Microstructural and Nano‐Mechanical Characterisation of Multicomponent Composites Nanocrystalline Matrix

Abstract

Multicomponent, Ti‐based, in situ formed composites with a nanocrystalline matrix are a promising new type of material for structural applications. The materials exhibit an excellent combination of mechanical properties resulting from the composite microstructure. This paper contains a detailed introduction to such materials and a review of the most recent developments in the specific areas of microstructural and nano‐mechanical characterization.

Enhanced microhardness in nanocomposite Ti60Cu14Ni12Sn4Ta10 processed by high pressure torsion

“…The dendrites are enriched in Ta and Sn and poor in Cu and Ni compared to the nominal composition. Taking into consideration that Ta and Sn are b-stabilizers [16], the dendrites are presumably a bTi solid solution; this is in agreement with previous results [2,4,17,18]. The analysis of the matrix reveals that, in fact, it is composed of a nanoscale eutectic which appears to have varying lamellae spacing, probably because of the different orientation of the eutectic colonies.…”

“…He et al [5] reported nanometer-sized grains (2-5 nm) inside the eutectic, which is supported by the current XRD line broadening, Table 1. The formation of a metastable equilibrium between b-Ti and NiTi was explained by Woodcock et al [17,18]. They suggested that the rapid cooling and the addition of Ta and Sn kinetically exclude the formation of the equilibrium CuTi 2 phase.…”

Severe plastic deformation of a Ti-based nanocomposite alloy studied by nanoindentation

“…EDX results show that the dendrites are enriched in Nb and Sn, while the matrix is enriched in Cu and Ni (see Table 1). Taking into account that Nb and Sn are b-stabilizers [19], the dendrites are assumed to be a b-Ti solid solution, in agreement with the XRD patterns (shown later) and previous results reported in the literature [2,4,20,21]. The C and D regions are enriched in Cu and Ni and presumably are intermetallic phases precipitated during cooling of the melt, after the formation of the dendrites.…”

“…The high cooling rate and the Cu content in the NiTi eutectic phases favour the formation of the NiTi martensitic product phases (orthogonal and monoclinic) from the austenitic parent phase (cubic) [25,26]. Woodcock et al suggested that the tetragonal CuTi 2 phase is the equilibrium phase in the rapidly quenched Ti 60 Cu 14 Ni 12 Sn 6 Ta 10 alloy, while the formation of the metastable b-TieNiTi eutectic is favoured by both the high cooling rate and the addition of Nb and Sn which kinetically exclude the formation of the equilibrium phase [20,21]. Our results indicate that, apart from the formation of the metastable eutectic, the tetragonal CuTi compound, which is also metastable, precipitates at the regions surrounding the dendrites and the eutectic counterparts.…”