Effects Of Hf Content Research Articles

Phase Transitions and Oxidation Behavior During Oxyacetylene Torch Testing of TaC–HfC Solid Solutions

Tantalum carbide (TaC) and hafnium carbide (HfC) have some of the highest melting temperatures among the transition metal carbides, borides, and nitrides, making them promising materials for high‐speed flight and high‐temperature structural applications. Solid solutions of TaC and HfC are of particular interest due to their enhanced oxidation resistance compared to pure TaC or HfC. This study looks at the effect of Hf content on the oxidation resistance of TaC–HfC sintered specimens. Five compositions are fabricated into bulk samples using spark plasma sintering (2173 K, 50 MPa, 10 min hold). Oxidation behavior of a subset of the compositions (100 vol% TaC, 80 vol% TaC + 20 vol% HfC, and 50 vol% TaC + 50 vol% HfC) is analyzed using an oxyacetylene torch for 60 s. The TaC–HfC samples exhibit a reduction in the oxide scale thickness and the mass ablation rate with increasing HfC content. The improved oxidation resistance can be attributed to the formation of a Hf6Ta2O17 phase. This phase enhances oxidation resistance by reducing oxygen diffusion and serving as a protective layer for the unoxidized material. The superior oxidation resistance of TaC–HfC samples makes these materials strong contenders for the development of high‐speed flight coatings.

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.

Device Process and Circuit Application Interaction for Harsh Electronics: Hf–In–Zn–O Thin Film Transistors as an Example

The effects of Hf content on the radiation hardness of Hf–In–Zn–O thin-film transistors (HIZO TFTs) and HIZO TFT-based circuits are systemically examined. The evaluated circuits, including current-starved ring oscillator, energy harvesting, and RF circuits, are essential for space electronic systems. It is shown that HIZO TFTs with low Hf concentration have better initial performance while TFTs with high Hf concentration are more stable against radiation. On the other hand, for circuit application, the stable HIZO TFTs are not necessarily preferred for all circuits. This letter demonstrates that understanding the device-circuit interactions is necessary for device optimization and circuit reliability improvements for harsh electronic systems.

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.

Influence of Hf content on structure and electric properties of PHT thin films with self-buffered layer by PLD

Three components of lead hafnate titanate (PbHfxTi1–xO3, PHT) thin films have been fabricated by pulsed laser deposition (PLD) on the Pt (111)/Ti/SiO2/Si (100) substrates. In order to reduce the mismatch between the thin films and substrates, low temperature self-buffered layer is adopted. The effects of Hf content on structure and electric properties of PHT thin films have been investigated. The PHT near the MPB (x = 0.48) shows the highest remnant polarization (2Pr = 93.23 μC/cm2) and capacitance, even if its leakage current is a little worse than others. It should be noticed that the PHT ferroelectric films have a good performance after 2.15 × 1010 fatigue reversals, which indicates that PHT films as a promising material can be applied in ferromagnetic random access memory (FRAM).

Effect of Hf content on martensitic transformation, microstructure, and mechanical properties of Cu50Zr50−xHfx alloys

The effect of Hf substituting for Zr of Cu50Zr50−xHfx alloys on the microstructure, martensitic transformation behavior, and mechanical properties is investigated. It is demonstrated that Cu50Zr50−xHfx alloys exhibit higher transformation temperature with a peak martensite reverse transformation temperature of 594 K for Cu50Zr42Hf8 alloy, smaller thermal hysteresis and better thermal stability in comparison to those of Cu50Zr50 alloy. Due to the appearance of hard brittle second phase (Zr,Hf)2Cu, the elastic modulus increases while the plasticity reduces with Hf substituting for Zr.

