D. Tech. Chemical, Metallurgical and Materials Engineering. / Aims to produce and improve the tribocorrosion property of Ti6Al4V by means of laser surface cladding with Ni and ZrO2. The results of this study would be useful for the design of high performance components for chemical and oil industry and potential applications in other engineering fields. The aim would be achieved through the following objectives: 1. Synthesize and characterise Ti, Ti-Ni and Ti-Ni-ZrO2 admixed powders. 2. Explore the feasibility of laser surface treatment of Ti6Al4V with Ti, Ti-Ni and Ti-Ni-ZrO2. 3. Investigate possible metallurgical interactions and phenomenon during and after laser surface cladding of the composite. 4. Evaluate the microstructural and mechanical properties of Ti based composites in terms of hardness. 5. Analyze the interaction between wear and corrosion wear as well as tribocorrosion resistance of the alloys and composites after laser surface cladding in 3.5 % NaCl and 1M H2SO4 environments.

Aim of the present work was to explore the possibility of improving strength of cast Mg by alloying additions, viz., Si and Zn+Al. All the alloys were produced by squeeze casting technique using squeeze pressure of 12MPa and their microstructure, tensile and corrosion properties were studied. Mg-Si system was chosen because the intermetallic compound Mg2Si possesses many desirable properties, such as, low density, high hardness, high melting point. Hence, there is scope for improving the strength of Mg by dispersion of primary Mg2Si particles. Addition of Si to Mg resulted in the formation of �-Mg, particles of primary Mg2Si and eutectic as microstructural constituents. The morphology of primary Mg2Si changed from polyhedral shaped particles to dendrites as Si content was increased from 3.57 to 5.5 wt%. Volume fraction of primary Mg2Si increased with increase in Si content. Particle size of primary Mg2Si also increased with increase in silicon content but at the same time it was found to be dependent on melt temperature, i.e., a lower particle size was obtained at higher melt temperatures. Addition of Al and Sr was made to Mg-2Si alloy in order to further increase the strength by solid solution strengthening and refinement/modification of primary Mg2Si particles/eutectic. Addition of 1.2 wt% Al to Mg-2Si alloy resulted in irregular type of morphology of Mg2Si particles and increased particle size. Addition of 0.2 wt% SrtoMg-2Si-1.2Al alloy resulted in slight refinement of primary Mg2Si particles and modification of eutectic. Addition of 0.4 wt% Sr resulted in both refinement and restoration of morphology of Mg2Si particles from irregular to polyhedral shape. This was accompanied by destruction of eutectic, and rods containing Mg, Si, Al and Sr were observed. The addition of 1.33 wt%Si to Mg resulted in improvement in 0.2%PS by about 80 MPa,UTS by about 40MPa and these values did not change much till the addition of 3.57 wt% Si. A drop in the strength values was observed at Si content of 5.5 wt%,where transition in morphology of primary Mg2Si occurred from polyhedral to dendrite. Addition of Si resulted in reduction in % elongation by about 2%. The addition of Al and Sr did not change the tensile properties of binary Mg-2Si alloy much. It was concluded that the volume fraction and size of primary Mg2Siparticles obtained with Si addition up to 3.57 wt% did not contribute much to strength and the strengthening mainly came from the eutectic present in the matrix. As Si content was increased to 5.5 wt% in order to increase the volume fraction of primary Mg2Si particles, the morphology of Mg2Si changed to dendritic type resulting in reduction in strength. Thus, the maximum increase in strength is achieved at near eutectic composition,i.e.,intheMg-1.33Sialloy,andfurtherincreaseinstrengthdoesnotseem to be feasible with this alloy system. The ductility of all the Mg-Si based alloys was also low, i.e, 0.5% elongation to fracture or less. Regarding the corrosion behaviour, the addition of Si to Mg deteriorated the corrosion resistance and the addition of Al and Sr further worsened it. Since further improvement in tensile properties did not seem feasible with Mg-Si alloy system, the focus was shifted to Mg-Zn-Al alloy system. There is scope for improvement in strength in Mg-Zn-Al alloy system by solid solution strengthening, grain refinement and precipitation hardening. It was observed that the addition of Zn and Al resulted in microstructure containing α-Mg grains and secondary phase at the grain boundary. XRD analysis showed the secondary phase to be Al5Mg11Zn4 but EDS analysis did not match with this composition. Therefore, the nature of this phase remains uncertain. Addition of 6 wt% Zn and 1 wt% Al resulted in improvement in strength as well as ductility: 0.2%PS improved by about 70 MPa, UTS by about 100 MPa and % elongation by about 7%. Addition of small amounts of Caresultedinrefinementofmicrostructurecausingimprovementinstrengthwithout much decrease in % elongation. Increase in Al content from 1 to 4 wt% resulted in increase in 0.2%PS but UTS slightly decreased, as % elongation reduced. Alloys subjected to T6 heat treatment showed improvement in strength but slight reduction in % elongation. ZA64 alloy in T6 condition gave 130 MPa 0.2%PS, 225 MPa UTS and 4.9% elongation, which are much higher tensile properties as compared Mg-Si alloys. All the three mechanisms mentioned above contribute to the strengthening. There is scope for further improvement in strength by employing a more suitable heat treatment. Regarding corrosion behaviour, addition of 6 wt% Zn and 1 wt% of Al to Mg did not deteriorate its corrosion resistance much. Addition of small amounts of Ca was found to be beneficial for corrosion resistance, whereas an increase in Al content lowered the corrosion resistance. Heat treatment also reduced the corrosion resistance.

