Pure Hf Research Articles

Combined HF+MW CVD Approach for the Growth of Polycrystalline Diamond Films with Reduced Bow

A combination of two methods of chemical vapor deposition (CVD) of diamond films, microwave plasma–assisted (MW CVD) and hot filament (HF CVD), was used for the growth of 100 µm-thick polycrystalline diamond (PCD) layers on Si substrates. The bow of HF CVD and MW CVD films showed opposite convex\concave trends; thus, the combined material allowed reducing the overall bow by a factor of 2–3. Using MW CVD for the growth of the initial 25 µm-thick PCD layer allowed achieving much higher thermal conductivity of the combined 110 µm-thick film at 210 W/m·K in comparison to 130 W/m·K for the 93 µm-thick pure HF CVD film.

High-performance multifunctional (Hf 0.2Nb 0.2Ta 0.2Ti 0.2Zr 0.2)C high-entropy ceramic reinforced with low-loading 3D hybrid graphene–carbon nanotube

There has been growing interest in the high-entropy ceramic (HEC) recently owing to its tailorable compositions and microstructures, versatile properties, together with promising structural and functional applications. However, inferior fracture toughness (<i>K</i>_IC) and damage tolerance restricted many practical applications of the HEC. Herein, we addressed this challenge by incorporating a three-dimensional graphene–carbon nanotube (3D G–CNT) as toughening agent in (Hf_0.2Nb_0.2Ta_0.2Ti_0.2Zr_0.2)C. The resulting enhanced 3D G–CNT/(Hf_0.2Nb_0.2Ta_0.2Ti_0.2Zr_0.2)C featured an outstanding toughness of 8.23 MPa·m^1/2, while remaining superior strength (763 MPa) and hardness (24.7 GPa). An ultralow friction coefficient (0.15) coupled with an ultralow wear rate (<i>w</i>, 2.6×10⁻⁷ mm³/(N·m)) in the 3D G–CNT/(Hf_0.2Nb_0.2Ta_0.2Ti_0.2Zr_0.2)C was obtained primarily as a function of lubricating scrolls, in which two-dimensional (2D) graphene acted as a tribolayer, and one-dimensional (1D) carbon nanotubes acted as nano ball bearings embedded inside. Strikingly, the 3D G–CNT/(Hf_0.2Nb_0.2Ta_0.2Ti_0.2Zr_0.2)C exhibited rather low thermal conductivity (<i>κ</i>) yet excellent electrical conductivity (<i>σ</i>, 1.3×10⁶ S/m) in comparison with the pure (Hf_0.2Nb_0.2Ta_0.2Ti_0.2Zr_0.2)C. This study provided great potential for maximizing the physical and functional properties of the HEC for various applications.

Investigation of the Effect of Molybdenum Silicide Addition on the Oxidation Behavior of Hafnium Carbonitride

In this study, the oxidation stability up to 1000 °C in air of the Hf(C,N)-MoSi2 composites was explored under non-isothermal and isothermal conditions. Composites with 1, 5, 10, and 20% volume fractions were produced by low-energy ball milling and subsequent spark plasma sintering. Differential scanning calorimetry (DSC) and thermogravimetric (TG) coupled with mass spectrometry were used to reveal the staging of the oxidation process depending on the additive content. It was found that samples containing 1 and 5 vol% MoSi2 had the lowest weight gain and the best oxidation behavior. The results of this study were supported by microstructural and phase analyses of the samples after isothermal treatment in a furnace. The samples with the lowest molybdenum disilicide content had a dense and thin protective oxide film on the surface, consisting of hafnium orthosilicate and monoclinic HfO2. The increase in the amount of MoSi2 contributed to the formation of a loose and porous oxide layer due to the increase in the concentration of volatile MoO3. However, all samples exhibited higher oxidation resistance compared to the pure Hf(C,N).

