| 1. |
- Huang, Shuo, et al.
(författare)
-
Thermal Expansion, Elastic and Magnetic Properties of FeCoNiCu-Based High-Entropy Alloys Using First-Principle Theory
- 2017
-
Ingår i: JOM. - : Springer. - 1047-4838 .- 1543-1851. ; 69:11, s. 2107-2112
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of V, Cr, and Mn on the magnetic, elastic, and thermal properties of FeCoNiCu high-entropy alloy are studied by using the exact muffin-tin orbitals method in combination with the coherent potential approximation. The calculated lattice parameters and Curie temperatures in the face-centered-cubic structure are in line with the available experimental and theoretical data. A significant change in the magnetic behavior is revealed when adding equimolar V, Cr, and Mn to the host composition. The three independent single-crystal elastic constants are computed using a finite strain technique, and the polycrystalline elasticity parameters including shear modulus, Young's modulus, Pugh ratio, Poisson's ratio, and elastic anisotropy are derived and discussed. The effects of temperature on the structural parameters are determined by making use of the Debye-Gruneisen model. It is found that FeCoNiCuCr possesses a slightly larger thermal expansion coefficient than do the other alloys considered here.
|
|
| 2. |
- Holmstrom, Erik, et al.
(författare)
-
High entropy alloys : Substituting for cobalt in cutting edge technology
- 2018
-
Ingår i: APPLIED MATERIALS TODAY. - : Elsevier BV. - 2352-9407. ; 12, s. 322-329
-
Tidskriftsartikel (refereegranskat)abstract
- Cemented carbide, also known as hard metal, is one of the most outstanding composite engineering materials since its commercial introduction in the 1920s. The unique combination of strength, hardness and toughness makes cemented carbides highly versatile materials for the most demanding engineering applications. In their simplest form, these materials are composites of tungsten carbide (WC) grains that are cemented with a ductile metallic binder phase, typically cobalt. However, despite the superiority of Co as binder material, there is a long-standing need to find alternative binders due to serious health concerns that have haunted the industry for nearly 80 years. In the present study, we develop a new cemented carbide with a high entropy alloy binder phase (CoCrFeNi) from raw materials to a fully functional, coated and gradient-sintered cutting tool insert. The new hard metal with reduced Co content is designed by using first principles theory and the CALPHAD method. The cutting tool was made by pressing the new hard metal in a standard geometry, sintered to have a thin binder phase enriched surface zone, free from cubic carbides and coated with protective layers of Ti(C,N) and Al2O3. The resulting cutting insert was tested in a real machining operation and compared to a state-of-the-art reference that had Co as binder phase. The cutting tool made of the newly developed cemented carbide has an exceptionally high resistance against plastic deformation at all tested cutting speeds in the machining test, outperforming the reference insert, which shows a linear increase in edge depression when the cutting speed is increased. This result opens up the possibility to utilize the unique properties of high entropy alloys for industrial applications, in particular, as binder phase in new cemented carbides.
|
|
| 3. |
- Karlsson, Dennis, et al.
(författare)
-
Binder jetting of the AlCoCrFeNi alloy
- 2019
-
Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 27, s. 72-79
-
Tidskriftsartikel (refereegranskat)abstract
- High density components of an AlCoCrFeNi alloy, often described as a high-entropy alloy, were manufactured by binder jetting followed by sintering. Thermodynamic calculations using the CALPHAD approach show that the high-entropy alloy is only stable as a single phase in a narrow temperature range below the melting point. At all other temperatures, the alloy will form a mixture of phases, including a sigma phase, which can strongly influence the mechanical properties. The phase stabilities in built AlCoCrFeNi components were investigated by comparing the as-sintered samples with the post-sintering annealed samples at temperatures between 900 °C and 1300 °C. The as-sintered material shows a dominant B2/bcc structure with additional fcc phase in the grain boundaries and sigma phase precipitating in the grain interior. Annealing experiments between 1000 °C and 1100 °C inhibit the sigma phase and only a B2/bcc phase with a fcc phase is observed. Increasing the temperature further suppresses the fcc phase in favor for the B2/bcc phases. The mechanical properties are, as expected, dependent on the annealing temperature, with the higher annealing temperature giving an increase in yield strength from 1203 MPa to 1461 MPa and fracture strength from 1996 MPa to 2272 MPa. This can be explained by a hierarchical microstructure with nano-sized precipitates at higher annealing temperatures. The results enlighten the importance of microstructure control, which can be utilized in order to tune the mechanical properties of these alloys. Furthermore, an excellent oxidation resistance was observed with oxide layers with a thickness of less than 5 μm after 20 h annealing at 1200 °C, which would be of great importance for industrial applications.
|
|
| 4. |
- Saketi, Sara, et al.
