Thesis (M. Eng. Sc.)--University of Queensland, 2002. / Includes bibliographical references.

This is the first systematic report on the synthesis of mechanically alloyed Fe-Ni powders ball milled at liquid nitrogen temperature. Pure Fe-Ni samples were ball milled in a SPEX 8000 shaker mill at liquid nitrogen temperature. X-ray diffractometry was used to determine the phase fractions of the bcc and fcc phases in the alloys and to determine the lattice parameters and crystallite size. The main objective of this project is to study how the milling at low temperatures affects the region of two phase co-existence, phase structure and crystallite size. It was found that the composition ranges of the bcc and fcc single phase regions were extended well beyond the equilibrium ranges. The results obtained for the samples ball milled at liquid nitrogen temperature were compared to the previous samples ball milled at room temperature.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Programa de Pós-Graduação em Física. / Made available in DSpace on 2012-10-22T14:28:16Z (GMT). No. of bitstreams: 1 237951.pdf: 4449107 bytes, checksum: cd5915d3c55cfdf7be35ef94a8022e25 (MD5) / Uma liga nanoestruturada Ga40Se60, foi produzida pela técnica Mechanical Alloying a partir de uma mistura de pós elementares Ga e Se. Depois de 5 horas de moagem foi observado a fase Ga40Se60 nanoestruturada já formada juntamente com uma fase amorfa minoritária. As propriedades estruturais, térmicas e ópticas da fase nanoestruturada Ga40Se60 foram investigadas por varias técnicas. A fase amorfa foi cristalizada para a possível fase Ga40Se60 após tratamento térmico em 723 K. Um novo padrão de difração foi medido para amostra tratada e sua interpretação foi feita pelo refinamento por método Rietveld. O processo de tratamento térmico promoveu melhora na determinação da difusividade térmica e também no valor do gap óptico. Os valores obtidos para a amostra tratada estão em acordo com aquelas reportadas na literatura. As ligas amorfas CoXNb1-X (X = 0,41 e 0,62) foram produzidas por Mechanical Alloying. A obtenção desses materiais amorfos ratificou cálculos baseados no modelo termodinâmico desenvolvido no Laboratório de Síntese e Caracterização de Materiais - LSCM da UFSC. Suas estruturas atômicas foram determinadas usando o método de Monte Carlo Reverso cujo dado de entrada para o método foi apenas um fator de estrutura total S(K), derivado de dados de difração de raios x medidos no Laboratório Nacional de Luz Sincrotron - LNLS. Os resultados alcançados mostraram que as ligas possuem estruturas atômicas com características semelhantes aquelas previstas pelo modelo aditivo de empilhamento aleatório de esferas rígidas (AHS) para misturas de Co e Nb, de mesma composição das ligas. As estruturas atômicas das ligas amorfas foram também foram comparadas com as estruturas cristalinas dos compostos CoNb, Co2Nb e Co3Nb. Para a liga amorfa Co41Nb59 observou-se que a estrutura amorfa possui alguma similaridade com a estrutura cristalina do composto CoNb. Foi também investigada a densificação da estrutura amorfa nas ligas amorfas CoXNb1-X (X = 0,25, 0,41 e 0,62) que foram produzidas por Mechanical alloying em função da concentração de cobalto. Foi observado que existe uma densificação máxima em torno da composição contento 41 at. % Co. Para valores superiores, a densidade diminui mais rapidamente do que para as ligas com concentrações de cobalto inferiores a 41 at. % Co. A nanostructured Ga40Se60 alloy was produced by Mechanical Alloying technique starting from blended Ga and Se powders. After 5 h of milling, the Ga40Se60 phase together with a minority amorphous phase was already observed. The structural, thermal and optics properties of Ga40Se60 phase were investigated by several techniques. The crystallization of the amorphous phase in a possible nanostructured Ga40Se60 alloy was reached by annealing the as-milled powder at 723 K. A new X-ray diffraction pattern was measured for annealed sample and its interpretation was made by refinement Rietveld method. The thermal diffusivity parameter and the optic gap energy for annealed sample were measured and the obtained values were compared with previous values measured for as-milled sample. The obtained values for the annealed sample are in agreement with those reported in the literature. The amorphous CoXNb1-X (X = 0.41 and 0.62) alloys were produced by Mechanical Alloying technique. Their productions by this technique were predicted through a Thermodynamic Approach developed by researchers from the LSCM. Their atomic structures were determined through Reverse Monte Carlo method using as input data their total structure factors S(K), which were derived from synchrotron x-ray diffraction data measured at the Laboratório Nacional de Luz Sincrotron - LNLS. The results have shown that the amorphous alloys have atomic structures with some characteristics to those predicted by the Additive Hard Spheres model (AHS) for Co and Nb mixtures containing the same nominal compositions of the amorphous alloys. In addition, the amorphous structures were also compared with the crystalline structures of CoNb, Co2Nb and Co3Nb compounds. It was observed that the Co41Nb59 amorphous structure has some similarities with that found for CoNb compound. We have also investigated the packing (densification) of amorphous structures present in the CoXNb1-X (X = 0.25, 0.41 and 0.62) alloys produced by Mechanical Alloying as a function of Co at. % . It was observed a maximum densification for a composition around of 41 at. % Co. For compositions containing Co concentration greater than this value, the density of the alloy seems to decrease rapidly, while for smaller concentration the reduction in the density seems to be more smoothly.

