Effect Of Hf Addition Research Articles

Effects of Hf addition on the microstructure and properties of Cu-Sn-P alloy

In this paper, the effects of Hf addition on the mechanical properties, electrical conductivity and microstructure of Cu-Sn-P alloy were investigated. The results show that the Hf addition can enhance the mechanical properties and electrical conductivity of Cu-Sn-P alloy. The alloy with 0.05 wt.% Hf exhibits the best comprehensive performance with yield strength of 625 MPa, tensile strength of 661 MPa and electrical conductivity of 16.8 %IACS. Compared with the Cu-Sn-P alloy without Hf addition, the yield strength and tensile strength are increased by 8.4% and 7.8%, and the electrical conductivity is increased by 24.4%. The increase in the strength of Hf-added alloy can be attributed to the synergistic effect of multiple strengthening mechanisms, including fine grain strengthening, twin strengthening, dislocation strengthening, precipitation strengthening and Σ3n (n = 1, 2, 3) grain boundary strengthening. Moreover, the Hf-P precipitates can be observed in the Hf-added alloy. According to the amount of Hf addition, these precipitates can manifest as the fine HfP2 phase and the coarse HfP phase. The formation of Hf-P precipitates contributes to the precipitation strengthening and the purification of Cu matrix, thus contributing to the improvement of strength and conductivity.

Effect of Hf addition on structural transformation and aging stability of Cu–15Ni–8Sn alloy

The Cu–15Ni–8Sn-xHf (wt.%, x = 0–0.6) alloys were prepared by vacuum melting, and the effect of Hf on the micro-structure of as-cast, as-solution-treated and as-aged alloys was systematically investigated, as well as the alloy aging stability. The Hf addition provided a significant role on refining the solidification structure and reducing the micro-segregation degree, and it also made γ-D03 phases more likely to form in needlelike-shape rather than lamellar-shape. With the presence of more Hf atoms, their existence form was accordingly changed from solid solute atoms to nano-scale precipitation phases and then to micron-scale segregation phase. A small content of Hf (0.1 wt%) could effectively improve the aging stability by inhibiting the growth of γ-D03. Once its content reached or exceeded 0.3 wt%, the harmful discontinuous precipitation was completely inhibited, and the common lamellar-shape γ-D03 locating around the grain boundary was no longer formed. Even the alloy failed at higher temperatures, it could only be carried out through the continuous precipitation method, namely the generation of needlelike-shape γ-D03 uniformly in the matrix. The appropriate Hf addition was capable of extending the alloy aging window, and the hardness of Cu–15Ni–8Sn-0.3Hf alloy could still exceed 360 HV even after 48 h aging.

Effect of Hf addition on microstructural evolution and corrosion behavior of nickel-based alloys in hydrochloric acid

The effect of hafnium (Hf) addition on microstructural evolution and corrosion behavior of nickel-based alloys was investigated. The findings indicated that adding Hf appropriately can increase the ratio of Cr2O3 and O2- species in the passive film, resulting in a greater resistance to localized corrosion. However, microgalvanic coupling occurred when precipitates were present in Hf0.5 and Hf1.0 alloys, with the face-centered cubic matrix acting as cathode and Hf-rich precipitates serving as anodes, leading to a preferential corrosion of the latter and a subsequent reduction in the corrosion resistance of the nickel-based alloys.

Effect of Hf addition on initial microstructure of (Ni, Pt)Al coating and inhibiting the detrimental sulfur during high temperature exposure at 1150 °C

Single-phase (Ni, Pt)Al coatings with and without Hf addition were prepared via electroplating a Pt/Pt-Hf layer and subsequent gaseous phase aluminisation. The initial microstructure and oxidation behaviour of two coatings were investigated comparatively. The results show that finer grains were obtained in Hf-doped Pt-plating layer and as-received (Ni, Pt)Al coating, which contributes to better high temperature performance and oxide scale peeling resistance. Additionally, Hf can effectively retard the θ-Al2O3 transformed to α-Al2O3 during the early oxidation and enhanced oxidation resistance during the stable oxidation. The effect of Hf on inhibiting detrimental sulfur in acid-(Ni, Pt)Al during high-temperature exposure were intensively discussed.