A highly efficient melamine/red phosphorus flame retardant for polyurethane‐based foams

AbstractA highly dispersed melamine/red phosphorus (MA/RP) composite flame retardant was prepared by means of simple mechanical grinding. After co‐thermal pretreatment with polyether polyol (PPG‐2000) at 135°C, organic–inorganic hybrid foams (MA/RP/HF) containing MA/RP flame retardant were prepared by the one‐step method using main raw materials such as polyisocyanate and sodium silicate. When 0.5 wt% MA/RP with the mass ratio of 1:5 is added, MA can realize the uniform dispersion of RP in the substrate and enhance its flame retardancy, and the obtained MA/RP/HF presents uniform and closed pores and excellent basic properties. The TG results reveal that MA/RP/HF shows good thermal stability and the corresponding char residual rate reaches 37.9% at 800°C. The flame retardant test results prove that MA/RP/HF is capable of passing the V‐0 grade, with the LOI value being 26.8%. According to the cone calorimeter analysis, its peak heat release rate and total heat release decrease by 30.1% and 51.7% compared with those of rigid polyurethane‐based foam and by 40.1% and 30.0% compared with those of pure HF, respectively. Finally, the synergistic flame retardancy mechanism of MA and RP on polyurethane‐based foam was discussed.

Defect-Engineered Composite Hf-Ta Anodic Memristors for Reram Applications

Various oxides and especially their modifications are in actual scientific focus for memristors fabrication due to their applications in non-volatile memories. Such devices exceed most limits of conventional memory technology. Memristors are recognized as resistive random access memories (ReRAMs), in which the data storage profits from a non-volatile change in the material resistance. The switching between a high resistance state (HRS) and a low resistance state (LRS) depends on the selection of electrodes and active (oxide) layers. This generally impacts the conductive pathways (filaments) formation, which is mediated by oxygen vacancies and/or cations, and their field-activated movement inside the oxide.Anodic oxides of valve metals (Al, Hf, Ta, Ti, Nb, Zr) have shown remarkable performances as memristive elements. Studies on Hf- and Ta-based memristors reported excellent electrical and memory properties, such as multi-level switching, high endurance and data retention. Even though for research purposes the synthesis of such oxide layers is commonly done by atomic layer deposition or sputtering, the electrochemical anodization process should not be neglected. This is a faster, less complex and inexpensive method, with precise composition and oxide thickness control through electrochemical parameters. The value of this approach is clearly emphasized by its continuous industrial implementation in various sectors.Previous works have confirmed that the performance of Hf or Ta anodic memristors can be improved by carefully selecting the anodization electrolyte or other electrochemical parameters1,2. These play a crucial role in positioning and sizing of conductive filaments within the oxide. This approach directly leads to defect-engineered memristors fabrication, which is nowadays a major motivation for investigating devices based on mixed oxides formed in different electrolytes. Predicting the position and shape/thickness of a conducting filament may eventually lead to enhanced device stability and resistive states control.The focus of the current work is on the behavior of anodic memristors based on ultra-thin Hf superimposed on Ta films. The main idea linked to the control of resistive filaments is based on the particularities of the anodization process, when the interface between both oxides is dynamically changing. In situ oxide self-nanostructuring is already known for various superimposed valve metals, including Hf and Ta. Their anodization leads to nanoscale oxide columns (“fingers”) formation, when a metal producing a more resistive oxide is superimposed on a metal producing a less resistive one. This phenomenon is recognized as an electrical version of the Rayleigh-Taylor effect and results from the ionic current preferring the less resistive paths, enhancing the growth of the correspondent oxide. Oxide resistivities and structures, transport numbers, Pilling-Bedworth ratios are all considered as determining factors for the anodization process of such superimposed systems. In the current work, anodization of Hf/Ta system leads to Rayleigh-Taylor effects since HfO2 is the more resistive oxide. The boundary between Hf and Ta oxides may influence the conductive pathways required for the memristive effect, thus being most relevant for fabrication of highly stable and forming-free memristors. Additionally, the use of superimposed films with gradient but complementary thicknesses allows investigating the ideal Hf/Ta ratios for which the best memristive behavior is obtained.3 From this study, one pronounced zone prominent for memristive applications is found for Hf/Ta thickness ratios between 4 and 5. Here, unipolar and bipolar memristors are identified, with remarkable endurance and retention capabilities. The CFs positioning is predefined by the development of Ta2O5 columnar structures grown during the anodization process. It is also possible that few CFs may be found in parallel, according to TEM observations, showing more than one Ta2O5 “finger”. Previous studies on pure Hf anodic memristors have confirmed concurrent competing CFs formation.2 Thus, one could assume that the memristive switching mechanism can be conditioned by the formation of oxides with such structures. The identified Hf/Ta ratio could be an excellent choice for improved memristors fabrication. Controlled O vacancies generation is a critical factor in switching uniformity and reproducibility. Therefore, oxide “fingers” formation is a promising electrochemical approach towards defect-engineered memristors. Further investigation of the composite oxide formation, particularly in Hf/Ta superimposed system, is topical. Until now, such systems were not recognized in the literature for the ReRAM applications. This is highly promising since both memory and electrical characteristics are improved by the forming-free nature of the memristors with CFs mediated by oxide nanostructuring. I. Zrinski et al., Nanomaterials 11, 1 (2021) https://doi.org/10.3390/nano11030666I. Zrinski et al. Appl. Surf. Sci. 565, 150608 (2021) https://doi.org/10.1016/j.apsusc.2021.150608I. Zrinski et al., J. Phys. Chem. Lett. 12, 8917 (2021) https://doi.org/10.1021/acs.jpclett.1c02346 Figure 1

