Fe–B–Si–Zr soft magnetic bulk glassy alloys

The present work is devoted to fabrication of Fe–B–Si–Zr multi-component bulk glassy alloys with good mechanical and soft magnetic properties. Glass formation in Fe–B system is first considered with an empirical cluster-plus-glue-atom model. A basic composition formula [B–B₂Fe₈]Fe is proposed as the framework for multi-component alloy design. Considering the structural stability of the model glass, Si and Zr are introduced to the [B–B₂Fe₈] cluster to replace the center B and shell Fe atoms, from which a series of Fe–B–Si–Zr alloys with composition formulas [Si–B₂Fe_8−xZr_x]Fe (x = 0–0.6) are derived. Copper mold casting experiment shows that bulk glassy alloys are formed within the Zr content range of x = 0.2–0.6, and the largest glass-forming ability appears at [Si–B₂Fe_7.6Zr_0.4]Fe with a critical size of 2.5 mm. The bulk glassy alloys exhibit high fracture strength as large as 3850 MPa. Magnetic property measurement indicates that these alloys exhibit good magnetic softness with high saturation magnetization (1.26–1.48 T) and low coercive force (1.6–6.7 A/m). The alloying effects of Si and Zr on bulk glass formation, thermal glass stability and magnetic softness are discussed with the empirical model.     

Formation of amorphous phase with crystalline globules in Fe–Cu–Si–B and Fe–Cu–Zr–B immiscible alloys

The microstructure of rapidly solidified melt-spun ribbons of (Fe_0.75M_0.10B_0.15)_100−xCu_x (M = Si, Zr) alloys was investigated focusing on amorphous-phase formation and the solidification structure. In this study, Fe–Cu–Si–B and Fe–Cu–Zr–B alloys were designed to show amorphous-phase formation and liquid-phase separation simultaneously. Amorphous-phase formation was confirmed in both Fe–Cu–Si–B and Fe–Cu–Zr–B alloys. Minor exceptions in a combination map of mixing enthalpy and quaternary predicted phase diagram are acceptable range for designing a quaternary Fe–Cu-based alloy system that shows liquid-phase separation in Fe-based and Cu-based liquids and the formation of an Fe-based amorphous phase.     

Effect of Fe additions on microstructure and mechanical properties of a multi-component Nb–16Si–22Ti–2Hf–2Al–2Cr alloy at room and high temperatures

The phase constitutions, microstructural evolutions, and mechanical properties of Nb–16Si–22Ti–2Hf–2Al–2Cr–xFe alloys (where x = 1, 2, 4, 6 at.%, hereafter referred to as 1Fe, 2Fe, 4Fe and 6Fe alloys, respectively) prepared by arc-melting were investigated. It was observed that the nominal Fe content affected the solidification path of the multi-component alloy. The as-cast 1Fe alloy primarily consisted of a dendritic-like Nb_SS phase and (α+γ)-Nb₅Si₃ silicide, and the as-cast 2Fe and 4Fe alloys primarily consisted of an Nb_SS phase, (α+γ)-Nb₅Si₃ silicide and (Fe + Ti)-rich region. In addition to the Nb_SS phase, a multi-component Nb₄FeSi silicide was present in the as-cast 6Fe alloy. When heat-treated at 1350 °C for 100 h, the 1Fe and 6Fe alloys almost exhibited the same microstructures as the corresponding as-cast samples; for the 2Fe and 4Fe alloys, the (Fe + Ti)-rich region decomposed, and Nb₄FeSi silicide formed. The fracture toughness of the as-cast and heat-treated Nb–16Si–22Ti–2Hf–2Al–2Cr–xFe samples monolithically decreased with the nominal Fe contents. It is interesting that at room temperature, the strength of the heat-treated samples was improved by the Fe additions, whereas at 1250 °C and above, the strength decreased, suggesting the weakening role of the Nb₄FeSi silicide on the high-temperature strength. As the nominal Fe content increased from 1 at.% to 6 at.%, for example, the 0.2% yield strength increased from 1675 MPa to 1820 MPa at room temperature; also, the strength decreased from 183 MPa to 78 MPa at 1350 °C.     

