Study On PMT Preparation, Structure And Performance Of NiCoMnIn Alloy Foam

It is known that shape memory alloy is a new functional material and a branch of a subject independently. Ferromagnetic shape memory alloy, because of its characteristics of high ferromagnetism, large magnetostriction, thermoelastic and magnetic shape memory effect, high response frequency and large strain-stress output, has attractived the considerable interests from material and physical scientists. The thesis studies detailedly on powder metallurgy technique(PMT) preparation and performance of Ni45Co5Mn36.7In13.3 alloy foam.Through the technics, it finds that NaCl is more fit for filling agent than NaAlO3, and NaCl can make NiCoMnIn alloy foam more close. The grain degree must small than 200 mush, because the sample breaks up, if it large than 200mush. The best anneal temperature is 930℃. The best of the holding temperature is 15min～20min, due to the largest porosity in this temperature interval. Along with proportion of the filling agent increasing, porosity and the hole size increases, and the joint capability of NiCoMnIn become worse gradually. The porosity decreases sharpely, when grain size of filling agent NaCl fines below 200 mush.The martensite transformation of the Ni45Co5Mn36.7In13.3 alloy decreases sharply and the structure becomes out-of-order state after milling-ball. The martensite transformation of original alloy is near 0℃, however, it changes to -80℃～-100℃after milling-ball.The yield strength of the foam materials is lower order of magnitude than original alloy. The lower yield strength of the ferromagnetic shape memory alloy presume that critical stress of driving martensite transformation decrease. It make martensite transformation easily in magnetic field or exterior stress so as to bringing the effect of the shape memory.Studying on the sample annealing at 930℃and holding for 25min, because of the long holding temperature, the porosity decreases and the cell walls of the foam material become solid. The martensite transformation increases and crash of the cell walls decreases under the same macrostress so that the reverse of the remain stain increase sharply in 12T magnetic field. It is of great significance to design large magnetic-field-induced reverse strain of the ferromagnetic shape memory alloy.