Fabrication and oxidation resistance of the hafnium carbonitride – Silicon carbide composites

The oxidation resistance of the hafnium carbonitride Hf(C,N), HfCN+10 wt% SiC and HfCN+20 wt% SiC ceramics were investigated using thermogravimetric analysis (TGA) and static oxidation experiments at 1200 °C. TGA data showed that in the 1400 °C temperature range weight gain of the Hf(C,N)-SiC ceramics almost halted, while the Hf(C,N) sample continued to oxidize. Experiments at 1200 °C and further microstructure investigations at the ceramic/oxide interfaces showed formation of a dense HfSiO4 barrier layer with low oxygen diffusivity allowing increased oxidation resistance compared to the pure Hf(C,N). A possible formation mechanism for the protective layer and its influence on oxidation was suggested. Also, it was shown that addition of the SiC powder to the Hf(C,N) allows decreasing consolidation temperature by 200 °C without mechanical properties loss. Hf(C,N) with 20 wt% SiC showed a high fracture toughness (5.1 MPa∙m1/2), high hardness (20.2 GPa), and lower density compared to the Hf(C,N) ceramics.

Room‐temperature mechanical properties of a high‐entropy diboride

AbstractThe mechanical properties of a (Hf,Mo,Nb,Ta,W,Zr)B2 high‐entropy ceramic were measured at room temperature. A two‐step synthesis process was utilized to produce the (Hf,Mo,Nb,Ta,W,Zr)B2 ceramics. The process consisted of a boro/carbothermal reduction reaction followed by solid solution formation and densification through spark plasma sintering. Nominally, phase pure (Hf,Mo,Nb,Ta,W,Zr)B2 was sintered to near full density (8.98 g/cm3) at 2000°C. The mean grain size was 6 ± 2 µm with a maximum grain size of 17 µm. Flexural strength was 528 ± 53 MPa, Young's modulus was 520 ± 12 GPa, fracture toughness was 3.9 ± 1.2 MPa·m1/2, and hardness (HV0.2) was 33.1 ± 1.1 GPa. A Griffith‐type analysis determined the strength limiting flaw to be the largest grains in the microstructure. This is one of the first reports of a variety of mechanical properties of a six‐component high‐entropy diboride.

Process for synergistic extraction of Hf(IV) over Zr(IV) from thiocyanic acid solution with TOPO and N1923

A novel process for the separation of Hf(IV) over Zr(IV) from thiocyanic acid solution using TOPO and N1923 as the extractant has been developed. It was observed that the mixture of TOPO and N1923 exhibited a synergistic effect on selective extracting the minor element of Hf(IV). Several crucial parameters influencing the separation process have been investigated. The extraction efficiency for Hf(IV) was found to be 86.3% under optimum conditions: TOPO+N1923 total concentration of 16 vol%, TOPO/N1923 ratio of 6/10, HSCN concentration of 2.0 M, ammonium sulfate concentration of 0.5 M and extraction O/A phase ratio of 2/1. Meanwhile, the separation factor for Hf(IV) over Zr(IV) could reach up to 21. Furthermore, the reverse extraction properties of the loaded organic phase were studied systematically. The results suggested that the co-extracted Zr(IV) could be scrubbed by 1.0 M H2SO4 with a separation factor of 24.13. Hf(IV) was then stripped from the loaded organic phase using 2.0 M NH4HCO3. The attractive characteristics of the newly designed process were the use of low thiocyanic acid solution, achieving higher extractability of Hf(IV) over Zr(IV), the recyclable process flow and the potential to prepare high pure Hf and Zr.