Towards improved integrated properties in FeCrPCB bulk metallic glasses by Cr addition

Fe-based soft-magnetic metallic glasses (MGs) of Fe_80−xCr_xP₉C₉B₂ (x = 0, 2, 5, 8 and 16 at.%) with high glass-forming ability (GFA), good soft-magnetic properties and high corrosion resistance are fabricated. With the addition of Cr to FePC-based alloys, the GFA and saturation magnetization (M_s) slightly decrease while the corrosion resistance effectively increases. The Fe–Cr–P–C–B BMGs exhibit good GFA and fully glassy rods can be produced up to 1.8 and 1.5 mm in diameter for the 2 and 5 at.% Cr added alloys, respectively. The alloys with 2 and 5 at.% Cr addition also show good soft-magnetic properties featured by high M_s of 1.16 and 1.04 T, low coercivity of 2.7 and 2.2 A/m, respectively. Besides, the corrosion behavior of the alloys was studied by immersion tests and potentiodynamic polarization measurements. It was found that the addition of Cr efficiently enhances the corrosion resistance of Fe–Cr–P–C–B alloys and the glassy alloy with 5 at.% Cr addition exhibits better corrosion resistance in comparison with the stainless steel SUS304 in 3 mass% NaCl solution. The combination of large GFA, good soft-magnetic properties, high corrosion resistance as well as low cost makes the Fe–Cr–P–C–B alloys as promising soft-magnetic and anti-corrosive materials for industrial applications.     

Partial liquidus projection and vertical sections in the system Al–Fe–Si–Ti

The quaternary system Al–Fe–Si–Ti was characterized in the Fe-rich part for thermal reactions, which were studied by differential thermal analysis (DTA). As-cast alloys were investigated in order to gain additional information about primary crystallization fields. Three sections through the liquidus projection were constructed at 50, 60 and 70 at.% Fe, considering the experimental data and those from literature. In addition, five selected vertical sections are presented. The microstructures of selected as-cast alloys in the primary crystallization fields of the Laves phase Fe₂Ti, the A2/B2 phase, FeSi and τ2 (FeSiTi) are discussed.     

Effects of B and Si on the fracture toughness of the Nb–Si alloys

Nb–Si alloys have been widely considered as the potential candidate materials for turbine applications. Optimal amounts of B and Si addition to Nb–18Ti–14Si (at%, F1) were identified based on Nb–Ti–Si–B phase diagram. Nb–18Ti–14Si–4.5B (F2) had been obtained desirable (Nb) + T2 eutectic and significantly improved fracture toughness from 7.85 (F1) to 11.98 MPa m^1/2. With extra 3Si addition, F3 (Nb–18Ti–17Si–4.5B) consisted of primary T2 and (Nb) + T2 eutectic, it retained comparable fracture toughness of 11.76 MPa m^1/2, even excessive amounts of primary T2 do not compromise fracture toughness.     

Study of the effect of Ti and Ge in the microstructure of Nb–24Ti–18Si–5Ge in situ composite

The effects of Ti and Ge on the microstructure and hardness of the as cast and heat treated Nb-24Ti–18Si–5Ge (at.%) alloy (ZF3) were studied. There was macrosegregation of Si. The phases present in the as cast alloy (ZF3-AC) were the (Nb,Ti)_ss, and the (Nb,Ti)₃(Si,Ge), β(Nb,Ti)₅(Si,Ge)₃ and hexagonal (Ti,Nb)₅(Si,Ge)₃ silicides, with the latter forming a eutectic with the solid solution. The same phases were present after heat treatment at 1200 °C for 100 h (ZH3-HT12) but only the (Nb,Ti)_ss, and the (Nb,Ti)₃(Si,Ge) and (Nb,Ti)₅(Si,Ge)₃ silicides were present after 100 h at 1500 °C (ZF3-HT15) where TiO₂ was also formed. Alloying with Ti did not stabilise the (Nb,Ti)_ss + (Nb,Ti)₃Si eutectic. The formation of the eutectic in ZF3-AC was strongly influenced by the partitioning behaviour of Ti in the solidifying melt that was enhanced by the presence of Ge. There were Ti rich areas in the (Nb,Ti)_ss and the (Nb,Ti)₃(Si,Ge) silicide only in ZF3-AC. The solubility of Ge in (Nb,Ti)₃(Si,Ge) increased after heat treatment at 1500 °C. The transformation of β(Nb,Ti)₅(Si,Ge)₃ to α(Nb,Ti)₅(Si,Ge)₃ progressed from ZF3-HT12 to ZF3-HT15 but equilibrium was not reached in ZF3-HT15. The synergy of Ti with Ge resulted to a strong hardening effect and a remarkable retention of the hardness. Alloying with Ti led to a reduction of the hardness of Nb₅Si₃ and to an increase of the hardness of Nb₃Si. The synergy of Ti with Ge resulted to a strong hardening effect for the (Nb,Ti)_ss.     