Microstructure, mechanical properties and oxidation resistance of Nb silicide based ultrahigh temperature alloys with Hf addition

Four Nb silicide based ultrahigh temperature alloys with compositions of Nb–22Ti–16Si–3Cr–3Al–2B–xHf (x=0, 2, 4 and 8) (at%) were prepared by vacuum non-consumable arc melting. The effects of Hf content on the phase selection, microstructure, room-temperature fracture toughness, compressive performance and isothermal oxidation behavior at 1250°C of the alloys have been investigated. The results show that the formation of α(Nb,X)5Si3 is suppressed and instead the formation of γ(Nb,X)5Si3 is promoted by Hf addition. The Hf addition (especially 8at%) improves the room-temperature fracture toughness of the alloy. The hardness of γ(Nb,X)5Si3 increases with its Hf concentration. The compression strength of the alloy is the highest at 4at% Hf, and then obviously reduces at 8at% Hf due to embrittlement of the alloy (especially that of γ(Nb,X)5Si3). The oxidation resistance of the alloy has been firstly ameliorated by the lower Hf addition (2at%) and then degraded by the higher Hf addition (especially 8at%). The details have been discussed.

Effect of Hf Content on Oxidation Resistance of Single Crystal Superalloy at 1000°C

The specimens of single crystal superalloy DD6 with 0.10% Hf and 0.47% Hf were prepared in the directionally solidified furnace. The effect of Hf content on the isothermal oxidation resistance of the second generation single crystal superalloy DD6 was studied at 1000°Cin ambient atmosphere. Morphology of oxides was examined by SEM, and their composition was analyzed by XRD and EDS. The experimental results show that the oxidation resistance of DD6 alloy with 0.47% Hf is better than that of the alloy with 0.10% Hf. The alloy with different Hf content all obeys parabolic rate law during oxidation for 100h at 1000°C. The increase of Hf content can promote the Al2O3 formation and decreases the proportion of NiO. The oxide grain size and the thickness of the oxide layer all reduce with increasing of Hf content. The oxide scale of the alloy with different Hf content is made up of an outer NiO layer with a small amount of Co3O4, inner Al2O3 and Cr2O3 layer with a small amount of TaO2.

Improvement in the negative bias stability of zinc oxide thin-film transistors by hafnium doping

Thin-film transistors (TFTs) with hafnium-doped zinc oxide (HZO) channels were fabricated and the effects of Hf content on the performance of ZnO-based TFT were investigated. HZO TFTs exhibit improved electrical characteristics, with increased ION/IOFF and decreased subthreshold swing. We also investigated the influence of hafnium doping on the bias stability of ZnO TFTs. HZO TFTs exhibited turn-on voltage (VON) shifts of −1 V in negative stress bias, compared with −8 V for intrinsic ZnO TFTs. The improvement in the VON shift may be due to a reduction in the total trap density resulting from the suppression of the defect-related oxidation state of the Zn ions caused by the high binding energy of Hf ions.

Ultrasonication as a Method of Investigation of the Mechanical Properties of Doped Hafnium Barium Titanate

The purpose of this study was to fabricate dense ceramic specimens from the system of BaTiO3-BaHfO3 and then to perform mechanical tests. The effect of Hf content on a microstructure and mechanical properties of the BaTiO3-BaHfO3 solid solution was investigated at room temperature. To determine the elastic constants (the Young′s modulus E, the shear modulus G, bulk modulus K and the Poisson′s ratio v) of BaHfxTi1-xO3 a method of measurement of the longitudinal (VL ) and transverse (VT ) ultrasonic wave velocities for this type of material was developed.

Improvement in the bias stability of tin oxide thin-film transistors by hafnium doping

Thin-film transistors (TFTs) were fabricated with hafnium doped tin oxide (HTO) channels, and the effects of Hf content on the device performance of SnO x based TFTs was investigated. HTO TFTs exhibit improved electrical properties with increased field effect mobility and decreased subthreshold swing. We also investigated the influence of hafnium doping on bias stability in SnO x TFTs. HTO TFTs exhibited turn-on voltage (V ON) shifts of + 7 V for positive stress bias, compared with + 18 V for SnO x TFTs. The improvement in the V ON shift may be due to reduction in total trap density resulting from the suppression of defects related oxidation state of the Sn ion caused by the high binding energies of Hf ions.

