Study On Fabrication And Corrosion-wear Resistance In Molten Aluminum Of TiAl₃/Ti₃AlC₂/Al₂O₃Composite

In the field of metallurgical, chemical, aerospace and automotive, corrosion-weardamage to the key components used in high temperature corrosive environment which underdynamic loading often results in tremendous economic losses. Many researches have focusedon the accelerated degradation of materials in corrosive gas, solution or particle erosionconditions. However, the corrosion-wear behavior of materials in high temperature metal melthas been rarely reported.The aim of the present investigation is to mainly understand the corrosion-wear damagebehavior of materials in the highly corrosive molten aluminum. According to the target, anin-situ Ti₃AlC₂and Al₂O₃cooperatively reinforced TiAl₃composite was synthesized from amechanically milled powder mixture by using an in situ reaction/hot pressing method. Thecorrosion-wear behaviors of TiAl₃/Ti₃AlC₂/Al₂O₃composite and H13tool steel in a moltenaluminum at750oC were investigated using a self-developed high temperaturecorrosion-wear test apparatus. The corrosion-wear mechanisms of these two materials werecompared and discussed. The main results and innovation are as follows:1. Based on the detailed analysis, the synthesis mechanism of TiAl₃/Ti₃AlC₂/Al₂O₃composite is proposed as follows: after the melting of Al, Al and TiO₂reacted immediately toform TiAl₃and the transitional phase TiO. Subsequently, Al₂O₃precipitated on the grainboundary of TiAl₃with the increasing of temperature. When reached the high temperaturesection, TiAl₃and TiC reacted to form Ti₃AlC₂. The total reaction is defined as:3TiO₂+11Al+2TiCâ†'2TiAl₃+Ti₃AlC₂+2Al₂O₃Due to the large amount of heat released in a very short time by the exothermic reaction, thesample internally generated transient liquid phase, which leading to instantaneous particlerearrangement and melt infiltration and resulting in a transient liquid phase dense. A fullydense Ti₃AlC₂/Al₂O₃/TiAl₃composite with homogeneous and fine microstructure wasfabricated from50h-milled Al-TiO₂-TiC powder mixture at1250oC and50MPa for10min.2. Due to the introduction of Ti₃AlC₂phase and the interpenetrating structure of TiAl₃matrix and Al₂O₃reinforcement, the composite achieved three-point bending strength,fracture toughness and compressive strength of⁶58.9MPa,⁷.9MPa/m1/2and¹742.0MPa,respectively. And the high compressive strength could be maintained of604.1MPa even at1000oC. The toughening of composite are primarily attributed to pull-out of the Ti₃AlC₂andAl₂O₃particles, crack deflection and crack bridging by the Ti₃AlC₂phase and as well as the deformation and delamination of Ti₃AlC₂particles.3. The investigation of50h cyclic oxidation behavior of composite at elevatedtemperature showed that the scales on composite are only Al₂O₃at700⁹00oC, while Al₂O₃and rutile TiO₂at1000oC. Though the oxidation scales are not dense, composite still exhibitsexcellent cyclic oxidation resistance in the temperature range of700¹000oC.4. A typical feature of materials corroded in molten aluminum is to generatedintemetallic compound layer between the substrate and molten aluminum. H13tool steel is atypical representative of these materials, so the corrosion-wear behavior of H13tool steel isinvestigated detailed. The results show that the corrosion-wear resistance of materials isdepended on the formation rate and characterization of intermetallic compound layer, as wellas the combination between the substrate and intermetallic zone. The corrosion-wear lossesare much higher than the simple sum of materials losses under plain corrosion and plain wear.The corrosion-wear volume loss of H13tool steel is about133⁴07mm3/h, and the synergyratio of corrosion-wear is not less than93.9%under the explored condition.5. Compared with H13tool steel, the corrosion-wear resistance of TiAl₃/Ti₃AlC₂/Al₂O₃composite has improved significantly. The corrosion-wear volume loss of composite is only0.84⁷.53mm3/h, which is dozens or even hundreds times less than that of H13. Under thecondition of low load or low velocity, the composite even exhibits negative synergy, and thehighest synergy ratio of corrosion-wear is47.5%. This is partly due to no intermetalliccompound formed in the interface, but just a little Ti dissolved into the molten aluminumwhen the composite corroded in Al melt. On the other hand, the interpenetrating structure ofTiAl₃matrix and Al₂O₃reinforcement improve the wear resistance of composite in moltenaluminum.