Increasing Hf Content Research Articles

Prevention of hot cracking in Ni-based superalloy via passivation layer formation during additive manufacturing

We investigated the prevention of hot cracking in a non-weldable Ni-based superalloy by utilizing a passivation layer formed through laser-based directed energy deposition. The addition of Hf to the Ni-based superalloy facilitated the formation of a passivation layer consisting of Hf oxide on the surface of the as-deposited sample. An increase in the amount (thickness) of the passivation layers with increasing Hf content resulted in a reduction in hot cracking occurrence. Specifically, the addition of 2.5 wt% Hf led to the formation of uniformly distributed fine oxides without inducing hot cracks. This passivation layer effectively inhibited the formation of coarsened Mo oxides, which typically occur during oxidation in the liquid state and contribute to the hot cracking of Ni-based superalloy. During oxidation in the liquid state, Hf diffuses out to the surface and forms a passivation layer, thereby suppressing the formation and growth of oxides to sizes large enough to induce hot cracking.

Effects of Zr and Hf on superelasticity, shape memory effect and microstructure of β-type (Ti–Zr–Hf)–Nb–Sn multi-principal element alloys with low magnetic susceptibility

(Ti–Zr–Hf)(97−x)–xNb–3Sn (Ti:(Zr + Hf) = 1:1) alloys were designed for biomedical superelastic alloys with magnetic resonance imaging (MRI) compatibility. The effects of Zr and Hf on constituent phases, superelasticity, shape memory effect and magnetic susceptibility were clarified. The specific Nb content for superelasticity and shape memory effect was also explored. It was found that the (Ti–Zr)–6.5Nb–3Sn alloy exhibited a superelastic recovery strain of 5.2 % with lower magnetic susceptibility compared to conventional Ti–Ni and Ti–Nb alloys. The magnetic susceptibility decreased with increasing Hf content. The (Ti–Hf)–9Nb–3Sn alloy showed a superelastic recovery strain of 0.9 % and very low magnetic susceptibility less than half of that of the conventional alloys. Based on the lattice parameters of these alloys, it was found that these alloys exhibited larger transformation lattice strain between a β phase and an α” phase than those of the Ti–Nb alloys, suggesting high potential to exhibit a large superelastic recovery strain. According to orientation analyses of constituting grains, the larger superelastic recovery strain in the (Ti–Zr)–6.5Nb–3Sn alloy than that of the (Ti–Hf)–9Nb–3Sn alloy is considered to be caused by a strong recrystallization texture of {001}β <110>β. By optimization of heat-treatment temperature, superelastic recovery strain of 3.6 % was achieved in the (Ti–0.5Zr–0.5Hf)–7.5Nb–3Sn alloy.

The effect of increasing hafnium on the microstructure, phase transformation temperatures and hardness of TiPtHf potential shape memory alloys

Shape Memory Alloys (SMAs) are popular due to their ability to regain their original shape after plastic deformation. Binary TiPt alloys have low shape memory effects and as such, alloying elements are added to improve these properties. The effect of alloying and increasing the Hf in binary Ti50Pt50 to form ternary Ti50Pt50−xHfx (x=6.25,12.5 and 18,25 at.%) on the microstructure, transformation temperatures and hardness in the as cast and solution heat treatment conditions were investigated. In the as-cast condition SEM EDS analysis showed that alloying with Hf resulted in the formation of dark grey interdendritic regions comprised of Ti-rich phases and the increase in Hf content (at. %) led to an increase in the size of these interdendrites. Solution heat treatment (SHT) of the alloy led to a decrease in the size of the dark grey interdendritic regions and the formation and increase of dark black regions with increasing Hf content (at. %). Differential scanning calorimetry showed that partial substitution of Pt with 6.25 at. % Hf decreased the transformation temperature of the alloy below that of Ti50Pt50 in both conditions. Increase in to Hf 12.5 and 18.25 at. % increased the transformation temperatures above those of Ti50Pt50 binary alloy in both conditions. SHT of 12.5 at. % Hf significantly reduced the AS and MS temperatures. Alloying and increase in Hf content (at. %) increased the hardness of the alloys above that of Ti50Pt50. SHT increased the hardness of the alloys above that of Ti50Pt50 and the as-cast alloys.

