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Advanced Technology for Materials Synthesis and Processing

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Advanced Materials Characterization".

Deadline for manuscript submissions: closed (30 June 2020) | Viewed by 62406

Special Issue Editor

Prof. Dr. Dermot Brabazon

E-Mail Website
Guest Editor
Mechanical and Manufacturing Engineering, Dublin City University, Dublin, Ireland
Interests: laser processing; material processing; material functionalisation; nanostructured materials; rapid prototyping; chromatography
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue of Materials is focused on recent developments in the area of Additive Manufacturing (AM) processing methods, materials and related implementation. AM production technologies have developed significantly in recent years. We have seen the development and implementation of new metals, polymers and ceramics; multi-material printing; shape memory alloys; nano and multi-scale material design; composites; and metamaterials. Production technologies development includes for metals: SLM, DED, and Ink jetting; for polymers: STL, SLS and Ink jetting; and for ceramic: STL, FDM composite, and Ink jetting. The sustainability of AM has been noted as an advantage of this production method compared to alternative conventional and assembly technologies, yet this remains an under examined area and while correct in the case of some part designs, it is not correct for all part designs. New breakthroughs for better in-situ monitoring and control of AM is an ever pressing issue in order to improve dimensional accuracy while maintaining part production rate and robust high levels of quality. While papers are encouraged in the above mentioned areas, papers are invited more broadly from this rapidly changing area of AM technology.

Prof. Dermot Brabazon
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Additive Manufacturing
  • 3D printing
  • rapid prototyping
  • solid freeform fabrication
  • composites
  • shape memory alloys
  • nano and multiscale material design
  • multi-material printing

Published Papers (16 papers)

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Research

Jump to: Review, Other

9 pages, 3606 KiB  
Article
Synthesis of Silver Nanoplates with the Assistance of Natural Polymer (Sodium Alginate) Under 0 °C
by Pengfei Yang, Yu Liang, Daxiao Zhang, Jin Zhang, Shijie Li and Weiguo Liu
Materials 2020, 13(17), 3827; https://doi.org/10.3390/ma13173827 - 30 Aug 2020
Cited by 3 | Viewed by 1876
Abstract
Some special conditions are important for chemical syntheses, such as high temperature and the medium used; unfortunately, uncontrollable influences are introduced during the process, resulting in unexpectedly low repeatability. Herein, we report a facile, environmentally friendly, stable, and repeatable methodology for synthesizing silver [...] Read more.
Some special conditions are important for chemical syntheses, such as high temperature and the medium used; unfortunately, uncontrollable influences are introduced during the process, resulting in unexpectedly low repeatability. Herein, we report a facile, environmentally friendly, stable, and repeatable methodology for synthesizing silver nanoplates (SNPs) at 0 °C that overcomes these issues and dramatically increases the yield. This method mainly employs sodium dodecyl sulfate (SDS) and sodium alginate (SA) as the surface stabilizer and assistant, respectively. Consequently, we produced hexagonal nanoplates and tailed nanoplates, and the characterization showed that SA dominates the clear and regular profiles of nanoplates at 0 °C. The tailed nanoplates, over time, showed the growth of heads and the dissolving of tails, and inclined to the nanoplates without tails. The synthesis method for SNPs used in this study—0 °C without media—showed high repeatability. We confirmed that these special conditions are not required for the synthesis of silver nanostructures (SNSs). Furthermore, we constructed a new method for preparing noble metal nanostructures and proved the possibility of preparing metal nanostructures at 0 °C. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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10 pages, 2656 KiB  
Article
Additive Manufacturing of Isotropic NdFeB PPS Bonded Permanent Magnets
by M. Parans Paranthaman, Volkan Yildirim, Tej Nath Lamichhane, Benjamin A. Begley, Brian K. Post, Ahmed A. Hassen, Brian C. Sales, Kinjal Gandha and Ikenna C. Nlebedim
Materials 2020, 13(15), 3319; https://doi.org/10.3390/ma13153319 - 26 Jul 2020
Cited by 23 | Viewed by 4051
Abstract
Extrusion based additive manufacturing of polymer composite magnets can increase the solid loading volume fraction with greater mechanical force through the printing nozzle as compared to traditional injection molding process. About 63 vol% of isotropic NdFeB magnet powders were compounded with 37 vol% [...] Read more.
