Effect of Nb on β → α ″ Martensitic Phase Transformation and Characterization of New Biomedical Ti-xNb-3Fe-9Zr Alloys

A new generation of Ti-xNb-3Fe-9Zr ( x = 15 , 20, 25, 30, 35 wt %) alloys have been designed using various theoretical approaches including DV-xα cluster, molybdenum equivalency, and electron to atom ratio. Afterward, designed alloys are fabricated using cold crucible levitation melting technique. The microstructure and mechanical performances of newly designed alloys are characterized in this work using scanning electron microscope and universal testing machine, respectively. Each alloy demonstrates monolithic β phase except Ti-35Nb-3Fe-9Zr alloy which display dual α ″ + β phases. Typically, niobium acts as an isomorphous beta stabilizer. However, in this work, formation of martensitic α ″ phases occurs at 35 wt % of niobium among the series of newly designed alloys. Furthermore, none of the alloys fail till the maximum load capacity of machine, i.e., 100 KN except Ti-35Nb-3Fe-9Zr alloy. Moreover, the Vickers hardness test is carried out on Ti-xNb-3Fe-9Zr alloys which demonstrate slip bands around the indentation for each alloy. Notably, the deformation bands and cracks around the indentations of each alloy have been observed using optical microscopy; Ti-35Nb-3Fe-9Zr demonstrates some cracks along with slip bands around its indentation. The Ti-25Nb-3Fe-9Zr alloy shows the highest yield strength of 1043 ± 20 MPa , large plasticity of 32 ± 0.5 % , and adequate hardness of 152 ± 3.90 Hv among the investigated alloys. The Ti-25Nb-3Fe-9Zr alloy demonstrates good blend of strength and malleability. Therefore, Ti-25Nb-3Fe-9Zr can be used effectively for the biomedical applications.

Synthesis of Nb0.8Hf0.2FeSb0.98Sn0.02 and Hf0.25Zr0.25Ti0.5NiSn0.98Sb0.02 Half-Heusler Materials and Fabrication of Thermoelectric Generators

In this study, half-Heusler (HH) thermoelectric materials Nb0.8Hf0.2FeSb0.98Sn0.02 (p-type) and Hf0.25Zr0.25Ti0.5NiSn0.98Sb0.02 (n-type) were synthesized using induction melting and spark plasma sintering. For alloying, a conventional induction melting technique was employed rather than arc melting, for mass production compatibility, and the thermoelectric properties of the materials were analyzed. The maximum dimensionless figures of merit (zTmax) were 0.75 and 0.82 for the p- and n-type material at 650 oC and 600 oC, respectively. These materials were then used to fabricate generator modules, wherein two pairs of p- and nlegs without interfacial metal layers were brazed on direct bonded copper (DBC)/Al2O3 substrates using a Zrbased alloy. A maximum power of 0.57 W was obtained from the module by applying a temperature gradient of 476 oC, which corresponds to a maximum power density of 1.58 W cm -2 when normalized by the area of the material. The maximum electrical conversion efficiency of the module was 3.22% at 476 oC temperature gradient. This value was negatively affected by the non-negligible contact resistivity of the brazed interfaces, which ranged from 6.63 × 10 -9 Ωm2 to 7.54 × 10 -9 Ω m2 at hot-side temperatures of 190 oC and 517 oC, respectively. The low electrical resistivity of the HH materials makes it especially important to develop a brazing technique for ultralow resistance contacts.

Extremely Fast and Cheap Densification of Cu2S by Induction Melting Method

The aim of this work was to obtain dense Cu2S superionic thermoelectric materials, homogeneous in terms of phase and chemical composition, using a very fast and cheap induction-melting technique. The chemical composition was investigated via scanning electron microscopy (SEM) combined with an energy-dispersive spectroscopy (EDS) method, and the phase composition was established by X-ray diffraction (XRD). The thermoelectric figure of merit ZT was determined on the basis of thermoelectric transport properties, i.e., Seebeck coefficient, electrical and thermal conductivity in the temperature range of 300–923 K. The obtained values of the ZT parameter are comparable with those obtained using the induction hot pressing (IHP) technique and about 30–45% higher in the temperature range of 773–923 K in comparison with Cu2S samples densified with the spark plasma sintering (SPS) technique.

