A significant precipitation-hardening response has been observed in rapidly quenched Al-6Ti-1.5Ni (wt.%) alloy aged isothermally in the temperature range 300-500°C, and the underlying precipitate microstructures characterised using transmission electron microscopy (TEM). Primary intermetallic dispersoids of cubic ternary phase in as-quenched alloy decompose rapidly during heat treatment and are replaced by uniform precipitation of fine-scale, coherent particles of a metastable L12 phase. These metastable precipitates evolve into a transitional, three-dimensional cross-like morphology and eventually into nano-scale ( < 100 nm) spheroidal particles of equilibrium D022 phase δ-Al3(Ti,Ni). The changes in form are accompanied by the development of a series of one-dimensional long period superlattices, culminating in formation of equilibrium b.c.t. phase. Maximum hardness (175 kg mm-2), which is associated with a dispersion of coherent intermediate precipitates and a minor fraction of δ-Al3(Ti,Ni), is comparable with that of conventional high strength precipitation-hardening alloys (150-200 VHN). The temperatures of this ageing response, together with the thermal stability of the precipitate phase(s), suggest that low density, rapidly quenched Al-Ti-Ni alloys, with weight ratio Ti:Ni in the range 3:1-4:1, may have potential for applications involving elevated temperatures (150-200°C), where the creep resistance of conventional precipitation-hardened alloys declines rapidly.
|Number of pages||11|
|Journal||Materials Science and Engineering A: Structural Materials: Properties, Microstructure and Processing|
|Publication status||Published - 30 Dec 1996|
- Precipitation-hardened alloys
- Transmission electron microscopy