Designing a toxic-element-free Ti-based amorphous alloy with remarkable supercooled liquid region for biomedical application

A series of toxic-element-free Ti–Zr–Ta–Si amorphous alloy ribbons have been successfully prepared by melt-spinning. The differential scanning carlorimetry (DSC), X-ray diffraction analysis, bending test and microhardness test are conducted for studying the thermal and mechanical properties. The results show that the Ti₄₂Zr₄₀Ta₃Si₁₅ metallic glass ribbon present excellent ductile behavior by the bending testing, without any fracture cracking after bending over 180 degree. In addition, this amorphous alloy possesses a very high glass transition and crystallization temperature of 799 and 898 K, respectively, as well as a very wide supercooled liquid region of 99 K. This amorphous alloy exhibits promising thermal stability during isothermal annealing at the middle temperature of its supercooled region, with more than 3000 s incubation time for isothermal annealing at 823 K (550 °C). This amorphous alloy also shows much lower value of corrosion current density (2.27 × 10⁻⁹ A/m²) than the 304 stainless steel in the 0.3 mass% sodium cloride solutions. This Ti₄₂Zr₄₀Ta₃Si₁₅ alloy is believed to be a promising based alloy for fabricating the bulk metallic glass foam by the spacer technique in the application of biomedical implants.     

Structure and mechanical properties of as-cast Ti–Si alloys

In the present work, the microstructure and mechanical properties of as-cast Ti–Si alloys with a Si content ranging from 1 to 12.5 wt% prepared using a dental cast machine were investigated and compared with commercially pure titanium (c.p. Ti). X-ray diffraction (XRD) for phase analysis was conducted using a diffractometer. Three-point bending tests were performed to evaluate the mechanical properties of all specimens and their microstructure and fractured surfaces were observed using scanning electron microscopy (SEM). Experimental results indicated that the diffraction peaks of the Ti–Si alloys matched those of α-Ti and Ti₅Si₃. All the Ti–Si alloys had higher bending strengths and bending moduli than those of c.p. Ti. For example, the bending strength of Ti–5Si was about 2.6 times that of c.p. Ti, and both Ti–10Si and Ti–12.5Si had the highest bending moduli, which were about 1.8 times higher than that of c.p. Ti. Additionally, Ti–1Si exhibited ductile properties and Ti–3Si and Ti–5Si had a combination of brittleness and ductility. When the Si content was 7.5 wt% or greater, the alloys showed brittle properties. Judging from the results of the mechanical properties and deformation behavior, Ti–1Si, Ti–3Si, and Ti–5Si can be considered highly feasible alloys for prosthetic dental applications if other properties necessary for dental casting are obtained.     

Effects of a small amount of Si or Ge addition on stability and hydrogen-induced internal friction of Ti34Zr11Cu47Ni8 glassy alloys

Effects of a small amount of Si or Ge addition on stability and hydrogen-induced internal friction behavior of Ti₃₄Zr₁₁Cu₄₇Ni₈ glassy alloys have been investigated by X-ray diffraction, thermal analysis and temperature dependence of internal friction. It is found that the addition of 1 at.% Si, 2 at.% Si or 1 at.% Ge is effective to stabilize the glassy state and that Si is more effective than Ge. The peak internal friction of the single glassy phase alloy increases with increasing hydrogen content below about 20 at.% H. It is found that (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₉Si₁ glassy alloys have lower peak internal friction than the Ti₃₄Zr₁₁Cu₄₇Ni₈ glassy alloys, while (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₈Si₂ and (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₉Ge₁ glassy alloys have much higher peak internal friction. It should be noted that a (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₈Si₂ glassy alloy containing 14.4 at.% H shows high internal friction, Q⁻¹ of about 4 × 10⁻². The peak temperature of the single glassy phase alloys decreases with increasing hydrogen content below about 20 at.%. It should be noted that the addition of an extremely small amount of Si is effective to increase the peak temperature of the single glassy phase alloys. The relationship between the tensile strength and specific damping capacity indicates that the hydrogenated (Ti₃₄Zr₁₁Cu₄₇Ni₈)₉₈Si₂ glassy alloys have almost the same potential for a damping material as crystalline Mn–Cu–Al and Cu–Al–Ni alloys and hydrogenated Zr–Cu–Al glassy alloys.     

