Formation Of Solid Solution Phase Research Articles

Solid-solution phase formation rules for high entropy alloys: A thermodynamic perspective

To save time and money before starting the production of a high entropy alloy (HEA), it is important to predict the possibility of HEA formation and the probable final microstructure using the solid solution phase formation thermodynamic rules. In this research, a step-by-step calculation of thermodynamic parameters is conducted to predict the possibility of formation and determine the final properties such as ∆Hmix­, ∆Smix, δr, δχ, Ω, VEC, and Tm for three Ni20Co20Cu15Fe20Mn25, Ni35Co20Cu5Fe5Mn35, and Ni5Co5Cu35Fe35Mn20 HEAs. Based on the obtained results, it is not possible to form a HEA with a solid solution structure for the Ni35Co20Cu5Fe5Mn35 and Ni5Co5Cu35Fe35Mn20 systems due to a low ∆Smix value of 11.28 J.mol-1.K-1. Based on the calculated values of ∆Hmix­, intermetallic compound formation and segregation are predicted for Ni35Co20Cu5Fe5Mn35 and Ni5Co5Cu35Fe35Mn20, respectively.

The simultaneous elimination of NOx and VOCs over industrial V-based catalytic filter: Reaction behaviors and catalyst structural evolutions

The effective elimination of multiple pollutants (e.g., SOx, NOx, VOCs, dusts) in a simple unit is a long-term goal in the field of flue gas purification. In this work, the simultaneous removal of NOx and toluene was explored over the industrial V2O5-MoO3/TiO2 catalytic filter. The catalytic evaluations show that two reactions may share the same type of active sites, and observed adverse interaction effects at low temperatures, which significantly weakened as the temperature increased. Water vapor plays an amazing role with almost 100% removal efficiency of both NOx and VOCs for long-term test under harsh conditions at 350 ℃. Multiple structural characterizations confirmed the great structure stability. Especially, the catalyst components can be sulfated by SO2 and become more dispersed and uniform owing to the formation of solid solution phase, which further improves the removal performance. Moreover, the mechanism over the dynamically balanced V5+/4+/3+-SO3/42- sites was proposed, and the main reaction pathway of toluene oxidation follows the route of benzaldehyde → benzoic acid → maleic anhydride → CO2. Particularly, the In-situ DFIRTS results further confirm the above reaction/interaction effects and sulfur/steam-resistance mechanisms during the simultaneous removal of both NOx and VOCs. The excellent sulfur/steam-resistance performance and special structure features of the industrial V-based catalytic filter foreshadow the promising industrial application prospect for the effective purification of flue gas containing VOCs.

Vacuum brazing of YSZ ceramic and TC4 alloy with a Ti20Zr20Hf20Cu20Ni20 high entropy amorphous alloy

The joint embrittlement induced by bulky intermetallic compounds (IMCs) formed during brazing greatly impairs the bonding strength of Yttria-stabilized zirconia (YSZ) ceramic and Ti6Al4V (TC4) alloy. To inhibit the growth of IMCs and prevent the formation of bulky phases, in this work, a Ti20Zr20Hf20Cu20Ni20 high-entropy amorphous alloy was innovatively used for brazing YSZ- TC4. The microstructure and mechanical properties of the joint brazed at different temperatures were studied in detail. The results show that the joint is mainly composed of the α-Ti solid solution phase and eutectoid microstructure which composites of α-Ti matrix and fine acicular (Ti, Zr, Hf)2(Cu, Ni) second phase. Through thermodynamic calculation, it was determined that the synergistic interaction of multi-principal elements significantly increased the mixing entropy of the joint and hence facilitated the formation of solid solution phases, inhibiting the formation of bulky IMCs. The maximum shear strength of the joint can be reached 240.5 MPa with the brazing parameters of 960 °C and 10 min, which was much higher than most of the commonly used Ag–Cu or Ti-based filler metal. This research proves that using high entropy amorphous alloy as filler metal is a promising method to reduce the formation of intermetallic compounds in the interfacial microstructure of brazed joints.