This thesis refers to Fe-based biodegradable materials and their potencial aplications in medicine, especially as temporary bone implants. This work generaly summaries aplications of biomaterial in medicine with more interest kept on biodegradable materials and their in-vivo corrosion. The experimental part refers to conduction of porous Fe-based materials with silica addition. The structure of prepared specimens is identified by EDX and XRD analysis. The imersion test and electrochemical studies were conducted to observe corrosion behaviour with respect to different concentration of silica. Potenciodynamic curves were obtained to determine corrosion potencial and corrosion current density of prepared samples.

Indiana University-Purdue University Indianapolis (IUPUI) / In recent years, magnesium alloys, due to their high strength and biocompatibility, have attracted significant interest in medical applications, such as cardiovascular stents, orthopedic implants, and devices. To overcome the high corrosion rate of magnesium alloys, coatings have been developed on the alloy surface. Most coating methods, such as anodic oxidation, polymer coating and chemical conversion coating, cannot produce satisfactory coating to be used in human body environment. Recent studies demonstrate that micro-arc oxidation (MAO) technique can produce hard, dense, wear-resistant and well-adherent oxide coatings for light metals such as aluminum, magnesium, and titanium. Though there are many previous studies, the understanding of processing conditions on coating performance remains elusive. Moreover, previous tests were done in simulated body fluid. No test has been done in a cell culture medium, which is much closer to human body environment than simulated body fluid. In this study, the effect of MAO processing time (1 minute, 5 minutes, 15 minutes, and 20 minutes) on the electrochemical behaviors of the coating in both conventional simulated body fluid and a cell culture medium has been investigated. Additionally a new electrolyte (12 g/L Na2SiO3, 4 g/L NaF and 4 ml/L C3H8O3) has been used in the MAO coating process. Electrochemical behaviors were measured by performing potentiodynamic polarization and electrochemical impedance spectroscopy tests. In addition to the tests in simulated body fluid, the MAO-coated and uncoated samples were immersed in a cell culture medium to investigate the corrosion behaviors and compare the difference in these two kinds of media. The results show that in the immersion tests in conventional simulated body fluid, the 20-minute MAO coated sample has the best resistance to corrosion due to the largest coating thickness. In contrast, in the cell culture medium, all MAO coated samples demonstrate a similar high corrosion resistance behavior, independent of MAO processing time. This is probably due to the organic passive layers formed on the coating surfaces. Additionally, a preliminary finite element model has been developed to simulate the immersion test of magnesium alloy in simulated body fluid. Comparison between the predicted corrosion current density and experimental data is discussed.