Investigation on the microstructure and creep behavior of laser remelted thermal barrier coating
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Laser surface modification of the thermal barrier coating was investigated with the aim of increasing creep resistance. Yttria-stabilized-zirconia (YSZ) with a CoNiCrAlY bond coat was deposited by air plasma spraying on equiaxed Ti–6Al–4V substrates. Analysis was carried out comparing uncoated samples with as-sprayed and laser remelted ones. A cross section and detailed characterization of coating surface was carried out by scanning electron microscopy and X-ray diffraction techniques. Mechanical properties in terms of microhardness and creep resistance were evaluated. Constant load creep tests were conducted at stress levels of 125 to 319 MPa at 500 °C and 600 °C. A dense ceramic layer of thickness about 40 μm was formed by laser remelted treatment and its microhardness surface was higher than the other layers. As-sprayed YSZ had higher creep resistance than other samples. Analysis of creep behavior showed that the steady-state creep rate of laser remelted samples had about 42% reduction in 600 °C condition, evidencing a higher creep resistance than uncoated material. SEM images revealed a ductile fracture with presence of equiaxed dimples.