Computational analysis of novel AlLiMgTiX light high entropy alloys

Phase formation rules include some terms and parameters are defined to predict the formation and stability of solid solution phases in light high entropy alloys (LHEAs). Calculation of the terms considering respective criteria for LHEAs, introduced the AlLiMgTiX alloy group (X = Zr, Nb) containing the lightest Al14Li11Mg35Ti15Zr25 alloy with theoretical density (ρth) of 3.36 g/cm3. Varying the atomic percentages of each composing element between 5 andto 35 in the AlLiMgTiX alloy group lead to a total of 3749 alloys with ρth less than or equal to 5 g/cm3. In theory, some terms like δ and Δχ representing atomic radii and electronegativity differences are used to design novel LHEAs, and minimizing values of such terms facilitates the formation of solid solution phases in the structure of LHEAs. According to calculations, Al10Li5Mg35Ti15Zr35 and Al20Li8Mg5Ti35Nb32 were the alloys with minimum values of Δχ and δ respectively. Hence, some experimental works were done to verify the design method and check the validity of terms in phase formation rules. On that account, the difficulties of alloying due to the presence of Li and Mg were overcome by reducing the total weight percentage of such elements resulting in the successful fabrication of bcc single solid solution phase Al21Li8Mg5Ti34Nb32 -LHEA via melting and casting method with a density of 5.28 g/cm3.

Ensemble-based machine learning models for phase prediction in high entropy alloys

High entropy alloys (HEAs), which are multi-component alloys having constituent elements in equi-atomic or near equi-atomic ratios, are receiving immense attention owing to their remarkable mechanical and physical properties. These unusual properties depend on one or more of the phases that these alloy systems constitute, namely solid solution (SS), intermetallic compound (IM), and amorphous (AM) phases. Therefore, phase prediction is crucial in selecting appropriate elements that lead to the formation of a HEA with desirable properties. In this work, machine learning (ML) models are used on a set of design parameters using multi-classification for HEA phase prediction. The ML models comprised ensemble-based (Random Forest and Stacked ensemble) and support vector machine (SVM) methods. To predict solid solution phase formation, researchers used atomic size difference and the parameter Ω=TmΔSmixΔHmix where Tm is average melting point, ΔSmix is entropy of mixing and ΔHmix is mixing enthalpy. The features used in this study are Ω, atomic size difference, average electron concentration, electronegativity difference, average melting point, mean atomic radius, mixing enthalpy, the entropy of mixing, and bulk modulus. The training dataset comprising of 601 as cast alloys is used with cross-validation for test data, and the phases SS, IM, AM, SS + IM, and IM + AM are predicted. The phase prediction accuracies are calculated using one-vs-rest, and precision-recall curves are plotted to determine the model performance. For phases AM, SS, and IM, the stacked ensemble displayed better accuracies when compared to SVM and Random Forest. The findings indicate that the stacked ensemble, which combines weak learners and meta-models, provides accuracy comparable to the neural network model accuracy reported in the literature. These findings provide insights to researchers and practitioners in selecting features and ML models while designing HEAs.

Microstructure and mechanical properties of two uranium-containing high-entropy alloys

This paper reports the microstructure and mechanical properties of two uranium-containing high-entropy alloys (HEAs), i.e., UMoNbTaHf and UMoNbTaTi. Both these alloys formed a simple solid solution without intermediate compounds in the solid state, indicating that the uranium-containing HEAs conform to the law of solid-solution phase formation and confirming that actinides can form HEAs. The UMoNbTaHf alloy achieved a body-centered cubic (BCC) structure (a = 332.1 pm), whereas the UMoNbTaTi alloy achieved a dual BCC structure comprising two BCC phases (a1 = 333.2 pm and a2 = 328.0 pm). By replacing the Hf in UMoNbTaHf with Ti, its room-temperature compressive yield strength decreased from 1147 MPa to 985 MPa, and its breaking strain increased from 7.7% to 39.5%. Further, its strength and toughness were balanced because of the formation of the dual BCC phase. UMoNbTaTi exhibited better strength and toughness than UMoNbTaHf. In addition, this study expands the application of HEAs design to actinide materials.