Damping behaviors and strain recovery characteristics of Hf-modified TiNb-based shape memory alloys

In the present study, the electron concentration, bond order and metallic average d-electron orbital energy level of Ti-Nb-Hf shape memory alloys were controlled by adjusting the Hf content, which further determined the phase constituents and phase stability. The Ti-Nb-Hf shape memory alloys with various Hf contents were composed of the α´´ martensite phase and β phase, regardless of Hf contents. With increasing Hf content, the martensitic transformation temperature (Ap) slightly increased. Hf addition could enhance the strength and optimize the strain recovery characteristics. A higher strength and larger recoverable strain can be obtained in Ti-Nb shape memory alloy modified by 2 at.% Hf due to grain refinement, precipitation strengthening and solution strengthening. Training can achieve perfect superelasticity with a completely recoverable strain of approximately 2%. In conclusion, the perfect combination of damping capacity and strain recovery characteristics can be attained by tailoring the Hf content in Ti-Nb-Hf shape memory alloys.

Machine learning guided alloy design of high-temperature NiTiHf shape memory alloys

With the increasing use of CubeSats in space exploration, the demand for reliable high-temperature shape memory alloys (HTSMA) continues to grow. A wide range of HTSMAs has been investigated over the past decade but finding suitable alloys by means of trial-and-error experiments is cumbersome and time-consuming. The present work uses a data-driven approach to identify NiTiHf alloys suitable for actuator applications in space. Seven machine learning (ML) models were evaluated, and the best fit model was selected to identify new alloy compositions with targeted transformation temperature (Ms), thermal hysteresis, and work output. Of the studied models, the K-nearest neighbouring ML model offers more reliable and accurate prediction in developing NiTiHf alloys with balanced functional properties and aids our existing understanding on compositional dependence of transformation temperature, thermal hysteresis and work output. For instance, the transformation temperature of NiTiHf alloys is more sensitive to Ni variation with increasing Hf content. A maximum Ms reduction rate of 6.12 °C per 0.01 at.% Ni is attained at 30 at.% Hf, and with a Ni content between 50 and 51 at.%.Graphical abstract

Evolution of the structure and properties of (Zr1-xHfx)B2 solid solution ceramics from first-principle theory

As typical ultra-high temperature ceramics, both ZrB2 and HfB2 have unique properties such as excellent mechanical performance and oxidation resistance, are promising candidates for the aerospace industry. In this work, the phase stability, electronic, mechanical and thermodynamic properties of (Zr1-xHfx)B2 solid solution ceramics were systematically studied performing by first-principles calculations. The calculated results of structural optimization and elastic constants are in good agreement with the experimental values, which confirms the reliability of the proposed model. The lattice parameters of the optimized (Zr1-xHfx)B2 solid solution ceramics are linearly related to the Hf content, while a decrease is detected as the increasing Hf content. The calculated elastic constants show that the addition of Hf is beneficial in improving the mechanical properties of the (Zr1-xHfx)B2 solid solution, including the elastic modulus, hardness and fracture toughness. In addition, the (Zr1-xHfx)B2 solid solution was found to be kinetically stable. From the trend of the calculated value of the Debye temperature, it can be found that the addition of Hf can effectively reduce the thermal conductivity of solid solution materials. Our work introduced an important theoretical framework, which is of great significance for the development of solid solution diboride material systems with adjustable composition and properties.

