Study On Micro-mechanical Behavior Of SiC_p/AA2009 Composite By In-situ High Energy X-ray Diffraction

Attribute to the excellent strength,stiffness,fatigue overall performance,low-density and low thermal expansion coefficient,silicon carbide particulate reinforced aluminum matrix composites(SiCp/Al)get great many industrialized countries’ attention.As a typical two-phase material with hard particulate reinforced soft matrix,stress transfer between the two phases and the residual stress within the material have a very significant impact on SiCp/Al composites performance.Therefore,studies on the stresss partition between Al matrix and SiC particles under loading,as well as the effect of pre-fatigue on micromechanics behavior have important significance on theory and practical applications.The micromechanical behavior of SiCp/AA2009 composite was studied by the in-situ high-energy X-ray diffraction technique based on the synchrotron source.The results show that:Al matrix and SiC particles showed significant anisotropy under applied loading.During the whole loading process,Al matrix started the plastic deformation when the loading increases to about 255 MPa.On the contrary,most SiC particles have only elastic deformation thoughtout loading.Load transfer from the A1 to the SiC along the loading direction and transverse direction was expected to occur as the Al/SiC composite during loading.In elastic deformation stage,applied load was transferred from the A1 matrix to SiC particles with lower efficiency,but transfered more efficiency during plastic deformation.In order to study the load partitioning between the two phases further,we used Bailey-Hirsch analytical model to simulate the micromechanic behavior SiCp/AA2009 composites,basing on high-energy X-ray diffraction experiment results.The results show that micromechanic behavior of SiCp/AA2009 composite during uniform plastic deformation process could be simulated by Bailey-Hirsch analytical model,and the simulation results is in good agreement with the experimental values.In uniform plastic deformation process,the stress of SiC particles is much greater than the stress of composite.On the contrary,the stress of A1 matrix is smaller than that of composite.This indicates that stress partition between the two phases significantly.Study on the internal residual stress of SiCp/AA2009 composite which under go the different pre-fatigue by high-energy X-ray diffraction technique,we can got following results that after the R = 0.09 pre-fatigue,compressive strains were found within 0.52 mm ahead of the U notch,and the maximum compressive strain of about-3348με(microstrain,10-6)was measured at the notch for the(311)reflection.Various crystallographic planes have different behaviors,in the region from 0.52 mm to in front of the noch,tensile strains for(111),(220)and(311)were found and became close to zero as the location is far away from the noch,while the(200)plane eventually tend to 1000 με.After R = 0.6 pre-fatigue,compressive strains were found within 0.5 mm ahead of the U notch,and the maximum compressive strain of about-2662 με was measured at the notch for the(111)reflection.In the region from 0.5 mm to in front of the noch,the strains for each plan became cdose to zero as the location is far away from the noch.After R =-0.09 pre-fatigue,tensile strains were found within 0.75 mm ahead of the U notch,and the maximum tensile strain of about 940 με was measured at the 0.25 mm ahead of the notch for the(200)reflection.After above pre-fatigue,there are several common phenomenons in the specimens under the loading:i)Along the crack propagation direction,lattice strains for each plane depend on whether the crack spreaded.Much lesser lattice strains were found in the rigion behind the crack tip,while ahead of the crack tip lattice strains were great larger.This is because that a part of stress relaxed after crack propagation,but ahead of the crack tip stress happened to concentrat.(ii)In the area parallel to the crack tip,lattice strains for each plane were much larger,as the location is far away from the noch.This is due to the area of the crack tip contains not only the crack tip,but also have some propagated crack,those cracks result in stress relaxation.(iii)In the area ahead of the crack tip,lattice strains for each plane reduced slightly,as the location is far away from the noch.That is because strains concentrate in certain areas ahead of the crack tip,in those areas,the farther away from the crack tip,the lower stresses are.