Extrusion based additive manufacturing of polymer composite magnets can increase the solid loading volume fraction with greater mechanical force through the printing nozzle as compared to traditional injection molding process. About 63 vol% of isotropic NdFeB magnet powders were compounded with 37 vol% of polyphenylene sulfide and bonded permanent magnets were fabricated while using Big Area Additive Manufacturing without any degradation in magnetic properties. The polyphenylene sulfide bonded magnets have a tensile stress of 20 MPa, almost double than that of nylon bonded permanent magnets. Additively manufactured and surface-protective-resin coated bonded magnets meet the industrial stability criterion of up to 175 °C with a flux-loss of 2.35% over 1000 h. They also exhibit better corrosion resistance behavior when exposed to acidic (pH = 1.35) solution for 24 h and also annealed at 80 °C over 100 h (at 95% relative humidity) over without coated magnets. Thus, polyphenylene sulfide bonded, additively manufactured, protective resin coated bonded permanent magnets provide better thermal, mechanical, and magnetic properties. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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19 pages, 5320 KiB  
Article
The Effect of the Distribution Head Tilt and Diffuser Variants on the Evenness of Sowing Rye and Oat Seeds with a Pneumatic Seed Drill
by Łukasz Gierz and Piotr Markowski
Materials 2020, 13(13), 3000; https://doi.org/10.3390/ma13133000 - 06 Jul 2020
Cited by 4 | Viewed by 2547
Abstract
Due to the sustainable development of agriculture machines with large working widths of 4–6 m or even 9–12 m are increasingly often used for agrotechnical operations. The sowing machinery whose working widths are much bigger than the width of the seed box is [...] Read more.
Due to the sustainable development of agriculture machines with large working widths of 4–6 m or even 9–12 m are increasingly often used for agrotechnical operations. The sowing machinery whose working widths are much bigger than the width of the seed box is equipped with a pneumatic system for transporting seeds from the seed box to coulters. One of the structural elements that affect the sowing accuracy in such seed drills is the distribution head with a diffuser. This article is about research on the influence of the distribution head deviation from the vertical position and constructional variants of the diffuser (the number of diffusion rings and the configuration of their position in the diffuser pipe, which is the distance between them) on the accuracy of distribution of a stream of rye and oat seeds (a seed-and-air stream), which differ in physical characteristics. The main elements, i.e., the innovative stream distributor in the head and the diffusion rings were made using an original design and the rapid prototyping method. The research proved that a change of 0–10° in the angle of the distribution head deviation from the vertical position significantly affected the sowing quality of oat seeds only. The position (density) of the diffusion rings in the lower section of the diffuser (near the supply elbow) was the most effective for both oat and rye seeds, where the average values of the coefficient of variation were 5.31% and 4.62%, respectively. The research results can be used to redesign the construction of the diffuser of the seed drill distribution head so as to reduce the resistance of transport of the seed-and-air mixture in order to improve seed sowing evenness. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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17 pages, 4919 KiB  
Article
Thermoluminescence Enhancement of LiMgPO4 Crystal Host by Tb3+ and Tm3+ Trivalent Rare-Earth Ions Co-doping
by Wojciech Gieszczyk, Barbara Marczewska, Mariusz Kłosowski, Anna Mrozik, Paweł Bilski, Anna Sas-Bieniarz, Paweł Goj and Paweł Stoch
Materials 2019, 12(18), 2861; https://doi.org/10.3390/ma12182861 - 05 Sep 2019
Cited by 26 | Viewed by 3016
Abstract
We investigated the influence of terbium and thulium trivalent rare-earth (RE) ions co-doping on the luminescent properties enhancement of LiMgPO4 (LMP) crystal host. The studied crystals were grown from the melt by micro-pulling-down (MPD) technique. Luminescent properties of the obtained crystals were [...] Read more.
