Phase Transformation of Ti(B,N) into TiB2 and TiN Studied by Atom Probe Tomography

• The phase transformation of supersaturated solid-solution cubic (c) Ti0.57(B0.28N0.72)0.43 thin films into the equilibrium phases TiN and TiB2 has been studied by a combination of X-ray diffraction, transmission electron microscopy, and atom probe tomography. The transformation was found to progress through nucleation and growth, first of TiN and c-TiB0.5N0.5, followed by transformation of the B-rich precipitates to TiB2. The two-step process is interpreted as Guinier-Preston zone formation due to the incoherency between c-TiN and hexagonal TiB2. The nucleation was furthermore observed to be unclassical, with non-equilibrium compositions and extensive interfacial regions in the nuclei.

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