Effect of Hf addition on the microstructure and mechanical properties of electron beam welded Mo-La2O3 alloy

Electron beam welding of La2O3 dispersion strengthened molybdenum alloy is conducted in this research. Hf interlayers with different thicknesses are introduced to joining Mo alloy via in-situ alloying to avoid grain boundary oxidation and improve the mechanical properties of joints. The porosity ratio within the weld reduces from 7.53% (without Hf interlayer) to 1% ∼ 2% (with Hf interlayers of 0.1 mm–0.35 mm). The microstructure of the weld is mainly composed of Mo base solid solution for the joints with a Hf interlayer of 0.05 mm. As the thickness of the Hf interlayers increases from 0.1 mm to 0.35 mm, HfMo2 is generated within the weld and the content of HfMo2 phase increases significantly. The introduction of Hf promotes the grain refinement of the weld owing to the generation of HfO2 precipitates, which provide more heterogeneous nucleation sites for the liquid metal to nucleate. In addition, the formation of HfO2 consumes the O elements in the weld and prevents the generation of MoO2 along grain boundaries, which is beneficial for the improvement of the mechanical properties of the joints. The results show that the introduction of Hf significantly improves the strength of the joint. The ultimate strength of the joint with a Hf interlayer of 0.1 mm especially for the joint with a Hf interlayer of 0.1 mm reaches 333 MPa, which is 6 times more than that of the joint without a Hf interlayer of 54 MPa.

Effect of Hf addition on evolution of microstructure and strengthening behavior in Ni-based ODS superalloy

In this study, two kinds of Zr-containing Ni-based ODS superalloys, ODS-Zr (Ni-20Cr-0.5Ti-0.3Al-0.6Zr-0.6Y2O3, wt%) and ODS-Zr+Hf (Ni-20Cr-0.5Ti-0.3Al-0.6Zr-0.8Hf-0.6Y2O3, wt%), were prepared by high-energy milling and hot isostatic pressing (HIP) process. Evolution of microstructure and tensile property caused by Hf addition was analyzed and discussed. The result showed that the addition of Hf changes significantly oxide type and refines oxide size. Y4Zr3O12, Y2TiO5 and three-type Y-Al oxides including monoclinic-structure Y4Al5O12 (YAM), orthogonal and hexagonal YAlO3(YAM and YAH) are found in ODS-Zr. In contrast, only Y2Hf2O7, Y4Zr3O12 and Y2TiO5 but no Y-Al oxides are viewed in ODS-Zr+Hf. The average diameter of oxides in ODS-Zr and ODS-Zr+Hf is 16.6 nm and 13.0 nm, respectively. The size difference between two alloys is ascribed to different oxide constitution in two alloys. Moreover, Hf addition enhances tensile strength of alloys at 25 °C and 700 °C meanwhile improves tensile ductility at 700 °C.

The Effect of Hf Addition on the Boronizing and Siliciding Behavior of CoCrFeNi High Entropy Alloys.

The effect of a boronizing and siliciding process on CoCrFeNiHf0.1–0.42 high entropy alloys was examined in this study. When increasing the amount of added Hf in CoCrFeNiHfx, the structure of the alloys gradually transformed from single-phase FCC to firstly Ni7Hf2 + FCC, and finally to C15 Laves and FCC phases. The boronizing/siliciding process resulted in the formation of a silicon-rich layer and a boride layer (BL). Increasing the amount of Hf in the alloys resulted in a decrease in the combined layer thickness, which was measured for CoCrFeNi, CoCrFeNiHf0.1, CoCrFeNiHf0.2, and CoCrFeNiHf0.42 to be 70 µm, 63 µm, 20 µm, and 15 µm, respectively. In contrast, the thickness of the transition zone/diffusion zone increased with more Hf in the alloys. While silicon atoms were gathered close to the BL, they were not transferred into the CoCrFeNi substrate. In contrast to the observation for CoCrFeNi, Si atoms penetrated through the Ni-rich phase (Ni7Hf2) in the CoCrFeNiHfx alloys. Furthermore, the Cr-B rich area (Cr5B3) in the coating limited the transport of Si into the CoCrFeNiHfx substrates. XRD analysis showed that the BL contained Ni2Si, FeB, Fe2B, Co2B, and Cr5B3 phases.