We investigated the influence of terbium and thulium trivalent rare-earth (RE) ions co-doping on the luminescent properties enhancement of LiMgPO4 (LMP) crystal host. The studied crystals were grown from the melt by micro-pulling-down (MPD) technique. Luminescent properties of the obtained crystals were investigated by thermoluminescence (TL) method. The most favorable properties and the highest luminescence enhancement were measured for Tb and Tm double doped crystals. A similar luminescence level can be also obtained for Tm, B co-doped samples. In this case, however, the low-temperature TL components have a significant contribution. The measured luminescent spectra showed a typical emission of Tb3+ and Tm3+ ions of an opposite trapping nature, namely the holes and electron-trapping sites, respectively. The most prominent transitions of 5D4 → 7F3 (550 nm for Tb3+) and 1D2 → 3F4 (450 nm for Tm3+) were observed. It was also found that Tb3+ and Tm3+ emissions show temperature dependence in the case of double doped LMP crystal sample, which was not visible in the case of the samples doped with a single RE dopant. At a low temperature range (up to around 290 °C) Tm3+ emission was dominant. At higher temperatures, the electrons occupying Tm3+ sites started to be released giving rise to emissions from Tb-related recombination centers, and emissions from Tm3+ centers simultaneously decreased. At the highest temperatures, emission took place from Tb3+ recombination centers, but only from deeper 5D4 level-related traps which had not been emptied at a lower temperature range. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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16 pages, 3798 KiB  
Article
The δ Phase Precipitation of an Inconel 718 Superalloy Fabricated by Electromagnetic Stirring Assisted Laser Solid Forming
by Feiyue Lyu, Fencheng Liu, Xiaoan Hu, Xiaoguang Yang, Chunping Huang and Duoqi Shi
Materials 2019, 12(16), 2604; https://doi.org/10.3390/ma12162604 - 15 Aug 2019
Cited by 16 | Viewed by 2842
Abstract
Fabricating an Inconel 718 superalloy using electromagnetic stirring assisted laser solid forming (EMS-LSF) is a novel method to modify its microstructure and mechanical properties by consuming the Nb element in the γ phase to alleviate interdendritic segregation. The precipitate of the δ phase [...] Read more.
Fabricating an Inconel 718 superalloy using electromagnetic stirring assisted laser solid forming (EMS-LSF) is a novel method to modify its microstructure and mechanical properties by consuming the Nb element in the γ phase to alleviate interdendritic segregation. The precipitate of the δ phase at 950 °C after EMS-LSF can help to achieve the uniform diffusion of Nb, and can also improve its mechanical properties. The precipitation behavior of the δ phase in an EMS-LSF Inconel 718 superalloy with different heat treatment processes has been investigated. The results show that the morphology of the δ phase changes from rod-like to a long-needle shape and tends to grow from the inter dendrite to the core dendrite with electromagnetic field intensity increasing, which is accompanied by the “cutting” and “dissolution” of the Laves phase. Through precipitation kinetics analysis, the precipitation rate of the δ phase is seen to increase with the electromagnetic field intensity increasing. Under a combination of electromagnetic stirring and laser solid forming, the microhardness of the Inconel 718 samples increased slightly due to the fact that a higher content of Nb was distributed in the core dendrite resulting from the serious convection of liquid metal, which can strengthen the matrix. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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12 pages, 4063 KiB  
Article
Study on In-Situ Synthesis Process of Ti–Al Intermetallic Compound-Reinforced Al Matrix Composites
by Qiong Wan, Fuguo Li, Wenjing Wang, Junhua Hou, Wanyue Cui and Yongsheng Li
Materials 2019, 12(12), 1967; https://doi.org/10.3390/ma12121967 - 19 Jun 2019
Cited by 10 | Viewed by 2541
Abstract
In this study, ball-milled powder of Ti and Al was used to fabricate Ti–Al intermetallic compound-reinforced Al matrix composites by an in-situ reaction in cold-pressing sintering and hot-pressing sintering processes. The detailed microstructure of the Ti–Al intermetallic compound-reinforced Al composite was characterized by [...] Read more.
