Processing of CuAlMn Shape Memory Foams with Open Spherical Pores by Silica-Gel Beads Infiltration Method
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TRODUCTION
HIGH damping is a basic character of porous materials since the deformation of pores and the movement of dislocations around the pores can help absorb much more vibration, sound, and other types of energy than can the corresponding bulk materials.[1] Metallic shape memory foams (SMFs) exhibit a more promising damping property compared with plain metal foams since the shape memory alloy (SMA) matrix can provide an additional damping relating to its particular thermoelastic martensitic transformation.[2] Copper-based SMFs are especially attractive as structural applications in civil engineering or the automotive industry due to their low cost and relatively high functional properties.[3] Imperfections of pore morphology such as irregular pore shape, nonuniform distribution of pores, and variations in pore size bring about a negative effect on the properties of solid foams.[4,5] Nonuniform pore morphology, especially, will cause a high scattering of mechanical properties in solid foams and a drastic drop in energy absorption efficiency.[6] Aluminum foams with spherical pores were reported to have higher compressive strength than were those with strip-shape pores.[7] It was also reported that only when the polyhedral pores were regular and had an aspect ratio close to unity could their foams’ mechanical properties rival those with spherical pores.[8] So it is crucial to gain uniformly HUA LI, Ph.D. Student, and BIN YUAN and YAN GAO, Professors, are with the School of Materials Science and Engineering, South China University of Technology, Tianhe District, Guangzhou 510641, P.R. China. Contact e-mail: [email protected] Manuscript submitted March 4, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
distributed pores with regular and equiaxed shape, like spheres or regular polyhedrons, especially for shape memory foams whose performance depends mainly on the functional properties of the matrix. Various methods manufacturing Cu-based SMFs have been developed in recent decades.[9] However, not all methods can control the pore morphology effectively. The molten metal infiltration process has been reported to have a good control of pore morphology,[10] and amorphous SiO2 beads, because of their spherical shape, low cost, stable chemical property, and high melting temperature, are a better choice as space holders for producing Cu-based SMFs[11] compared with NaCl particles,[12] fluoride,[13] and NaAlO2 powders,[14] which either have too low of a melting point or an irregular shape. Recently, amorphous SiO2 beads were used as space holders by Castrodeza[15] to synthesize porous CuZnAl SMAs with an almost spherical pore morphology. Further experiments demonstrated that the Cu-based SMFs prepared with amorphous SiO2 beads showed a similar shape memory effect[16] and a pseudoelastic effect[17] to the bulk materials and exhibited a promising damping capacity up to 40 pct at room temperature,[18] indicating that the uniform spherical pores have no obvious negative effects on the functional properties of the Cu-based SMA matrix. Ho
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