Factors determining solid solution phase formation and stability in CoCrFeNiX0.4 (X=Al, Nb, Ta) high entropy alloys fabricated by powder plasma arc additive manufacturing

In high entropy alloys (HEAs), the formation of solid solution phase is governed by main factors such as mixing entropy, mixing enthalpy, atomic radii, and atomic size difference. However, factors such as electronegativity, valence electron concentration, and melting point, also significantly influence the formation of the solid solution phase, individually or in combination in specific alloys, and are often less studied and reported. In this work, CoCrFeNiX0.4 (X = Al, Nb, Ta, elements with equi-atomic radii) high entropy alloys have been prepared by powder plasma arc additive manufacturing (PPA-AM). The effect of equi-atomic radii element addition on the microstructural evolution was studied. The results showed that although Al, Nb, and Ta were equi-atomic radii element additions, the resulting HEAs had variations in their phase formation and mechanical properties. Following observations were made: (i) Al addition: FCC + BCC +Sigma phase formation with lowest hardness and (ii) Nb and Ta addition: FCC + Laves phase + Eutectic phases formation with relatively high hardness (>85%–～110% increase). Considering other factors that determine the formation of solid solution phase, it has been identified that: (i) high melting point of the metal has a superior influence on the formation of topologically closed packed phases (TCP) solid solution phase and (ii) elements with large electronegativity differences tends to be rich in the second solid solution phase. The HEAs deposited by PPA-AM have similar/better mechanical stability when compared to the as-cast alloys. Using an innovative AM technology to fabricate HEAs, this work emphasizes the importance of the control of multiple variables in manipulating the solid solution phase formation and mechanical properties of HEAs.

Preparation and Properties of Co/Fe Multilayers and Co-Fe Alloy Films for Application in Magnetic Field Sensors

In magnetoelectric sensors for the detection of weak magnetic fields, the magnetostrictivecomponent is required to show a high strain at small magnetic field changes. Co-Fe alloys, amongrare earth free materials, have one of the largest saturation magnetostriction and are magnetically softat the same time. In this study, Co-Fe alloy films with 66 at.-% Co are prepared by magnetron sputterdeposition of Co/Fe-multilayers which differ in their individual layer structure and in a subsequentrapid thermal annealing process. The influence of the initial bilayer period and the annealing temperatureon the phase formation and film structure are investigated. X-ray diffraction revealed a higherfraction of the desired face-centered cubic solid solution for thicker individual layers after the 800 °Cannealing. The change of the electrical in-plane resistivity reaches a minimum around 500 °C and iscorrelating well with the observed grain growth and solid solution phase formation. The investigationof magnetic properties with vibrating sample magnetometry shows coercive fields of 3.2 kA/m and2.2 kA/m for fully alloyed films with initial bilayer periods of 25 nm and 250 nm, respectively.

Hydrogen storage properties of Ti2FeV BCC solid solution

This paper deals with hydrogen storage properties of Ti-V based BCC solid solution incorporated with Fe. The alloy with composition Ti2FeV was prepared by arc melting method. X-ray diffraction (XRD) and energy dispersive X-ray analysis studies confirmed formation of solid solution phase with uniform composition and BCC structure. SEM studies revealed the formation of irregular shaped particles with size in the range of few microns up on hydrogenation of the parent alloy. The alloy shows maximum hydrogen storage capacity of 3.41 wt.% at 20 bar and 303 K and the thermodynamic parameters established near room temperature suitability of the alloy for solid state hydrogen storage applications. Hydrogenation kinetics is found to be quite fast and detailed kinetic analysis were done to underscore the hydrogenation mechanism. Activation energy during the initial stage of hydrogenation is found to be 30.8 kJ/mol. The value decreases to 14.4 kJ/mol for extended duration of hydrogenation, and this is explained based on difference in rate determining steps existing at different time scales. Extent of hydrogen absorption as a function of temperature and time for Ti2FeV alloy.

