Effects of Sn content on thermal stability and mechanical properties of the Ti60Zr10Ta15Si15 amorphous alloy for biomedical use

The (Ti₆₀Zr₁₀Ta₁₅Si₁₅)_100−xSn_x (x = 0, 4, 8, 12 at.%) amorphous ribbons were prepared by the single roll melt-spinning method, and the effects of the Sn content on the thermal stability, the elastic modulus and nanohardness of the Ni-free Ti-based alloys were investigated. It is found that Sn additions decrease the glass formation ability of the Ti₆₀Zr₁₀Ta₁₅Si₁₅ alloy. The content of Sn addition has an important impact on the elastic modulus and nanohardness of the alloys. The amorphous alloy with 4% Sn addition exhibits the highest the elastic modulus and nanohardness, which are 111 GPa and 7.0 GPa, respectively. The correlation between the mechanical properties and Sn content was discussed based on the free volume containing in the as-spun ribbons.     

Investigation of glass-forming ability,deformation and corrosion behavior of Ni-free Ti-based BMG alloys designed for application as dental implants

We developed new Ti-based bulk metallic glassy (BMG) alloys in Ti–Zr–Pd–Cu–Sn system without Ni element for application as biomaterials. These BMG alloys have a high potential to be applied as metallic biomaterials in various forms, such as melt-spun ribbons and cylindrical rods with a diameter of 4 mm. We also investigated of new Ti-based BMG alloys with higher glass-forming ability (GFA) for medical market as dental implants. These Ti-based BMG alloys do not contain Ni, Al and Be elements which are well known to be harmful for human body. In particular, a rod sample of the Ti_44.1Zr_9.8Pd_9.8Cu_30.38Sn_3.92Nb₂ BMG alloy with a diameter of 3 mm produced by copper mold casting exhibits a compressive strength of 1990 MPa and a Young's modulus of 99 GPa. In addition, the Ti_44.1Zr_9.8Pd_9.8Cu_30.38Sn_3.92Nb₂ BMG shows a large supercooled liquid region of 62 K and a reduced glass-transition temperature, T_rg( = T_g / T_m) of 0.61. The high thermal stability of the supercooled liquid allowed the fabrication of cylindrical rod specimens up to 5 mm in diameter. Thus the studied alloy exhibits high glass-forming ability (GFA) and a large size enough to be used for dental implants. The Ti_44.1Zr_9.8Pd_9.8Cu_30.38Sn_3.92Nb₂ BMG alloy also has a high corrosion resistance and is passivated at the lower passive current density of approximately 10^? 2 A m^? 2, 10^? 3 A m^? 2 and 10^? 2 A m^? 2, in 1 mass% lactic acid, PBS (phosphate-buffered saline without calcium and magnesium salts solution) and HBSS (Hank's balance salt solution without calcium, magnesium and phenol red), respectively, at 310 K, which are lower than those of pure Titanium and Ti–6Al–4V alloy.     

Composition design and mechanical properties of ternary Cu–Zr–Ti bulk metallic glasses

The new compositions of ternary Cu–Zr–Ti bulk metallic glasses are predicted by integrating calculation of vacancy formation energy, mixing enthalpy and configuration entropy of the alloys based on thermodynamics of glass formers. The monolithic amorphous rods of 3 mm diameter have been successfully fabricated, and characterized by X-ray diffractometry, differential scanning calorimetry, scanning electronic microscopy, transmission electronic microscopy and compression tests. The results show that the designed alloys possess good glass forming ability and excellent mechanical properties. The mechanical properties of the samples can be effectively improved by regulating their composition. The monolithic amorphous rod of Cu₅₀Zr₄₄Ti₆ exhibits a high fracture strength of 1855 MPa and excellent plastic deformation up to ∼7.4%. The formation and propagation of shear bands in samples are also investigated. The enhancement of plastic deformation is mainly contributed to multiplication and intersection of shear bands.     

