, regardless of vibrations. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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19 pages, 8872 KiB

Open AccessFeature PaperArticle

Femtosecond Laser Texturing of Surfaces for Tribological Applications

by Jörn Bonse, Sabrina V. Kirner, Michael Griepentrog, Dirk Spaltmann and Jörg Krüger

Materials 2018, 11(5), 801; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11050801 - 15 May 2018

Cited by 142 | Viewed by 8968

Abstract

Laser texturing is an emerging technology for generating surface functionalities on basis of optical, mechanical, or chemical properties. Taking benefit of laser sources with ultrashort (fs) pulse durations features outstanding precision of machining and negligible rims or burrs surrounding the laser-irradiation zone. Consequently, additional mechanical or chemical post-processing steps are usually not required for fs-laser surface texturing (fs-LST). This work aimed to provide a bridge between research in the field of tribology and laser materials processing. The paper reviews the current state-of-the-art in fs-LST, with a focus on the tribological performance (friction and wear) of specific self-organized surface structures (so-called ripples, grooves, and spikes) on steel and titanium alloys. On the titanium alloy, specific sickle-shaped hybrid micro-nanostructures were also observed and tribologically tested. Care is taken to identify accompanying effects affecting the materials hardness, superficial oxidation, nano- and microscale topographies, and the role of additives contained in lubricants, such as commercial engine oil. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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16 pages, 2420 KiB

Open AccessArticle

The Effect of the Traverse Feed Rate on the Microstructure and Mechanical Properties of Laser Deposited Fe₃Al (Zr,B) Intermetallic Alloy

by Magdalena Łazińska, Tomasz Durejko, Tomasz Czujko and Zbigniew Bojar

Materials 2018, 11(5), 792; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11050792 - 14 May 2018

Cited by 5 | Viewed by 2899

Abstract

The results of the fabrication of components made with Fe-30%Al-0.35%Zr-0.1%B alloy powder using the Laser Engineered Net Shaping (LENS^TM) system operated at different traverse feed rates are described in this paper. The temperature of the molten metal pool was recorded during this process. Depending on the assumed feed rate, the formation of Zr–based precipitates with various morphologies and distributions was observed in the structure of the investigated material. It was found that as the traverse speed increased, spheroidization, refinement, and a more homogeneous distribution of these precipitates occurred. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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11 pages, 8748 KiB

Open AccessArticle

Multifunctional Hierarchical Surface Structures by Femtosecond Laser Processing

by Clemens Kunz, Frank A. Müller and Stephan Gräf

Materials 2018, 11(5), 789; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11050789 - 12 May 2018

Cited by 29 | Viewed by 5328

Abstract

Hierarchical surface structures were fabricated on fused silica by using a fs-laser with a pulse duration τ = 300 fs and a wavelength λ = 512 nm. The resulting surface structures were characterized by scanning electron microscopy, atomic force microscopy and white light interference microscopy. The optical properties were analyzed by transmittance measurements using an integrating sphere and the wettability was evaluated by measuring the water contact angle θ. The silanization of structured fused silica surfaces with trichloro(1H,1H,2H,2H-perfluorooctyl)silane allows to switch the wettability from superhydrophilic (θ = 0°) to superhydrophobic behavior with θ exceeding 150°. It was shown that the structured silica surfaces are a suitable master for negative replica casting and that the hierarchical structures can be transferred to polystyrene. The transmittance of structured fused silica surfaces decreases only slightly when compared to unstructured surfaces, which results in high transparency of the structured samples. Our findings facilitate the fabrication of transparent glass samples with tailored wettability. This might be of particular interest for applications in the fields of optics, microfluidics, and biomaterials. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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12 pages, 6629 KiB

Open AccessArticle

Microstructure and Solidification Crack Susceptibility of Al 6014 Molten Alloy Subjected to a Spatially Oscillated Laser Beam

by Minjung Kang, Heung Nam Han and Cheolhee Kim

Materials 2018, 11(4), 648; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11040648 - 23 Apr 2018

Cited by 28 | Viewed by 5562

Abstract

Oscillating laser beam welding for Al 6014 alloy was performed using a single mode fiber laser and two-axis scanner system. Its effect on the microstructural evolution of the fusion zone was investigated. To evaluate the influence of oscillation parameters, self-restraint test specimens were fabricated with different beam patterns, widths, and frequencies. The behavior of hot cracking propagation was analyzed by high-speed camera and electron backscatter diffraction. The behavior of crack propagation was observed to be highly correlated with the microstructural evolution of the fusion zone. For most oscillation conditions, the microstructure resembled that of linear welds. A columnar structure was formed near the fusion line and an equiaxed structure was generated at its center. The wide equiaxed zone of oscillation welding increased solidification crack susceptibility. For an oscillation with an infinite-shaped scanning pattern at 100 Hz and 3.5 m/min welding speed, the bead width, solidification microstructure, and the width of the equiaxed zone at the center of fusion fluctuated. Furthermore, the equiaxed and columnar regions alternated periodically, which could reduce solidification cracking susceptibility. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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12 pages, 8717 KiB