Effect of Hf additions on phase transformation, microstructural stability, and hardness of nanocrystalline 304L stainless steels synthesized by mechanical alloying

304L stainless steels with Hf additions were nanostructured by mechanical alloying (MA) and annealed at temperatures up to 1100 °C. The results showed that face-centered cubic (fcc) phase in 304L transformed to body-centered cubic (bcc) phase during MA. The in-situ studies revealed that bcc-to-fcc phase transformation completed after 105 min annealing at 900 °C for 304L, whereas Hf addition increased the required time and temperature for the complete transformation. The grain size of 304L stainless steel was ~10 nm after MA and remained ~167 and ~293 nm after annealing at 900 and 1100 °C, respectively, with Hf addition in comparison to 960 nm average grain size of base 304L stainless steel after annealing at 900 °C. The hardness of 304L increased from ~200 HV to 408 HV after MA and remained 329 HV after annealing at 1100 °C with Hf addition as opposed to 195 HV hardness of 304L.

Tailoring the magnetic properties and microstructure of NdFeB ribbon alloys by Hf addition

In this paper, the effects of Hf addition on phase composition, Curie temperature, exchange coupling effect, coercivity mechanism, room temperature magnetic properties, high temperature magnetic properties and thermal stability of NdFeB alloys with different Nd content (27–31 wt%) are systematically studied. Hf addition showed different effects on the magnetic properties of NdFeB alloys at different Nd contents and different test temperatures. At 300 K, the intrinsic coercivity is increased with low Nd content (27 wt%), while the remanence and the maximum magnetic energy product are significantly improved with higher Nd content (29 wt%, 31 wt%). At 398 K, the intrinsic coercivity, the remanence, the maximum magnetic energy product and the temperature stability improved in NdFeB alloys with high Nd content (29 wt%, 31 wt%).

Effects of Hf additions on the microstructures and mechanical properties of Ni-rich Ni55Ti45 alloys

The microstructural characterization and mechanical properties of the oil quenched binary Ni55Ti45 alloy and Hf-modified Ni55Ti45-xHfx (x = 3, 5, 7 at.%) alloys were investigated. The results showed that the microstructure of binary alloy is composed of NiTi phase, nanoscale Ni4Ti3 precipitates, and a small amount of Ti4Ni2O and Ni3Ti2 phases. The Hf additions suppresses the formation of the Ti4Ni2O and Ni3Ti2 phases and promotes the HfO2 particles. When the Hf content is less than 5 at.%, the main precipitated phase is still Ni4Ti3, but which is gradually refined and spheroidized with the increase of Hf content. While the Ni4Ti3 phases disappeared and the fine H-phases precipitated massively in the Ni55Ti38Hf7 alloy. With the gaining content of Hf, the Vickers hardness increases, but the fracture toughness and tensile strength increase first and then decrease. When the addition of Hf is 3 at.%, the alloy possesses the best property with the fracture toughness of 21.02 MPa/m1/2 and the tensile strength of 2.25 GPa.

Preparation and strengthening mechanisms of in-situ HF catalyzed highly porous mullite with whisker frame structure

Using HF as catalyst and based on sol-gel chemical precursor powder molding and sintering process, porous mullite with whisker frame structure was in-situ synthesized in the blank body. Due to the high efficiency catalysis of HF, this structure has both of high porosity and high strength. The effects of HF addition and sintering temperature on the formation of mullite whisker frame, phase transition process, porosity and strength of porous materials were discussed, and the optimal process parameters were determined. The mechanism of strengthening the porous materials was preliminary analyzed, and under the catalysis of HF, the close connection between whisker frame lap joints was formed. When the porosity of mullite is up to 83.22%, the compressive strength of can reach 16.48 MPa.

The effect of Hf on solidification cracking inhibition of IN738LC processed by Selective Laser Melting

The effects of Hf addition on defects and mechanical properties of the “hard-to-weld” superalloy IN738LC manufactured by Selective Laser Melting (SLM) process were studied. The addition of Hf inhibits cracking in SLMed IN738LC. Cracking free and low porosity IN738LC parts were obtained in a wide range of process parameters. The study shows that the cracks were refilled by Hf-riched melt and the relative density was increased, thus the tensile properties at 700 and 850 °C were improved.