Effect of Stoichiometry on Shape Memory Properties of Ti-Ni-Hf-Cu-Nb Shape Memory Alloys Manufactured by Suspended Droplet Alloying

A novel Ti-Ni-Hf-Cu-Nb shape memory alloy has been developed by a new combinatorial alloy synthesis method, the Suspended Droplet Alloying. The influence of alloying elements on the transformation temperature, the microstructure and the shape memory effect of this alloy have also been studied. It was found that Cu has a greater negative influence on the transformation temperature of Ti-Ni-Hf-CuX alloys (about −5 K/at.%) than on the Ti-Ni-CuX alloys (−0.67 K/at.%). In addition, the negative effect intensifies with increasing Hf content. The transformation temperature rapidly decreases with increasing Nb composition in the Ti-Ni-Cu-Nb and Ti-Ni-Hf-Cu-Nb alloys, with the solid solution of Nb in the matrix being 1 at.%. A Ti-Ni-Cu-Hf-Nb alloy with high thermal cycle stability has been developed, where the alloying elements affect the transformation behaviour via altering the slipping energy and forming different types of precipitations.

Fabrication and electrical conductivity of Lu2(Ti1-x Hf x )2O7 transparent ceramics prepared by spark plasma sintering

ABSTRACT Lu2(Ti1-x Hf x )2O7 (x = 0–0.5) transparent ceramics were fabricated by reactive spark plasma sintering using commercially available Lu2O3, TiO2 and HfO2 powders. Effect of Hf content x on the phase evolution, microstructure, density, transmittance and electrical conductivity of the resulting ceramics were investigated. Lu2(Ti1-x Hf x )2O7 transparent ceramic had a pyrochlore structure in the range of x = 0–0.3, while preserved a defect-fluorite structure at x = 0.4–0.5. The lattice parameter and theoretical density increased linearly with increasing Hf content x. The average grain size decreased at x = 0–0.3 and kept almost constant at x = 0.4–0.5. All the samples exhibited a dense microstructure and the highest in-line transmittance was 57% at 550 nm at x = 0. The highest bulk conductivity was 1.7 × 10−2 S m−1 at 1073 K for Lu2(Ti0.8Hf0.2)2O7, with an activation energy of 1.16 eV.

Microstructure, phase relationships and microhardness of Fe60Al40–n Hf n alloys (n = 1, 3, and 5 at.%)

Abstract The microstructural evolution, solidification behavior, phase relationships, microhardness and room temperature magnetic properties of the hypoeutectic Fe60Al40-n Hf n (n = 1, 3, and 5 at.%) compositions are investigated in detail. The micro-structure of the studied alloys is composed of Fe–Al based dendrites and eutectic mixture. The components of the eutectic are B2 Fe–Al based and HfFe6Al6 τ1 phases. With increasing Hf fraction, the amounts of eutectic and τ1 phases increase continuously which results in significant strengthening. Based on the differential scanning calorimetry results, the eutectic reaction temperature is measured as 1251 °C. Fe60Al40-n Hf n alloys show weak room temperature ferromagnetism and their magnetization values also increase with increasing Hf content.

Mechanical and Thermal Behavior of Cu84−xAl13Ni3Hfx Shape Memory Alloys

The physical characteristics of a shape memory alloy can be controlled by different production techniques and the rate of constituents’ contribution. In this study, CuAlNiHf shape memory alloys, with three different amounts of Hf, were produced by the induction melting method. Many measurements such as differential scanning calorimetry (DSC), scanning electron microscope, energy dispersive X-ray, and the stress–strain test were carried out. The DSC measurement showed that the austenite transformation temperatures were decreased by doping more amount of hafnium into the alloy. All specimens showed a wide temperature hysteresis, which decreased by increasing Hf content. Also, the elastic modulus was raised by increasing the Hf amount. Although $${\gamma }_{1}^{{\prime}}$$ and $${\beta }_{1}^{{\prime}}$$ are the dominant phases in the CuAlNiHf with low Hf composition, substituting Cu with Hf enhanced the amount $${\beta }_{1}^{{\prime}}$$ -phase compared to $${\gamma }_{1}^{{\prime}}$$ -phase.