(författare)
-
Wear behaviour of two different cemented carbide grades in turning 316 L stainless steel
- 2018
-
Ingår i: Materials Science Forum. - : TRANS TECH PUBLICATIONS LTD. - 0255-5476 .- 1662-9752. ; 941, s. 2367-2372, s. 2367-2372
-
Tidskriftsartikel (refereegranskat)abstract
- Cemented carbides are the most common cutting tools for machining various grades of steels. In this study, wear behavior of two different cemented carbide grades with roughly the same fraction of binder phase and carbide phase but different grain size, in turning austenitic stainless steel is investigated. Wear tests were carried out against 316L stainless steel at 180 and 250 m/mincutting speeds. The worn surface of cutting tool is characterized using high resolution scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), Auger electron spectroscopy (AES) and 3D optical profiler.The wear of cemented carbide in turning stainless steel is controlled by both chemical and mechanical wear. Plastic deformation, grain fracture and chemical wear is observed on flank and rake face of the cutting insert. In the case of fine-grained, the WC grains has higher surface contact with the adhered material which promotes higher chemical reaction and degradation of WC grains, so chemical wear resistance of the composites is larger when WC grains are larger. The hardness of cemented carbide increase linearly by decreasing grain size, therefore mechanical wear resistance of the composites is larger when WC grains are smaller.
|
|
| 5. |
- Calamba, Katherine, et al.
(författare)
-
Effect of nitrogen vacancies on the growth, dislocation structure, and decomposition of single crystal epitaxial (Ti1-xAlx)N-y thin films
- 2021
-
Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 203
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of varying nitrogen vacancies on the growth, microstructure, spinodal decomposition and hardness values of predominantly single crystal cubic phase c-(Ti1-xAlx)N-y films was investigated. Epitaxial c-(Ti1-xAlx)N-y films with y = 0.67, 0.79, and 0.92 were grown on MgO(001) and MgO(111) substrates by magnetron sputter deposition. High N vacancy c-(Ti1-xAlx)N-0.67 films deposited on MgO(111) contained coherently oriented w-(0001) structures while segregated conical structures were observed on the films grown on MgO(001). High resolution STEM images revealed that the N-deficient growth conditions induced segregation with small compositional fluctuations that increase with the number of N vacancies. Similarly, strain map analysis of the epitaxial c-(Ti1-xAlx)N-y (001) and (111) films show fluctuations in strain concentration that scales with the number of N vacancies and increases during annealing. The spinodal decomposition coarsening rate of the epitaxial c-(Ti1-xAlx)N-y films was observed to increase with decreasing N vacancies. Nanoindentation showed decreasing trends in hardness of the as-deposited films as the N vacancies increase. Isothermal post-anneal at 1100 degrees C in vacuum for 120 min revealed a continuation in the increase in hardness for the film with the largest number of N vacancies (y = 0.67) while the hardness decreased for the films with y = 0.79 and 0.92. These results suggest that nitrogen-deficient depositions of c-(Ti1-xAlx)N-y films help to promote a self-organized phase segregation, while higher N vacancies generally increase the coherency strain which delays the coarsening process and can influence the hardness at high temperatures.
|
|
| 6. |
- Dong, Zhihua, et al.
(författare)
-
Invariant plastic deformation mechanism in paramagnetic nickel-iron alloys
- 2021
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 118:14
-
Tidskriftsartikel (refereegranskat)abstract
- The Invar anomaly is one of the most fascinating phenomena observed in magnetically ordered materials. Invariant thermal expansion and elastic properties have attracted substantial scientific attention and led to important technological solutions. By studying planar faults in the high-temperature magnetically disordered state of Ni1-cFec, here we disclose a completely different anomaly. An invariant plastic deformation mechanism is characterized by an unchanged stacking fault energy with temperature within wide concentration and temperature ranges. This anomaly emerges from the competing stability between the face-centered cubic and hexagonal close-packed structures and occurs in other paramagnetic or nonmagnetic systems whenever the structural balance exists. The present findings create a platform for tailoring high-temperature properties of technologically relevant materials toward plastic stability at elevated temperatures.
|
|
| 7. |
- Huang, Shuo, et al.
(författare)
-
Strengthening Induced by MagnetoChemical Transition in Al-Doped Fe-Cr-Co-Ni High-Entropy Alloys
- 2018
-
Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 10:6
-
Tidskriftsartikel (refereegranskat)abstract
- Alloys with adjustable mechanical performance are of fundamental interest in material designs. Here, we investigate the magnetic- and chemical-ordering behavior of the ferromagnetic Fe-Cr-Co-Ni-Al-x (1 <= x <= 2.5) high-entropy alloys with the help of first-principle alloy theory. The lattice constants and the single- and polycrystalline elastic parameters for partially ordered and random structures are considered. In contrast to the trend found for the completely disordered phase, we demonstrate that ordering driven primarily by Al results in an enhanced Young's modulus, especially at high-Al concentrations, which is in line with the observed increase of the hardness for systems with a body-centered-cubic underlying lattice. The results suggest that outstanding strength and ductility can be realized by proper control of the ordering level in single- and multiphase high-entropy alloys.
|
|
| 8. |
- Li, Xiaoqing, et al.
