Study On The Toughness Of SiC/Al Interface Using Four-point Bending Test

Particle-reinforced metal matrix composites(PRMMCs)have excellent specific strength,specific stiffness,thermal conductivity,fatigue and heat resistant,and etc.,making them important engineering materials that are widely used in aerospace,automotive,electronic and military applications.The structure and properties of the reinforcement/matrix interface significantly affect the bulk properties of PRMMCs.However,up to date,there is not an effective method to experimentally measure the interface bonding properties of PRMMCs.In addition,although it is known that different particle surface treatments would lead to different interfacial structures and properties,in what particular ways and extents that the interfacial structures and properties are affected by particle surface treatment is still to be revealed.In this study,to simplify the problem and avoid the complexities associated with the shape and crystallinity of the particle reinforcement,we fabricated SiC/Al bilayer model composite with 4H single crystal SiC wafers that have the same hexagonal crystal structure as the SiCp reinforcement,and pure aluminum.To achieve different interfacial structures and properties,different SiC surface treatments(high-temperature oxidation and HF pickling)were used,and four-point bending tests were carried out to directly and quantitatively measure the SiC/Al interfacial toughness.Combined with site-specific transmission electron microscopic(TEM)analysis,the correlation between the interface structure and the interfacial properties was studied.High temperature oxidation and pickling processes were found to improve the SiC surface morphology and structure,and changed interface structures of the SiC-Al composite.After three SiC surface treatments,Al near the interface with high dislocation density was mainly single crystal,and the thickness of SiC/Al interfacial layer has a significant difference:interfacial layer thickness after high-temperature oxidation>interfacial layer thickness of the untreated state>interfacial layer thickness after pickling treatment.Using TEM and electron diffraction spectroscopic(EDS)analysis,the interfacial layer was determined to be amorphous Al2O3.Four-point bending test can effectively and directly measure the interfacial toughness.Designing a reasonable sample dimension is critical for such a characterization.After careful consideration and experiments,the sample was chosen to have a dimension of 30mm×3mm×1mm,where the crack propagated along the interface in the bending test.It was then found that SiC surface treatments indeed improved the interface toughness:high-temperature oxidation treatment gives the highest toughness(3.92±0.11 J/m2),while the initial state resulted in the lowest toughness(0.99±0.11J/m2),and the interfacial toughness of pickling treatment was found to be 1.41 ±0.20J/2.These results actually showed the same trend with the mechanical performance of bulk SiCp-Al composites using the same SiCp surface treatments.The analysis of the interfacial fracture morphology demonstrated that the fracture surface(the SiC side)was clean in the initial state and HF pickled samples,while the fracture surface was rough with many residuals in samples treated by high-temperature oxidation,which was likely caused by crack propagation along Al/Al2O3 side of the interface in four-point bending test.In summary,the interfacial toughness characterized by the four-point bending method can be used to evaluate the mechanical performance of the SiCp-Al MMCs.Therefore,it may provide a novel and effective method for systematic study on the mechanical properties and the interface structures,which may lead to improved design and modeling of PRMMCs.