Effects of Cr contents in Fe-based bulk metallic glasses on the glass forming ability and the corrosion resistance

Fe-based bulk metallic glasses of Fe_69.9?xC_7.1Si_3.3B_5.5P_8.7Cr_xMo_2.5Al_2.0Co_1.0 (x = 0.0, 2.3–12.3) with high glass forming ability and good corrosion resistance were fabricated using industrial raw materials. Glass forming ability of the Fe-based bulk metallic glasses tends to decrease with the Cr content, while the corrosion resistance increases with the Cr content. A homogeneous passive layer on the amorphous sample with 12.3 at% Cr can be formed leading to superior corrosion resistance of the amorphous sample to an austenitic stainless steel (SUS304) in the 0.5 M H₂SO₄ and 1N HCl solutions at 298 K. Fe-based bulk metallic glasses with an optimum combination of glass forming ability and corrosion resistance can be produced in large quantities through a systematic control of the Cr content for extensive practical applications.     

Pseudo-quinary Ti20Zr20Hf20Be20(Cu20 -xNix) high entropy bulk metallic glasses with large glass forming ability

A series of pseudo-quinary Ti₂₀Zr₂₀Hf₂₀Be₂₀(Cu_20 -xNi_x) (x = 2.5, 5, 7.5, 10, 12.5, 15, 17.5 and 20 at.%) high entropy bulk metallic glasses (HE-BMGs) with large glass forming ability (GFA) were successfully prepared by copper mold tilt-casing. The critical diameters (D_c) of these HE-BMGs are all above 12 mm. In particular, the developed Ti₂₀Zr₂₀Hf₂₀Be₂₀(Cu_7.5Ni_12.5) and Ti₂₀Zr₂₀Hf₂₀Be₂₀Ni₂₀ high entropy alloys (HEAs) can be produced in the amorphous state with diameters up to 30 mm and 15 mm, respectively, which are the largest HE-BMG and quinary HE-BMG hitherto. The two HE-BMGs also exhibit high yield strength, together with the plastic strain values of (3.0 ± 1.1) % and (4.0 ± 0.9) %, respectively. With increasing Ni additions in the pseudo-quinary HEAs, the crystallization growth resistance and thermal stability have been improved, which is apparently due to the sluggish diffusion of the atoms in the HEAs.     

High yield strength bulk Ti based bimodal ultrafine eutectic composites with enhanced plasticity

Ti-based bulk metallic glass (BMGs) and their bimodal composites are linked with the pronounced strain hardening after yielding but with much low value of strength. Therefore, developing Ti-based alloys with high yield strength and high plasticity is the current challenge. Here, we report the synthesis of ultra-fine grained bulk (UFG) (Ti_0.705Fe_0.295)_100−xGa_x (0 ⩽ x ⩽ 2) bimodal eutectic composites with not only high strength and larger plasticity but also with high yield strength which is one of the important mechanical property for structural application. Reasonably high strength, high yield strength, strain to failure ratio, and enhanced plasticity of ∼7 ± 0.8% was observed in (Ti_70.5Fe_29.5)₉₈Ga₂ composite which is superior than Ti-based BMGs and bimodal composites. Modification of degree of eutectic structure refinement and volume fraction of constituent phases with the addition of Ga are the crucial factors in enhancing the mechanical properties of Ti–Fi–(Ga) composites.     

Rapid screening of potential metallic glasses for biomedical applications

This paper presents a rapid screening process to select potential titanium and zirconium based metallic glasses (MGs) for bio-material applications. Electrochemical activity of 7 MGs including 6 bulk metallic glasses and 1 thin-film deposited MG in simulation body and human serum is first inspected. A low-voltage potential state test is also developed to simulate the cell membrane potential that the implant MGs will suffer. Results show that the MGs composed of Ti₆₅Si₁₅Ta₁₀Zr₁₀ and Ta₅₇Zr₂₃Cu₁₂Ti₈ exhibit excellent electrochemical stability in both simulation body fluid and human serum. In addition, the copper content in the MGs plays an important role on the electrochemical activity. MGs with the copper content higher than 17.5% show significant electrochemical responses. The cytotoxicity of the solid MG samples and the corrosion released ions are also evaluated by an in-vitro MTT test utilizing the murine bone marrow stem cells. Results indicate that all the solid MG samples show no acute cytotoxicity yet the corrosion released ions show significant toxicity for murine bone marrow stem cells. The rapid screening process developed in the present study suggests that the Ti₆₅Si₁₅Ta₁₀Zr₁₀ metallic glass has high potential for biomedical applications due to its good electrochemical stability and very low cytotoxicity.     

