The FCC to FCT transformatioinn Mn-22at%Cu and -26at% Cu alloysh asb een examined by
means of X-ray diffractiaonnd opticaaln d electromni croscopiewsi th a coolings tage.T he c parametera
nd the c/ar atioo f theF CT martensitdee creasew ith decreasintge mperaturea,b ruptlyb elow the
transformatiotne mperaturea nd then very slowly,s howing a characteristoifc t he second ordert ype
phase transformationO.n the otherh and, the opticalm icroscopys hows a coexistencoef untransformed
and transformedr egionse,x hibitinag characteristoifc t hef irsotr dert ypep hase transformation.
B anded relieifs o bservedi n the transformedr egion,w hich correspondst o the formationo f
tetragonatlw ins.N o internaslt ructuraes latticien variansth eari so bservedi n theb anded twinse ven
by electromni croscopy.T he banded regione xpandsa nd ther eliecfo ntrasti ncreasewsi th decreasing
temperatureC.o rrespondinglyt,h e electronm icroscopye xhibitlsa mellarc ontrastb elow the transformationt
emperatureH.o wever, very fines triatioanps pear priort o the lamellaarp pearance.B oth
thel amellaarn d striatioanrse paralletlo {011} planeso f theF CT martensitea,n d ares upposed to be
tetragonatlw insi ntroducedt o reliesae t etragonadli stortiodnu e to theF CC to FCT transformation
and them agnetict ransformatiorne,s pectivelTyh.e temperatured ifferenbce tweent hes tructuraaln d
magnetict ransformationiss a bout a few of ten degrees,b eingi n agreementw ith thati n a previous
work.