| SiC particle reinforced aluminum matrix composites have low production cost,easy industrial production,good mechanical properties,are widely used in aerospace,electronic packaging and automobile manufacturing.In the high temperature environment,the material will creep,so in recent years,researchers have conducted a lot of research on the creep behavior of SiC/Al composites.However,due to limitations in observation,there are many studies on tensile creep,and only two-dimensional local observations can be made on creep damage.Nowadays,technology of synchrotron radiation tomography is developing very rapidly.It can be used to observe and quantitatively analyze the internal structure of the material in three dimensions without destroying the sample.This method break the limitations of traditional tissue morphology observation.In this paper,the matrix material and SiC/Al composites were prepared by powder metallurgy method,and then the compression creep experiments under different temperatures and different stress were carried out and the compression creep mechanism was analyzed.Then the three-dimensional observation of creep voids distribution and evolution of materials under compression creep conditions was carried out by synchrotron radiation tomography.In this paper,2219 Al,5vol.%SiC/2219 Al and 15 vol.%SiC/2219 Al materials were prepared by hot pressing at 853 K for 1 hour under pressure of 23 MPa.It can be found that SiC particles were well distributed and no obvious defects were found in the hot-pressed compact.Hardness,yield strength,and compressive strength increased with the increasing SiC content.Vertical section and cross sectional analysis of the specimens for compression creep showed that more voids existing at the junction of SiC and Al in the cross-section than voids in the vertical section.It was found from the compression creep behavior of three prepared materials prepared that the steady-state creep rate increased with the increasing of temperature and stress,decreased with the increasing of SiC content.The apparent activation energy of the composite is higher than that of the matrix 2219 Al alloy,and decreased with the increasing of stress,but the creep activation energy of all materials is greater than the self-diffusion activation energy of pure Al.By using the threshold stress analysis,the true creep stress index of the three materials is about 5,the threshold stress decreased with the increasing of temperature,and increased with the increasing of SiC content.After considering the influence of temperature,the creep data of all materials can be normalized,indicating that the compression creep behavior is controlled by the self-diffusion of the Al matrix at high temperature and follows the law of dislocation climb creep mechanism.Different experiments for Synchrotron radiation tomography of 15 vol.%SiC/2219 Al compression creep specimens at 523 K and 89 MPa showed that the closer for areas to the middle of the sample,the more damage they had.As the volume of the voids increased the number of voids correspondingly decreased sharply.It was found that the increases of strain were often accompanied by the formation of a large number of tiny voids,and larger voids were often formed by the growth of the original voids or the combination of adjacent voids.During the whole creep process,the voids tended to grow in a direction perpendicular to the applied stress,and the voids tended to occur at the junction of the SiC and 2219 Al matrix,and small cavities gathered together to form a larger wedge void due to the applied load.Since the voids tended to grow in a direction of perpendicular to the applied stress,the local stress state around the voids also gradually increased,resulting in a loss of effective cross-sectional area growing faster and larger than the vertical section. |
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