Characterization of corrosion phenomena of Zr–Ti–Cu–Al–Ni metallic glass by SEM and TEM

Corrosion phenomena are investigated for a Zr₅₉Ti₃Cu₂₀Al₁₀Ni₈ metallic glass immersed in hydrofluoric acid (HF) in open-circuit conditions and by means of electron microscopies (SEM and TEM). Several morphologies develop on the corroded surface and especially large and deep pits. TEM study demonstrates that Cu-rich nanocrystals of 5–10 nm are formed inside the corrosion pits (on their walls) during the corrosion process. These nanocrystals are not only by-products of the corrosion process but they very likely play a role in the development of the corrosion pitting morphology. They could have a dual role: (i) protecting the capped areas against dissolution and (ii) speeding the dissolution of neighboring uncapped areas by the creation of local galvanic cells.     

A new TiCuHfSi bulk metallic glass with potential for biomedical applications

A new Ti_41.3Cu_43.7Hf_13.9Si_1.1 bulk metallic glass (BMG), free of Ni, Al and Be elements, was designed using the proper mixing of binary deep eutectics. The alloy exhibited excellent glass forming ability (GFA) and could be cast into single glassy rod up to 3 mm in diameter by copper mould casting method. The appropriate atomic-size mismatch, the large negative heat of mixing among constituent elements, and the possible formation of glassy HfSiO₄ facilitated its superior GFA. The BMG also showed good mechanical properties with fracture strength of 1685 MPa and Young’s modulus of 95 GPa as well as better corrosion resistance in both NaCl and Hank’s solutions, compared with pure Ti and Ti–6Al–4V alloy. The above results demonstrated that the developed BMG is promising in biomedical applications.     

Biomedical TiNbZrTaSi alloys designed by d-electron alloy design theory

We report on the formation of ultrafine-grained (Ti_69.71Nb_23.72Zr_4.83Ta_1.74)_100 − xSi_x (at.%, x = 0, 2 and 5) alloys designed by d-electron alloy design theory and fabricated by spark plasma sintering of nanocomposite powder precursor. The designed and fabricated alloys exhibit a high yield and fracture strength of 1296 MPa and 3263 MPa along with an ultra-large fracture strain of 65% under compression. Meanwhile, they display low elastic modulus of 37–48 GPa. The high-performance titanium alloys without toxic elements show high potential for application as biomaterials.     

Effect of substitution of Si by Al on microstructure and synthesis behavior of Ti5Si3 based alloys fabricated by mechanically activated self-propagating high-temperature synthesis

The effect of substitution of Si by Al and mechanical activation on microstructure, phase composition, ignition and combustion temperature of Ti₅Si₃ based alloys and composites that were prepared by mechanically activated self-propagating high-temperature synthesis (MASHS) method was investigated. For this purpose elemental powders of titanium, silicon and aluminum were mixed according to the 5Ti + 3(1 − X)Si + 3XAl formula, where X = 0, 0.2, 0.4, 0.6. The samples were characterized by X-ray diffraction (XRD) analytical technique and scanning electron microscope (SEM) equipped with an energy-dispersive spectrum (EDS) analyzer. The results have shown that formation of Ti₅Si₃ during milling stage is postponed by adding Al into the system. Presence of Al in the Ti–Si system have a significant effect on the phase composition of the final products. Substitutional solid solution of Ti₅(Si, Al)₃ and Ti₅Si₃–Ti₃Al composite are formed by increasing Al amount in the system. Furthermore combustion temperature and crystallites size of Ti₅Si₃ is reduced with addition of Al into the Ti–Si system. Moreover, solubility of Al in Ti₅Si₃ is increased with enhancing the X up to 0.4, after that, the solubility of Al in Ti₅Si₃ is ceased, due to achieving the solubility limit of Al in the Ti₅Si₃. The average crystallites size of Ti₅Si₃ are decreased with increasing milling time prior to the reaction.     

Plastic deformation behaviors of Ni- and Zr-based bulk metallic glasses subjected to nanoindentation

Plastic deformation behaviors of Ni₄₂Ti₂₀Zr_21.5Al₈Cu₅Si_3.5 and Zr₅₁Ti₅Ni₁₀Cu₂₅Al₉ bulk metallic glasses at room temperature were studied by nanoindentation testing and atomic force microscopy under equivalent indentation experimental conditions. The different chemical composition of these two bulk metallic glasses produced variant tendencies for displacement serrated flow to occur during the loading process. The nanoindentation strain rate was calculated as a function of indentation displacement in order to verify the occurrence of displacement serrated flow at different loading rates. Atomic force microscopy revealed decreasing numbers of discrete shear bands around the indentation sites as loading rates increased from 0.025 to 2.5 mNs^− 1. Variations in plastic deformation behaviors between Ni and Zr-based glasses materials can be explained by the different metastable microstructures and thermal stabilities of the two materials. The mechanism governing plastic deformation of these metallic glasses was analyzed in terms of an established model of the shear transformation zone.     

