Residual microstructure associated with impact craters in TiB2/2024Al composite

School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China.
Micron (Impact Factor: 1.99). 02/2012; 43(2-3):344-8. DOI: 10.1016/j.micron.2011.09.011
Source: PubMed


Residual microstructures associated with hypervelocity impact craters in 55 vol.% TiB(2)/2024Al composite were investigated by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). TiB(2)-Al interface, TiB(2) particles and Al matrix before and after hypervelocity impact were compared to discuss the effect of hypervelocity impact. A new Al(x)O(1-x) phase with the fcc structure and the crystal parameter of 0.69 nm was formed at TiB(2)-Al interface. Stacking fault with width of 10-20 nm was formed along the (001) plane of TiB(2) particle. Formation of nanograins (≈ 100 nm) was observed within Al matrix, moreover, lamellar S' phase was transformed into lenticular or spherical S phase after hypervelocity impact.

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    ABSTRACT: Interfacial structure in 55%TiB(2)/Al composite before and after high speed impact was investigated in detail. It is found that there is no stacking fault in original TiB(2) particle before fabrication or in TiB(2) particle in composite. However, after the composite is impacted by 1.2mm projectile with the velocity of 2.5km/s, stacking fault forms along the (0001) plane around the edge of TiB(2) particle and grows with a step-like epitaxial way, resulting from the high pressure of shock wave. At the bottom of crater in the target, Al matrix around the TiB(2) particle was molten and then oxidated, which results in the formation of Al(x)O(1-x) (x<1) phase between TiB(2) particle and Al matrix. It is found that TiB(2) particle and Al(x)O(1-x) phase combine well and have no reacted layer at the interface and there exists an orientation between two phases: [Formula: see text] , [Formula: see text] .
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    ABSTRACT: Characteristic of dislocations in TiB2 particles associated with hypervelocity impact craters in 65 vol.% TiB2/Al composite were investigated by transmission electron microscopy (TEM). Two kinds of dislocation networks in as-impacted TiB2 particles were identified. One is hexagonal dislocation networks including 1/3〈1¯ 2 1¯ 0〉, 〈0 0 0 1〉, 1/3〈1¯ 2 1¯ 3〉 type dislocations on {0 0 0 1}, {1 0 1¯ 0}, and {1 2 3¯ 0} planes. Another one is the hexagonal dislocation networks including 1/3〈1 1 2¯ 0〉, 〈0 0 0 1〉, and 1/3〈112¯3〉 type dislocations on {0 0 0 1}, {1 0 1¯ 0}, and {1 1¯ 0 0} planes. Formation of dislocation network should be contributed to the parallel sets of “a” type dislocations (1/3〈1 1 2¯ 0〉 or 1/3〈1¯ 2 1¯ 0〉 type dislocations) reacting with parallel sets of “b” type dislocations (〈0 0 0 1〉 type dislocations) to form “c” type dislocations (1/3〈1 1 2¯ 3〉 or 1/3〈1¯ 2 1¯ 3〉 type dislocations). Moreover, dislocations reaction processes do not result in an energy reduction, and are called quasi-equilibrium configurations. Formation of dislocations may result from high temperature or pressure generated by hypervelocity impact. During the cooling from high temperature and unloading from high pressure, dislocations in TiB2 particles rearranged and transformed to dislocation networks to lower the defect energy.
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