Yes / Titanium alloys are known for their excellent corrosion resistance; however, low surface hardness results in poor wear resistance, which limits its potential application. This study employs a novel two-step process to embed a hard Ni coating containing a mixture of nanosized particles (Al2O3 and TiO2) into the surface of the Ti-6Al-4V alloy using an electric arc produced during the inert tungsten gas welding process. The surface of the sample was evaluated using Vickers Microhardness, Scanning electron microscopy, Energy dispersive spectroscopy and pin-on-plate wear testing. Microstructural analysis showed that impregnating the titanium surface with Ni/(Al2O3 and TiO2) nanomaterials resulted in the formation of a hard martensitic structure to a depth of approximately 2 mm below the surface. The changes observed are driven by modification of the surface chemistry and the presence of nickel, causing grain size reduction, solid solution strengthening and dispersion strengthening of the treated layer by the nanoparticles. The hardness of the treated layer increased by more than 180% when 40 nm Al2O3 and 30 nm TiO2 particles were embedded into the surface. Similarly, the wear resistance of the treated surface improved by 100%.

M. Tech. (Department of Metallurgical Engineering, Faculty of Engineering Technology), Vaal University of Technology. / Solid titanium (Ti), Ti-6Al-4V (wt.%), and Ti-24Nb-4Zr-8Sn (wt.%) materials were fabricated from powders using spark plasma sintering (SPS). The starting materials comprised of elemental powders of ASTM Grade 4 titanium (Ti), aluminium (Al), vanadium (V), niobium (Nb), zirconium (Zr), and tin (Sn). The powders were initially characterised and milled prior to sintering. The micronpowders were milled in an attempt to produce materials with nanostructured grains and as a result improved hardness and wear resistance. The produced solid Ti-24Nb-4Zr-8Sn alloy was compared to solid titanium (Ti) and Ti-6Al-4V (Ti64) on the basis of density, microstructure, hardness, corrosion, and biocompatibility. Relative densities above 99.0% were achieved for all three systems. CP-Ti and Ti64 had both 100% relative density, and Ti2448 showed a slightly lower density of 99.8%. Corrosion results showed that all three materials exhibited good corrosion resistance due to the formation of a protective passive film. In 0.9% NaCl Ti2448 had the highest current density (9.05 nA/cm2), implying that its corrosion resistance is relatively poor in comparison to Ti (6.41 nA/cm2) and Ti64 (5.43 nA/cm2), respectively. The same behavior was observed in Hank's solution. In cell culture medium, Ti2448 showed better corrosion resistance with the lowest current density of 2.96 nA/cm2 compared to 4.86 nA/cm2 and 5.62 nA/cm2 of Ti and Ti64 respectively. However, the current densities observed are quite low and insignificant that they lie within acceptable ranges for Ti2448 to be qualified as a biomaterial. Cell proliferation test was performed using murine osteoblastic cells, MC3T3-E1 at two cell densities; 400 and 4000 cells/mL for 7 days incubation. Pure titanium showed better cell attachment and proliferation under both conditions suggesting that the presence of other oxide layers influence cell proliferation. No significant difference in cell proliferation was observed between Ti64 and Ti2448.

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A heightened interest in intelligent material systems has occurred in recent years due to their remarkable adaptive abilities. Intelligent materials systems, which contain sensors and actuators coupled by means of active control, frequently utilize composite materials as the skeletal structure. In order for composite materials to be utilized in intelligent material systems to their utmost capability, many material properties, including the interfacial shear strength between the embedded sensor or actuator and the matrix must be thoroughly understood.. Investigations were performed in order to examine the effects of different variables on the interfacial characteristics between a nitinol fiber and a composite matrix. First, rough, clean fiber surfaces were found to provide the best adhesion to the matrix due to the mechanical interaction of the matrix with the rough surface finish. Second, it was determined that the interfacial shear strength is not dependent upon embedded fiber length. Third, a very small diameter fiber will break before pulling out of the matrix, but overall, large fibers have a greater interfacial strength. Fourth, it was found that the initial prestrain on the fiber during processing had no effect on the interfacial shear strength of the fiber to the matrix. Fifth, it was determined that fatigue does not degrade the shear strength of any of the different initial pres trains. Finally, it was found that a coating that does not adhere well to the fiber neither macroscopically degrades nor enhances interfacial strength. / Master of Science