Microstructural and mechanical properties of jointed ZrO2/Ti–6Al–4V alloy using Ti33Zr17Cu50 amorphous brazing filler

Ceramic ZrO₂ and metallic Ti–6Al–4V alloy are jointed by using a Ti₃₃Zr₁₇Cu₅₀ (at.%) amorphous alloy as a solder at 1123–1273 K in a high vacuum. It is demonstrated that the microstructure and mechanical properties are significantly influenced by the brazing temperature, the heat time and the cooling rate. The brazing seam jointing ZrO₂ with Ti–6Al–4V is composed of ZrO₂/Cu₂Ti₄O, (Ti,Zr)₂Cu/TiO, Ti₂O/CuTi₂, (Ti,Zr)₂Cu/CuTi₂/Ti–6Al–4V alloys and compounds, of which the increasing thickness weakens the shear strength as the brazing temperature, the heat time the cooling rate increase. The maximum shear strength of the brazing joints reaches 162 MPa with the optimal technical parameters: the brazing temperature of 1173 K, the heat time of 10 min and the cooling rate of 5 K/min. The fracture of the joint occurs in the brittle seam layer nearby the side of ZrO₂.     

Metallic glass–steel composite with improved compressive plasticity

A Zr_52.5Cu₁₈Ni_14.5Al₁₀Ti₅ bulk metallic glass toughened with a commercially available spring-shaped steel wire has been produced by centrifugal casting. The addition of the steel spring significantly affects shear band nucleation and propagation through the blockage, deflection and multiplication of shear bands at the glass–spring interface. As a result of the more homogeneous distribution of the plastic strain, the room temperature plasticity increases from 0.9% for the monolitic glass to about 4% for the glass–spring composite. Given the low volume fraction of the spring used in the composite (4.2 vol.%), these results demonstrate the extreme effectiveness of the steel spring for improving the plasticity of the metallic glass.     

Microstructural evolution during annealing and rolling Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass

The microstructural evolution of the Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ bulk metallic glass during annealing and rolling deformation was studied. After annealing at 680 K for 0.5 h, phase separation is observed, and nanocrystallization is further induced by the subsequent rolling deformation. Increasing annealing time to 1.5 h leads to the formation of both nanocrystals and large-size particles of the Zr–Cu fcc phase. After rolling, the volume fraction of nanocrystals increases slightly while the Zr–Cu particles disappear. The presence of phase separation and nanocrystals during annealing reduce the thermal stability of the glass and accelerate the subsequent crystallization driven by rolling. During rolling the two annealed specimens exhibit the good ductility.     

Effect of transition metals on energy absorption during strain-controlled fatigue of an aluminum alloy

Tensile and low cyclic fatigue tests were used to assess the influence of micro-additions of Ti/V/Zr on the performance of Al–7Si–1Cu–0.5Mg (wt.%) alloys in the as-cast and T6 heat-treated conditions and their improvement was compared to the base alloy. The microstructure of the as-cast Al–7Si–1Cu–0.5Mg (wt.%) base and modified alloys consisted of α-Al, eutectic Si, and Cu, the Mg- and Fe-based phases Al_2.1Cu, Al_8.5Si_2.4Cu, Al_7.2Si_8.3Cu₂Mg_6.9 and Al₁₄Si_7.1FeMg_3.3. In addition, the micro-sized Ti/V/Zr-rich phases Al_6.8Si_1.4Ti, Al_21.4Si_4.1Ti_3.5VZr_3.9, Al_6.7Si_1.2TiZr_1.8, Al_2.8Si_3.8V_1.6Zr and Al_5.1Si_35.4Ti_1.6Zr_5.7Fe were identified in the modified alloys. It was also noticed that increasing the content of Ti–V–Zr changed the morphology of Ti/V/Zr-rich phase. The tensile test results showed that the T6 heat-treated alloy modified with the addition of a higher content of Ti–V–Zr achieved the highest tensile strength of 343 MPa over the base alloy and alloys modified with additions of Ti, Ti–Zr and lower contents of Ti–V–Zr. The plastic strain energy density coefficient of the alloy modified with the addition of a higher content of Ti–V–Zr in the T6 temper condition was higher than the other studied alloys and reached 162 MJ m⁻³. The fatigue life of the same alloy was considerably longer than that of the other studied alloys, including the base alloy. The fractography revealed that all the studied alloys showed similar fracture behavior. The tensile cracks propagated through the eutectic Si and primary phases, exhibiting intergranular fracture along with some cleavage-like features of the plate-shaped Zr–Ti–V-rich intermetallics with the presence of fatigue striations on the latter, indicating their ductile nature. It is believed that the morphological changes of intermetallic precipitates containing Zr, Ti and V enhance the fatigue life of the alloy modified with additions of larger amounts of Ti–V–Zr in the T6 condition.     

