Bulk and porous metastable beta Ti-Nb-Zr(Ta) alloys for biomedical applications

In this work, metastable beta Ti-Nb-Zr(Ta) ingots were manufactured by vacuum arc melting. The ingots thus obtained were divided into two batches: the first subjected to cold rolling (CR) from 30 to 85% of thickness reduction and subsequent annealing in the 450 to 900 °C temperature region, and the second atomized to produce 100 μm size powders. This powder was used to manufacture open-cell porous material. Regardless of the CR intensity, Ti-(18…20)Nb-(5…6)Zr (at.%) samples subjected to 600 °C (1 h) annealing showed a significant material softening due to the stress-induced martensitic transformation. The Young's modulus of these alloys varied between 45 and 55 GPa, and the yield stress, between 300 and 500 MPa. The obtained Young's moduli, which are comparable to 55-66 GPa of concurrent beta-titanium alloys and 45-50 GPa of superelastic Ti-Ni alloys, come close to those of cortical bones. Compression testing of the porous material as a function of porosity (from ~ 45 to 66%) and interconnected cell size (d₅₀ from 300 to 760 μm) showed the following properties: Young's modulus from 7.5 to 3.7 GPa, which comes close to that of trabecular bones, and ultimate compression strength, of from 225 to 70 MPa.     

Nd60Fe30 − xNixAl10 bulk metallic glasses with high hard magnetic properties

Bulk metallic glasses (BMGs) Nd₆₀Fe_30 − xNi_xAl₁₀ were prepared by suction cast method. The glass forming abilities (GFAs) and the hard magnetic properties of the BMGs were examined by differential scanning calorimeter (DSC) and vibrating sample magnetometer (VSM), respectively. The results show that the largest GFA (T_x / T_m = 0.61) of the alloys was obtained when Fe was substituted by 10% Ni and the rods of Nd₆₀Fe₂₀Ni₁₀Al₁₀ have the coercivity up to 323 kA/m and the remanence up to 9.41 Am²/kg as high as Nd-Fe-Co-Al, the Nd-Fe-based BMGs with highest hard magnetic properties up to date. The homogeneous distribution of Fe-rich nano-clusters, Nd(FeNiAl)₂, in amorphous matrix is responsible for the enhancement.     

Corrosion performances in simulated body fluids and cytotoxicity evaluation of Fe-based bulk metallic glasses

The aim of this work is to investigate the corrosion resistance and biocompatibility of three kinds of Fe based bulk metallic glasses (BMGs), Fe₄₁Co₇Cr₁₅Mo₁₄C₁₅B₆Y₂ (BMG1), (Fe₄₄Cr₅Co₅Mo₁₃Mn₁₁C₁₆B₆)₉₈Y₂ (BMG2), and Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Er₂ (BMG3) by electrochemical measurements and indirect contact cytotoxicity assays, respectively. In comparison with 316 L SS biomedical steel, Fe based BMGs show better corrosion resistance in both simulated body fluids (Hank's solution and artificial saliva). The OCP curves show that the passive film on the Fe based BMG surfaces is quite stable, like 316 L SS. The corrosion current densities obtained from the anodic polarization curves from the lowest to highest are as follows: BMG3 < BMG1 < BMG2 < 316 L SS. The EIS analysis indicates that the Fe Based BMGs have larger polarization resistance value than that of 316 L SS except for BMG2 in artificial saliva. The pitting corrosion potentials of Fe based BMGs are much higher than that of the 316 L SS, resulting in very few ions releasing into the electrolytes while a significant amount of Ni and Fe ions release was found for 316 L SS under the same condition. The indirect cytotoxicity results suggest that all three Fe based BMG extracts have no cytotoxicity to L929 and NIH3T3 cells. All these results demonstrate that Fe based BMGs will open up a new path for the biomedical applications, especially in dental implantology.     