In this study, ball-milled powder of Ti and Al was used to fabricate Ti–Al intermetallic compound-reinforced Al matrix composites by an in-situ reaction in cold-pressing sintering and hot-pressing sintering processes. The detailed microstructure of the Ti–Al intermetallic compound-reinforced Al composite was characterized by optical microscopy (OM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), and electron backscattered diffraction (EBSD). The results indicate that a typical core–shell-like structure forms in the reinforced particles. The shell is composed of a series of Ti–Al intermetallic compounds and has good bonding strength and compatibility with the Al matrix and Ti core. With cold-pressing sintering, the shell around the Ti core is closed, and the shell thickness increases as the milling time and holding time increase. With hot-pressing sintering, some radiating cracks emerge in the shell structure and provide paths for further diffusion of Ti and Al atoms. The Kirkendall effect, which is caused by the difference between the diffusion coefficients of Ti and Al, results in the formation of cavities and a reduction in density degree. When the quantity of the intermetallic compounds increases, the hardness of the composites increases and the plasticity decreases. Therefore, factors that affect the quantity of the reinforcements, such as the milling time and holding time, should be determined carefully to improve the comprehensive properties of the composites. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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11 pages, 7286 KiB  
Article
Effect of Multi-Directional Forging on the Microstructure and Mechanical Properties of β-Solidifying TiAl Alloy
by Ning Cui, Qianqian Wu, Kexiao Bi, Jin Wang, Tiewei Xu and Fantao Kong
Materials 2019, 12(9), 1381; https://doi.org/10.3390/ma12091381 - 28 Apr 2019
Cited by 12 | Viewed by 3054
Abstract
This study systematically investigated the influence of multi-directional forging (MDF) on the microstructural evolution, hot deformation behavior, and tensile properties of a β-solidifying TiAl alloy. The initial lamellar microstructure of an as-cast alloy was remarkably refined and homogenized by three-step MDF. High temperatures [...] Read more.
This study systematically investigated the influence of multi-directional forging (MDF) on the microstructural evolution, hot deformation behavior, and tensile properties of a β-solidifying TiAl alloy. The initial lamellar microstructure of an as-cast alloy was remarkably refined and homogenized by three-step MDF. High temperatures and multi-pass deformations were conducive to the decomposition of lamellae. A crack-free billet was obtained through three-step MDF, with a deformation temperature of 1250 °C and a forging speed of 0.1 mm/s, indicating that MDF can be applied to β-solidifying TiAl alloys by the proper control of the alloy composition and process parameters. Microstructural observation showed that the billet mainly consists of fine and equiaxed γ grains and a small amount of β phase. The tensile properties of the multi-directional forged alloy were also significantly improved, due to microstructure refinement. The ultimate tensile strength (UTS) and elongation (δ) at room temperature were 689.4 MPa, and 0.83%, respectively. The alloy exhibits excellent ductility at 700 °C. When the temperature was increased to 700 °C, the UTS decreased to 556 MPa and δ increased to 5.98%, indicating that the alloy exhibits excellent ductility at 700 °C. As the temperature further increased to 750 °C, δ dramatically increased to 46.65%, indicating that the ductile-brittle transition temperature of the alloy is between 700 °C and 750 °C. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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15 pages, 6847 KiB  
Article
Laser Polishing of Additive Manufactured 316L Stainless Steel Synthesized by Selective Laser Melting
by Muhannad A. Obeidi, Eanna McCarthy, Barry O’Connell, Inam Ul Ahad and Dermot Brabazon
Materials 2019, 12(6), 991; https://doi.org/10.3390/ma12060991 - 26 Mar 2019
Cited by 74 | Viewed by 6637
Abstract
One of the established limitations of metal additive manufacturing (AM) methods, such as selective laser melting (SLM), is the resulting rough surface finish. Laser polishing is one method that can be used to achieve an improved surface finish on AM printed parts. This [...] Read more.
