scholarly journals Processing Conditions Optimization for the Synthesis and Consolidation of High-Entropy Diborides

2021 ◽  
Vol 23 (3) ◽  
pp. 213
Author(s):  
S. Barbarossa ◽  
M. Murgia ◽  
R. Orrù ◽  
G. Cao
Keyword(s):  
Single Phase ◽  
Processing Conditions ◽  
High Entropy ◽  
Temperature Conditions ◽  
Final Density ◽  
Plasma Sintering ◽  
High Temperature Synthesis ◽  
Surface Oxides ◽  
Spark Plasma ◽  
Lower Temperature

The fabrication by Spark Plasma Sintering (SPS) of bulk high entropy ceramics from powders obtained by Self-propagating High temperature Synthesis (SHS) is addressed in this work. The effect produced by the introduction of 1 wt.% of graphite to the powders before SPS is investigated under different temperature conditions. The final density and composition of sintered (Hf0.2Mo0.2Zr0.2Ti0.2Ta0.2)B2 and (Hf0.2Mo0.2Zr0.2Ti0.2Nb0.2)B2 ceramics are found to be negatively affected by the presence of oxide impurities in the powders. While product composition can be progressively improved when the temperature is increased from 1800 to 1950 °C, residual porosities remain relatively high if using additive-free powders. In contrast, the introduction of 1 wt.%C markedly allows for oxides elimination by carbothermal reduction mechanism. Products consolidation is correspondingly enhanced so that relative densities of about 97% are attained. Other than the latter effect, surface oxides removal also makes powders more reactive, thus the synthesis of single-phase products is promoted. In particular, fully homogeneous (Hf0.2Mo0.2Zr0.2Ti0.2Ta0.2)B2 ceramics are obtained at relatively lower temperature conditions (1850 °C).

scholarly journals Fabrication and Characterization of Quinary High Entropy-Ultra-High Temperature Diborides

Ceramics ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 108-120
Author(s):  
Simone Barbarossa ◽  
Roberto Orrù ◽  
Valeria Cannillo ◽  
Antonio Iacomini ◽  
Sebastiano Garroni ◽  
...  
Keyword(s):  
High Temperature ◽  
Single Phase ◽  
Nominal Composition ◽  
High Entropy ◽  
Chemical Complexity ◽  
Alternative Processing ◽  
Plasma Sintering ◽  
High Temperature Synthesis ◽  
Spark Plasma

Due to their inherent chemical complexity and their refractory nature, the obtainment of highly dense and single-phase high entropy (HE) diborides represents a very hard target to achieve. In this framework, homogeneous (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2, (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2, and (Hf0.2Zr0.2Nb0.2Mo0.2Ti0.2)B2 ceramics with high relative densities (97.4, 96.5, and 98.2%, respectively) were successfully produced by spark plasma sintering (SPS) using powders prepared by self-propagating high-temperature synthesis (SHS). Although the latter technique did not lead to the complete conversion of initial precursors into the prescribed HE phases, such a goal was fully reached after SPS (1950 °C/20 min/20 MPa). The three HE products showed similar and, in some cases, even better mechanical properties compared to ceramics with the same nominal composition attained using alternative processing methods. Superior Vickers hardness and elastic modulus values were found for the (Hf0.2Nb0.2Ta0.2Mo0.2Ti0.2)B2 and the (Hf0.2Zr0.2Ta0.2Mo0.2Ti0.2)B2 systems, i.e., 28.1 GPa/538.5 GPa and 28.08 GPa/498.1 GPa, respectively, in spite of the correspondingly higher residual porosities (1.2 and 2.2 vol.%, respectively). In contrast, the third ceramic, not containing tantalum, displayed lower values of these two properties (25.1 GPa/404.5 GPa). However, the corresponding fracture toughness (8.84 MPa m1/2) was relatively higher. This fact can be likely ascribed to the smaller residual porosity (0.3 vol.%) of the sintered material.

scholarly journals Application of Hydride Process in Achieving Equimolar TiNbZrHfTa BCC Refractory High Entropy Alloy

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1020 ◽  
Author(s):  
Bhupendra Sharma ◽  
Kentaro Nagano ◽  
Kuldeep Kumar Saxena ◽  
Hiroshi Fujiwara ◽  
Kei Ameyama
Keyword(s):  
Titanium Hydride ◽  
Single Phase ◽  
Strengthening Mechanism ◽  
High Entropy Alloy ◽  
Mechanically Alloyed ◽  
High Entropy ◽  
Plasma Sintering ◽  
Bcc Structure ◽  
Spark Plasma ◽  
Tih2 Powder

For the first time, an equiatomic refractory high entropy alloy (RHEA) TiNbZrHfTa compact with a single-phase body-centered cubic (BCC) structure was fabricated via a titanium hydride (TiH2) assisted powder metallurgy approach. The constituent pure Ti, Zr, Nb, Hf, and Ta powders were mechanically alloyed (MA) with titanium hydride (TiH2) powder. The resultant MA powder was dehydrogenated at 1073 K for 3.6 ks and subsequently sintered through spark plasma sintering (SPS). Additionally, TiNbZrHfTa counterparts were prepared from pure elements without MA with TiH2. It was observed that the compact prepared from pure powders had a chemically heterogeneous microstructure with hexagonal close packed (HCP) and dual BCC phases. On the other hand, despite containing many constituents, the compact fabricated at 1473 K for 3.6 ks via the hydride approach had a single-phase BCC structure. The Vickers microhardness of the TiNbZrHfTa alloy prepared via the hydride process was Hv 520 (±30). The exceptional microhardness of the alloy is greater than any individual constituent, suggesting the operation of a simple solid-solution-like strengthening mechanism and/or precipitation hardening. In addition, the heat treatments were also carried out to analyze the phase stability of TiNbZrHfTa prepared via the hydride process. The results highlight the substantial changes in the phase as a function of temperature and/or time.