Anelastic relaxation due to hydrogen in Ti-35Nb-7Zr-5Ta alloy

Titanium and its alloys are frequently used in the production of prostheses and dental implants due to their properties, such as high corrosion resistance, low elasticity modulus, and high mechanical strength/density relation. Among the Ti-based alloys, Ti-35Nb-7Zr-5Ta (TNZT) is one that presents the smallest elasticity modulus (around 45 GPa), making it an excellent alternative to be used as a biomaterial. In this paper, mechanical spectroscopy measurements were made of TNZT alloys containing several quantities of hydrogen in solid solution. Mechanical spectroscopy measurements were made by using a torsion pendulum, operating at an oscillation frequency in the interval 2-20 Hz, temperature in the range 100-300 K, heating rate of about 1 K/min, and vacuum lower than 10⁻⁵ Torr. A relaxation structure and a reduction in the elasticity modulus were observed for the heat-treated and doped samples. The observed peak was associated with the interaction of hydrogen trapped by oxygen atoms around the titanium atom of the metallic matrix.     

A study of atomic layer deposited LiAlxOy films on Mg-Li alloys

LiAl_xO_y films with thicknesses of 65-200 nm were deposited by the atomic layer deposition (ALD) technique on the LZ101 Mg-Li alloy. The ALD-deposited LiAl_xO_y films exhibit an amorphous structure and have an atomic ratios of Li:Al:O = 1:1:2. The potentio-dynamic polarization tests show that the corrosion resistance of Mg-Li alloys can be significantly improved due to the dense and pinhole-free structure as well as the excellent coverage and conformity of the ALD-deposited LiAl_xO_y films.     

Strengthening and toughening of Mg-Cu-(Y, Gd) bulk metallic glasses by minor addition of Be

Mg₆₅Cu₂₅Re₁₀ and Mg₆₅Cu₂₄Be₁Re₁₀ (Re = Y, Gd) bulk metallic glasses (BMGs) were successfully fabricated by conventional Cu-mold casting method. By the addition of 1 at.% Be, the compressive strengths of Mg₆₅Cu₂₄Be₁Y₁₀ and Mg₆₅Cu₂₄Be₁Gd₁₀ alloys are increased from 760 MPa and 860 MPa to 930 MPa and 1025 MPa, respectively. The fracture morphology is changed from nanometer scale corrugation to micrometer scale dimple and vein pattern, indicating that the addition of minor Be obviously improves the toughness of the alloys. The fracture morphologies with different size of plastic zone in Mg-based BMGs provide probability for understanding the fracture mechanism of BMGs.     

High-performance composites based on all-aromatic liquid crystal thermosets

In this study, a new high-performance liquid crystal ester-based thermoset for composite applications was investigated. All-aromatic liquid crystalline thermosets (LCTs) are a promising class of polymers that offer a unique combination of properties such as solvent resistivity, high modulus, high strength, low coefficient of thermal expansion and high after cure glass-transition temperatures (T_g ? 150 °C). Fully cured LCTs offer superior thermo-mechanical properties over high-performance thermoplastic polymers such as PPS, PEEK and PEI. For this study we used a 9000 g mol⁻¹ ester-based LCT based on cheap and readily available monomers, i.e. 4-hydroxybenzoic acid (H), isophthalic acid (I) and hydroquinone (Q), abbreviated by us as HIQ-9. Composite panels prepared from T300 carbon fiber (5-harness satin weave) showed in-plane shear strength of 154 MPa and an in-plane shear modulus of 3.7 GPa. The tensile strength and modulus were measured to be 696 MPa and 57 GPa, respectively. A post-mortem inspection showed that the interfacial strength was excellent and no delamination was observed in the test specimen. Preliminary results show that LCT-based composites exhibit a better combination of (thermo) mechanical properties over PPS and PEI-based composites.     

Gd–Ni–Al bulk glasses with great glass-forming ability and better mechanical properties

A series of Gd–Ni–Al ternary glassy alloys with the maximum diameter of 4 mm were obtained by common copper mold casting. The maximum values of the reduce glass transformation temperature (T _g/T _m) and the distance of supercooling region ΔT _x of these alloys in this study were 0.648 and 50 K, respectively. The compressive fracture strength (σ _f) and Young’s modulus (E) of Gd–Ni–Al glassy alloys were 1,240–1,330 MPa and 63–67 GPa, respectively. The magnetic properties of these BMGs were investigated. The Gd–Ni–Al bulk glassy alloys with great glass forming ability and good mechanical properties are promising for the future development as a new type of function materials.     