One of the established limitations of metal additive manufacturing (AM) methods, such as selective laser melting (SLM), is the resulting rough surface finish. Laser polishing is one method that can be used to achieve an improved surface finish on AM printed parts. This study is focused on the laser surface polishing of AM parts using CO2 laser beam irradiation. Despite the fact that several researchers have investigated the traditional abrasive polishing method, there is still a lack of information reporting on the laser surface polishing of metal parts. In this study, AM 316L stainless steel cylindrical samples were polished using CO2 laser beam irradiation in continuous wave (CW) working mode. Two design of experiment models were developed for the optimization of the input processing parameters by statistical analysis of their effect on the resulting roughness. The processing parameters investigated were the laser beam power, the rotational speed of the sample, the number of laser scan passes, the laser beam focal position, and the percentage overlap of the laser tracks between consecutive passes. The characterization of the measured roughness and the modified layer microstructure was carried out using 3D optical and scanning electron microscopy (SEM). A maximum reduction of the roughness from 10.4 to 2.7 µm was achieved and no significant change in the microstructure phase type and micro-hardness was observed. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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11 pages, 7089 KiB  
Article
Effect of Shear Strain Rate on Microstructure and Properties of Austenitic Steel Processed by Cyclic Forward/Reverse Torsion
by Zhimin Zhang, Qingshan Dong, Bo Song, Hong He, Linjiang Chai, Ning Guo, Bingshu Wang and Zhongwen Yao
Materials 2019, 12(3), 506; https://doi.org/10.3390/ma12030506 - 07 Feb 2019
Cited by 9 | Viewed by 3384
Abstract
In this work, commercial AISI 304 stainless steel rods were subjected to cyclic forward/reverse torsion (CFRT) treatments at low-speed and high-speed torsion at room temperature. Microstructures in the core and surface layers of the CFRT-treated samples were systematically characterized. Results show that the [...] Read more.
In this work, commercial AISI 304 stainless steel rods were subjected to cyclic forward/reverse torsion (CFRT) treatments at low-speed and high-speed torsion at room temperature. Microstructures in the core and surface layers of the CFRT-treated samples were systematically characterized. Results show that the CFRT treatment can introduce martensite phase on the surface of the rods via strain-induced martensitic transformation. High-speed twisting is more effective in inducing martensite in the surface layer compared to low-speed twisting. During the stretching process, the overall strain-hardening behavior of the gradient material is related to the content of its gradient defects. Higher gradient martensite content results in a higher surface hardness of the material, but less overall tensile properties. The effect of twisting speed on torsion behavior and the strain-hardening mechanisms in tensile of the gradient structured steels was also addressed. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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10 pages, 1727 KiB  
Article
Control over the Percentage, Shape and Size of the Graphite Particles in Martensitic White Castings Alloyed with Cr, Nb and Mg
by Alberto Cofiño-Villar, Florentino Alvarez-Antolin, Juan Asensio-Lozano and Maria Garcia-Garcia
Materials 2019, 12(1), 185; https://doi.org/10.3390/ma12010185 - 08 Jan 2019
Cited by 3 | Viewed by 2747
Abstract
This paper presents the results obtained regarding the control by manufacturers of the percentage, shape, and size of the precipitated graphite in the working layer of duplex work-rolls used in hot strip mill finishing stands. This working layer is manufactured in a martensitic [...] Read more.
