Perspectives on the exploitation of CuZnAl alloys, FeMnSi-based alloys and ZrO2-containing shape-memory ceramics

Cu-Zn-Al alloys possess advantages for exploitation such as low cost, easy fabrication and excellent shape memory effect (SME). The deficiencies of Cu-Zn-Al shape memory alloys, i.e. the appearance of the stabilization of martensite, degradation of SME in prolonged application and the rather low fatigue life, can be overcome by various processing such as immediate up-quenching, alloying addition for retarding the incubation of bainite formation and grain refinement. Fe-Mn-Si based alloys are one-way shape memory material with high strength, high action temperatures, good workability and low cost. Addition of nitrogen or rare earth (RE) elements can considerably strengthen the austenite and lower the Neel temperature in Fe-Mn-Si alloys. Partial replacement of Mn with Cr and addition of RE elements to Fe-Mn-Si may reduce its stacking fault energy. Nitrogen and RE elements also lower the M-s temperature of Fe-Mn-Si and Fe-Mn-Si-Cr, stabilizing the austenite after shape recovery. The newly developed Fe-25Mn-6Si-5Cr-0.14N alloy possesses not only a complete shape memory recovery with a recoverable strain of 3% through only one cycle of training, but also the nice corrosion resistance in aqueous solution of NaOH and NaCl. The SME of Fe-Mn-Si-RE is superior to that of Fe-Mn-Si, e.g. its recoverable strain is about two-fold larger than that of Fe-Mn-Si when the pre-strain epsilon>3%. The exploitation of the Fe-Mn-Si-Cr-N and Fe-Mn-Si-RE alloys as coupling materials seems to be foresighted. Studies on (8similar to12)mol%CeO2-(0.25-0.75)mol%Y2O3-ZrO2 with various grain size and density after different sintering processes show that 8mol%CeO2-0.5mol%Y2O3-ZrO2 fabricated by sintering at 1773K for 6 hours exhibits best SME, i.e. a complete shape memory recovery and a recoverable strain of 1.2% at high temperatures (above 773K). The shape memory ceramics 8Ce-0.5Y-TZP is worthy to be developed.