Elemental effect on formation of solid solution phase in CoCrFeNiX and CoCuFeNiX (X = Ti, Zn, Si,Al) high entropy alloys

ABSTRACTThe paper aims to investigate the effect of elements addition, its enthalpy of mixing, crystal structure and atomic size difference on the formation of solid solution phase during the synthesis of high entropy alloy (HEA) by mechanical alloying. For this CoCrFeNiX and CoCuFeNiX (where X = Ti, Zn, Si, Al), alloys were prepared by mechanical alloying. The phases formed during mechanical alloying were characterised by X-ray diffraction analysis, transmission electron microscopy and differential scanning calorimetry. Titanium and Aluminium addition facilitate solid solution formation during mechanical alloying. Formation of a BCC and FCC solid solution phase was observed for CoCrFeNiX and CoCuFeNiX system (where X = Ti, Al), respectively. Single solid solution phase was not observed for CoCrFeNiZn, CoCrFeNiSi, CoCuFeNiZn and CoCuFeNiSi HEA up to 20 hours of milling.

Solid solution hardening in nanolaminate ZrN-TiN coatings with enhanced wear resistance

Coating architectures with a microstructure controlled on nanoscale enables the attainment of enhanced mechanical, tribological and other properties. In the present study, we fabricated nanolaminate ZrN/TiN systems with various modulation periods, L, ranging from 1 to 100 nm using pulsed DC magnetron sputtering. It was observed that a modulation period of L = 10 nm is a threshold value for the transition from a periodic to a solid solution structure. We demonstrate that the coatings with L<10 nm displayed a single-phase solid solution with a Zr-rich composition of Ti0.35Zr0.65N. This indicates the effect of mixing and/or diffusion between the two phases that occurred during the film growth. The crystallite size was found to vary with the modulation periodicity: we obtained 11–12.5 nm for the Ti0.35Zr0.65N solid solution, and 14.5–25 nm for the laminate structure. The solid solution and interface strengthening were found to be the main cause of the hardening of the nanolaminate structure presenting a hardness of 32–35 GPa, significantly higher than for the individual TiN (21 GPa) and ZrN (16 GPa) single-layer coatings. The hard, solid solution system was found to exhibit the highest wear resistance corresponding to the highest values of the H/E and H3/E2 ratios related to a high resistance to plastic deformation and a high toughness. Finally, a model for the Ti0.35Zr0.65N solid solution phase formation related to internal residual stress is proposed.

Effective inhibition of Cr(VI) in the Al2O3-CaO-Cr2O3 refractory castables system through silica gel assisted in-situ secondary phase tuning

Cr2O3 is the best-known corrosion resistant refractory materials under high temperature extremely harsh environment. However, the formation of toxic, carcinogenic & water-soluble Cr(VI) compounds during its application remained a major predicament. Here, we have introduced a facile route to fabricate the Al2O3-CaO-Cr2O3 refractory castables to mitigate Cr(VI) using basic silica sol (pH∼9) via in-situ secondary phase modification. Basic silica sols 0.25, 0.49 and 0.98 wt% (CaO/SiO2 ratio of 5.8, 2.9 and 1.45 respectively) were doped by keeping the castables properties reasonable. Addition of silica drastically reduces the mid-temperature (500–1100 °C) formation of Cr(VI) phase (CaCrO4), while relatively higher temperature Cr(VI) phase (hauyne, Ca4Al6CrO16) totally disappeared from 900 to 1300 °C. However, at 1300–1500 °C, silica addition promote the solid solution phase formation like Ca(Al,Cr)12O19 and (Al,Cr)2O3 where chromium exists as +3 oxidation state. Also, silica addition reduces the dimensional tolerance of the castables at a higher temperature associated with the secondary phases (dehydration of cement phases and expansive formation of CaAl12O19). A comparable mechanical strength (up to 156 MPa) and a remarkable Cr(VI) reduction (up to 94%) could be achieved upon silica addition.

Optimization of Diffusion Bonding of Pure Copper (OFHC) with Stainless Steel 304L

This work deals with determination of optimum conditions of direct diffusion bonding welding of austenitic stainlesssteel type AISI 304L with Oxygen Free High Conductivity (OFHC) pure copper grade (C10200) in vacuum atmosphere of (1.5 *10-5 mbr.). Mini tab (response surface) was applied for optimizing the influence of diffusion bonding parameters (temperature, time and applied load) on the bonding joints characteristics and the empirical relationship was evaluated which represents the effect of each parameter of the process. The yield strength of diffusion bonded joint was equal to 153 MPa and the efficiency of joint was equal to 66.5% as compared with hard drawn copper. The diffusion zone reveals high microhardness than copper side due to solid solution phase formation of (CuNi). The failure of bonded joints always occurred on the copper side and fracture surface morphologies are characterized by ductile failure mode with dimple structure. Optimum bonding conditions were observed at temperature of 650 ◦C, duration time of 45 min. and the applied stress of 30 MPa. The maximum depth of diffuse copper in stainless steel side was equal 11.80 µm.