Atomic scale observation of FCC twin, FCC → 9R and 9R → 12R’ transformations in cold-rolled Hafnium

The face-centered cubic (FCC) twin, FCC →9R and 9R → 12R’ transformations were observed simultaneously in cold-rolled pure Hf. The formation of FCC twin was due to the Shockley partial dislocations extended in the different basal planes. For FCC →9R transformation, the collective gliding of Shockley partial dislocations along (111) planes with every three atomic layers eventually lead to the stacking sequence of close-packed structure, i.e. ACBACBACBA changed to ABACACBCBA. The 9R → 12R’ transformation was related to the formation of the full dislocations at every three atomic layers.

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

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.

Theoretical and matrix isolation studies of infrared spectra of the H2CO∙∙∙HF hydrogen-bonded complex

The equilibrium geometry, the binding energy, and harmonic and anharmonic spectral parameters of H2CO and HF monomers and the H2CO∙∙∙HF complex are calculated in the MP2/6-311++G(3df,3pd) approximation with the basis set superposition error taken into account. Anharmonic calculations are carried out using the second-order vibrational perturbation theory. The changes in transition frequencies and intensities of monomeric IR bands upon formation of the 1:1 complex are analyzed. A high intensity value (53 km mol–1) is predicted for the overtone band of the out-of-plane HF libration. The variational method was used to solve anharmonic vibrational problems in 1D–4D subspaces involving the H–F stretch. The influence of anharmonicity on spectral and structural parameters was studied. The variational calculation confirmed the high intensity value for the overtone of the HF librational mode from the perturbative calculation. Matrix-isolation experiments were performed in N2 at T = 8 K to record the absorption spectra of pure H2CO and HF and H2CO/HF mixtures in the IR region. The spectral features related to the H–F, C=O, and C–H stretches and the in-plane HF librational motion were reliably identified. The predictions of our perturbative calculations for isolated compounds, especially for the band shifts upon complexation, are in satisfactory agreement with the experimental matrix-isolation findings. The only exception is the H–F stretching mode in the complex because of the high anharmonicity of HF and strong interaction of free HF molecules with a matrix environment. Of particular interest is the observation of a rather strong band at 1069 cm–1, which is close to 1072 cm–1 predicted for the overtone of HF out-of-plane librational mode.

Effect of composition and size of the reference population in genotype imputation efficiency of INDUSCHIP in HF Crossbred cattle

The objective of this study was to investigate the effect of composition and size of the reference population in imputation efficiency of INDUSCHIP v2 in Indian HF crossbred cattle. Data set consisted of a total of 869 cattle from 14 Indicine breeds, 2 crossbreds (HF and Jersey crossbreds) and 2 exotic breeds (HF, Jersey) genotyped with Illumina BovineHD (Illumina, San Diego, CA) panel. Post QC, 846 animals and 449955 SNPs remained for imputation study. 3 test groups each with randomly selected 25 HFCB animals with subset genotype of INDUSCHIP v2 were created, whereas with HD genotyping data of remaining animals, 3 different categories of reference groups were created namely reference 1 (HF, Jersey, all 14 Indicine breeds, HF and Jersey crossbreds), reference 2 (HF, HF crossbred, Sahiwal, Gir and Kankrej ) and reference 3 (pure HF, Sahiwal, Gir and Kankrej). Imputation efficiency of INDUSCHIP v2 was expressed in terms of concordance rate and Dosage R2 (DR2). Reference groups 1 and 2 were found to be better than Reference group 3. Further, the size of the reference population had an impact on imputation efficiency. The concordance rate and DR2 decreased with decline about population size. However, a reference population with 280 animals was found to be sufficient to obtain a concordance rate of around 95% or more and DR2 around 0.93. More number of HF, HF crossbred, Sahiwal, Gir and Kankrej animals need to be HD genotyped and incorporated in the reference population to improve the imputation efficiency of INDUSCHIP v2.