Open AccessArticle

The Microstructure Evolution of a Fe₃Al Alloy during the LENS Process

by Krzysztof Karczewski, Tomasz Durejko and Tomasz Czujko

Materials 2018, 11(3), 390; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11030390 - 07 Mar 2018

Cited by 6 | Viewed by 3227

Abstract

A Fe₃Al intermetallic alloy has been successfully prepared by the laser-engineered net shaping (LENS) process. The applied process parameters were selected to provide various cooling rates during the solidification of the laser-melted material. The macro- and microstructure and the micro- and macrotexture of Fe₃Al samples were investigated. The influence of the cooling rate on grain morphology and texture is discussed. For the applied cooling rate range of 0.64 × 10⁴ K/s–2.6 × 10⁴ K/s, the structure is characterized by the presence of columnar grains for which the growth is directed upwards from the substrate. The intensity of the microtexture varies with the height of the sample and the cooling rate. The intensity of the texture increases with the decrease in the cooling rate. The samples that were obtained with low and medium cooling rates are characterized by the well-developed <100> and <111> macrotextures. The Fe₃Al alloy that was produced with a high cooling rate did not show a specific texture, which is reflected in the fairly uniform distribution of the normalized density intensity. Only a very weak texture with a <100> type component was observed. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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18 pages, 90590 KiB

Open AccessArticle

Microstructures and Properties of Laser Cladding Al-TiC-CeO₂ Composite Coatings

by Xing He, Dejun Kong and Renguo Song

Materials 2018, 11(2), 198; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11020198 - 26 Jan 2018

Cited by 33 | Viewed by 4727

Abstract

Al-TiC-CeO₂ composite coatings have been prepared by using a laser cladding technique, and the microstructure and properties of the resulting composite coatings have been investigated using scanning electron microscopy (SEM), a 3D microscope system, X-ray diffraction (XRD), micro-hardness testing, X-ray stress measurements, friction and wear testing, and an electrochemical workstation. The results showed that an Al-Fe phase appears in the coatings under different applied laser powers and shows good metallurgical bonding with the matrix. The dilution rate of the coating first decreases and then increases with increasing laser power. The coating was transformed from massive and short rod-like structures into a fine granular structure, and the effect of fine grain strengthening is significant. The microhardness of the coatings first decreases and then increases with increasing laser power, and the maximum microhardness can reach 964.3 HV_0.2. In addition, the residual stress of the coating surface was tensile stress, and crack size increases with increasing stress. When the laser power was 1.6 kW, the coating showed high corrosion resistance. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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12 pages, 8075 KiB

Open AccessArticle

Study of the Microstructure and Cracking Mechanisms of Hastelloy X Produced by Laser Powder Bed Fusion

by Giulio Marchese, Gloria Basile, Emilio Bassini, Alberta Aversa, Mariangela Lombardi, Daniele Ugues, Paolo Fino and Sara Biamino

Materials 2018, 11(1), 106; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11010106 - 11 Jan 2018

Cited by 126 | Viewed by 8325

Abstract

Hastelloy X (HX) is a Ni-based superalloy which suffers from high crack susceptibility during the laser powder bed fusion (LPBF) process. In this work, the microstructure of as-built HX samples was rigorously investigated to understand the main mechanisms leading to crack formation. The microstructural features of as-built HX samples consisted of very fine dendrite architectures with dimensions typically less than 1 µm, coupled with the formation of sub-micrometric carbides, the largest ones were mainly distributed along the interdendritic regions and grain boundaries. From the microstructural analyses, it appeared that the formation of intergranular carbides provided weaker zones, which combined with high thermal residual stresses resulted in hot cracks formation along the grain boundaries. The carbides were extracted from the austenitic matrix and characterized by combining different techniques, showing the formation of various types of Mo-rich carbides, classified as M₆C, M₁₂C and M_nC_m type. The first two types of carbides are typically found in HX alloy, whereas the last one is a metastable carbide probably generated by the very high cooling rates of the process. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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13210 KiB

