Interlayer structure and properties in synthesized NiAl/Ti coatings on steel substrates

Abstract

Titanium was used as an interlayer to enhance the adhesion between steel substrates and NiAl coatings produced through self-propagating high-temperature synthesis. However, the heat released by the Ni/Al reaction affects the interaction between the coating and interlayer. This study investigates the effect of interlayer thickness on the structure and properties of the interlayer of NiAl coatings. The coating was prepared using a Ni/Al mixture. The interlayer was composed of Ti with thicknesses of 0.31 mm, 0.53 mm, and 0.83 mm. Induction heating was employed to initiate the combustion synthesis of Ni/Al, including heating the Ti layer. The products' microstructures were analyzed using scanning electron microscopy and X-ray diffraction. Vickers microhardness was performed across the coating and interlayer zones. The thermal expansion coefficient of the materials composing the interlayer was calculated. The result shows that NiAl formed in the coating zone, indicating the complete synthesis reaction of the Ni/Al mixture. Ti2Ni–Ti3Al composite and Ti alloy were produced in the lower and higher interlayer thicknesses, respectively. Ni and Al diffuse from the coating to the interlayer, confirming that the Ni/Al and Ti have reacted in the interlayer. The average hardness of Ti2Ni–Ti3Al composite and unreacted Ti is 978.7 ± 7.6 HV and 479.1 ± 7.78 HV, respectively. The hardness distribution in the interlayer with different thicknesses gives evidence of the microstructure transformation. This study shows that a higher interlayer thickness is preferable for coating applications in a high-temperature environment due to the lowest thermal expansion coefficient mismatch to NiAl coatings.

Keywords

• NiAl coatings
• Combustion synthesis
• Titanium
• Interlayer thickness