Fig. 1. SEM morphologies of the surfaces and cross-sections of Al–Si/Al2O3 coatings at different laser power (a: surface, 600 W; b: cross-section, 600 W; c: surface, 700 W; d: cross-section, 700 W; e: surface, 800 W; f: cross-section, 800 W).Figure optionsDownload full-size imageDownload high-quality image (1403 K)Download as PowerPoint slide
Fig. 2 shows the XRD patterns (with a copper sealed tube source，RIGAKU D/MAX 2500 V/PC, Japan) of the Al–Si/Al2O3 coatings by laser PSI-6206 hybrid spraying at different laser power. It showed that the surface of Al–Si/Al2O3 coatings sprayed by laser plasma hybrid spraying was composed of γ-Al2O3 and α-Al2O3. With the increasing of laser power, the content of phase γ-Al2O3 gradually decreased, while the content of phase α-Al2O3 gradually increased. Because phase γ-Al2O3 has lower nucleation energy than α-Al2O3, molten Al2O3 forms γ-Al2O3 earlier than α-Al2O3 during the process of phase cooling. Since phase γ-Al2O3 is not stable, it will transform into stable phase α-Al2O3 soon. Therefore, during the process of laser plasma hybrid spraying, with the increasing of laser power, the thermal effect of the coatings would also increase, as well as phase α-Al2O3 would transform into stable phase α-Al2O3 more fully.