Effect of Hf Content on the Microstructures and Stress Rupture Properties of DD6 Single Crystal Superalloy

Abstract The effect of Hf content on the microstructures after heat treatment and stress rupture properties of DD6 single crystal superalloy was investigated. The results show that with increasing of Hf content in the range of current research, the residual γ/γ' eutectic increases apparently, the size of γ' particles in dendritic cores has no obvious change and that in interdendritic decreases after heat treatment. With the increase of Hf content, the stress rupture life increases at first and decreases afterwards, and the elongation displays fast increasing first, and slow rising afterwards at 1100 °C, 140 MPa. At last the relationship between the microstructures and stress rupture properties of DD6 alloy with different Hf contents was discussed.

Ionic Conductivity and Viscosity of Low Temperature Molten Fluorides Containing HF

The effects of HF content on the ionic conductivity and the viscosity of low temperature molten fluorides, (CH3)4NF·mHF, (CH3)3N·mHF, KF·mHF, and NH4F·mHF melts, were investigated. The ionic conductivity of the (CH3)3N·mHF and (CH3)4NF·mHF melts increased, whereas their viscosity decreased with increasing the m value. The ionic conductivity and the viscosity of the (CH3)3N·mHF melts were lower and higher, respectively, than those of the (CH3)4NF·mHF melts at a given m value and a given temperature. The activation energy for ionic migration decreased with increasing the m value in both systems. Similar effects of the m value on the conductivity and viscosity were obtained for the KF·mHF and NH4F·mHF melts. The KF·mHF melts exhibited lower conductivity and higher viscosity than the NH4F·mHF melts at a given m value and a given temperature. It was concluded that these effects of the HF content can be explained in terms of the concentration change of molecular HF and the resulting change in electrostatic cation-anion interactions.

Dynamic Young's Modulus and Mechanical Properties of Ti−Hf Alloys

Ti−Hf alloys are expected to have lower modulus and higher strength than pure Ti since. Hf has been suggested to have the potential to enhance the strength and to reduce the Young's modulus of Ti alloys at the same time. In the present study, binary Ti−Hf alloys with Hf contents from 5 to 40 mass% were designed and fabricated. The effects of Hf content on the microstructures, dynamic Young's modulus and mechanical properties of Ti−Hf alloys were investigated with the aim of biomedical applications. The microstructures were examined using a scanning electron microscopy and an X-ray diffraction analysis. The experimental results indicate that all the studied Ti−Hf alloys exhibit lamellar HCP martensite (α′) structure under the given solution treatment, and increasing Hf content can gently reduce the Young's modulus but strongly enhance the strength of Ti−Hf alloys.

The effect of Hf content on the phase structures and electrochemical properties of V 2.1TiNi 0.5Hf x ( x=0–0.25) hydrogen storage alloys

The phase structures and electrochemical properties of the V 2.1TiNi 0.5Hf x ( x=0–0.25) alloys were investigated. It is found that the addition of Hf ( x≥0.05) into the V 2.1TiNi 0.5 alloy changes the secondary phase from the b.c.c. TiNi-based phase to a C14 Laves phase with hexagonal structure, in the form of a three-dimensional network along the grain boundaries of the main phase. The amount of the C14 Laves phase increases with increasing Hf content. The discharge capacity of the Hf added alloys remains high. The V 2.1TiNi 0.5Hf 0.05 alloy electrode has a discharge capacity of 444 mAh/g (discharge current: 25 mA/g), exceeding that of the V 2.1TiNi 0.5 alloy. Proper Hf content ( x≤0.12) is advantageous for improving the high-rate dischargeability of V 2.1TiNi 0.5Hf x alloys. The presence of Hf always leads to a degradation in cycle stability of the alloys, mainly due to the increase of the V content in the secondary phase and the increasing tendency to form cracks on the alloy surface in cycling.