Study on the structure and properties of fine-grained alumina fast sintered with high heating rate

Fine-grained alumina was obtained in 2 min by a new densification method based on Self-propagating High-temperature Synthesis plus Quick Pressing (SHS/QP). The sample was densified to more than 99% of theoretical density under a large mechanical pressure (100 MP) and a fast heating rate (1600 °C/min). Compared with the alumina sample obtained by spark plasma sintering (SPS) at lower heating rates (100 or 500 °C/min), almost no grain growth was found in the sample obtained in this work. The microstructure and mechanical properties were studied. Hardness value of 18.6 ± 0.4 GPa and fracture resistance value of 3.4 ± 0.3 MPa m^1/2 were measured for fine-grained alumina of this work. The densification mechanism was discussed.     

Additive Manufacturing of Advanced Multi‐Component Alloys: Bulk Metallic Glasses and High Entropy Alloys

Bulk metallic glasses (BMGs) and high entropy alloys (HEAs) are both important multi‐component alloys with novel microstructures and unique properties, which make them promising for applications in many industries. However, certain hindrances have been identified in the fabrication of BMGs and HEAs by conventional techniques due to the intrinsic requirements of BMGs and HEAs. With the advent of metal additive manufacturing, new opportunities have been perceived to fabricate geometrically complex BMGs and HEAs with tailorable microstructure theoretically at any site within the specimen, which are not achievable using conventional fabrication techniques. After providing some background and introducing the conventional fabrication techniques for BMGs and HEAs, this review will focus on the current status, development, and challenges in metal additive manufacturing of BMGs and HEAs including different additive manufacturing techniques being used, microstructure design and evolution, as well as properties of the fabricated BMGs and HEAs. A future outlook of metal additive manufacturing of BMGs and HEAs will also be provided at the end.

     

Processing of porous Ti and Ti5Mn foams by spark plasma sintering

Titanium and its alloys are one of the best metallic biomaterials to be used for implant application. In this study, porous Ti and Ti5Mn alloy with different porosities were successfully synthesized by powder metallurgy process with the addition of NH₄HCO₃ as space holder and TiH₂ as foaming agent. The consolidation of powder was achieved by spark plasma sintering process (SPS) at 16 MPa and pressureless conditions. The morphology of porous structure was investigated by using scanning electron microscopy (SEM) and X-ray micro-tomography (μ-CT). Nano-indentation tester was used to evaluate Young’s modulus of the porous Ti and Ti5Mn alloy. Experimental results showed that pure Ti sample, which sintered under pressure of 16 MPa, full relative density was achieved even at a relative low sintering temperature 750 °C; however, in the case of pressureless condition at sintering temperature 1000 °C the porosity was 53% and Young’s modulus was 40 GPa. The Ti5Mn alloy indicated a good pore distribution, and the porosity decreased from 56% to 21% by increasing the sintering temperature from 950 °C to 1100 °C. Young’s modulus was increased from 35 GPa to 51.83 GPa with increasing of the sintering temperatures from 950 °C to 1100 °C.     

Mechanical properties of gradient pulse biased amorphous carbon film

A new method to prepare compositional amorphous carbon (a-C) film termed gradient pulse bias is presented. The a-C film prepared this way showed outstanding mechanical and excellent tribological properties. The hardness and reduced modulus of the film are calculated to be 66 GPa and 320 GPa respectively. A wear rate of 1.3 × 10^− 8 mm³/N m and frictional coefficient of 0.1 was also recorded. The novel film is also compared with multilayered and single layer a-C film prepared using the same system.     