Effects of Mo, Nb, Ta, Ti, and Zr on Mechanical Properties of Equiatomic Hf-Mo-Nb-Ta-Ti-Zr Alloys.

Nowadays refractory high-entropy alloys (RHEAs) are regarded as great candidates for the replacement of superalloys at high temperature. To design a RHEA, one must understand the pros and cons of every refractory element. However, the elemental effect on mechanical properties remains unclear. In this study, the subtraction method was applied on equiatomic HfMoNbTaTiZr alloys to discover the role of each element, and, thus, HfMoNbTaTiZr, HfNbTaTiZr, HfMoTaTiZr, HfMoNbTiZr, HfMoNbTaZr, and HfMoNbTaTi were fabricated and analyzed. The microstructure and mechanical properties of each alloy at the as-cast state were examined. The solid solution phase formation rule and the solution strengthening effect are also discussed. Finally, the mechanism of how Mo, Nb, Ta, Ti, and Zr affect the HfMoNbTaTiZr alloys was established after comparing the properties of these alloys.

Constructing and Characterizing TiAlN Thin Film by DC. Pulsed Magnetron Sputtering at Different Nitrogen/Argon Gas Ratios

In this survey, the magnetron sputtering with Dc. Pulsed mode was embroiled to deposit TiAlN thin film on AISI 316 as a substrate. All the plasma magnetron parameters were fixed excluding the nitrogen gas ratio which was varied from 10% to 50% with step interval of 10% with respect to argon. The structure, mechanical, tribological and electrochemical peculiarities of TiAlN films were studied. The TiAlN deposition rate is decreased in regard with increasing the nitrogen gas ratio where, the film thickness recorded a maximum value of 3 µm at nitrogen gas ratio of 10 %. X-ray configurations demonstrated the formation of solid solution phase of TiAlN with different orientations. The TiAlN coating has (111) preferred orientation at 10 and 20% nitrogen gas ratios while has (200) preferred orientation at 30- 50% nitrogen gas ratios. The crystallite size is decreased with increasing the nitrogen gas ratio. The results depicted that, the microhardness of TiAlN film is increased with decreasing the nitrogen gas ratio and recorded a maximum value of approximately 850 HV0.015 at 10% N2. Additionally, the tribological properties of the coated AISI 316 with TiAlN are enhanced compared with the uncoated sample. The wear volume loss of the coated sample at 10% N2 has a value of nearly 9X104 µm3 which is low in comparison with AISI 316 substrate that has a value of 4.5X106 µm3. The corrosion resistance of all TiAlN coatings was better than the uncoated sample. It was demonstrated; the change in nitrogen gas ratio affected the physicochemical characteristics of the TiAlN coating.

Stabilization of Nickel-Rich Layered Cathode Materials of High Energy Density by Ca Doping

Lithium-ion batteries have been considered the most important devices to power mobile or small-sized devices due to their high energy density. LixCoO2 has been studied as a cathode material for the Li-ion battery. However, the limitation of its capacity impedes the development of high capacity cathode materials with Ni, Mn, etc. in them. The substitution of Mn and Ni for Co leads to the formation of solid solution phase LiNixMnyCo1-x-yO2 (NMC, both x and y 0.8 in the metal site), poor cycle retention capability still remains to be overcome. In this study, aiming to improve the stability of the physical and chemical bonding, we investigate the stabilization effect of Ca in the Ni-rich layered compound Li(Ni0.83Co0.12Mn0.05)O2, and then Ca is added to the modified secondary particles to lower the degree of cationic mixing of the final particles. For the optimization of the final grains added with Ca, the Ca content (x = 0, 2.5, 5.0, 10.0 at.%) versus Li is analyzed.

