Study On Preparation And Aging Behavior Of Fe-Cu-Ni Model Alloy

In this paper,model alloys with different compositions are prepared by smelting,and aging treatment is performed at 500? and 600?,so that Cu can form Cu-rich clusters in the alloy in a short time which can effectively hinder the movement of dislocations.Then,through the influence of Cu content and Ni content on the distribution,size and morphology of precipitated phases during the aging process and the law of age hardening,the embrittlement mechanism of Cu precipitation relative to Fe-Cu model alloy is clarified.In the process of experimental design,refer to the alloy composition of the reactor pressure vessel steel(RPVS)and the service environment,select experimental samples with higher element content(The content of Cu element is much higher than that in RPV steel),increase the aging temperature(Higher than the service temperature of RPV steel),accelerate the desolvation and decomposition of the supersaturated solid solution,and be more conducive to detecting the precipitation of the Cu-rich phase.The testing of samples under different aging conditions through hardness experiments shows that with the aging time increases: the hardness will gradually increase in the under-aging,the hardness near the aging peak will reach the maximum value in the aging stage,and the hardness will decrease in the over-aging.High aging temperature will speed up the aging process and shorten the time to reach the aging peak,but the peak hardness will be lowered.Increasing the content of Cu in the alloy will significantly enhance the hardening effect and speed up the aging process.When driving force of desolvation and decomposition is sufficient,adding Ni to the alloy will shorten the time to reach the aging peak and enhance the hardening effect.Through characterization methods such as OM,SEM,EDS,TEM,XRD,SANS,etc.,the characteristics of crystal grain size,precipitation behavior at grain boundaries,and the size,number,and morphology of microscopic clusters are detected and analyzed.The effect of aging time on micro-clusters is as follows: First,under the action of a certain driving force for desolvation and decomposition,non-uniform nucleation occurs at grain boundaries and a small number of defects,and some clusters with larger volume and lower concentration are formed,There is a certain hindrance for dislocation movement;then the Cu element aggregates at the nucleation position and some separate precipitates appear,and the dislocation cuts through these clusters and the precipitates to produce a good hardening effect;finally the precipitates grow and coarsen,The dislocation changes from cutting to bypassing the precipitation phase and the hardening effect is weakened.Increasing the aging temperature will reduce the supersaturation of Cu in the ferrite matrix,and the desolvation and decomposition are more likely to occur non-uniform nucleation at defects and grain boundaries,and the aggregation of microscopic clusters is faster,The degree of aggregation is more compact,but the size of the precipitated phase is very uneven and the number is small,so it can quickly reach the aging peak,but the hardness peak is lower.Over aging,a separate precipitated phase will grow and coarsen fast.Increasing the Cu content,the size distribution range of the precipitated phase is wider,the concentrated size is larger,and coarsening speed of the precipitated phase is accelerated.Adding Ni element under a sufficient driving force for desolvation and decomposition helps increase the nucleation position of the precipitated phase,inhibits the coarsening process of the precipitated phase,and keeps the precipitated phase in a form that effectively hinders the movement of dislocations.