Open AccessArticle

Reactive Fabrication and Effect of NbC on Microstructure and Tribological Properties of CrS Co-Based Self-Lubricating Coatings by Laser Cladding

by Liuyang Fang, Hua Yan, Yansong Yao, Peilei Zhang, Qiushi Gao and Yang Qin

Materials 2018, 11(1), 44; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11010044 - 28 Dec 2017

Cited by 23 | Viewed by 5050

Abstract

The CrS/NbC Co-based self-lubricating composite coatings were successfully fabricated on Cr12MoV steel surface by laser clad Stellite 6, WS₂, and NbC mixed powders. The phase composition, microstructure, and tribological properties of the coatings ware investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS), as well as dry sliding wear testing. Based on the experimental results, it was found reactions between WS₂ and Co-based alloy powder had occurred, which generated solid-lubricant phase CrS, and NbC play a key role in improving CrS nuclear and refining microstructure of Co-based composite coating during laser cladding processing. The coatings were mainly composed of γ-Co, CrS, NbC, Cr₂₃C₆, and CoC_x. Due to the distribution of the relatively hard phase of NbC and the solid lubricating phase CrS, the coatings had better wear resistance. Moreover, the suitable balance of CrS and NbC was favorable for further decreasing the friction and improving the stability of the contact surfaces between the WC ball and the coatings. The microhardness, friction coefficient, and wear rate of the coating 4 (Clad powders composed of 60 wt % Stellite 6, 30 wt % NbC and 10 wt % WS₂) were 587.3 HV_0.5, 0.426, and 5.61 × 10⁻⁵ mm³/N·m, respectively. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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10188 KiB

Open AccessArticle

Thermal, Spectral and Laser Properties of Er³⁺:Yb³⁺:GdMgB₅O₁₀: A New Crystal for 1.5 μm Lasers

by Yisheng Huang, Feifei Yuan, Shijia Sun, Zhoubin Lin and Lizhen Zhang

Materials 2018, 11(1), 25; https://0-doi-org.brum.beds.ac.uk/10.3390/ma11010025 - 25 Dec 2017

Cited by 11 | Viewed by 4265

Abstract

A novel laser crystal of Er³⁺:Yb³⁺:GdMgB₅O₁₀ with dimension of 26 × 16 × 12 mm³ was grown successfully from K₂Mo₃O₁₀ flux by the top seeded solution growth method. The thermal [...] Read more.

A novel laser crystal of Er³⁺:Yb³⁺:GdMgB₅O₁₀ with dimension of 26 × 16 × 12 mm³ was grown successfully from K₂Mo₃O₁₀ flux by the top seeded solution growth method. The thermal diffusivity and specific heat capacity were measured to calculate the thermal conductivity of the crystal. The absorption and fluorescence properties of the crystal at room temperature were investigated in detail. The Judd-Ofelt method was used to analyze the polarized absorption spectra. The emission cross-section of the ⁴I_13/2→⁴I_15/2 transition was calculated by the Füchtbauer-Ladenburg formula and the relevant gain cross-sections were estimated. Continuous-wave laser output of 140 mW at 1569 nm with the slope efficiency of 17.8% was demonstrated in a plano-concave resonator. The results reveal that Er³⁺:Yb³⁺:GdMgB₅O₁₀ crystal is a promising material for 1.5 μm lasers. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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32700 KiB

Open AccessArticle

Effects of Pulse Parameters on Weld Microstructure and Mechanical Properties of Extra Pulse Current Aided Laser Welded 2219 Aluminum Alloy Joints

by Xinge Zhang, Liqun Li, Yanbin Chen, Zhaojun Yang, Yanli Chen and Xinjian Guo

Materials 2017, 10(9), 1091; https://0-doi-org.brum.beds.ac.uk/10.3390/ma10091091 - 15 Sep 2017

Cited by 12 | Viewed by 5370

Abstract

In order to expand the application range of laser welding and improve weld quality, an extra pulse current was used to aid laser-welded 2219 aluminum alloy, and the effects of pulse current parameters on the weld microstructure and mechanical properties were investigated. The effect mechanisms of the pulse current interactions with the weld pool were evaluated. The results indicated that the coarse dendritic structure in the weld zone changed to a fine equiaxed structure using an extra pulse current, and the pulse parameters, including medium peak current, relatively high pulse frequency, and low pulse duty ratio benefited to improving the weld structure. The effect mechanisms of the pulse current were mainly ascribed to the magnetic pinch effect, thermal effect, and electromigration effect caused by the pulse current. The effect of the pulse parameters on the mechanical properties of welded joints were consistent with that of the weld microstructure. The tensile strength and elongation of the optimal pulse current-aided laser-welded joint increased by 16.4% and 105%, respectively, compared with autogenous laser welding. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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