The amorphous alloys have attracted great attention due to their characteristics and future potential. This research is intended to synthesis new amorphous alloy with high glass forming ability as well as low density. The addition of lighter-weight elements such as Al, Ti, Zr, Ni and Cu are tried. The selected vitrification methods in this study are solid-state accumulated roll bonding (ARB) and arc-melting of multi-element alloys. Although the procedures of solid-state reaction are more complicated than that of casting, the influence of cooling rate on amorphization process is not important. Various Zr based binary, ternary, and pentanary alloys are synthesized by the ARB method. Besides, two pentanary alloys are also developed by arc melting method for the properties comparison with those made by ARB. The evolutions of hardness, strain accumulation, the enhanced diffusion, nanocrystalline phase size, amorphous volume fraction, elastic modulus, and relative energy states in various Zr based alloy systems during ARB are characterized and analyzed by transmission electron microscopy (TEM), in correlation with X-ray diffraction results. It appears that compatible initial foil hardness would be most beneficial to the nanocrystallization and amorphization processes during the room temperature ARB; the influence would overwhelm the atomic size effect (i.e., the anti-Hume-Rothery rule) applicable for solidification processing such as drop casting or melt spinning. Meanwhile, the estimated diffusion rates during ARB are higher by several orders of magnitude than the lattice diffusion in bulk materials and the hardness is seen to increase with increasing ARB cycles. The last stage for the nanocrystalline phase to suddenly transform into the amorphous state is examined, coupled with thermodynamic analysis. From the experimental observations and interfacial energy calculations for multilayered films, it is demonstrated that the rapid increase of interfacial free energy of the nanocrystalline phases with increasing ARB cycles appears to be a determining role in enhancing amorphization process. The local spatial distributions of the nanocrystalline and amorphous phases are seen under TEM to be non-uniform, varying significantly in size and quantity in different regions. The diffraction spots and rings in the TEM diffraction patterns are still originated from the pure elements, meaning that the nanocrystalline phases are those unmixed hard particles left from the previous severe deformation and diffusion processes. A critical size of the nanocrystalline phases around 3 nm is consistently observed in all binary, ternary, and pentanary Zr-X based alloys, below the critical size a sudden transformation from the nanocrystalline to amorphous state would occur. Finally, the hardness and Young¡¦s modulus of the nanocrystalline and amorphous materials are estimated based on the microhardness results. On the other hand, a pentanary alloy (according to the composition of the synthesized ARB specimens) is also made by the arc melting method for comparison. The sharp peaks are still observed in XRD pattern of the as-melted alloys. Hence, the melt spinning method is followed. A nearly completely amorphous state is obtained in the melt spun alloy. The hardness readings of the prepared alloys are all significantly higher than those typically for metallic alloys. Moreover, the resulting Zr based amorphous alloys made by ARB possess glass transition and crystallization temperatures similar to those processed by melt spinning or drop casting.