Aging response of the Ti–Nb system biomaterials with β-stabilizing elements

Effects of aging temperature and the contents of β-stabilizing elements on the composition of martensite α′′ in two Ti–Nb alloys and the resulting mechanical properties were investigated for biomedical applications. The microstructures were examined by means of optical microscopy (OM) and X-ray diffraction (XRD). Vickers hardness, compressive elastic modulus and the yield strength have been measured. The results show that the decomposition mode of the martensite α′′ in two studied alloys depends on aging treatment and the contents of β-stabilizing elements. Various microstructures such as α, (α + β) and (β + ω) phases were observed to precipitate in the studied alloys after the aging treatments performed at 523 K, 773 K, 883 K and 1023 K for 0.5 h, respectively. Afterwards, the Ti–24Nb–6Zr–7.5Sn–2Fe alloy was aged at 773 K for 1 h. The compressive elastic modulus and mechanical properties of the two alloys are found to be sensitive to the microstructural change caused by aging temperature. For the Ti–24Nb–6Zr–7.5Sn–2Fe alloy, after aging at 773 K for 1 h, its yield strength, compressive elastic modulus and Vickers hardness reach 846 MPa, 26 GPa and 398 HV, respectively. This aged alloy exhibits proper comprehensive mechanical property and strength-to-modulus ratio for biomedical implant applications.     

Effect of Ca and Sr additions on high temperature and corrosion properties of Mg-4Al-2Sn based alloys

This study examined the effects of Ca and Sr addition on the creep and corrosion properties of Mg-Al-Sn based alloys with the aim of developing new Mg-Al-Sn-x alloys for automotive powertrain applications. The materials were cast using the squeeze casting process to obtain a dense microstructure without pores. Creep tests were carried out at a constant temperature between 150 °C and 200 °C and a constant applied stress between 50 and 80 MPa until the minimum creep rate had been reached. Potentiodynamic and immersion tests were carried out to evaluate corrosion properties of the alloys. The creep and corrosion resistance were improved by adding Ca and Sr.     

Electrical resistance behaviour of Fe-24 wt.%Mn alloy under high pressure

Electrical resistance behaviour of Fe-24 wt.%Mn SMA was studied up to a pressure of ∼6 GPa by using an opposed anvil high pressure device. The system shows a steep rise in resistance up to ∼1 GPa and thereafter a monotonic decrease up to ∼6 GPa during the forward cycle, whereas it shows a monotonic increase during the return cycle. XRD studies of the as-prepared and pressure quenched samples show a mixed α, γ and ε phase in the former and a predominantly ε phase in the latter, indicative of a possible structural transition at ∼1 GPa, as evidenced from the resistance maximum. The decrease in the transition pressure, when compared with alloys of lower Mn concentration, provides a clue that it should be possible to further reduce the transition pressure to the predominantly ε phase by alloying with suitable elements, which may have positive effect on the shape memory of the alloy.     

Mechanical properties of cellulose nanofiber (CNF) reinforced polylactic acid (PLA) prepared by twin screw extrusion

The aim of this study was to develop cellulose nanofiber (CNF) reinforced polylactic acid (PLA) by twin screw extrusion. Nanocomposites were prepared by premixing a master batch with high concentration of CNFs in PLA and diluting to final concentrations (1, 3, 5 wt.%) during the extrusion. Morphology, mechanical and dynamic mechanical properties (DMA) were studied theoretically and experimentally to see how different CNF concentrations affected the composites’ properties. The tensile modulus and strength increased from 2.9 GPa to 3.6 GPa and from 58 MPa to 71 MPa, respectively, for nanocomposites with 5 wt.% CNF. The DMA results were also positive; the storage modulus increased for all nanocomposites compared to PLA; being more significant in the high temperature region (70 °C). The addition of nanofibers shifted the tan delta peak towards higher temperatures. The tan delta peak of the PLA shifted from 70 °C to 76 °C for composites with 5 wt.% CNF.     

