Deposits rich in alkali-metal chlorides and sulfates can cause severe high-temperature degradation of heat-transfer components in biomass-fired boilers. In this study, Ti–Al–C coatings were produced on grade TA2 commercially pure titanium substrates by laser cladding using elemental Ti, Al, and C powders. The optimized processing parameters were a laser power of 1.2 kW, a scanning speed of 500 mm/min, a powder feed rate of 3.22 g/min, and an overlap ratio of 40%. The as-clad coatings were subsequently vacuum-annealed at 1200 and 1300 °C for 2 h. Their phase constitution, microstructure, microhardness, cyclic oxidation behavior, and deposit-induced corrosion behavior were evaluated.
The as-clad coating was dominated by Ti₃Al, with TiAl and TiC as secondary phases. Electron diffraction patterns obtained from selected interfacial regions were consistent with the local presence of antiperovskite Ti₃AlC adjacent to Ti₃Al. Although this observation indicated the local coexistence of Ti₃AlC and Ti₃Al, bulk X-ray diffraction showed that annealing increased the fraction of the Ti₂AlC MAX phase at the expense of the Ti–Al intermetallic phases. The maximum microhardness increased from 448 HV_0.1 in the as-clad condition to 748 HV_0.1 after annealing at 1300 °C.
During cyclic oxidation for 240 h, the as-clad coating exhibited mass gains of 0.14 and 1.59 mg/cm² at 600 and 700 °C, respectively. At 800 °C, its mass gain reached 6.63 mg/cm² after 168 h and then decreased sharply because of oxide-scale spallation. In contrast, the coatings annealed at 1200 and 1300 °C showed no abrupt mass loss at 800 °C and exhibited final mass gains of 2.74 and 1.90 mg/cm², respectively.
Deposit-induced corrosion tests were conducted at 600 °C for 168 h in the presence of KCl–Na₂SO₄ deposits and an atmosphere containing SO₂, O₂, and H₂O. TP347H boiler steel, tested as a reference material, underwent extensive scale spallation and showed a final mass loss of 28.69 mg/cm². In contrast, the Ti–Al–C coatings did not exhibit catastrophic spallation and retained comparatively stable corrosion-product scales. Cross-sectional analyses revealed Ti-rich outer oxides and Al-rich inner reaction layers. Annealing promoted Al transport toward the corrosion front and facilitated the development of a more continuous Al₂O₃-rich layer, thereby improving scale integrity. These findings demonstrate that post-cladding annealing regulates phase evolution and protective-scale formation in Ti–Al–C coatings, providing an effective approach to improving their high-temperature surface-protection performance.
 

laser cladding; Ti–Al–C coating; Ti2AlC MAX phase; cyclic oxidation; deposit-induced corrosion