Effect of DC-pulsed magnetron sputtering power on structural, tribological and biocompatibility of Ti–Zr–N thin film

The DC-pulsed magnetron sputtering was employed to deposit Ti–Zr–N thin film on AISI 316 substrates. All the plasma parameters were kept to be constant except the plasma-processing power which was varied from 125 to 250 W. The structure, tribological, electrochemical and biocompatibility properties of Ti–Zr–N films have been investigated. X-ray patterns confirmed the formation of solid solution phase of Ti–Zr–N with different orientations. The results depicted that, the microhardness of Ti–Zr–N film increases with increasing the plasma-processing power to reach a maximum value of approximately 1050 HV0.015 at 200 W. Moreover, the tribological properties of AISI 316 coated with Ti–Zr–N were found to be superior compared with the uncoated sample. The wear rate of the coated sample at 225 W has a value of nearly 0.0034 mm3/Nm which is very low in comparison with AISI 316 substrate that has a value of 0.137 mm3/Nm. The biological properties of the examined samples were evaluated by investigating the proliferation of MC3T3-E1 osteoblast cells on the surface. The proliferation rate of the osteoblast cells was enhanced on Ti–Zr–N films prepared at low plasma power. It has been demonstrated that the surface roughness and surface energy besides the surface chemical compositions affect the tribo-mechanical and biocompatibility features of Ti–Zr–N surfaces.

Big-data analysis of phase-formation rules in high-entropy alloys

Big-data analysis of phase-formation rules of high-entropy alloys (HEAs) was conducted and a phase formation rule from a dynamic view was deduced. It was indicated in literatures that cooling rate has a strong influence on the phase formation of HEAs. Higher cooling rate may promote the generation of amorphous phase, and accordingly suppress the formation of intermetallics. Meanwhile, it was also shown that cooling rate had little impact on the formation of solid-solution phase. To demonstrate this rule, a series of FeCoNi(AlSiB)x HEAs ribbons were fabricated by a melt-spinning technique, and the microstructure, mechanical, and magnetic properties were also investigated. The results show that all ribbons exhibit disordered solid-solution structure. The addition of boron changes the alloy from ductility to brittleness, but without evident change of magnetic properties. The alloy in the nominal composition of FeCoNi(AlSi)0.2 has the best combination of mechanical and magnetic properties. A distinct feature of HEAs in magnetization was noticed and explained.

EFFECT OF NITROGEN GAS RATIO ON THE PROPERTIES OF TI-ZR-N COATINGS DEPOSITED BY PULSED MAGNETRON SPUTTERING

The aim of this paper was to study the effectiveness of N2/Ar gas ratio on the mechanical and tribological properties of Ti-Zr-N films coated on (AISI 304 stainless steel) substrate. The thin films were produced at 150 W pulsed magnetron sputtering (PMS) technique operated for 90 min. The structure and tribo-mechanical properties of the Ti-Zr-N coatings were investigated at different N2 /Ar gas pressure ratio. X-ray diffraction (XRD), microhardness, surface roughness, wear and friction, corrosion performance and surface energy were investigated. The analysis of X-ray diffraction (XRD) indicated a formation of solid solution phase of (Ti-Zr)N with (FCC) structure and a chemical compound phase of TiN. The solid solution phase (Ti-Zr)N has the orientation (111). The microhardness of the thin films has high values compared to associated value of (AISI 304 stainless steel) substrate; up to 4-folds. Furthermore, the wear performance was improved from 73.06 mm3/m for AISI substrate to 5.01 mm3/m after depositing Ti-Zr-N. The coefficient of friction was decreased from nearly 0.69 for the austenitic substrate to nearly 0.12 after coating with Ti-Zr-N. Over and above, the corrosion resistance substantially improved (factor of 1000 times) after the coating.

Phase formation criteria assessment on the microstructure of a new refractory high entropy alloy

This work focuses on the evaluation of various parametric models for the formation of solid solution phases in high entropy alloys. The actual observation of MoWHfZrTi microstructure, along with the theoretical suggestions for single phase selection is discussed. The micro-segregated obtained structure is explained in terms of introducing a possible mechanism based on the estimation of thermodynamic parameters and further analysis of the experimental evidence upon solidification. High values of both micro and macro hardness characterize the synthesized system, indicating a solid solution strengthening mechanism.