Thermal conductivity and hardness of three single-phase high-entropy metal diborides fabricated by borocarbothermal reduction and spark plasma sintering

2020 ◽  
Vol 46 (5) ◽  
pp. 6906-6913 ◽  
Author(s):  
Joshua Gild ◽  
Andrew Wright ◽  
Kathleen Quiambao-Tomko ◽  
Mingde Qin ◽  
John A. Tomko ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Spark Plasma Sintering ◽  
Single Phase ◽  
High Entropy ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Metal Diborides

Investigations of the coupling of spin-orbital in MgTi2O4 by the magnetic entropy measurements

2014 ◽  
Vol 28 (29) ◽  
pp. 1450232 ◽  
Author(s):  
Yuanyuan Zhu ◽  
Rongjun Wang ◽  
Li Wang ◽  
Yong Liu ◽  
Rui Xiong ◽  
...  
Keyword(s):  
Single Phase ◽  
Entropy Change ◽  
Antiferromagnetic Order ◽  
Magnetic Entropy ◽  
Spin Orbital ◽  
Absolute Value ◽  
Spin Entropy ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
Lower Temperature

Single phase MgTi 2 O 4 compound was synthesized by spark plasma sintering (SPS) method. The temperature dependence of the magnetic susceptibility and specific heat measurements show that MgTi 2 O 4 takes place in phase transition at 258 K. Magnetic entropy measurements show that the change of magnetic entropy ΔSM is positive and ΔSM increases more quickly than H2/3 near the transition; while ΔSM is negative and |ΔSM| (the absolute value) increases slowly with applied field increasing at lower temperature. The change of ΔSM at different temperature range is suggested to be related not only to spin entropy change, but also orbital entropy change. The magnetic phases of MgTi 2 O 4 are suggested to be Pauli paramagnetic, collinear antiferromagnetic and non-collinear antiferromagnetic order with temperature decrease.

scholarly journals Understanding the Links between the Composition-Processing-Properties in New Formulations of HEAs Sintered by SPS

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 888
Author(s):  
Paula Alvaredo-Olmos ◽  
Jon Molina-Aldareguía ◽  
Alvaro Vaz-Romero ◽  
Estela Prieto ◽  
Jesús González-Julián ◽  
...  
Keyword(s):  
High Hardness ◽  
Processing Parameters ◽  
Heating Rates ◽  
High Entropy ◽  
Plasma Sintering ◽  
Mechanical Study ◽  
Spark Plasma ◽  
Processing Properties ◽  
Bcc Phase ◽  
Hardness Values

This work presents two new compositions of high entropy alloys (HEAs) that were designed with the aim of obtaining a body-centered cubic (BCC) phase with high hardness values and a moderate density. Sintering was performed using Spark Plasma Sintering (SPS) with different heating rates to determine the influence of the processing parameters on the phase formation. The microstructural study revealed that the presence of Ni in the composition promoted phase separation, and the mechanical study confirmed a clear influence on the mechanical properties of both the composition and heating rate. The combination of microscopy with compression and nanoindentation tests at room and high temperature made it possible to advance our understanding of the relationships between the composition, processing, and properties of this emerging group of alloys.

scholarly journals Vacuum brazing of Al2O3 and 3D printed Ti6Al4V lap-joints using high entropy driven AlZnCuFeSi filler

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ashutosh Sharma ◽  
Byungmin Ahn
Keyword(s):  
Strength Properties ◽  
Lap Joints ◽  
High Entropy Alloy ◽  
Face Centered Cubic ◽  
High Entropy ◽  
Plasma Sintering ◽  
Spark Plasma ◽  
3D Printed ◽  
Face Centered ◽  
Alloy Filler

AbstractIn this work, we studied the brazing characteristics of Al2O3 and 3D printed Ti–6Al–4V alloys using a novel equiatomic AlZnCuFeSi high entropy alloy filler (HEAF). The HEAF was prepared by mechanical alloying of the constituent powder and spark plasma sintering (SPS) approach. The filler microstructure, wettability and melting point were investigated. The mechanical and joint strength properties were also evaluated. The results showed that the developed AlZnCuFeSi HEAF consists of a dual phase (Cu–Zn, face-centered cubic (FCC)) and Al–Fe–Si rich (base centered cubic, BCC) phases. The phase structure of the (Cu–Al + Ti–Fe–Si)/solid solution promises a robust joint between Al2O3 and Ti–6Al–4V. In addition, the joint interfacial reaction was found to be modulated by the brazing temperature and time because of the altered activity of Ti and Zn. The optimum shear strength reached 84 MPa when the joint was brazed at 1050 °C for 60 s. The results can be promising for the integration of completely different materials using the entropy driven fillers developed in this study.

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