Effects of boronizing treatment on microstructural development and mechanical properties of additively manufactured TC4 titanium alloys

Microstructure and mechanical properties of additively manufactured TC4 alloys were investigated, following boronizing treatment. The treatment process was carried out at temperatures ranging from 950 to 1050 °C and held for 8–15 h. The microstructural features of fabricated boride layers were examined by optical microscopy. The phase compositions of the boride layers were analyzed by X-ray diffraction. The hardness profile through the boride layers was also determined. The results showed that the boride layer of additively manufactured TC4 had a thickness of 51 μm and was composed of an outer TiB2 layer on the top of TiB layer; TiB whiskers wedged into the matrix, forming a strong bond between the boride layer and substrate. The diffusion activation energy was determined to be 80.9 kJ/mol. The matrix was found to transfer from needlelike α′ martensite phase to α + β biphasic compounds. The newly formed boride layer can reach 1680 HV in hardness, thus imparting a strong protection to 3D-printed part.