AlTiN layer effect on mechanical properties of Ti-doped diamond-like carbon composite coatings

Ti/Ti-doped diamond-like carbon (DLC) and Ti/AlTiN/Ti-DLC composite coatings were deposited by magnetron sputtering on W18Cr4V high speed steel substrates. The effect of the AlTiN support layer on the properties of these composite coatings was investigated through microstructure and mechanical properties characterization, including hardness, elastic modulus, coefficient of friction and wear properties measured by scanning electron microscopy, Raman spectroscopy, scratch and ball-on-disk friction tests. Ti and AlTiN interlayers have a columnar structure with 50-80 nm grains. The hardness and elastic modulus of Ti/Ti-DLC and Ti/AlTiN/Ti-DLC coatings is 25.9 ± 0.4, 222.2 ± 6.3 GPa and 19.3 ± 1, 205.6 ± 6.7 GPa, respectively. Adhesion of Ti-DLC, Ti/AlTiN/Ti-DLC and AlTiN/Ti-DLC coatings expressed as the critical lateral force is 26.5 N, 38.2 N, and 47.8 N, respectively. Substrate coefficient of friction without coatings is 0.44, and it is 0.1 for Ti/Ti-DLC and Ti/AlTiN/Ti-DLC coatings. Wear resistance of Ti/AlTiN/Ti-DLC composite coatings is much higher than Ti/Ti-DLC coatings based on the wear track width of 169.8 and 73.2 μm, respectively, for the same experimental conditions.     

Mechanical properties of gradient and multilayered TiAlSiN hard coatings

Multicomponent coatings based on different metallic and non-metallic elements possess the combined benefit of individual components leading to further improvement of coating properties. In this study, monolayered Ti-Al-N, multilayered Ti-Al-N/TiN, gradient Ti-Al-Si-N, and multilayered Ti-Al-Si-N/TiN coatings were synthesized by using a cathodic-arc evaporation (CAE) system. In addition to Ti, Ti₃₃Al₆₇ and Al₈₈Si₁₂ cathodes were used for the deposition of Ti-Al-N, and Ti-Al-Si-N coatings, respectively. The gradient Ti_0.50Al_0.43Si_0.07N, and multilayered Ti_0.50Al_0.43Si_0.07N/TiN with nanograins separated by disordered grain boundaries possessed lower residual stress (− 2.8 ~ − 4.8 GPa) than that of monolayered Ti-Al-N (− 6.8 GPa) and multilayered Ti-Al-N/TiN coatings (− 5.7 GPa). The highest hardness was obtained for the gradient Ti_0.50Al_0.43Si_0.07N (38 ± 2 GPa) with Ti/(Ti + Al + Si) content ratio being 0.5. On the contrary, the multilayered Ti_0.50Al_0.43Si_0.07N/TiN possessed the highest H³/E^?2 ratio of 0.182 ± 0.003 GPa, indicating the best resistance to plastic deformation, among the studied coatings.     

Role of ex-situ oxygen plasma treatments on the mechanical and optical properties of diamond-like carbon thin films

Role of ex-situ oxygen plasma (OP) treatment on mechanical properties of diamond-like carbon (DLC) thin films is explored. The DLC film after this treatment shows superhardness behaviour, maximum hardness of 46.3 GPa and elastic modulus of 423.2 GPa are obtained when film grown at self bias of 100 V followed by 10 min OP treatment. Moreover, the colour of the coating is fed after OP treatment, leading it to a colourless coating with significantly enhanced transmittance and improved antiglare property. Such OP treated DLC films may find their applications as protective coatings on cutting tools, automobile parts, magnetic storage media and colourless coating in packaging, as the DLC films posses brown colour.     

Dynamic and static fracture analyses of graphene sheets and carbon nanotubes

Dynamic and static fracture properties of Graphene Sheets (GSs) and Carbon nanotubes (CNTs) with different sizes are investigated based on an empirical inter-atomic potential function that can simulate nonlinear large deflections of nanostructures. Dynamic fracture of GSs and CNTs are studied based on wave propagation analysis in these nanostructures in a wide range of strain-rates. It is shown that wave propagation velocity is independent from strain-rate while dependent on the nanostructure size and approaches to 2.2 × 10⁴ m/s for long GSs. Also, fracture strain shows extensive changes versus strain-rate, which has not been reported before. Fracture stress is determined as 115 GPa for GSs and 122 GPa for CNTs which are independent from the strain-rate; in contrast to the fracture strain. Moreover, fracture strain drops at extremely high strain-rates for GSs and CNTs. These features are considered as capability of carbon nanostructures for reinforcing nanocomposites especially under impact loadings up to high strain-rates.