Crystallization kinetics of plasma sprayed basalt coatings

Crystallization kinetics concerning the conversion of a glass coating layer made from natural basalt volcanic rock to glass-ceramic have been investigated. The basalt-based coatings were deposited on AISI 1040 steel substrates pre-coated with Ni–5 wt.% Al using atmospheric plasma spraying system. Glass coatings were heat treated at 800, 900 and 1000 °C for 1–4 h in order to obtain glass-ceramic coating layer. DSC and XRD analysis revealed the crystallization of augite [(CaFeMg)SiO3]. Heat treatment is effective for the amorphous phase to convert into crystalline in atmospheric plasma sprayed basalt coating depending on heat treatment time and temperature. Optical microscopy was used for metallographic examinations. The kinetics of the augite was studied by applying DSC measurements carried out different heating rates and the activation energies of crystallization and viscous flow were measured as 324 and 364 kJ mol−1, respectively. Avrami exponents for crystallization were 1.85–2.74 which indicates that internal crystallization dominates the overall crystallization.