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The present study reports the glass-forming ability, density change on crystallization and corrosion behavior of newly developed rare-earth free Cu-based metallic glasses (CBMGs). The critical casting thickness of these new CBMGs increased from 15 mm at 8 at.% Hf to 22 mm at 12 at.% Hf, reaching a maximum value of 28.5 mm at 13.5 at.% Hf. It dropped to 24 mm and 15 mm thereafter, for 15 and 20 at.% Hf, respectively. The alloys showed a monotonic increase in density going from 8 at.% Hf to 20 at.% Hf, with the density of amorphous samples increasing from 7.83 g/cm3 to 8.84 g/cm3 and crystallized samples increasing from 7.92 g/cm3 to 8.91 g/cm3. Potentiodynamic polarization tests carried out in 0.1, 0.2 and 0.5 M NaCl solution at 25 °C showed a direct correlation between corrosion resistance and Hf content in the order: 8 at.% < 13.5 at.% < 20 at.% Hf. Increase in NaCl concentration also had a significant impact on the corrosion intensity due to the chaotropic effect. Scanning electron microscopy of corroded sample surfaces showed formation and eventual merging of individual micro cracks resulting in a mud-cracking pattern. Energy-dispersive X-ray spectroscopy maps of pitted regions revealed reduction in Zr and Al concentration with increase in Hf and Cu percentage for all compositions. An increase in the O concentration along with the appearance of new peaks in the X-ray photoelectron spectroscopy results, measured post corrosion, confirmed the formation of metal oxides and oxyhydroxides in the passive layer.

A small amount of Hf was employed as a new additive to improve B removal in the electromagnetic solidification refinement of Si with an Al–Si melt, because Hf has a very strong affinity for B. The segregation ratio of Hf between the solid Si and Al–Si melt was estimated to range from 4.9 × 10−6 to 8.8 × 10−7 for Al concentrations of 0 to 64 at.%, respectively. The activity coefficient of Hf in solid Si at its infinite dilution was also estimated. A small addition of Hf (

The alloy TiFe has interesting hydrogen storage properties for practical applications: low cost, operation at room temperature, and good hydrogen capacity. However, the first hydrogenation is difficult and increases the cost of the alloy. In this work, we studied the effect of adding hafnium to TiFe in order to enhance the first hydrogenation process. TiFe + x Hf alloys, with x = 0, 4, 8, 12, and 16 wt.%, were synthesized by arc melting. The microstructure of the as-cast alloys was investigated by scanning electron microscopy and electron microprobe analysis. These alloys consisted of B2-TiFe, C14-Laves, and BCC (Body Centered Cubic) phases. A minimum of 8 wt.% of hafnium is required to obtain an enhancement of the first hydrogenation. In the first hydrogenation, the material reaches its maximal hydrogen capacity in less than two hours at room temperature and under 20 bars of hydrogen. Hafnium addition also had the effect of lowering the plateau pressure in the pressure-composition isotherm. It could be concluded that hafnium has a positive effect on the activation properties of TiFe.

To investigate the effect of hafnium addition on the solidifi cation structure, Ti-46Al alloys with nominal compositions of Ti-46Al-xHf (x = 0, 3, 5, 7) (at.%) were arc-melted into small ingots in an argon atmosphere. The characteristics of the macrostructures and microstructures were studied using a linear intercept method, OM, SEM (BSE), XRD and TEM. The results showed that the ingots with Hf have near lamellar microstructure in columnar and dendrite morphology. The hafnium concentration has a strong effect on the columnar spacing refi nement. Increasing Hf from 0 to 7 (at.%), the columnar spacing can be reduced from ~ 1000 to ~ 400 μm. Constitute phases of the ingots are α2, a small amount of B2 and c. Most of the B2 phases, richer in Hf and leaner in Al and Ti, exist on the node of the dendrite core in block shape and a little across the lamellar colonies in stick shape. The c phases exist on the boundaries of lamellar colonies in small cellular shape. There also exists a segregation of Hf on the columnar and dendrite core. Particularly, both the α- and β-phase form from the melt as prior phases. The possible phase sequencing during solidifi cation and solid-state transformations with Hf is given in this paper.

A small amount of Hf was employed as a new additive to improve B removal in the electromagnetic solidification refinement of Si with an Al–Si melt, because Hf has a very strong affinity for B. The segregation ratio of Hf between the solid Si and Al–Si melt was estimated to range from 4.9 × 10−6to 8.8 × 10−7for Al concentrations of 0 to 64 at.%, respectively. The activity coefficient of Hf in solid Si at its infinite dilution was also estimated. A small addition of Hf (<1025 parts per million atoms, ppma) significantly improved the B removal. It was confirmed that the use of an increased Hf addition, slower cooling rate, and Al-rich Al–Si melt as the refining solvent removed B more efficiently. B in Si could be removed as much as 98.2% with 410 ppma Hf addition when the liquidus temperature of the Al–Si melt was 1173 K and the cooling rate was 4.5–7.6 K min–1. The B content in Si could be controlled from 153 ppma to 2.7 ppma, which meets the acceptable level for solar-grade Si. [ABSTRACT FROM PUBLISHER]

Pure MoS x and MoS x + Hf thin films were deposited by magnetron sputtering and characterized by RBS, GAXRD, XPS, high temperature oxidation tests and tribological tests. Hf content was set at 12 at.% by RBS and GAXRD analyses revealed a complete amorphization caused by Hf incorporation. XPS analyses indicated that hafnium is inserted in MoS x in the form of HfS x , moreover, such compound was responsible for inhibiting the formation of MoS. These factors are closely correlated with improvements obtained in oxidation resistance, friction coefficient, wear rate and lifespan of MoS x thin films. • MoS x and MoS x + Hf thin films were deposited by magnetron sputtering. • Hafnium incorporation promotes a complete amorphization of the coating. • Hafnium atoms are present in the MoS x matrix as HfS x structure. • It was observed MoS structure only for pure MoSx coatings. • MoS x + Hf coating possess better tribological properties when compared to MoS x. [ABSTRACT FROM AUTHOR]

The alloy TiFe has interesting hydrogen storage properties for practical applications: low cost, operation at room temperature, and good hydrogen capacity. However, the first hydrogenation is difficult and increases the cost of the alloy. In this work, we studied the effect of adding hafnium to TiFe in order to enhance the first hydrogenation process. TiFe + x Hf alloys, with x = 0, 4, 8, 12, and 16 wt.%, were synthesized by arc melting. The microstructure of the as-cast alloys was investigated by scanning electron microscopy and electron microprobe analysis. These alloys consisted of B2-TiFe, C14-Laves, and BCC (Body Centered Cubic) phases. A minimum of 8 wt.% of hafnium is required to obtain an enhancement of the first hydrogenation. In the first hydrogenation, the material reaches its maximal hydrogen capacity in less than two hours at room temperature and under 20 bars of hydrogen. Hafnium addition also had the effect of lowering the plateau pressure in the pressure-composition isotherm. It could be concluded that hafnium has a positive effect on the activation properties of TiFe. [ABSTRACT FROM AUTHOR]