This paper presents the results obtained regarding the control by manufacturers of the percentage, shape, and size of the precipitated graphite in the working layer of duplex work-rolls used in hot strip mill finishing stands. This working layer is manufactured in a martensitic white cast iron alloyed with Cr and Nb to promote the precipitation of M3C and MC carbides, which provide a high wear resistance. The thermal cycling behavior of this layer also has a decisive influence on its service life. In this context, the percentage of graphite and its morphology play a very important role against said thermal cycling. With the aim of studying their effect on the sphericity of graphite, the analyzed industrial manufacturing factors worth highlighting include the liquidus temperature, the %Si, the use of an FeSi inoculant with traces of Lanthanum, inoculation with different amounts of FeB and SiCaMn, and the addition of Mg. At the periphery of the working layer, it was found that the use of the FeSi inoculant with traces of La promoted an increase in the density of counts of graphite, and that inoculation with FeB and the addition of 0.02% Mg diminished the nodularity of the graphite. Furthermore, throughout the entire thickness of the working layer, an increase in the amount of SiCaMn of up to 0.6 kg/T produced an increase in the size of the graphite particles and a marked improvement in their nodularity. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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15 pages, 9052 KiB  
Article
Fabrication of La2O3 Uniformly Doped Mo Nanopowders by Solution Combustion Synthesis Followed by Reduction under Hydrogen
by Siyong Gu, Mingli Qin, Houan Zhang and Jidong Ma
Materials 2018, 11(12), 2385; https://doi.org/10.3390/ma11122385 - 27 Nov 2018
Cited by 10 | Viewed by 3502
Abstract
This work reports the preparation of La2O3 uniformly doped Mo nanopowders with the particle sizes of 40–70 nm by solution combustion synthesis and subsequent hydrogen reduction (SCSHR). To reach this aim, the foam-like MoO2 precursors (20–40 nm in size) [...] Read more.
This work reports the preparation of La2O3 uniformly doped Mo nanopowders with the particle sizes of 40–70 nm by solution combustion synthesis and subsequent hydrogen reduction (SCSHR). To reach this aim, the foam-like MoO2 precursors (20–40 nm in size) with different amounts of La2O3 were first synthesized by a solution combustion synthesis method. Next, these precursors were used to prepare La2O3 doped Mo nanopowders through hydrogen reduction. Thus, the content of La2O3 used for doping can be accurately controlled via the SCSHR route to obtain the desired loading degree. The successful doping of La2O3 into Mo nanopowders with uniform distribution were proved by X-ray photon spectroscopy and transmission electron microscopy. The preservation of the original morphology and size of the MoO2 precursor by the La2O3 doped Mo nanopowders was attributed to the pseudomorphic transport mechanism occurring at 600 °C. As shown by X-ray diffraction, the formation of Mo2C impurity, which usually occurs in the direct H2 reduction process, can be avoided by using the Ar calcination-H2 reduction process, when residual carbon is removed by the carbothermal reaction during Ar calcination at 500 °C. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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11 pages, 6572 KiB  
Article
Effect of Electric Current Pulse on Microstructure and Corrosion Resistance of Hypereutectic High Chromium Cast Iron
by Haiyang Lv, Rongfeng Zhou, Lu Li, Haitao Ni, Jiang Zhu and Tong Feng
Materials 2018, 11(11), 2220; https://doi.org/10.3390/ma11112220 - 08 Nov 2018
Cited by 10 | Viewed by 4213
Abstract
The effect of electric current pulse on the microstructure and corrosion resistance of hypereutectic high chromium cast iron was explored. The morphology of carbides in solidification microstructure was observed by an optical microscope and a scanning electron microscope and the composition was determined [...] Read more.