Effects of Hf on the microstructure and mechanical properties of CoCrFeNi high entropy alloy

In this study, the effects of hafnium addition on the microstructure and mechanical properties of CoCrFeNi high entropy alloy were investigated. The CoCrFeNiHfx (x = 0, 0.1, 0.2, 0.3 and 0.4, x values in molar ratio) high entropy alloys were prepared by vacuum arc melting. The microstructure and phase identities were studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. With increasing Hf contents, the structure of CoCrFeNiHfx HEAs changed from FCC single phase to Ni7Hf2 + FCC, then to Ni7Hf2 + C15 Laves + FCC, and finally to C15 Laves + FCC phases when x values changed from 0 to 0.4. Hypoeutectic microstructures were observed in CoCrFeNiHfx (x = 0.1–0.3) HEAs. Fully eutectic structure with lamellaes of FCC phase and C15 Laves phase formed in CoCrFeNiHf0.4 HEA. The Vickers hardness and compressive yield strength of the alloys increased while the plastic strain reduced with increasing Hf contents, which were resulted from solid solution strengthening and second phase strengthening. The CoCrFeNiHf0.1 showed a better combination of strength and ductility in tensile tests. Lateral fracture surfaces indicated that the primary FCC phase in CoCrFeNiHf0.2 could effectively hinder the propagation of micro-cracks to prevent catastrophic failure during compression. The results of this study can provide a better understanding about the phase development in Hf-containing HEAs and its effects on the mechanical properties of such systems.

Composition, Structure, and Mechanical Properties of (Ti–Hf)N Coatings on Titanium Alloy

Variations of the composition, structure, and mechanical properties (hardness, elastic modulus) of (Ti–Hf)N coatings with increasing Hf content (Ti : Hf ratio) are reported. As test samples, VT6 titanium alloy plates covered by a magnetron-sputtered titanium hafnium nitride coating have been taken. To see how the coating characteristics depend on Hf content, samples with rated compositions (Ti0.9Hf0.1)N, (Ti0.85Hf0.15)N, (Ti0.8Hf0.2)N, and (Ti0.7Hf0.3)N have been studied. The surface and depth element distributions have been found, and the phase composition and the dependence of the titanium nitride lattice parameter on Hf content in the coating have been determined. The depth profiling of a coating’s hardness and elastic modulus has been conducted by instrumental indentation. Hardness and elastic modulus have been found to be maximal (~35 and ~500 GPa, respectively) in (Ti0.85Hf0.15)N and (Ti0.8Hf0.2)N coatings. In addition, the depth distribution of Hf in these coatings has turned out to be most uniform.

Состав, структура и механические свойства (Ti-Hf)N-покрытий на титановом сплаве

AbstractVariations of the composition, structure, and mechanical properties (hardness, elastic modulus) of (Ti–Hf)N coatings with increasing Hf content (Ti : Hf ratio) are reported. As test samples, VT6 titanium alloy plates covered by a magnetron-sputtered titanium hafnium nitride coating have been taken. To see how the coating characteristics depend on Hf content, samples with rated compositions (Ti_0.9Hf_0.1)N, (Ti_0.85Hf_0.15)N, (Ti_0.8Hf_0.2)N, and (Ti_0.7Hf_0.3)N have been studied. The surface and depth element distributions have been found, and the phase composition and the dependence of the titanium nitride lattice parameter on Hf content in the coating have been determined. The depth profiling of a coating’s hardness and elastic modulus has been conducted by instrumental indentation. Hardness and elastic modulus have been found to be maximal (~35 and ~500 GPa, respectively) in (Ti_0.85Hf_0.15)N and (Ti_0.8Hf_0.2)N coatings. In addition, the depth distribution of Hf in these coatings has turned out to be most uniform.

First-principles study the structural, electronic, vibrational and thermodynamic properties of Zr1−xHfxCoH3

The structural, electronic, vibrational and thermodynamic properties of Zr1−xHfxCoH3 (x = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) are investigated using first principles approach based on the virtual crystal approximation (VCA). The results indicate the series Zr1−xHfxCoH3 have the similar physical properties. When Hf concentration increases gradually, the lattice parameter reduces and the thermodynamic stability first decreases and then increases, respectively. The calculated results of charge distributions and electron localization function (ELF) suggest that the interactions of HCo and HZr1−xHfx are primarily metallic with a small covalent component. The band structure and the corresponding density of states (DOS) around the Fermi level (Ef) indicate the metallicity enhances and the electrical conductivity is better with increasing Hf content. The phonon density of states imply that with the increase of Hf content, the covalent interactions between H(4c2) and Zr1−xHfx are weakened, while the covalent interactions between H(8f1) and Zr1−xHfx basically remained unchanged (H(4c2) and H(8f1) represent the hydrogen atoms occupying 4c2 and 8f1 site, respectively), which is consistent with the results of charge density. Finally, the thermodynamic properties are obtained and discussed on the base of the obtained vibrational properties.