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 9, 2009) Includes bibliographical references.

The mechanical alloying (MA) process and hot isostatic pressing (HIP) were used to synthesize bulk amorphous Ni-Ti alloy as an alternative to the traditional methods of casting multi-component metallic alloys. Samples milled cryogenically for 10 hours provided a homogeneous lamella structure with spacing of 30-110 nm. X-ray diffraction and transmission electron microscopy studies indicated that there were alloying and amorphous phase within the layers of the MA powder prior to annealing or HIPing. The amount of amorphous phase increased with time when the milled powder was annealed at a constant temperature and with temperature when annealing time was held constant. The microhardness of the powder correspondingly increased with the amount of amorphous formed in the powders. The HIPing of the MA powder produced a close to 100% amorphous compact with some dispersion of nanocrystals in the amorphous matrix. However, densification was not achieved. / Master of Science

Alumina particles filled Ultra-high Molecular Weight Polyethylene (UHMWPE), with Al2O3 contents 0, 1, and 2.5 wt% were milled for up to 10 hours by the mechanical alloying (MA) process performed at room temperature to produce composite powders. Compression molding was utilized to produce sheets out of the milled powders. A partial phase transformation from orthorhombic and amorphous phases to monoclinic phase was observed to occur for both the un-reinforced and reinforced UHMWPE in the solid state, which disappeared after using compression molding to produce composite sheets. The volume fraction of the monoclinic phase increased with milling time, mostly at the expense of the amorphous phase. The melting temperature decreased as a function of milling time as a result of modifications in the UHMWPE molecular structure caused by the milling. At the same time, for a given alumina composition the activation energy of melting increased with milling time. Generally, the crystallinity of the molded sheets increased with milling time, and this caused the yield strength and elastic modulus to increase with milling time for a given alumina composition. However, the tensile strength and ductility remained about the same. / Master of Science

No description available.

The influence of mechanical alloying (MA) milling time, temperature, sintering method and microstructure on the mechanical properties of a tungsten carbide-cobalt (WC-Co) hardmetal, based on 10wt% Co, has been established. The effects of high-energy milling for 30, 60, 180 and 300 min and the interrelation between milling time and powder properties, and the resultant effects on the mechanical properties of the consolidated WC-10Co material, has been obtained for a horizontally designed ball mill. Nanostructured WC-10Co powder was synthesised after 60 min cyclic milling at room temperature with an average WC domain size of 21 nm. In direct comparison, a WC-10Co composition MA at -30°C for 60 min produced an average WC domain size of 26 nm with a higher lattice strain. WC domain size showed a slight increase with milling time, measured at 27 nm after 300 min ball milling. Extended ball milling (300 min) reduced the mean particle size from 0.148 μm for 60 min milling to 0.117 μm. Thermal analysis showed that the onset temperature of the WC-Co eutectic was related to particle size with increased milling time reducing the onset temperature from 1344°C after 60 min milling to 1312°C after 300 min milling. Onset temperature was further reduced by the addition of vanadium carbide (VC), reducing the onset temperature to 1283°C after 300 min milling. Powder contamination increased with increased milling time with Fe content measured at ~ 3wt% after 300 min ball milling. Milling at -30°C reduced Fe contamination to an almost undetectable level. Increased ball milling time resulted in decreased levels of green density with the powders milled for 30 and 300 min achieving 62.5% and 59.5% TD, respectively. Relative density increased for the powder milled at -30°C compared to the RT milled powder due to its flattened, slightly rounded morphology. A large difference in VC starting particle size compared to WC and Co led to non-uniform dispersion of the inhibitor during milling. Densification and hardness reached optimum levels for the 60 min milled powder for both pressureless sintering and sinter-HIP. Both properties decreased with increased milling time, regardless of the sintering method. Low temperature milling resulted in a higher hardness value of 1390 HV30 compared to 1326 HV30 for the 60 min, RT milled material after pressureless sintering. Densification levels of the doped materials were restricted to < 90% TD for both sintering methods due to inhomogeneity in the microstructures. Palmqvist fracture toughness (WK) of the RT milled powders increased with increased milling time and increasing WC grain size for both sintering methods. WK reached 11.6 MN.m3/2 with 300 min milling after pressureless sintering but reached 16.1 MN.m32 for the same material after sinter-HIP due to the effect of mean WC grain size and binder phase mean free path. The -30°C milled powder exhibited higher fracture toughness for both sintering methods than the 60 min, RT milled material. Spark plasma sintering (SPS) showed that the onset of densification was dependent upon particle size with the powder from 300 min milling showing an onset temperature of ~ 800°C compared to ~ 1000°C for the 60 min milled powder. The low temperature milled powder showed an onset temperature of ~ 980°C, which suggested that low temperature milling provided enhanced densification kinetics.

