Ultrasonic Coupling Processing: a Novel Technique for Fabrication of Metal Matrix Surface Composites
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METAL matrix surface composites (MMSCs) integrate high hardness and a high elastic modulus, which also have excellent thermal stability of reinforced phase with high toughness and plasticity and excellent heat conductivity of metallic matrix. The MMSCs make the matrix have strong toughness, while at the same time making the surface layer have high wear resistance and corrosion resistance and improving further the service performance of the matrix. The MMSCs are a new type of functional composites.[1] At present, particle-reinforced metallic matrix surface composites are mainly prepared by centrifugal casting, electromagnetic separation, laser cladding, plasma spraying processing, friction stir processing, etc.[2–6] However, due to the high density and high specific surface energy of reinforced phase or particles, and the bad wettability existing between the reinforced phase and the metallic melt, reinforced phase particles are apt to sedimentation or conglomeration, and their strengthening effect on the matrix is weakened. Because a high intensity ultrasonic wave can accelerate the diffusion and mass-transfer behavior of metallic melt due to the cavitation effect and acoustic streaming,[7] ultrasonic treatment is used in the purifying, degassing, and refinement of metallic melt.[8–10] Meanwhile, an ultrasonic can improve the wettability between reinforced phase and metallic melt, disperse particles homogeneously, and improve the interfacial compatibility between the reinforced phase and matrix.[11] Y.L. LI and F.R. CAO, Associate Professors, and Y.B CHEN, Assistant Professor, are with the School of Materials and Metallurgy, Northeastern University, Shenyang 110004, People’s Republic of China. Contact e-mail: [email protected] H.K. FENG, Ph.D. Student, is with the School of Materials Science and Engineering, Jilin University, Changchun 130025, People’s Republic of China. Manuscript submitted April 25, 2008. Article published online July 29, 2009 2178—VOLUME 40A, SEPTEMBER 2009
Therefore, ultrasonic can be used to prepare the composites.[11,12] In this study, a ‘‘horn crucible’’ used to perform the ultrasonic treatment of metallic melt is a part of the ultrasonic horn. Further, it can achieve strong soundenergy coupling between ultrasonic and metallic melt. At the same time, ultrasonic exerts sound radiation force on reinforced particles in metallic melt. When the particles overcome Stokes force, gravity, and buoyancy, they will move and stabilize finally at a certain interface of the melt, taking on graded distribution. Therefore, particle-reinforced surface composites can be prepared under ultrasonic coupling processing (UCP). In this work, strong UCP was applied to the metallic melt to obtain the pressure fluctuation and thermal stirring effect during ultrasonic processing, which can disperse and refine the TiAl3 particle phase. Then, the intensity of sound was reduced and the stable stationary wave field was formed to drive the TiAl3 particles to move. The metallic melt solidified after TiAl3 clustering on the su
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