Abstract
Multifunctional materials with more than two good properties are widely required in modern industries. However, some properties are often trade-off with each other by single microstructural designation. For example, nanostructured materials have high strength, but low ductility and thermal stability. Here by means of spark plasma sintering (SPS) of nitrided Ti particles, we synthesized bulk core-shell structured Ti alloys with isolated soft coarse-grained Ti cores and hard Ti-N solid solution shells. The core-shell Ti alloys exhibit a high yield strength (~1.4 GPa) comparable to that of nanostructured states and high thermal stability (over 1100 °C, 0.71 of melting temperature), contributed by the hard Ti-N shells, as well as a good plasticity (fracture plasticity of 12%) due to the soft Ti cores. Our results demonstrate that this core-shell structure offers a design pathway towards an advanced material with enhancing strength-plasticity-thermal stability synergy.
Highlights
In this work, we designed and synthesized bulk core-shell structured Ti-N alloys by mean of spark plasma sintering (SPS) of nitrided Ti particles
The lamellar α-Ti in the inner core was nucleated from β-Ti and preferred to grow along the direction with the lowest strain energy based on the theory of solid phase transformation when cooling from the temperature above α-βtransus point (882 °C)[17]
An electro probe (EP) compositional profile (Fig. 1c) reveals that the outer shell is enriched in N and the N concentration decreases gradually from the shell surface to the core-shell interface
Summary
The present core-shell Ti-N alloys possess much higher room temperature yield strength (>1 GPa) after high annealing temperatures T (>1000 °C) compared with the literature data in which σsof 1 GPa could be obtained only when T is smaller than 300 °C. A core-shell structured bulk Ti-N alloy with soft Ti cores and Ti-N shells was successfully synthesized by means of a unique methodology combining nitriding of Ti powders and subsequent SPS sintering Both phase transformation and SPS technology play key roles in obtaining such a novel architecture. Our results demonstrate that this novel architecture offers a designation pathway towards an advanced material with enhancing strength-plasticity-thermal stability synergy
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