Effect of Different Concentrations of Titanium Oxide (TiO2) Addition on the Crystallization Behaviour and Some Properties of Alkaline Earth Aluminosilicate Glass-Ceramics

Glass-ceramics in the CaO-MgO-Al2O3-SiO2 quaternary base glass system was produced via melting technique using feldspar, limestone and magnesite as sources of starting materials. Glass-ceramics production involves making a base glass, annealing and cooling to room temperature and then reheating the base glass to nucleation and crystal growth temperatures. Characterization of the produced glass-ceramics was carried out using a scanning electron microscope (SEM). The effects of the crystallization process on some properties such as hardness, chemical durability in acid and alkali media of samples were determined. The results portrayed that glass-ceramic samples to which various amounts of TiO2 (2,4,6,8 and 10 wt.%) were incorporated showed the formation of crystalline phases dispersed in the matrix of their respective residual glassy phases. Significant improvement in hardness, as well as minimum weight loss, were recorded for all the glass-ceramic samples. On the contrary, the glass samples did not crystallize despite subjecting them to heat treatment, their hardness values were low and they were not resistant to acid (1M HCl) and alkali (1M NaOH) attacks. The inability of TiO2 addition to fully transform them into glass-ceramics remains a shortcoming. However, the glass-ceramic samples obtained from this study can be used for tiling works.

Highly Porous 3D Printed Tantalum Scaffolds Have Better Biomechanical and Microstructural Properties than Titanium Scaffolds

Objective. To test the biomechanical properties of 3D printed tantalum and titanium porous scaffolds. Methods. Four types of tantalum and titanium scaffolds with four alternative pore diameters, #1 (1000-700 μm), #2 (700-1000 μm), #3 (500-800 μm), and #4 (800-500 μm), were molded by selective laser melting technique, and the scaffolds were tested by scanning electronic microscope, uniaxial-compression tests, and Young’s modulus tests; they were compared with same size pig femoral bone scaffolds. Results. Under uniaxial-compression tests, equivalent stress of tantalum scaffold was 411 ± 1.43 MPa, which was significantly larger than the titanium scaffolds ( P < 0.05 ). Young’s modulus of tantalum scaffold was 2.61 ± 0.02 GPa, which was only half of that of titanium scaffold. The stress-strain curves of tantalum scaffolds were more similar to pig bone scaffolds than titanium scaffolds. Conclusion. 3D printed tantalum scaffolds with varying pore diameters are more similar to actual bone scaffolds compared with titanium scaffolds in biomechanical properties.

Need for Standardization: Influence of Artificial Canal Size on Cyclic Fatigue Tests of Endodontic Instruments

The aim was to evaluate the influence of artificial canal size on the results of cyclic fatigue tests for endodontic instruments. Dynamic cyclic fatigue at body temperature using continuous tapered nickel–titanium F6-SkyTaper instruments (Komet, Lemgo, Germany), size 25/.06 with an amplitude of 3 mm, was tested in four different simulated root canals: (A) size of the instrument +0.02 mm (within the tolerances of the instruments); (B) +0.05 mm; (C) +0.10 mm; (D) parallel tube with 1.25 mm in diameter. The artificial canals (angle of curvature 60°, radius 5.0 mm, center of curvature 5.0 mm) were produced by a LASER-melting technique. Time and cycles to fracture, and lengths of the fractured instruments were recorded and statistically analyzed (Student–Newman–Keuls; Kruskal–Wallis test). Time to fracture significantly increased with increasing size of the artificial canals in the following order: A < B, C < D (p < 0.05). Length of separated instruments continuously decreased with increasing canal sizes. The parallel tube produced the significantly shortest fragments (p < 0.05). Within the limitations of this study, dynamic cyclic fatigue of endodontic instruments depends on the congruency of the instruments’ dimensions with that of the artificial canals. In future cyclic fatigue testing, due to the closer match of canal and instrument parameters, it is necessary to adjust the artificial canal sizes to the size of the instruments within the manufacturing tolerances of the instruments.