The transformations occurring in the sub-stoichiometric Ti(C,N) – W - Al system processed by high energy ball mill were investigated. The milling parameters included the milling time and the temperature comprising milling at subzero temperature and above 25°C. Two sub-stoichiometric Ti(C,N) stocks were selected, the Ti(C0.5N0.05) containing more interstitial elements than the Ti(C0.5N0.5)0.6.The transformation stages and mechanisms of alloying are discussed with respect to the changes in crystal structures of the powder constituents. The milling atmosphere had an effect on the lattice strain of milled products, and hence on the kinetics of solid state dissolution between the powder constituents, but it did not affect the fracturing process. The release of the stored crystallite lattice strain energy was the major determinant in mechanical alloying, with particle size reduction playing a necessary, but less significant role. The strain energy and the fine particle size contributed to the increased chemical reactivity with oxygen of the powders milled for shorter times. The affinity of the powders with oxygen decreased after W dissolution in Ti(C,N), and the subsequent decrease in lattice strains. The annealing behaviour of Ti(C0.5N0.05) - 40wt% W and Ti(C0.5N0.5)0.6 - 40wt% W mechanically alloyed powders were investigated using XRD, TEM, SEM and DTA techniques. It was observed that the reaction start and finish temperatures between constituents were lower in the system that had higher residual lattice strains after milling. The compositions of the intermetallic compounds and the solid solutions formed were dependent on the milling conditions and the annealing temperature. Thermal alloying was observed during annealing of Ti(C0.5N0.05) - 40wt% W mechanically alloyed products, whereas de-mixing of W-rich phases from the metastable solid solution occurred during annealing of the Ti(C0.5N0.5)0.6 - 40wt% W milled powders. The effects of Al addition and milling at subzero temperatures on the transformation of Ti(C0.5N0.05)-W powder mixtures were investigated. Addition of Al powder improved the kinetics of solid solution between powder constituents. The effect of Al was ascribed to the increase of lattice strain during short milling time followed of relaxation at longer time, and to the fast diffusion of atoms. Also, it was noticed that the high viscosity of the process control agent could inhibit the alloying process. Multiple three-component compounds could be formed. Aluminium preferably reacted with tungsten. The W(Al,C) and W(Al,Ti) formed were stable, thus solubility of W in Ti(C0.5N0.05) in the presence of Al was limited. The evolution of the morphologies of Ti(C,N)-W mixtures show that fracturing of hard particles dominated in the early stage of milling in the absence of Al, whereas with Al, plastic deformation of particles and cold welding of Ti(C,N) and W particles by the softer Al prevailed at the same time. Longer milling time improved the homogeneity and the formation of nanostructured binder pools in the sintered products. Lower oxygen contents in sintered PcBN were achieved by mechanically alloying Ti(C,N), W and Al in the high energy ball milling stage. Low level of Co in the infiltration layer was also achieved when sintering PcBN with this type of binder. A link was established between the addition of Al at the attrition milling stage and high oxygen content in the sintered PcBN, thus should be avoided. The pressure and temperature applied during sintering or annealing had a strong effect on the compositions and the crystal structures of the phases formed in the mechanically alloyed binder. The lattice strains of the binder and the PcBN were higher in the sintered materials prepared with the Ti(C0.5N0.5)0.6-W binder than in those made using the Ti(C0.5N0.05)-W alloys.