Synthesis of bulk amorphous alloy and composites by warm rolling process

We report the fabrication of monolithic bulk amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy and amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy reinforced Cu matrix composite using a combination of RCRF (Repeated Cold Rolling and Folding) and warm rolling processes. Based on the TTT curve established for the amorphous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ alloy, the crystallization of the amorphous ribbon is prevented during warm rolling process. The micro-hardness of the amorphous alloy (600±30 Hv) is comparable with those for other Ni-based amorphous alloys.     

Quaternary Ti–Zr–Be–Ni bulk metallic glasses with large glass-forming ability

The glass-forming ability (GFA) of Ti–Zr–Be ternary alloys is dramatically improved by partially replacing Be with Ni. Centimeter-scale fully amorphous samples can be obtained in a wide Ni content range of 4 at.%–12 at.%. In particular, some of the developed Ti–Zr–Be–Ni alloys exhibit a critical diameter up to 20 mm, which is larger than that of other quaternary Ti-based bulk metallic glasses (BMGs). Moreover, Ni addition also enhances the yield strength and compressive plastic strain of Ti–Zr–Be alloys obviously. Based on the experimental results, the effect of substituting elements addition on the glass-forming ability of Ti–Zr–Be alloys has been systematically investigated and an empirical composition design method for the development of novel Ti-based BMGs with large GFA has been proposed.     

A study on the mechanochemical behavior of TiO2–Al–Si system to produce Ti5Si3–Al2O3 nanocomposite

In the present study Ti₅Si₃–Al₂O₃ nanocomposite was synthesized by a displacement reaction between Al and TiO₂ in ball milling of TiO₂, Al and Si powders. The effect of milling time and heat treatment temperatures were also investigated. The structural changes of powder particles during mechanical alloying were investigated by X-ray diffraction (XRD). Morphology and microstructure of powders were characterized by scanning electron microscopy (SEM). It was found that after 10 h of MA, the reaction between Al and TiO₂ initiated in a gradual mode and after about 45 h of milling, the reaction was successfully completed. The final product consisted of Ti₅Si₃ intermetallic compound with a crystallite size of 13 nm and amorphous Al₂O₃. Heat treatment of this structure at 1050 °C led to the crystallization of Al₂O₃ and ordering of Ti₅Si₃. The crystallite size of Ti₅Si₃ and Al₂O₃ after annealing at 1050 °C for 1 h remained in nanometer scale. So the final product appeared to be stable upon annealing.     

Improvement of the bonding interface of a sintered Al 2014–(Ti5Si3)p composite by the copper coating of the reinforcement

AA 2014 aluminium-based composites reinforced with (5–20 wt.%) Ti₅Si₃ intermetallic particles, with and without Cu coating, were obtained in a Turbula powder mixer from commercially-available prealloyed powders. Mechanical alloying was used for the deposition of Cu on the surface of the Ti₅Si₃ particles. Compaction of the specimens was performed using a hydraulic press and a floating die. The results show that the liquid formation and phase distribution are modified by the copper coating of the ceramic reinforcement, resulting in changes in the materials microstructure and the mechanical properties. The presence of the reinforcement particles improves densification of the composites. Improved densification was found for the 2014 + Ti₅Si₃ composites. 2014 + Ti₅Si₃–Cu composites exhibit superior mechanical properties compared to the 2014 + Ti₅Si₃ composites.