(författare)
-
First-principles investigation of the micromechanical properties of fcc-hcp polymorphic high-entropy alloys
- 2018
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- High-entropy alloys offer a promising alternative in several high-technology applications concerning functional, safety and health aspects. Many of these new alloys compete with traditional structural materials in terms of mechanical characteristics. Understanding and controlling their properties are of the outmost importance in order to find the best single-or multiphase solutions for specific uses. Here, we employ first-principles alloy theory to address the micro-mechanical properties of five polymorphic high-entropy alloys in their face-centered cubic (fcc) and hexagonal close-packed (hcp) phases. Using the calculated elastic parameters, we analyze the mechanical stability, elastic anisotropy, and reveal a strong correlation between the polycrystalline moduli and the average valence electron concentration. We investigate the ideal shear strength of two selected alloys under shear loading and show that the hcp phase possesses more than two times larger intrinsic strength than that of the fcc phase. The derived half-width of the dislocation core predicts a smaller Peierls barrier in the fcc phase confirming its increased ductility compared to the hcp one. The present theoretical findings explain a series of important observations made on dual-phase alloys and provide an atomic-level knowledge for an intelligent design of further high-entropy materials.
|
|
| 9. |
- Muscas, Giuseppe, et al.
(författare)
-
Nanostructure-driven complex magnetic behavior of Sm2CoMnO6 double perovskite
- 2022
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 906
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetic double perovskite oxides have steadily emerged as an important class of functional materials. A clear understanding of the complex interactions that govern the magnetic behavior, and thereby, the functionality in these mixed valence compounds, however, remains elusive. In this study, we show that the complex nanostructure that forms in these compounds is at the root of their magnetic behavior. Using complementary experimental and micromagnetic simulation results, we have uncovered the complex nanostructure of polycrystalline Sm2CoMnO6, a typical double perovskite oxide, and established how the nanostructure drives its magnetic behavior. Our results show that Sm2CoMnO6 exhibits a Griffiths phase with the formation of ferromagnetic clusters above the ordering temperature. The isothermal magnetization curves show no sign of saturation, even at the highest measured field (9 T), and irreversibility in the entire magnetic field range. Despite a very clear indication of the presence of antiferromagnetic antisite defects, surprisingly, no antisite defect-induced exchange bias occurs. This is explained from the micro magnetic simulations that confirm the presence of ferromagnetic nanoclusters and nanosized, random, and uncorrelated antisite defects, resulting in no exchange bias. This work provides a clear understanding of the role of antisite defects, in particular, on how their structure can lead to the presence/absence of exchange bias. The fundamental insight offered in this work fills an important knowledge gap in the field and will be of immense value in realizing the true potential of double perovskite oxides for future technological applications. (C)& nbsp;2022 The Author(s). Published by Elsevier B.V.
|
|
| 10. |
- Schönecker, Stephan, et al.
(författare)
-
Harnessing elastic anisotropy to achieve low-modulus refractory high-entropy alloys for biomedical applications
- 2022
-
Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 215
-
Tidskriftsartikel (refereegranskat)abstract
- A high-priority target in the design of new metallic materials for load-bearing implant applications is the reduction of Young's modulus approximating that of cortical bone in the predominant loading direction. Here, we explore how directionally preferential bulk elastic properties of implant materials are achieved by harnessing elastic anisotropy. Specifically focusing on recently proposed biocompatible refractory high-entropy alloys (RHEAs) in the body-centered cubic structure, we conduct systematic densityfunctional theory calculations to investigate the single-crystal elastic properties of 21 Ti-containing RHEAs. Our results provide evidence that the valence electron count has a dominant influence on elastic anisotropy and crystal directions of low Young's modulus and high torsion modulus in the RHEAs. By means of modeling the orientation distribution function for crystallographic texture, we examine the effect of non-random texture on the anisotropic poly-crystalline Young's modulus and torsion modulus with varying texture sharpness. We adopt fiber textures that can result from rolling and distinct texture orientations that can form during rapid directional solidification. We discuss the potential for lowering Young's modulus in the RHEAs by using single crystals or textured aggregates. Furthermore, we prepare four of the theoretically considered alloys by arc-melting and report their lattice parameters, quasi isotropic Young's moduli, and Wickers hardnesses.
|
|