Alloying effects in polycrystalline γ′ strengthened Co–Al–W base alloys

A polycrystalline hot working ingot metallurgy processing route for γ/γ^′ Co–Al–W superalloys has been developed. Based on Co–7Al–7W (at%), substitutions of Mo, V, Ti, Ta, Ni, Si, Fe and Cr were examined. The γ^′ solvus was found to follow the same trends as those exhibited by alloys with higher γ^′ fractions considered by other investigators. Excessive Cr additions were found to lead to discontinuous coarsening and eventually, the loss of the γ^′ phase from the microstructures observed. Ni additions were examined, with some success, and found to restore the γ′ phase and raise the solvus temperature. It was found that the addition of 13 at.% Cr improved the oxidation resistance at 800 °C by over 40 times.     

Interdiffusion and reaction between Zr and Al alloys from 425° to 625 °C

Zirconium has recently garnered attention for use as a diffusion barrier between U–Mo nuclear fuels and Al cladding alloys. Interdiffusion and reactions between Zr and Al, Al-2 wt.% Si, Al-5 wt.% Si or AA6061 were investigated using solid-to-solid diffusion couples annealed in the temperature range of 425° to 625 °C. In the binary Al and Zr system, the Al₃Zr and Al₂Zr phases were identified, and the activation energy for the growth of the Al₃Zr phase was determined to be 347 kJ/mol. Negligible diffusional interactions were observed for diffusion couples between Zr vs. Al-2 wt.% Si, Al-5 wt.% Si and AA6061 annealed at or below 475 °C. In diffusion couples with the binary Al–Si alloys at 560 °C, a significant variation in the development of the phase constituents was observed including the thick τ₁ (Al₅SiZr₂) with Si content up to 12 at.%, and thin layers of (Si,Al)₂Zr, (Al,Si)₃Zr, Al₃SiZr₂ and Al₂Zr phases. The use of AA6061 as a terminal alloy resulted in the development of both τ₁ (Al₅SiZr₂) and (Al,Si)₃Zr phases with a very thin layer of (Al,Si)₂Zr. At 560 °C, with increasing Si content in the Al–Si alloy, an increase in the overall rate of diffusional interaction was observed; however, the diffusional interaction of Zr in contact with multicomponent AA6061 with 0.4–0.8 wt.% Si was most rapid.     

Influence of Ti and Zr additions on solidification of Fe base intermetallics precipitating Laves phase

Abstract

Fe–Al–Zr and Fe–Al–Ti alloys are potential candidates for high temperature structural applications. Ti and Zr additions strongly enhance the mechanical properties of Fe–Al based alloys by the precipitation of a Laves phase. The quaternary Fe–Al–Zr–Ti system combines the benefits of the precipitation of the Laves phase and reduction in weight due to the aluminium addition. Such alloys are promising candidates for the development of new casting alloys which could be substituted for heavier and more expensive stainless steels. This study aims to enhance the knowledge concerning the solidification of alloys belonging to the iron rich corner of the Fe–Al–Ti–Zr quaternary system. Before studying the solidification process of the quaternary alloys, it is mandatory to know how the corresponding ternary systems behave. Experimental results are presented concerning the equilibria in the iron rich corner of the Fe–Al–Zr and Fe–Ti–Zr systems to determine new data or clarify uncertainties in the literature. These results are then synthesised to help to understand the stable Laves phase structure in quaternary alloys.     

Compositional effects of Zr-rich multi-component brazing alloys on the corrosion of Zr alloy joints

High-temperature corrosion of Zircaloy-4 joints brazed by various Zr(Ti)–Cu–Ni-based multi-component alloys was studied to draw up the compositional guideline of the brazing alloy. From the compositional and microstructural effects of the joints on the corrosion, there was strong evidence for galvanic corrosion susceptibility of primary α-Zr grains (usually Sn-containing) owing to alloying of nobler Ti and its concentration gradient in a joint, inducing a microgalvanic corrosion. The Ti concentration for corrosion inhibition was proposed to be less than about 1.0 at.%. The results clearly demonstrate that the exclusion of Ti is needed for the use of Zr-rich multi-component brazing alloys.     