The Effect of Hf Addition on the Boronizing and Siliciding Behavior of CoCrFeNi High Entropy Alloys

The Effect of Hf Addition on the Boronizing and Siliciding Behavior of CoCrFeNi High Entropy Alloys

Effect of Hf addition on solidification and hot isostatically pressed microstructures of the Ti-48Al-2Cr-2Nb (at%) intermetallic alloy

The microstructural evolutions during solidification and hot isostatic pressing (HIP) of Ti-48Al-2Cr-2Nb-xHf (4822-xHf, x = 0, 2, 4, 6 at%) intermetallic alloys were investigated using both experimental observations and thermodynamic calculations. The primary solidification phase of all the studied alloys was β, albeit it was predicted by Thermo-Calc to be α for the alloys containing 4% and 6%Hf. In agreement with the Thermo-Calc calculations, the solidification path of the base 4822 alloy encountered a peritectic reaction. Although alloying by 2%Hf did not change the solidification path, further increase in Hf content caused an additional eutectic reaction following the peritectic one. The eutectic microstructure was composed of two orthorhombic phases with TiAl2 and Al3Hf2 compositions and this finding was the first evidence of such phases in a quinary alloy with Cr, Nb, and Hf. It was found that Hf acted as a weak β stabilizer as it showed a low partitioning tendency in β and the β single-phase field was not formed in the high-Hf alloys. A finer dendritic microstructure was characterized in the high-Hf alloys due to the Hf solubility limit in the 4822 alloy. Interestingly, α2 laths dissolved in the Hf-containing alloys after HIP treatment and instead rode-like precipitates of Al3Hf2 emerged at newly formed γ/γ interfaces. The precipitation mechanism of Al3Hf2 particles was discussed.

Effects of Hf addition on the structure, mechanical and tribological properties of CrN film

Alloying elements in binary nitride is considered as a promising method to design hard and tough films. Hf atoms are proposed to be incorporated in CrN nitrid films to form ternary nitrides, which may possess the improved mechanical and tribological properties. In this study, Cr1-xHfxN [x = Hf/(Cr + Hf)] films were sputtering deposited by incorporating Hf into CrN film in an mixed atmosphere of Ar and N2. The influences of Hf addition on the microstructure, mechanical and tribological properties of Cr1-xHfxN films were investigated. The results show that the hardness and fracture toughness of CrN film is significantly improved due to solid solution strengthening by incorporating Hf atoms. Thanks to the improved hardness and toughness, the wear resistance of CrN film is enhanced. A high H/E and H3/E2 values, which are regarded as the reflection of toughness of hard films, are obtained from Cr0.69Hf0.31N film with higher hardness (30.49 GPa). The lowest wear rate of about 1.03 × 10−6 mm3/Nm is also presented for Cr0.69Hf0.31N film, which corresponds to higher H/E(~0.125) and H3/E2(~0.481 GPa).

Effects of Hf addition on the microstructure, magnetic properties and coercivity mechanism of Nd-Ce-Fe-B ribbons fabricated by melt-spinning technique

Abstract In this paper Hf doped (Nd0.8Ce0.2)13Fe82−xB5Hfx (x = 0, 0.5, 1.0, 2.0, 3.0) ribbons were fabricated by melt-spinning technique, and their microstructure, magnetic properties and coercivity mechanism have been investigated methodically. It is found that the coercivity of (Nd0.8Ce0.2)13Fe82−xB5Hfx ribbons is enhanced for 0 ≤ x ≤ 2.0 at.% while the remanence decreases slightly. The optimal comprehensive magnetic properties Jr = 7.5 kG, Hcj = 12.7 kOe, and (BH)max = 12.3 MGOe, are obtained at x = 1.0 at.%. The grain size decreased with the addition of Hf and more uniform microstructure evolved. The coercivity mechanism of the (Nd0.8Ce0.2)13Fe82−xB5Hfx (x = 0–3.0) ribbons is found to be the pinning mechanism based on the systematic investigations and analysis. The synchronization of the grain refinement and the pinning effect lead to the improvement of magnetic properties.