Metallic materials have considerable importance in biomedical tissue reconstruction structural failed. Currently, the production of new alloys, titanium has been encouraged for biomedical use so as to reduce limitations and elastic modulus of alloy marketed cytotoxicity, in particular Ti-6Al-4V. Alloys Ti-Nb-Sn are an alternative for this purpose. In the current study, alloy Ti-35Nb-2,5SN were obtained by melting the arc, solubilized at 1000 ° C for 12 hours, hot-rolled with 40% reduction in water and cooled. The content of nitrogen and oxygen was verified by melting in an atmosphere of inert gas. The microstructures were characterized by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction. The characteristics in fatigue and corrosion - fatigue alloy were determined according to the guidelines noted in ASTM E466. Specimens were machined and fatigue SN curves obtained in air and in an environment with 0.9% NaCl. The micromechanics of fracture were analyzed by scanning electron microscope (SEM). The results were compared with published data for beta stabilized alloys and discussed the potential application of new alloys. / Os materiais metálicos biomédicos apresentam notável importância na reconstrução de tecidos estruturais que falharam. Atualmente, a produção de novas ligas de titânio tem sido incentivada para uso biomédico a fim de reduzir as limitações quanto ao módulo de elasticidade e citotoxicidade das ligas comercializadas, em particular a liga Ti-6Al-4V. As ligas de Ti-Nb-Sn surgem como alternativa para esta finalidade. No estudo atual, ligas de Ti-35Nb-2,5Sn foram obtidas por fusão a arco voltaico, solubilizadas, laminadas a quente com 40 % de redução e resfriadas em água. O teor de nitrogênio e oxigênio foi verificado por fusão em ambiente de gás inerte. As microestruturas foram caracterizadas por microscopia ótica, microscopia eletrônica de varredura (MEV) e difração de raios-X. Corpos de prova de fadiga foram usinados e submetidas a ensaio para obtenção de curvas S-N ao ar e em ambiente com 0,9 % de NaCl e baixa frequência. Os micromecanismos de fratura foram analisados em microscópio eletrônico de varredura (MEV). Os resultados foram comparados com os dados publicados na literatura para outras ligas beta estabilizadas e foram discutidos os potenciais de aplicação das novas ligas. Os resultados dos ensaios mostraram que o limite de fadiga tende a coincidir com a tensão limite para o início do movimento de discordâncias.

A compositionally graded Ti-xCr (10≤x≤30 wt%) alloy has been fabricated using Laser Engineered Net Shaping (LENSTM) to study the microstructural phase evolution along a compositional gradient in both as-deposited and heat treated conditions (1000°C followed by furnace cooling or air cooling). The alloys were characterized by SEM BSE imaging, XRD, EBSD, TEM and micro-hardness measurements to determine processing-structure-property relations. For the as-deposited alloy, α-Ti, β-Ti, and TiCr2 (C15 Laves) phases exist in varying phase fractions, which were influential in determining hardness values. With the furnace cooled alloy, there was more homogeneous nucleation of α phase throughout the sample with a larger phase fraction of TiCr2 resulting in increased hardness values. When compared to the air cooled alloy, there was absence of wide scale nucleation of α phase and formation of ω phase within the β phase due to the quicker cooling from elevated temperature. At lower concentrations of Cr, the kinetics resulted in a diffusionless phase transformation of ω phase with increased hardness and a lower phase fraction of TiCr2. In contrast at higher Cr concentrations, α phase separation reaction occurs where the β phase is spinodally decomposed to Cr solute-lean β1 and solute-rich β2 resulting in reduced hardness.

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