Fractionation process of high-silica magmas through the lens of zircon crystallization: A case study from the Tengchong Block, SW China

The generation of high-silica magma is generally considered to occur as a result of liquid-crystal segregation from a crystal mush. Yet whether high-silica melts could undergo significant fractionation process after the segregation remains unclear. This study contributes to this topic through the lens of zircon geochemistry of the ~130 Ma high-silica granite in the Tengchong block, SW China. The high-silica granite, with SiO2 ~76%, displays low Zr/Hf and EuN/Eu*N, and high Rb/Sr ratios. The zircons crystallized from the granite can be divided into two groups. The group 1 zircons are characterized by lower Hf (<12,200 ppm), and show relatively lower U (710–1103 ppm, averaging 891 ppm) and Yb (688–1106 ppm, averaging 903 ppm), and higher EuN/Eu*N (0.11–0.18). By contrast, the group 2 zircons have higher Hf (>12,200 ppm), and display elevated U values (936–2429 ppm, averaging 1557 ppm) and Yb values (755–1556 ppm, averaging 1134 ppm), as well as lower EuN/Eu*N (0.01–0.1). The increasing Hf content from group 1 to group 2 zircons, presence of fluorite inclusions in high-Hf zircon, and similarity in Hf isotope between the two groups of zircon consistently support the high-silica granite has witnessed a highly fractionated crystallization process. The presence of these two groups of zircons is considered to reflect two-stage in-situ fractionation processes, which display distinct REE (rare earth elements) compositions in the magma system in response to differing precipitated mineral assemblages. In light of the change of zircon REE within each group, the percentage of minerals co-precipitating with zircons in each stage was estimated. The results showed that 35.24% quartz, 18.60% feldspar, 0.25% apatite, 0.14% zircon, 0.12% allanite, and 0.05% titanite fractionated in the early stage, and 67.50% quartz, 23.41% feldspar, 0.15% zircon, 0.10% allanite, 0.07% apatite, and 0.06% titanite fractionated in the second stage. The discovery of different zircons and corresponding estimation in this study provide a new line of evidence for the fractionation of high-silica melt.

Microstructure, mechanical properties and shape memory effect of Cu–Hf–Al–Ni alloys

ABSTRACTThe influence of hafnium element’s incorporation on a Cu–xHf–13.0Al–4.0Ni (wt-%) (x = 0.5, 1.0 and 2.0) high-temperature shape memory alloy was investigated systematically. The results show that the matrix of Cu–xHf–13.0Al–4.0Ni (x = 0.5, 1.0 and 2.0) alloys is 18R martensite, and an orthorhombic-structured Cu8Hf3 phase is formed and distributed at the grain boundaries. The grain size is significantly reduced with increasing Hf content. The mechanical properties of Cu–xHf–13.0Al–4.0Ni (x = 0.5, 1.0 and 2.0) alloys are improved by Hf doping due to the combination of refinement strengthening, solid solution strengthening and second phase strengthening. After heating under pre-strain of 10%, the shape memory effect of the Cu–1.0Hf–13.0Al–4.0Ni alloy reaches 5.6%, which is obviously higher than that of the Cu–13.0Al–4.0Ni alloy.