Effect of Hf additions on phase stability and mechanical properties of binary W-Hf alloys: A first-principles study

In this paper, the effect of hafnium alloying element on phase stability and mechanical properties of binary tungsten-hafnium alloys was calculated using the first principles technology. Firstly, we investigated the cell volumes, lattice constants and formation energies of binary W1-xHfx (x = 0, 0.0625, 0.125, 0.1875, 0.25 and 0.5) alloys. It is shown that binary tungsten-hafnium alloys remain maintain BCC structures. When the concentration of hafnium atoms is lower than 12.5%, the structures of binary tungsten-hafnium alloys are thermodynamically stable. The elastic constants of binary tungsten-hafnium alloys were calculated based on the optimized atomic lattice. Then the elastic modulus and other mechanical parameters are deduced according to the relevant formulas. It is shown that the mechanical strength of binary tungsten-hafnium alloy decreases with increasing hafnium concentration, which is lower than the mechanical strength of pure tungsten metal. However, the mechanical strength of binary tungsten-hafnium alloys is higher than that of pure hafnium metal. In addition, it can be effective to improve the ductility of pure tungsten metal based on hafnium alloying tungsten.

High-temperature oxidation behaviour of minor Hf-doped β-NiAl single crystals in dry and humid atmospheres

Oxidation behaviour of undoped β-NiAl and β-NiAl-0.05Hf single crystals were investigated at 1100 °C in 20 vol% O2 + Ar and 15 vol% H2O + Ar, respectively. On contrary to the well-known beneficial effect of Hf additions on the oxidation behaviour of polycrystalline β-NiAl, severe-scale spallation is observed for β-NiAl-0.05Hf single-crystal alloy, especially in dry atmosphere. It is proposed that the presence of the grain boundaries in the polycrystalline substrate enables proper content of Hf segregating at the grain boundaries of the oxide scale and at the scale–substrate interface, which promotes the conditions required for reactive element effect. Once the reactive element effect of Hf does not work, its strong affinity with oxygen will accelerate the process of high-temperature oxidation. However, the absence of the grain boundaries as fast diffusion paths partially compromises the adverse influence of water vapour on cyclic oxidation resistance of β-NiAl single crystal, resulting in considerable suppression of the oxidation rate and less loss of protection compared with that in dry atmosphere. In addition, interfacial cavities are observed in dry and humid atmospheres, which may eventually result in the spallation of the oxide scale.

The oxidation performance of plasma-sprayed NiAl bond coat: Effect of Hf addition in bond coat and substrate

NiAl bond coats with and without Hf addition (0.1 at.%) were deposited on two types of superalloy substrates (i.e., DZ125L, no Hf, and DZ125, 0.51 at.% Hf) using plasma spraying technique, and isothermally oxidized at 1150 °C. It demonstrates that Hf addition in the bond coat is more effective than in the superalloy substrate for improving the bond coat oxidation resistance. In addition, though the substrate chemistry could affect the bond coat oxidation performance, this effect was very sensitive to the chemistry of the bond coat - obvious for the RE (reactive element)-free NiAl bond coat, but less obvious for the RE-containing bond coats (NiAlHf and NiCoCrAlY). Moreover, compared with the NiCoCrAlY bond coat, the NiAlHf bond coat showed significantly improved oxidation resistance, regardless of the substrate chemistry, suggesting that NiAlHf bond coat prepared by plasma spraying is a promising candidate for the thermal barrier coating application.

Effects of Hf addition on the thermal stability of 16Cr-ODS steels at elevated aging temperatures

In this paper, the effects of hafnium (Hf) addition on the thermal stability of the microstructure and tensile properties of Al-containing 16Cr-ODS steels were investigated. High temperature aging tests of the ODS steels with and without Hf were conducted at 750 °C, 950 °C and 1150 °C for 100 h respectively. And the microstructure evolution after thermal aging was investigated using transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The results indicated that Hf addition could improve the coarsening resistance of the oxide particles and the grains during aging treatment due to the formation of stable Y2Hf2O7 particles. Tensile tests on the aged-steels showed that the ultimate tensile strength and yield strength of 16Cr-Hf-ODS steel were higher than those of 16Cr-ODS steel. It was considered that the excellent thermal stability and tensile properties of 16Cr-Hf-ODS steel were related with the refined microstructure.