Growth kinetics of infiltration layer on TC21 alloy surface by solid powder-pack boriding and aluminizing

Abstract

Surface modification of titanium alloys via boriding and aluminizing remains crucial for enhancing mechanical properties. However, the intricate growth mechanisms governing layer formation are incompletely understood. This study systematically investigates the microstructural evolution and diffusion dynamics of borided and aluminized layers on TC21 titanium alloy. Boriding and aluminizing treatments were conducted at various temperatures and holding times, and the samples were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron probe microanalysis (EPMA). The borided layer consists of an outer TiB₂ layer and underlying TiB whiskers, while the aluminized layer comprises an Al₃Ti compound layer and an aluminum diffusion layer. The layer thicknesses were measured, and the growth kinetics were modeled using the diffusion equation $d^2=\mathrm{Dt}$. The diffusion activation energies were determined as 216.40 kJ/mol for [B] atoms in the borided layer and 348.63 kJ/mol for [Al] atoms in the aluminized layer. The growth processes of both layers were systematically analyzed and discussed based on the experimental observations.