Effect of Age and Season on the Seminal Traits of Pure HF Bulls Under Tropical Condition

The study was conducted to assess the effect of age and season on seminal traits of pure HF bulls under tropical condition. A total of 30 HF bulls of age group up to 3, 4-5, 6-7, 8 and above 8 years were selected and divided into 3 seasons viz rainy, summer and winter. The breeding bulls were kept under intensive system of rearing as per MSP guidelines of India. Semen was collected, evaluated and data analyzed by using standard procedures. The overall production and all the seminal traits viz volume, initial motility and post thaw motility was found to be better in summer season as compare to rainy and winter season. However, there was no significant change in concentration due to season. Among all the age groups, 8 years and above were found to produce highest volume, post thaw motility and eventually more production. Highest percentage of initial motility was recorded among the youngest group of bulls and concentration was significantly (plessthan0.01) high in the age group 6-7years followed by 8 and above 8 years of age. The study revealed that age and season have highly significant (plessthan0.01) effect on all the seminal traits and production.

Magnetic resonance imaging (MRI) compatible ZrX (X = Hf, Mo and Ru) alloys with enhanced mechanical properties as alternative biomedical applications

Novel magnetic resonance imaging (MRI) compatible P6/mmm-Zr8Hf4, Fd3m-Zr2Mo4 and Pm3m-ZrRu alloys with ultralow magnetic moment have been uncovered via first-principles evolutionary simulations. Their optimized lattice constants, elastic moduli, Vickers hardness, tensile strength, fracture toughness and ductility index have been calculated and discussed. These phases are thermodynamically, mechanically and dynamically stable. The calculated density of states reveals their metallic nature and hardness origin. Hardness and tensile strength of all specimens were significantly improved compared with those of pure Zr, Hf, Mo and Ru elements. Particularly, Zr2Mo4 and ZrRu phases also exhibit impressive ductile behavior.

Investigation into chemical function in a Mn4+-activated Li-phase cryolite synthesis for green synthetic design

Herein, a series of obstinate Mn4+-activated Li-phase cryolites Li3GaF6:Mn4+ have been newly synthesized and optimized via solvent composition regulation at traditional co-precipitation reaction. The phase purity, morphology, luminescence property and white light-emitting diode application of as-synthesized phosphor have been carefully investigated. Under 460 nm excitation, Li3GaF6:Mn4+ emits sharp lines at 633 nm with color purity of 99.75%. Notably, more than 15 times emission increment is realized based on partial replacement of toxic HF by CH3COOH (HAc) and little addition of H2O from the pure HF reaction system. The specific functions of chemicals in synthesis process are systematically studied via step-by-step synthesis optimization with single alteration in solvent compositions. It is disclosed that HF was used to dissolve insoluble reagents, provide H+ and F− ions; HAc offered weaker acidity; moderate H2O stimulated the ionization of weak acids. Besides, efficient Li3GaF6:Mn4+ tends to be formed in weaker acid environment with enough F− ions. Importantly, the employment of HAc and H2O immensely reduces the toxicity of reaction system. These findings on chemical function confirmation might enlighten the HF-free green co-precipitation synthesis of Mn4+-doped fluorides by using suitable raw material and solvent combinations.

Synthesis of single-phase high-entropy carbide powders

High-entropy carbide powders were produced by a two-step synthesis process consisting of carbothermal reduction followed by solid solution formation. Nominally pure (Hf,Zr,Ti,Ta,Nb)C in a single-phase rock salt structure had an average particle size of about 550 nm and an oxygen content of 0.2 wt%. The fine particle size was due to the use of high-energy ball milling prior to carbothermal reduction combined with the relatively low synthesis temperature of 1600 °C. Oxygen content was minimized by completion of the carbothermal reduction reactions under vacuum. This is the first report of synthesizing a high-entropy carbide powder using individual transition metal oxides and carbon as precursors.

Hardness of promising intermetallics obtained by the solid-state reaction of refractory carbides with iridium

Solid-state reactions of refractory carbides MC (M = Hf, Ta, W) with iridium powder at 1600 °C result in the formation of the corresponding MIr3±x intermetallic solid solution. Vickers microhardness tests of MIr3 intermetallics were performed using the load of 10 gf (HV0.01), and the local elemental composition was determined by energy dispersive spectroscopy (EDS) for each indentation area. The results of indentation tests showed that MIr3 intermetallics are much harder than pure Hf, Ta, W, or Ir (top-hardness metals), with the hardness 900–1400 HV0.01. The hardness value is affected by the real elemental composition of MIr3±x solid solution. Free carbon released during the interaction of metal carbide with iridium can contribute to the microhardness values.

