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TiO2 addition induced grain refinement and hardening of laser-clad FeCrAl coating on T91 steel.

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Title: TiO2 addition induced grain refinement and hardening of laser-clad FeCrAl coating on T91 steel.
Authors: Dong, Haiyu1 (AUTHOR), Chai, Linjiang1 (AUTHOR) chailinjiang@cqut.edu.cn, Wang, Chuanmei1 (AUTHOR), Liu, Hongliang1 (AUTHOR), Hu, Chaodan1 (AUTHOR), Zhao, Xiaotong1 (AUTHOR), Yang, Yimeng1 (AUTHOR), Zhang, Min2 (AUTHOR)
Source: Materials Characterization. Jul2025, Vol. 225, pN.PAG-N.PAG. 1p.
Subjects: Aluminum oxide, Titanium dioxide, Martensitic transformations, Laser heating, Hardness testing
Abstract: To overcome the shortcoming of FeCrAl coatings liable to form coarse columnar grains, this work explores the influence of TiO₂ addition on grain structure and hardness characteristics of laser-clad FeCrAl coatings on T91 steel. Results show that the cross-sections of the FeCrAl and FeCrAl/TiO 2 coating samples consist of three regions: cladding zone (CZ), heat-affected zone (HAZ) and substrate, with distinct microstructural features. The CZ of the FeCrAl coating sample is composed of coarse columnar grains (average size 35.5 ± 0.7 μm), while the FeCrAl/TiO 2 coating consists of uniform equiaxed grains with an much smaller average size of 7.8 ± 0.4 μm. Analysis indicates that the TiO 2 particles added into the initial powders undergo decomposition during laser heating and re-precipitate as Ti-rich nano-particles during subsequent cooling, which can act as heterogeneous nucleation sites and promote the formation of equiaxed grains. The HAZs of both the laser-clad samples are composed of fine martensitic laths, with specific orientation relationships followed during the martensitic transformation, resulting in distinct misorientation characteristics. Hardness tests show that the FeCrAl and FeCrAl/TiO 2 coatings have average hardnesses of 264.1 ± 3.6 HV and 327.6 ± 10.4 HV, respectively, both much greater than the substrate (206.4 ± 2.9 HV). Quantitative analysis of microstructural characteristics indicates that the greater hardness of the FeCrAl/TiO 2 coating can be ascribed to combined grain-refinement strengthening, second-phase strengthening and solid-solution strengthening. • FeCrAl and FeCrAl/TiO 2 coatings were fabricated on T91 steel using powder-feeding laser cladding. • FeCrAl coating predominantly comprises coarse columnar grains with dispersed Al 2 O 3 and AlN nano-particles. • FeCrAl/TiO 2 coating mainly consists of fine and uniform equiaxed grains with dispersed Al 2 O 3 and TiN nano-particles. • FeCrAl/TiO 2 coating possesses higher much hardness than FeCrAl coating and substrate. • TiO 2 addition induced hardening can be jointly ascribed to grain-refinement, solid-solution, and second-phase strengthening. [ABSTRACT FROM AUTHOR]
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Abstract:To overcome the shortcoming of FeCrAl coatings liable to form coarse columnar grains, this work explores the influence of TiO₂ addition on grain structure and hardness characteristics of laser-clad FeCrAl coatings on T91 steel. Results show that the cross-sections of the FeCrAl and FeCrAl/TiO 2 coating samples consist of three regions: cladding zone (CZ), heat-affected zone (HAZ) and substrate, with distinct microstructural features. The CZ of the FeCrAl coating sample is composed of coarse columnar grains (average size 35.5 ± 0.7 μm), while the FeCrAl/TiO 2 coating consists of uniform equiaxed grains with an much smaller average size of 7.8 ± 0.4 μm. Analysis indicates that the TiO 2 particles added into the initial powders undergo decomposition during laser heating and re-precipitate as Ti-rich nano-particles during subsequent cooling, which can act as heterogeneous nucleation sites and promote the formation of equiaxed grains. The HAZs of both the laser-clad samples are composed of fine martensitic laths, with specific orientation relationships followed during the martensitic transformation, resulting in distinct misorientation characteristics. Hardness tests show that the FeCrAl and FeCrAl/TiO 2 coatings have average hardnesses of 264.1 ± 3.6 HV and 327.6 ± 10.4 HV, respectively, both much greater than the substrate (206.4 ± 2.9 HV). Quantitative analysis of microstructural characteristics indicates that the greater hardness of the FeCrAl/TiO 2 coating can be ascribed to combined grain-refinement strengthening, second-phase strengthening and solid-solution strengthening. • FeCrAl and FeCrAl/TiO 2 coatings were fabricated on T91 steel using powder-feeding laser cladding. • FeCrAl coating predominantly comprises coarse columnar grains with dispersed Al 2 O 3 and AlN nano-particles. • FeCrAl/TiO 2 coating mainly consists of fine and uniform equiaxed grains with dispersed Al 2 O 3 and TiN nano-particles. • FeCrAl/TiO 2 coating possesses higher much hardness than FeCrAl coating and substrate. • TiO 2 addition induced hardening can be jointly ascribed to grain-refinement, solid-solution, and second-phase strengthening. [ABSTRACT FROM AUTHOR]
ISSN:10445803
DOI:10.1016/j.matchar.2025.115194