Browsing by Author "Smith, RI"

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    High-temperature thermal stability of Ti2AlN and Ti4AlN3: a comparative diffraction study
    (Elsevier, 2011-01) Low, IM; Pang, WK; Kennedy, SJ; Smith, RI
    The susceptibility of Ti2AlN and Ti4AlN3 to high-temperature thermal dissociation in a dynamic environment of high-vacuum has been investigated using in situ neutron diffraction. Under high vacuum, these ternary nitrides decomposed above 1400°C through the sublimation of Al, and possibly Ti, to form a surface coating of TiNx (0.5 ≤ x ≤ 0.75). The kinetics of isothermal phase decomposition were modelled using the Avrami equation and the Avrami exponents (n) of isothermal decomposition of Ti2AlN and Ti4AlN3 were determined to be 0.62 and 0.18, respectively. The characteristics of thermal stability and phase transitions in Ti2AlN and Ti4AlN3 are compared in terms of the rate of decomposition, phase relations and microstructures. © 2010, Elsevier Ltd.
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    In situ diffraction study on decomposition of Ti2AlN at 1500–1800°C in vacuum
    (Elsevier, 2010-11-25) Pang, WK; Low, IM; Kennedy, SJ; Smith, RI
    The susceptibility of Ti2AlN to thermal dissociation at 1500–1800°C in high-vacuum has been studied using in situ neutron diffraction. Above 1500°C, Ti2AlN decomposed to TiNx primarily through the sublimation of aluminium (Al). The kinetics of isothermal phase decomposition at 1550°C was modelled using a modified Avrami equation. An Avrami exponent (n) of 0.338 was determined, indicative of the highly restricted out-diffusion of Al between the channels of Ti6N octahedra. The characteristics of thermal stability and phase transition in Ti2AlN are discussed. Characterisation of surface compositions and examination of cross-sectional microstructures of decomposed Ti2AlN, using synchrotron radiation diffraction and SEM, respectively, verify the findings of the neutron diffraction; that Ti2AlN decomposes to TiNx at the surface primarily via the sublimation of Al from grain boundaries. © 2010, Elsevier Ltd.
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    Study of high-temperature thermal stability of MAX phases in vacuum
    (American Ceramic Society, 2010-01-28) Low, IM; Pang, WK; Kennedy, SJ; Smith, RI
    The susceptibility of two MAX phases (Ti2AlN and Ti 4AlN3) to high-temperature thermal dissociation in a dynamic environment of high-vacuum has been investigated using in-situ neutron diffraction. In high vacuum, these phases decomposed above 1400°C through the sublimation of Ti and Al elements, forming a surface coating of TiN. The kinetics of isothermal phase decomposition was modelled using the Avrami equation and the Avrami exponent (n) of isothermal decomposition of Ti 2AlN and Ti4AlN3 was determined to be 0.62 and 0.18 respectively. The characteristics of thermal stability and phase transitions in Ti2AlN and Ti4AlN3 are compared and discussed.