The effect of electric current pulse on the microstructure and corrosion resistance of hypereutectic high chromium cast iron was explored. The morphology of carbides in solidification microstructure was observed by an optical microscope and a scanning electron microscope and the composition was determined by an electron probe micro-analyzer. The microhardness of primary carbides and corrosion resistance of samples were also compared. Under the active of electric current pulse, the microstructure of hypereutectic high chromium cast iron was homogenized and its performance improved accordingly. On treatment by electric current, the morphology of primary carbides changed from thick long rods to hexagonal blocks or granular structures. The interlayer spacing of eutectic carbide decreased from ~26.3 μm to ~17.8 μm. Size statistics showed that the average diameter of primary carbide decreased from ~220 μm to ~60 μm. As a result, microhardness increased from 1412 HV to 1511 HV. No obvious microcrack propagation was found at the microindentation sites. The average length of microcracks decreased from ~20.7 μm to ~5.7 μm. Furthermore, corrosion resistance was remarkably enhanced. The average corrosion rate decreased from 2.65 mg/cm2·h to 1.74 mg/cm2·h after pulse current treatment. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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10 pages, 4754 KiB  
Article
Effect of Duty Cycle on Properties of Al2O3 Ceramic Coatings Fabricated on TiAl Alloy via Cathodic Plasma Electrolytic Deposition
by Shaoqing Wang, Faqin Xie, Xiangqing Wu and Jixiang An
Materials 2018, 11(10), 1962; https://doi.org/10.3390/ma11101962 - 12 Oct 2018
Cited by 4 | Viewed by 2303
Abstract
In order to study the effect of duty cycle during the cathodic plasma electrolytic deposition (CPED) process, Al2O3 ceramic coatings were fabricated via the CPED technique on prepared TiAl alloy in an Al(NO3)3 electrolyte with different duty [...] Read more.
In order to study the effect of duty cycle during the cathodic plasma electrolytic deposition (CPED) process, Al2O3 ceramic coatings were fabricated via the CPED technique on prepared TiAl alloy in an Al(NO3)3 electrolyte with different duty cycles. Microstructure, morphology, and chemical compositions of coatings were analyzed by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The mechanical properties, such as thickness, hardness, and binding strength, were also characterized, and heat-resistance and wear-resistance tested. The results indicated that duty cycle mainly affected the relative crystallinity of CPED coatings. As the duty cycle increased, the crystallinity of CPED coatings increased, the content of Al(OH)3 and γ-Al2O3 decreased, and the content of α-Al2O3 increased. The thickness and bonding strength both increased firstly and then decreased, while hardness increased as duty cycle increased. Heat-resistance and wear-resistance of TiAl alloy with CPED coating was highly improved compared to that of TiAl alloy substrate without CPED coating. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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11 pages, 3795 KiB  
Article
A Study on the Effect of Ultrasonic Treatment on the Microstructure of Sn-30 wt.% Bi Alloy
by Shuo Wang, Jinwu Kang, Xiaopeng Zhang and Zhipeng Guo
Materials 2018, 11(10), 1870; https://doi.org/10.3390/ma11101870 - 01 Oct 2018
Cited by 5 | Viewed by 2865
Abstract
The effect of ultrasonic treatment on the microstructure of Sn-30 wt.% Bi alloy was studied at different temperatures. Results showed that the ultrasonic treatment could effectively refine the microstructure of Sn-30 wt.% Bi alloy at a temperature range between the liquidus and solidus. [...] Read more.