Microstructural characterization and mechanical properties of Excel (Zr-3.5%Sn-0.8%Mo-0.8%Nb), a dual phase αZr-hcp and βZr-bcc pressure tube material, is discussed in the current study which is presented in manuscript format. Chapter 3 discusses phase transformation temperatures using different techniques such as quantitative metallography, differential scanning calorimetry (DSC), and electrical resistivity. It was found that the αZr → αZr+βZr and αZr+βZr → βZr transformation temperatures are in the range of 600-690°C and 960-970°C respectively. Also it was observed that upon quenching from temperatures below ~860°C the martensitic transformation of βZr to –hcp is halted and instead the microstructure transforms into retained βZr with ω hexagonal precipitates inside βZr grains. Chapter 4 deals with aging response of Excel alloy. Precipitation hardening was observed in samples water-quenched from high in the αZr+βZr or βZr regions followed by aging. The optimum aging conditions were found to be 450°C for 1 hour. Transmission electron microscopy (TEM) showed dispersion of fine precipitates (~10nm) inside the martensitic phase. Energy dispersive X-ray spectroscopy (EDS) showed the chemical composition of precipitates to be Zr-30wt%Mo-25wt%Nb-2wt%Fe. Electron crystallography using whole pattern symmetry of the convergent beam electron diffraction (CBED) patterns together with selected area diffraction (SAD) polycrystalline ring patterns, suggests the -6m2 point group for the precipitates belonging to hexagonal crystal structure, with a= 2.936 Å and c=4.481 Å, i.e. c/a =1.526. Crystallographic texture and high temperature tensile properties as well as creep-rupture properties of different microstructures are discussed in Chapter 5. Texture analysis showed that solution treatment high in the αZr+βZr or βZr regions followed by water quenching or air cooling results in a more random texture compared to typical pressure tube texture. Variant selection was observed upon water quenching while partial memory effect and some transformation texture with variant selection was observed in the air-cooled sample. The results of creep-rupture tests suggest that fully martensitic and aged microstructure has better creep properties at high stress levels (>700 MPa) while the microstructure from air cooling from high in the αZr+βZr region is less sensitive to stress and shows better creep properties compared to the as-received annealed microstructure at lower stresses (<560 MPa). / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2012-08-23 16:22:45.395

No description available.

Zirconium base alloys have very good metallic glass forming ability. In this study,the Zr-Cu-Ni ternary isotherm at 800¢J were determined by using metallography,electron-probe microanalysis and X-ray diffraction.The main objective is to provide the necessary information for alloy design to form new Zr-base with better glass forming ability.

Zr-2.5Nb is used as pressure-tube material in CANDU (CANada Deuterium Uranium) reactors. Under reactor operating conditions, pressure tubes undergo anisotropic dimensional changes, and thermal creep contributes to this deformation. In a previous study, the limited textures available to Zr-2.5Nb significantly restricted the understanding of the relationship between texture and creep anisotropy. Moreover, there has been no research performed to investigate textures and stress states simultaneously for this material, which would provide a valuable resource for developing creep anisotropy models and optimizing textures to improve creep resistance. Cold-worked Zr-2.5Nb fuel sheathing (FS) and micro pressure tubes (MPT) with various textures and microstructures were used as experimental materials. The tubes were machined as thin-wall standard (ratio of axial to transverse stress 0.5) and end-loaded (ratio of axial to transverse stress = 0.25~0.75) capsules and were internally pressurized and sealed. Stress and temperature dependence tests were performed on standard capsules under transverse stresses of 100~325MPa at 300~400°C to establish a regime in which dislocation glide is the likely strain producing mechanism. An average stress exponent vaule of 6.4 was obtained, indicating that dislcation creep is the likely dominant mechanism. Texture and stress state dependence tests were performed on standard and end-loaded capsules under a nominal transverse stress of 300MPa at 350°C. It was evident that creep anisotropy strongly correlates with textures under different stress states. A self-consistent polycrystalline model SELFPOLY7 based only upon crystallographic texture was employed to simulate the creep anisotropy of the tubes. However, the model cannot fit all the experimental data well by using a uniform critical resolved shear stress (CRSS) ratio of the operating slip systems. A modification was made, by taking into account the pre-existing dislocation distributions generated during cold work, and an improvement was achieved. This work provides a valuable resource for understanding the effect of texture, stress states and microstructure on anisotropic creep of cold-worked Zr-2.5Nb tubes. The current research also provides a strategic direction to improve creep anisotropy predictions. The large sets of experimental data supply a database to evaluate and develop improved models. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2009-08-14 11:16:08.67

No description available.

