Temperature dependent elastic modulus of HVOF sprayed Ni-5%Al on 304 stainless steel using nondestructive laser ultrasound technique

In this study, NiAl coating was produced on 304 stainless steel material using High velocity oxygen-fuel (HVOF) spray technique. The influence of oxygen flowrate on the microstructure, porosity and hardness of the coating was investigated. Further, the mechanical properties of HVOF sprayed samples were determined at various temperatures using optical, laser excitation with interferometer reception, completely non-contact and nondestructive based laser ultrasound technique. The outcomes of this study indicate that the microstructure and properties of the coatings are sensitive to the oxygen flowrate. A coating with highest hardness and less porosity was achieved while increasing the oxygen content. Higher Young's modulus was observed at 20 °C and gradually decreases with the rise in temperature. The behavior of Young's modulus and Poisson's ratio at elevated temperature indicates that originate from the existence of a gas flow rate in the NiAl coating, leading to reduced flexural strength with increased temperature. Both inversion and experimentation result shows a good agreement in elastic properties of HVOF coated sample. The proposed laser ultrasound technique is valid for remote, noncontact and nondestructive characterization of the Young's modulus and Poisson's ratio of the coatings in elevated temperature environments.