Structure And Properties Of The Porous Cualmn Shape Memory Alloys

In the present study, a porous CuAlMn shape memory alloy (SMA) wasfabricated via sintering-dissolution method by using NaCl particulates as thespace-holders. In order to further improve the damping capacity, a porous CuAlMnshape memory alloy filled with polystyrene was also fabricated by sol-gel method.Appropriate heat treatments, examination of macroscopic and microscopicmorphologies, phase analysis as well as the damping test were carried out on theresultant specimens. The results showed that:1. Optimum fabrication process of the porous CuAlMn shape memory alloyshould be: pressing under400MPa and subsequent sintering at785℃for3h and thensintering at985℃for3h. The resultant material exhibits uniformly distributed andinterconnected macroscopic pores.2. Optimum solution and quenching process is as follows: specimens aresubjected to quench treatment in oil after holding at850℃-900℃for1h. Afterquenching treatment, and γ2phases formed during furnace-cooling processcompletely disappear. The matrix of the CuAlMn alloy is mainly composed ofself-accommodated M18R matensites. Through the investigation o n the effect ofaging on the microstructures and martensitic transformation behaviors, it is found thatthe aging in parent phase at relatively low temperature within a short time canefficiently decrease the concentration of quenching vacancies and the average size ofmatensites. The optimum aging process should be aging at350℃for15min.3. Adding small amount of Ti element can efficiently refine the grain size of theporous CuAlMn shape memory alloy. Research results indicate that the optimum adding amount of Ti element is0.2wt.%.4. Low frequency damping behavior of the porous CuAlMn shape memory alloyshows that two internal friction (IF) peaks arise at around200℃and150℃duringheating and cooling. The two IF peaks have been ascribed to the reverse and directmartensitic transformation, respectively. Compared with the bulk specimen, theporous specimens have significantly enhanced damping capacities. Stress modeconversion and stress concentration around pores, the production and movement ofdislocations under applied cyclic loading, as well as the microplastic deformationcaused by the localized stresses are the predominant mechanism of the enhancementof the damping capacity. The porous CuAlMn SMAs filled with polystyrene showgreatly superior damping capacity to the porous CuAlMn SMAs owing to thesuperposition of several individual damping sources.