The effect of ultrasonic treatment on the microstructure of Sn-30 wt.% Bi alloy was studied at different temperatures. Results showed that the ultrasonic treatment could effectively refine the microstructure of Sn-30 wt.% Bi alloy at a temperature range between the liquidus and solidus. Application of the ultrasound could fragment the primary Sn dendrites during solidification due to a mixed effect of ultrasonic cavitation and acoustic streaming. The divorced eutectic formed when the ultrasonic treatment was applied for the whole duration of the solidification. The eutectic phase grew and surrounded the primary Sn dendrite, and pure Bi phase grew in between the Sn dendritic fragments. The mechanism of the fragmentation of dendrites and the divorced eutectic structure by ultrasonic treatment was discussed. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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Review

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20 pages, 4000 KiB  
Review
Advances in Selective Laser Melting of Nitinol Shape Memory Alloy Part Production
by Josiah Cherian Chekotu, Robert Groarke, Kevin O’Toole and Dermot Brabazon
Materials 2019, 12(5), 809; https://doi.org/10.3390/ma12050809 - 08 Mar 2019
Cited by 61 | Viewed by 12335
Abstract
Nitinol (nickel-titanium or Ni-Ti) is the most utilized shape memory alloy due to its good superelasticity, shape memory effect, low stiffness, damping, biocompatibility, and corrosion resistance. Various material characteristics, such as sensitivity to composition and production thermal gradients, make conventional methods ineffective for [...] Read more.
Nitinol (nickel-titanium or Ni-Ti) is the most utilized shape memory alloy due to its good superelasticity, shape memory effect, low stiffness, damping, biocompatibility, and corrosion resistance. Various material characteristics, such as sensitivity to composition and production thermal gradients, make conventional methods ineffective for the manufacture of high quality complex Nitinol components. These issues can be resolved by modern additive manufacturing (AM) methods which can produce net or near-net shape parts with highly precise and complex Nitinol structures. Compared to Laser Engineered Net Shape (LENS), Selective Laser Melting (SLM) has the benefit of more easily creating a high quality local inert atmosphere which protects chemically-reactive Nitinol powders to a higher degree. In this paper, the most recent publications related to the SLM processing of Nitinol are reviewed to identify the various influential factors involved and process-related issues. It is reported how powder quality and material composition have a significant effect on the produced microstructures and phase transformations. The effect of heat treatments after SLM fabrication on the functional and mechanical properties are noted. Optimization of several operating parameters were found to be critical in fabricating Nitinol parts of high density. The importance of processing parameters and related thermal cooling gradient which are crucial for obtaining the correct phase structure for shape memory capabilities are also presented. The paper concludes by presenting the significant findings and areas of prospective future research in relation to the SLM processing of Nitinol. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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7 pages, 2261 KiB  
Letter
Contrastive Studies between Laser Repairing and Plasma Arc Repairing on Single-Crystal Ni-Based Superalloy
by Cheng Wang, Qiuliang Li, Xin Zhou, Wenxin Zhu, Runqiu Huang, Zhihao Pan, Kai Chen and Chang He
Materials 2019, 12(7), 1172; https://doi.org/10.3390/ma12071172 - 10 Apr 2019
Cited by 6 | Viewed by 3476
Abstract
Laser repairing and plasma arc repairing experiments on the single-crystal Ni-based superalloy DD407(Ni-7.82Cr-5.34Co-2.25Mo-4.88W-6.02Al-1.94Ti-3.49Ta in wt.%) were carried out in this paper, and the differences in microstructures and mechanical properties varying with depth between the two repairing methods were studied. Comparing the two repairing [...] Read more.
Laser repairing and plasma arc repairing experiments on the single-crystal Ni-based superalloy DD407(Ni-7.82Cr-5.34Co-2.25Mo-4.88W-6.02Al-1.94Ti-3.49Ta in wt.%) were carried out in this paper, and the differences in microstructures and mechanical properties varying with depth between the two repairing methods were studied. Comparing the two repairing processes, both the fusion zone can maintain single-crystal epitaxial growth with no significant cracks and have similar fine γ′ precipitates. Nevertheless, the columnar-to-equiaxed transition phenomenon occurred on the top of the fusion zone during the laser re-melting process but was not very obvious on the top surface of the fusion zone during the plasma arc re-melting process. In addition, both the DD407 superalloy conducted with the two repairing processes had a large microhardness and a great Young’s modulus in the fusion zone. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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