Mg-Zn-Zr (ZK) alloys are widely employed in weight critical applications due to their high specific strength properties. Zinc and zirconium are added into the alloy for the purpose of forming precipitation hardening and grain refinement, respectively. However, both elements are likely to form some intermetallic compounds and may have effect on strengthening of the alloys. The purpose of this work was to explore this interaction to understand how to optimise the composition and processing of ZK alloys. In the present study, ZK60 with composition of 6 wt.%Zn and 0.6 wt.%Zr was heat treated by solutionizing and aging at various temperatures and times. The resultant microstructure was characterised by using optical microscope, X-ray Diffractometer (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and the age hardening response determined by using Vicker's microhardeness testing. The results show that the interaction between zinc and zirconium causes stable compound formation, including hcp (Zn_2Zr) Laves phase and cubic Zn_2Zr phase. These compounds are distributed unevenly, causing beta'_1 strengthening precipitate to form inhomogeneously during aging. This reduces the strengthening effect of aging, e.g. low age hardening response. It has been shown that the areas containing Zn_2Zr particles are essentially free of strengthening beta'_1 precipitates, an undesirable microstructure. The aged hardening and strengthening of ZK60 alloys accounting for the interaction between Zn and Zr has been explored through a new model for ZK alloys. The simulated age hardening strengthening in ZK60 is similar to the combination of the grain size strengthening and solution strengthening. The prediction has shown that the benefit of adding zirconium, which is grain boundary strengthening improvement by refining grain size, is balanced by a depletion in age hardening response. The total strength is estimated to increase by 15% if the grain size, that is normally obtained by zirconium alloying, could be achieved by another grain refinement method without the loss of zinc solute. The experiments and the models have identified the importance of considering the interaction between Zn and Zr when optimising the processing and composition of ZK magnesium alloys. That had never been emphasised and very well presented. In particular, when ZK alloys are used in wrought applications, control of grain size by recrystallisation rather than Zr may be beneficial in enabling a greater age hardening response.

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There is no unified phenomenological model available for Zr alloys that allows for the inclusion of a complete set of texture input parameters in order to describe the anisotropic behaviour during plastic deformation at different strain rates and thermal creep. This research shows how AVBO, an anisotropic version of VBO, can be enhanced by introducing single crystal based tensors to describe the material response to different Kearns factors, which uniquely describe the texture of a sample with two numbers only. It is demonstrated with the aid of published thermal creep test data that small tensile deformation behaviour of Zr-2.5Nb is consistent with predominant slip of Zr alloy crystals parallel to their single crystal α basal planes, supporting the strategy to model the behaviour of these HCP materials with a phenomenological constitutive model. It is demonstrated that the new version of AVBO, ATXVBO, predicts trends consistent with a slip mechanism parallel to the basal planes. Multi-objective optimization was employed successfully to determine the set of 67 constants. It is proven that the theory relies on a limited number of tests to perform optimization of all the unknown constants. Numerous validation and sensitivity evaluations were performed to test the optimized solutions despite the limited availability of plastic deformation test data with documented texture information. It is demonstrated that, in order to capture dynamic strain aging effects, different strategies will be required at different evaluation temperatures. It is also shown that although texture variation can be accommodated that different manufacturing routes each requires a unique optimized set of constants. / Thesis / Doctor of Philosophy (PhD) / A unified phenomenological theory ATXVBO has been established that can predict the deformation of HCP materials, including Zr alloys, that can account for texture variation. It is postulated that the inelastic polycrystal properties can be derived from hypothetical single crystal properties and the Kearns factors, used to describe the texture.

There are numerous classes of N-heterocyclic carbenes (NHCs) that have been synthesized since the discovery of stable NHCs in 1988. Their application as ligands in metal complexes has received much attention because of their strong sigma-donor and poor pi-acceptor properties. Within these NHC metal complexes, we are interested in studying zirconium metal complexes with pincer NHC ligands. Recently, achiral CCC-NHC pincer zirconium complexes were synthesized and their catalytic activity in intramolecular hydroamination of aminoalkenes were reported. Herein is reported new reaction conditions which yield pure, chiral CCC-NHC Zr pincer mono(amido) dibromo complex. The enantiopure crystal structure of the same complex is reported. Attempts to synthesize chiral CCC-NHC Zr pincer bis- and tris- amido complexes with the iodo salt of the ligand precursor are summarized. Moreover, syntheses of chiral bis(imidazolinium) ligand precursors with different counter anions are reported with optimized reaction conditions.