Microstructure and Properties of Ti–Al Coating on Titanium Alloy Surface Assisted by Electromagnetic Field

The effect of an alternating electromagnetic field on the microstructure and properties of the Ti-Al coating on the titanium alloy surface is studied. The Ti-Al coating is prepared on the surface of titanium alloy by using an alternative electromagnetic field assisted by high temperature thermal diffusion. The preparation method is simple and easy to operate. The microstructure and element distribution of the coating under different magnetic field intensities are analyzed. The mechanism of improving the comprehensive properties of coatings by alternative electromagnetic fields with different intensities is discussed. The test results show that the outer surface of TA₁₅ titanium alloy diffused at 850 °C without magnetic field is not smooth, the quality is poor, and internal structure cracks appear. No obvious cracks are found in the coating microstructure of 850 °C diffused by a magnetic field with 10 A current intensity, but there are still some holes. A large number of holes and cracks appear in the coating microstructure with 850 °C diffusion under the magnetic field with 15 A current intensity; mostly longitudinal cracks are perpendicular to the interface and penetrating through the interface, which may be caused by the thermal effect of the magnetic field. The coating diffused under the magnetic field of 20 A current intensity has good overall quality, good bonding with the substrate, relatively flat interface, dense, uniform, and fine structure, and no obvious cracks and holes are found. The main phases are TiAl, Ti₃Al and elemental Al, and Ti₃Al has obvious texture, with an average equivalent diameter of 3.2 μm. TiAl has no obvious texture and has an average equivalent diameter of 2.2 μm. The electromagnetic stirring effect makes the strengthening phase in the coating more evenly distributed and reduces component segregation. With the increase of magnetic field intensity, the stress concentration and cracking sensitivity decrease and the migration distance of Ti atoms from the matrix to the coating direction increases. The interfacial hardness of the coating extends outward at first and then decreases, and the maximum hardness reaches 468.2 HV_0.2. The cracking sensitivity of the coating is reduced by the magnetic field, and the microstructure and properties of the coating are improved.