New high-temperature copper alloys

New high-strength, high-temperature Cu-Ni-Si alloys have been developed using additions of Cr, Zr, and/or Ti. These new alloys remain as precipitation hardenable as the base alloy, but the main strengthening phase may be different than Ni₂Si (e.g., Cr₂Ti). Substantial increases in mechanical strength were observed at both room and high temperature (773 K) when additions of Cr+Zr+Ti and Cr+Zr were made. Industrial testing of these alloys indicated a sevenfold increase in the lifetime of lateral blocks in continuous casting equipment of copper alloys.     

Electron-irradiation-induced nano-crystallization in quasicrystal-forming Zr-based metallic glass

Phase selection in electron-irradiation-induced crystallization and crystal-to-amorphous-to-crystal (C–A–C) transition at 298 K in quasicrystal-forming Zr–Pt metallic glass alloys were investigated. Two types of f.c.c. nano-crystalline precipitates were formed in amorphous Zr₈₀Pt₂₀ and Zr_66.7Pt_33.3 alloys under electron irradiation; such unique nano-crystalline structures were not observed during thermal annealing. It was inferred that unique phase selection in electron-irradiation-induced crystallization and thermal crystallization can be explained by the large negative chemical mixing enthalpy (ΔH_chem) in Zr–Pd and Zr–Pt alloys.     

Untersuchung über das Korrosionsverhalten von Zirkoniumlegierungen. IV. Das Lochfraßverhalten Zirkoniumlegierungen

Investigation into corrosion behaviour of zirconium alloys. IV-Pitting behaviour of zirconium alloys Electrochemical investigations into the resistance of a number of Zr-alloys in different solutions against pitting corrosion have shown that additions of Va- and VIa-group metals and in particular Ti improve the resistance of pure Zr. Metals forming local elements decrease pitting corrosion resistance. Minor amounts of Fe, Ni and Cr have practically no influence. The pitting corrosion resistance of Zr and its alloys decreases with increasing concentration of chloride ions in the solutions. Additions of SO₄-ions retard the beginning of the pitting but do not shift the pitting corrosion potential. NO₃-ions on the other hand produce a real inhibition. Newly developed methods for the quick determination of the pitting corrosion potential were very useful for the described investigations.     

The effect of vanadium and grain refiner additions on the nucleation of secondary phases in 1xxx Al alloys

High purity Al–0.3 wt% Fe–0.1 wt% Si alloys with different Si, V and grain refiner contents were melt spun to produce microstructures of submicron secondary phases entrained in a higher melting point Al matrix. On reheating, a dispersion of eutectic liquid droplets forms that represents an exaggerated version of the liquid puddles that solidify pinched-off between Al dendrite arms during conventional casting. The subsequent resolidification of the droplets, analysed using differential scanning calorimetry (DSC), allows the nucleation-controlled aspects of secondary phase selection to be studied. The droplets solidify as the metastable FeAl_m phase in ribbons containing ≃500 ppm V or ≃100 ppm V plus Al–Ti–B, Al–Ti–C or Al–B grain refiner. This phase contributes to the “fir-tree” surface defect in commercial sheet products. This work suggests that the combination of V and Al–Ti–B promotes FeAl_m in commercial ingots, and confirms that solidification rate and bulk Si content also influence phase content.     

Microstructure and mechanical properties of Ti–Nb–Fe–Zr alloys with high strength and low elastic modulus

Zr was added to Ti–Nb–Fe alloys to develop low elastic modulus and high strength β-Ti alloys for biomedical applications. Ingots of Ti–12Nb–2Fe–(2, 4, 6, 8, 10)Zr (at.%) were prepared by arc melting and then subjected to homogenization, cold rolling, and solution treatments. The phases and microstructures of the alloys were analyzed by optical microscopy, X-ray diffraction, and transmission electron microscopy. The mechanical properties were measured by tensile tests. The results indicate that Zr and Fe cause a remarkable solid-solution strengthening effect on the alloys; thus, all the alloys show yield and ultimate tensile strengths higher than 510 MPa and 730 MPa, respectively. Zr plays a weak role in the deformation mechanism. Further, twinning occurs in all the deformed alloys and is beneficial to both strength and plasticity. Ti–12Nb–2Fe–(8, 10)Zr alloys with metastable β phases show low elastic modulus, high tensile strength, and good plasticity and are suitable candidate materials for biomedical implants.