Multicomponent Hf-Nb-Ti-V-Zr nitride coatings by reactive magnetron sputter deposition

Multicomponent nitride coatings of the Hf-Nb-Ti-V-Zr system with different Hf content (0–18 at.%) were deposited using reactive dc magnetron sputtering. Coatings with lower Hf content (0–7 at.%) were found to consist of a single solid solution phase with NaCl-type structure (space group Fm-3m). Coatings with higher Hf content (10–18 at.%) showed a two-phase material consisting of cubic Fm-3m and tetragonal I4/mmm solid solution phase. The lattice distortion, estimated by calculating the δ-parameter under the assumption of a single solid solution phase, varied between 3.8 and 4.0% and slightly decreased with increasing Hf content. SEM and TEM cross section images showed a columnar microstructure with columns that were frayed on the surface or throughout the whole column. The column size decreased as Hf content increased. The hardness increased from 8 to 19 GPa with increased Hf content, which most probably is related to the change in microstructure rather than change in lattice distortion. The electrical resistivity for all samples ranged between 231 and 286 μΩcm.

Effect of Hf on the microstructure, mechanical properties, and oxidation behavior of sputtered CrAlN films

Al-rich CrAlN films with a varying Hf content between 0 and 11.6 at.-% were synthetized by dc magnetron sputtering. The structural changes in the morphology and topography caused by Hf were evaluated by scanning electron microscopy. In addition, the phase composition of the Hf-alloyed CrAlN films was determined utilizing X-ray diffraction. The hardness and indentation modulus were determined using nanoindentation. In order to evaluate the effect of Hf on the oxidation behavior, the films were tempered in ambient air at 800 °C and subsequently analyzed.The incorporation of Hf leads to a morphological change from a fully-dense structure with small columns to a structure with more pronounced columns, which are visible as larger column tops on the surface. The Al-rich CrAlHfN films consist of the Wurtzite structure of AlN. A hardness decrease from 22.2 to 18.6 GPa is observed with an increasing Hf content and ascribed to the structural changes. When exposed to higher temperatures, the Hf-alloyed CrAlN films form an oxide layer, whose thickness is affected by the Hf content. An improved oxidation resistance is already achieved by a small amount of 2.0 at.-% of Hf.

Effects of Hf content on nanotubular structure of Ti-29Nb-xHf ternary alloys

In this study, the effects of Hf content on the nanotubular structure of Ti-29Nb-xHf ternary alloys were investigated. The Ti-29Nb-xHf ternary alloys had Hf concentrations between 0wt.% and 15wt.% and were manufactured using a vacuum arc-melting furnace. Formation of a nanotube structure on these alloys was achieved by an electrochemical method in a 1M H3PO4+0.8wt.% NaF electrolyte solution. The microstructures of the Ti-29Nb-xHf alloys changed from a needle-like structure to an equiaxed structure with increasing Hf content. The surface characteristics were analyzed by field-emission scanning electron microscopy, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and a wettability test.The Ti-29Nb-xHf alloys had an equiaxed grain structure with α″+β phases, and the α″ phase disappeared with an increase in the Hf content. The Ti-29Nb-15Hf alloy showed higher intensity β-phase peaks in the XRD patterns compared to Ti-29Nb-3Hf and Ti-29Nb-7Hf alloys. The average length of the nanotubes increased and the nanotubes became highly ordered as the Hf content increased. The contact angles of the surface with the nanotubes were lower than those of surfaces without nanotubes.

Probing Long- and Short-Range Disorder in Y2Ti2–xHfxO7 by Diffraction and Spectroscopy Techniques

We studied the long-range average and short-range local structures in Y2Ti2–xHfxO7 (x = 0–2.0) using diffraction and spectroscopy techniques, respectively. Both neutron and synchrotron X-ray powder diffraction data show a clear phase transition of the average structure from ordered pyrochlore to disordered defect-fluorite at x ≈ 1.6; the long-range anion disorder appears to develop gradually throughout the entire pyrochlore region in contrast to the rapid loss of cation ordering from x = 1.4 to 1.6. The commonly observed two-phase region around the pyrochlore/defect-fluorite phase boundary is absent in this system, demonstrating high sample quality. X-ray absorption near-edge structure (XANES) results at the Y L2-, Ti K- and L3,2-, Hf L3-, and O K-edges indicate a gradual local structural evolution across the whole compositional range; the Y coordination number (CN) decreases and the CN around Ti and Hf increases with increasing Hf content (x). The spectroscopic results suggest that the local disorder occ...