Effects Of Lab6 On The High-Temperature Oxidation Behavior Of Tic+Tibx Reinforced Titanium Matrix Composite Coatings Fabricated By Laser Cladding

The effects of LaB6 addition on the oxidation behavior of TiC+TiBx reinforced titanium matrix composite coatings at the temperature of 600 degrees C were investigated. The results showed that severe oxidation occurred on the Ti-6Al-4V after oxidation at 600 degrees C for 50 h. The oxidation weight gain of the (TiC+TiBx)/Ti coating without LaB6 addition (2.43 mg/cm(2)) was reduced to 49.6% that of the Ti-6Al-4V substrate (4.9 mg/cm(2)). Though (TiC+TiBx)/Ti coatings improved the oxidation resistance for the surface of Ti-6Al-4V substrates, cracks were easily formed between the coarse rod-like TiB2 and the titanium matrix during the high temperature resulting in less high-temperature oxidation protection. When the LaB6 addition gradually increased from 0 wt% to 1.0 wt%, the oxidation weight gain decreased from 2.43 mg/cm(2) to 1.30 mg/cm(2), and the linear rate constant K-p1 decreased from 0.04752 to 0.02703. The oxidation law gradually changed from the linear law to the parabolic law when the LaB6 addition increased to 1.5 wt%, which indicated the oxide layer gradually became dense and protective. The oxidation weight gain decreased from 1.23 mg/cm(2) to 0.87 mg/cm(2) when the LaB6 addition increased from 1.5 wt% to 2.0 wt%, while increased instead when the LaB6 addition increased to 2.5 wt%. An appropriate amount of LaB6 (2.0 wt%) addition significantly improved the oxidation resistance of the coating with the lowest parabolic velocity constant K-p2 = 0.01418 due to the refinement of grain sizes of the coating, especially the refinement of the coarse rod-like TiB2 phase, which decreased the crack forming sensibility and increased the compactness and continuity of the oxidation layer. A small amount of in-situ formatted La2O3 at the grain boundaries acted as a barrier also blocked the ingress of oxygen.