Thesis (Ph. D. (Physics)) -- University of Limpopo, 2013. / A combination of ball milling experiments and ab initio calculations in this study successfully yielded results that shed light into understanding the fundamental basis for immiscibility and the concept of mechanical alloying in Ti-Mg system. In addition, the conditions for achieving extended solid solubility in elements that usually do not dissolve in each other under thermodynamic equilibrium conditions have been predicted using ultrasoft (US) and norm-conserving (NC) pseudopotentials. Hydostatic pressures required to stabilize ordered phases were determined. Our new systematic representation of martensitic transformation (MT) paths as a result of dislocation necessary to induce α→FCC, α→BCC and α→ω phase transitions led to, for the first time, a direct determination of CRSS and tensile strength for Ti and Mg HCP metals. Furthermore, a new ω phase which is less stable than α phase at 0 GPa is proposed. Based on this phase, α→ω deformation path which yielded the onset of uniaxial transition pressure of 4.167 GPa is reported. Attempts of synthesizing Ti-Mg solid solutions by means of Simoloyer high energy ball mill were not successful; however, nanocrystalline Mg-TiH2-x composites were instead formed. These results were attributed to quick formation of metastable Ti hydrides or cold welding at early stages of BM prior to alloying, thus serving as possible obstacles to forming such solid solutions. The deformed Ti crystals adsorbed H+ from the stearic acid leading to formation of metastable orthorhombic TiH2-x phase which later transformed to a tetragonal TiH2-x or even cubic TiH2 when stoichiometric amount of H2 had been adsorbed. Although the yield was significantly lower, the product of milling a mixture of coarse Mg and fine Ti particles was comprised of Ti particles adhering around ductile Mg particles in a core shell manner. The adhesion of the fine hard titanium particles on the surface of the large ductile magnesium particles impeded the further plastic deformation of the titanium particles, thus suppressing the formation of the faults necessary for mechanical alloying. Nanocrystalline Ti powder of about 40 nm was produced by 30h ball milling. During BM of Ti powder, solid-state transformation from HCP to FCC occurred in the presence of PCA with lattice parameters of 4.242 and 4.240 Å after 24 and 30 h, respectively, v due to protonation. When Ti powder was milled in the absence of PCA, no phase transformation was observed for both uninterrupted and interrupted milling cycles. In addition, nanocrystalline Mg powder with crystallite size varying between 60 and below 40 nm was produced by ball milling. However, no solid-state transformation took place even if the powder was milled for 90 h. Therefore, we evidently report for the first time that the interstitial H+ is the driving force for α → FCC phase transformation in ball milled Ti powder. Our theoretical results predicted the ω phase to be the ground-state structure of Ti at 0K and P=0 GPa, in support of other previously reported calculations. We noticed that the stability of the α phase was surpassed by that of the FCC lattice at ~ 100 GPa, corresponding with sudden sharp rise in c/a ratio, hence attributed to α → FCC phase transition. Similar results were obtained for Mg at 50 GPa, although in this case the crossing of lattice energies coincided with minimum c/a. However, using our proposed HCP→BCC MT path mechanism for Mg, it is evident that the minimum c/a at 50 GPa corresponds to a change in the preferred deformation slip from basal (below 10 GPa) to prismatic rather than phase transition. Nonetheless, the proposed MT model predicts that both elemental Ti and Mg prefer to deform via prismatic slip as indicated by lower shear stress as well as CRSS values compared to those calculated for basal slip. Theoretical findings from ab initio calculations on hypothetical ordered Ti-Mg phases indicated absence of intermetallic phases at equilibrium conditions, in agreement with experimental data. However, the formation becomes possible at 80 GPa and above with respect to c/a ratio but requires at least 200 GPa with respect to stable lattices. Using calculated heats of formation, elasticity and DOS, it has been possible to show that L12 TiMg3 could not form even at high pressure as 250 GPa. Nonetheless, both approaches indicate that forming an intermetallic compound between Ti and Mg requires a crystal structure change, α→FCC for Ti and HCP→BCC for Mg. Proposed DFT-based solid solution model for predicting phase stability and elastic properties of binary random alloys, with Mg-Li system serving as a test case, successfully yielded reliable results comparable to experimental data. This method was successfully applied to study an immiscible Ti-Mg system and the solubility limit vi was for the first time theoretically established. Based on formation energy of Ti-Mg solid solutions, our calculations predicted for the first time that the solubility of up to 60 and 100 at.% Mg into Ti with the use of USP and NCP, respectively, to be thermodynamically favourable with necessary lattice kinetics being the main challenge. Nonetheless, NCP proved to be reliable in predicting structural and elastic properties of disordered alloys.