Aging and thermal behavior of a PVA/Al microspheres slurry for aluminizing purposes

The aging and thermal behavior of an environmentally friendly slurry composed of water, polyvinylalcohol (PVA) and aluminum microspheres for aluminizing superalloy substrates is studied in this work. Different ratios of the slurry components were characterized at room temperature by Fourier-Transformed Infrared Spectroscopy (FTIR), while for the intermediate (<550 °C) and high (<1100 °C) temperatures differential scanning calorimetry (DSC) and coupled thermo-gravimetric analysis (TGA)/differential thermal analysis (DTA) techniques were respectively employed. Aging the slurry with time at room temperature confirmed the stability of the solutions up to five days (FTIR). DSC and coupled TGA–DTA allowed to characterize the specific temperature of the organic binder (melting at 220 °C and PVA decomposition from 275 °C), as well as the deshydroxylation (460 °C), melting (660 °C) and oxidation reactions associated with the metallic Al in the slurry. Bonding of Al to PVA was confirmed from the broad temperature intervals at which PVA decomposed when compared to pure PVA. The energetic evolutions with temperature for aged and unaged slurries also seemed to be similar regardless of the Al particle size. It is therefore concluded that the slurries remained very stable with time and their evolution with temperature could allow successful application to aluminize superalloy substrates.