Effect Of Quenching And Aging Process On The Second Phase Precipitation Of Zr-Sn-Nb Alloy

In this paper,multiple characterization and analysis techniques including optical microcope(OM),scanning electron microscopy(SEM)and transmission electron microscopy(TEM)were jointly employed to investigate Zr-1.0Sn-1.0Nb-0.3Fe alloys.Systematic work was conducted on the effects of quenching and aging process on microstructure and precipitation behavior of second phase particles(SPPs)in Zr-Sn-Nb alloys.The main conclusions obtained by present work are as following:With the water cooling temperture droping,the microstructure evolves in a sequence as: present martensitic(1030°C)? present martensitic and basket-weave widmanstatten structure(900°C)?Lenticular structure(800°C and 700°C).There are some {101(?)1} twins being obversed in sample which quenched at 1030°C and 900°C.Moreover,the average ?-plate width increases as the water cooling temperature droping.Retained ? phase in strip and block accompanied with ? phase in white granular was observed in 4 states of specimens.There are Fe and Nb elements exist in retained ?-Zr,and the Nb element increased with the interrupted quenching temperature droping.The orientation relationship(OR)between ? and ? matrix corresponds with the well-known Burgers OR,is {0002}??{110}?,<11(?)0>?//<111>?.While the retained ? and ? phase were determined to be obeying two ORs as followed:(0001)?//(111)?,[2(?)-0]?//[(?)01]? or((?)010)?//((?)21)?,[10(?)2]?//[0(?)2]?.In the aging process,with the extension of aging time and the diffusion of alloying elements,the size and quantity of the SPPs increase and generally precipitate out at the lath interface or grain boundary,and then gradually expand and disperse in the matrix.In terms of the diffusion of alloying elements,the diffusion rate of Fe is higher than that of Nb,so the Zr-Fe phase is precipitated earlier than the Zr-Nb-Fe phase.In the process of aging,the residual ? gradually break down,but at the aging temperature of 650°C(above monotectoid reaction temperature)and holding in long time,monotectoid reaction and precipitation of ?-Zr with lager sizes and high Nb element occur in samples.The precipitation sequence of SPPs in samples under 1030°C and 900°C during aging process at 580°C and 650°C is different,but there are almost the same law of precipitation between them.In the 580°C ageing process,the residual ? and ? phase resolved and the Zr3 Fe phase with the crystal structure of Orthorhomic was observed firstly.While the Zr(Nb,Fe)2 phase with HCP structure and the(Zr,Nb)2Fe with with FCC structure were observed in later aging process,and the Zr3 Fe phase will disappear.In addition to the above transformation process,monotectoid reaction and precipitation of ?-Zr occured in samples aged at 650°C.The law of precipitation is also closely between the samples quenched at 800°C and 700°C.The residual ? and ? phase resolved in samples at early aging time,the Zr(Nb,Fe)2 phase existed in samples aged at 580°C,the monotectoid ?-Zr and the Zr(Nb,Fe)2 phase be obversed in samples aged at 650°C.Besides,there are no(Zr,Nb)2Fe were observed in samples aged 800°C or 700°C.