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Alloys, Volume 2, Issue 1 (March 2023) – 5 articles

Cover Story (view full-size image): Nickel has been used as an alloying element for steel for more than a century. Its key function is increasing corrosion resistance in austenitic stainless steels. Adding nickel to ordinary carbon steels not only enhances strength but significantly improves low-temperature toughness. This is inherently related to the effect of “cold softening”. For demanding cryogenic applications, nickel-alloyed steels are subjected to double quenching and tempering treatments. Here, nickel helps to stabilize a phase fraction of retained austenite providing high fracture toughness. These superior properties of nickel alloyed carbon steels are crucially important in the global transition towards a green energy economy. View this paper
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12 pages, 6742 KiB  
Article
Using Molecular Dynamic Simulation to Understand the Deformation Mechanism in Cu, Ni, and Equimolar Cu-Ni Polycrystalline Alloys
by Sepehr Yazdani and Veronique Vitry
Alloys 2023, 2(1), 77-88; https://doi.org/10.3390/alloys2010005 - 15 Mar 2023
Cited by 4 | Viewed by 2495
Abstract
The grain boundaries and dislocations play an important role in understanding the deformation behavior in polycrystalline materials. In this paper, the deformation mechanism of Cu, Ni, and equimolar Cu-Ni alloy was investigated using molecular dynamic simulation. The interaction between dislocations and grain boundary [...] Read more.
The grain boundaries and dislocations play an important role in understanding the deformation behavior in polycrystalline materials. In this paper, the deformation mechanism of Cu, Ni, and equimolar Cu-Ni alloy was investigated using molecular dynamic simulation. The interaction between dislocations and grain boundary motion during the deformation was monitored using the dislocation extraction algorithm. Moreover, the effect of stacking fault formation and atomic band structure on the deformation behavior was discussed. Results indicate that dislocations nucleate around the grain boundary in copper, the deformation in nickel changes from planar slip bands to wavy bands, and high density of dislocation accumulation as well as numerous kink and jog formations were observed for the equimolar Cu-Ni alloy. The highest density of the Shockley dislocation and stacking faults was formed in the equimolar Cu-Ni alloy which results in the appearance of a huge gliding stage in the stress–strain curve. The grain boundaries act as a sinking source for vacancy annihilation in Ni and Cu; however, this effect was not observed in an equimolar Cu-Ni alloy. Finally, radial distribution function was used to evaluate atom segregation in grain boundaries. Full article
(This article belongs to the Collection Feature Paper Collection of Advanced Research on Alloys)
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22 pages, 2624 KiB  
Article
Density-Based Optimization of the Laser Powder Bed Fusion Process Based on a Modelling Framework
by Harry O. Psihoyos and George N. Lampeas
Alloys 2023, 2(1), 55-76; https://doi.org/10.3390/alloys2010004 - 27 Feb 2023
Cited by 3 | Viewed by 2761
Abstract
One of the main challenges encountered in the Laser-based Powder Bed Fusion (L-PBF) Additive Manufacturing (AM) process is the fabrication of defect-free parts. The presence of defects severely degrades the mechanical performance of AM parts and especially their fatigue strength. The most popular [...] Read more.
One of the main challenges encountered in the Laser-based Powder Bed Fusion (L-PBF) Additive Manufacturing (AM) process is the fabrication of defect-free parts. The presence of defects severely degrades the mechanical performance of AM parts and especially their fatigue strength. The most popular and reliable method to assess the ability of the employed process parameters for the fabrication of full-density parts is the process windows map, also known as printability map. However, the experimental procedure for the design of the printability maps and the identification of the optimum-density process parameters is usually time-consuming and expensive. In the present work, a modelling framework is presented for the determination of a printability map and the optimization of the L-PBF process based on the prediction and characterization of melt-pool geometric features and the prediction of porosity of small samples of 316L SS and Ti-6Al-4V metal alloys. The results are compared with available experimental data and present a good correlation, verifying the modelling methodology. The suitability of the employed defect criteria for each material and the effect of the hatch-spacing process parameter on the optimum-density parameters are also presented. Full article
(This article belongs to the Collection Feature Paper Collection of Advanced Research on Alloys)
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11 pages, 2869 KiB  
Article
Powder Metallurgy Processing and Characterization of the χ Phase Containing Multicomponent Al-Cr-Fe-Mn-Mo Alloy
by Tomasz Stasiak, Mourtada Aly Sow, Matthieu Touzin, Franck Béclin and Catherine Cordier
Alloys 2023, 2(1), 44-54; https://doi.org/10.3390/alloys2010003 - 13 Feb 2023
Viewed by 2025
Abstract
High entropy alloys present many promising properties, such as high hardness or thermal stability, and can be candidates for many applications. Powder metallurgy techniques enable the production of bulk alloys with fine microstructures. This study aimed to investigate powder metallurgy preparation, i.e., mechanical [...] Read more.