Microstructural and mechanical characterisation of Fe-14Cr-0.22Hf alloy fabricated by spark plasma sintering

Fe-14Cr pre-alloyed powder and pure Hf powder were mechanically alloyed to produce powder with nominal composition Fe-14Cr-0.22Hf (wt. %) that was consolidated by the spark plasma sintering (SPS) technique in order to investigate the ability of Hf to produce a nanometric dispersion of oxide particles in a ferritic matrix. Comprehensive microstructural and mechanical characterisation of the as-milled powder and the consolidated material was performed using electron microscopy, X-ray diffraction, atom probe tomography and indentation techniques. It was shown that Hf additions can effectively produce, by internal oxidation, a fine scale dispersion of Hf-O nanoparticles in the consolidated material. A uniform grain structure was produced in the alloy. Although the nanoparticle dispersion was not homogeneous at the finest scale, the resulting dispersion strengthening contributed significantly to the hardness. According to these results, internal oxidation of reactive elements rather than direct addition of oxides may offer additional opportunities in the design and development of oxide dispersion strengthened steels.

Novel Synthesis of Anhydrous and Hydroxylated CuF2 Nanoparticles and Their Potential for Lithium Ion Batteries.

Anhydrous nanoscopic CuF2 is synthesized from alkoxides Cu(OR)2 (R=Me, tBu) by their reaction either in pure liquid HF at -70 °C, or under solvothermal conditions at 150 °C using excess HF and THF as solvent. Depending on the synthesis method, nanoparticles of sizes between 10 and 100 nm are obtained. The compound is highly hygroscopic and forms different hydrolysis products under moist air, namely CuF2 ⋅2 H2 O, Cu2 (OH)F3 , and Cu(OH)F, of which only the latter is stable at room temperature. CuF2 exhibits an electrochemical plateau at a potential of ≈2.7 V when cycled versus Li in half cell Li-ion batteries, which is attributed to a non-reversible conversion mechanism. The cell capacity in the first cycle depends on the particle size, being 468 mAh g-1 for ≈8 nm crystallite diameter, and 353 mAh g-1 for ≈12 nm crystallite diameter, referred to CuF2 . However, such a high capacity cannot be sustained for several cycles and the capacity rapidly fades out. The cell voltage decreases to ≈2.0 V for CuF2 ⋅2 H2 O, Cu2 (OH)F3 , and Cu(OH)F. As all the compounds studied in this work show irreversible conversion reactions, it can be concluded that copper-based fluorides are unsuitable for Li-ion battery applications.

Development of hafnium metal and titanium-hafnium alloys having apatite-forming ability by chemical surface modification.

Hafnium (Hf) has attracted considerable attention as a component of biomedical titanium (Ti) alloys with low Young's moduli and/or shape-memory functionalities, because its cytotoxicity is as low as that of Ti. The drawback of metals is that their bone-bonding ability is generally low. It is known that apatite formation in the body is a prerequisite for bone-bonding. Although several chemical treatments have been proposed for preparing Ti for bone-bonding, there have been no similar investigations for Hf. In the present study, NaOH- and heat-treatments were applied to pure Hf and Ti-Hf alloys and their bone-bonding ability was assessed in vitro with the use of simulated body fluid (SBF). After NaOH- and heat-treatments, anatase formed on alloys with low Hf content (20-40% (atom%) Hf); mixtures of sodium titanate and hafnium titanate formed on alloys with similar Ti and Hf content (60% Hf); and hafnium oxide formed on alloys with high Hf content (80% Hf and pure Hf). Precipitates of apatite were observed on all the metals in SBF, except for the alloy with 60% Hf. We speculated that the hafnium titanate formed on this alloy had a low apatite-forming ability owing to its high negative surface charge, which inhibited P adsorption. The apatite-forming abilities of the Ti-Hf alloys strongly depended on their Hf content. The present results indicate that Hf-based materials have good potential for bone-bonding. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2519-2523, 2018.