Detrimental Interfacial Reaction And Its Effect On Property Of SiC_p/Al Composite

Fabrication process of high volume fraction SiCp/Al composite by pressureless infiltration could be influenced by several parameters.Unwanted interfacial reaction between silicon carbide(SiC)and molten aluminum alloy become possible during the long-time infiltration process at elevated temperature.Interfacial product aluminum carbide(Al4C3)will give rise to spontaneous degradation of the composite.In the present paper,X-ray diffraction(XRD),scanning electron microscopy(SEM),and transmission electron microscopy(TEM)were used to study the spatial distribution characteristics of the interfacial product(Al4C3),phase transformation and microstructural evolution during degradation,and the effect of AI4C3 on the mechanical property of the SiCp/Al composite.XRD analysis shows that the interfacial product Al4C3 phase can only be identified in sample 1#in the vicinity of the infiltrating interface(aluminum alloy and SiC preform).However,degradation behavior could be observed on the surface of all four samples(1-4#)with the area ratio of the degradation decreasing gradually f-rom 25.00%to 1.20%along the direction of infiltration.The average particle size of SiC extracted from the spontaneous pulverized product is 38.11?m and 48.22?m,which is much smaller than that of the original silicon carbide particle(73.16?m).Meanwhile,there is no corrosion pitting on the surface of the original SiC particles,while the SiC particles extracted from the composite presents a serrated morphology or a number of corrosion pits,revealing severe interfacial reaction in the vicinity of the alloy/preform infiltrating interface.The results show that the degree of the unwanted interfacial reaction decreases with the increase of infiltration depth in high volume fraction SiCp/Al composites.The results of phase constitution of the pulverized product and microstructure of the composite confirm that the hydrolysis of Al4C3 is the key to give rise to severe degradation of SiCp/Al composite.During degradation process new powder with lamellar morphology was observed,comprising alternating lamellae of the unreacted Al4C3 and amorphous Al2O3 displaying a porous structure,and low fraction of crystalline Al(OH)3.The results indicate that the phase transformation of the Al4C3 should be in the sequence:crystalline Al4C3?crystalline AI(OH)3?amorphous Al2O3.In the fracture process of SiCp/Al composites,SiC particles mainly exhibit transgranular fracture,only a small amount presenting debonding phenomenon near the interfacial region.The flexural strength of the composites is in the range of 283MPa and 308MPa,which is lower than that of the SiCp/AI composite without interfacial reaction(flexure strength?390MPa).The SiC/Al interface of the composite is replaced by the SiC/Al4C3/Al interface.During degradation,the hydrolysis of Al4C3 will give rise to the physical separation of SiC particle and aluminum matrix.Then it would be well-reasoned that bulk SiCp/Al composite becomes a pile of powder and loses its perfect physical and mechanical properties.