High entropy alloys present many promising properties, such as high hardness or thermal stability, and can be candidates for many applications. Powder metallurgy techniques enable the production of bulk alloys with fine microstructures. This study aimed to investigate powder metallurgy preparation, i.e., mechanical alloying and sintering, non-equiatomic high entropy alloy from the Al-Cr-Fe-Mn-Mo system. The structural and microstructural investigations were performed on powders and the bulk sample. The indentation was carried out on the bulk sample. The mechanically alloyed powder consists of two bcc phases, one of which is significantly predominant. The annealed powder and the sample sintered at 950 °C for 1 h consist of a predominantly bcc phase (71 ± 2 vol.%), an intermetallic χ phase (26 ± 2 vol.%), and a small volume fraction of multielement carbides—M6C and M23C6. The presence of carbides results from carbon contamination from the balls and vial during mechanical alloying and the graphite die during sintering. The density of the sintered sample is 6.71 g/cm3 (98.4% relative density). The alloy presents a very high hardness of 948 ± 34 HV1N and Young’s modulus of 245 ± 8 GPa. This study showed the possibility of preparing ultra-hard multicomponent material reinforced by the intermetallic χ phase. The research on this system presented new knowledge on phase formation in multicomponent systems. Moreover, strengthening the solid solution matrix via hard intermetallic phases could be interesting for many industrial applications. Full article
(This article belongs to the Special Issue High-Entropy Alloys)
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15 pages, 5198 KiB  
Article
Microstructure Evolution by Thermomechanical Processing in the Fe-10Al-12V Superalloy
by Pedro A. Ferreirós, Abraham A. Becerra, Uriel A. Sterin, Martina C. Ávalos, Raúl E. Bolmaro and Gerardo H. Rubiolo
Alloys 2023, 2(1), 29-43; https://doi.org/10.3390/alloys2010002 - 31 Jan 2023
Viewed by 2390
Abstract
Nowadays, great efforts are being made to develop bcc-superalloys for medium- and high-temperature applications. However, the high brittle-to-ductile transition temperatures (BDTT) have restricted their application. Therefore, designing hot-processing routes to obtain a refined grain in these new superalloys is required. Particularly in the [...] Read more.
Nowadays, great efforts are being made to develop bcc-superalloys for medium- and high-temperature applications. However, the high brittle-to-ductile transition temperatures (BDTT) have restricted their application. Therefore, designing hot-processing routes to obtain a refined grain in these new superalloys is required. Particularly in the Fe-10Al-12V (at%) alloy, we have recently tested the BDTT shifting and, using physical models, it was indicated that a combination of L21-precipitate sizes with small grain sizes could shift the BDTT below room temperature. Here, we will present the study that allowed us to design the processing route for grain refinement in the tested superalloy. Molds of different geometry and with metallic and sand walls were used to test two different types of casting. Carbide conditioning treatments for improving the sizes and distribution were studied. The recrystallization process was explored first by hot rolling and post-annealing in stepped geometry samples with two different columnar grain orientations. Finally, we analyzed the grain microstructure obtained along a hot processing route consisting of carbide conditioning treatment, forging into a squared bar, and hot rolling up to a 2.8 mm thickness strip. Full article
(This article belongs to the Collection Feature Paper Collection of Advanced Research on Alloys)
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28 pages, 5129 KiB  
Review
Nickel Alloying in Carbon Steel: Fundamentals and Applications
by Hardy Mohrbacher and Andreas Kern
Alloys 2023, 2(1), 1-28; https://doi.org/10.3390/alloys2010001 - 11 Jan 2023
Cited by 4 | Viewed by 12155
Abstract
Nickel is an important and widely used alloying element in carbon steels. Some of its prominent metallurgical effects in these steels are moderate solid solution strengthening, mild hardenability and, importantly, a strong promotion of toughness, especially at low temperatures. The first uses of [...] Read more.
Nickel is an important and widely used alloying element in carbon steels. Some of its prominent metallurgical effects in these steels are moderate solid solution strengthening, mild hardenability and, importantly, a strong promotion of toughness, especially at low temperatures. The first uses of nickel as an alloying element in commercial steel production date back to the early 20th century. The aim of the current review is to give the reader a thorough and concise overview of nickel functionalities relevant to modern carbon steel production. The interaction of nickel with other alloying elements and processing conditions is also considered. Examples will be given demonstrating the advantages of nickel alloying in selected steel grades and applications. Full article
(This article belongs to the Collection Feature Paper Collection of Advanced Research on Alloys)
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