Study On Preparation Of 8Cr And 15Cr Ferrite And ODS Alloy By Mechanical Alloying And Spark Plasma

Nanostructured oxide dispersion strengthened（ODS）alloy has excellent resistance to radiation swelling and good high temperature mechanical properties.It is the majorcandidate structural material for the first wall of fusion reactor.The performanceadvantages of the nano-structured ODS alloy mainly come from the ultra-high density nano-scale oxide dispersion strengthened phase inside the material.At present,theperformance of the ODS alloy has not archived the design requirements of the first wall cladding material for the fusion reactor yet.There is still improvement indeed for the composition control and preparation process of the ODS alloy.Mechanical alloying can effectively refine the alloy powder and oxide dispersion strengthening phase and make it evenly dispersed in the alloy matrix.Mechanical alloying parameters have a hugeinfluence on the properties of alloy powder and its alloy after sintering andsolidification.Reasonable control of mechanical alloying time can effectively guarantee the performance of ODS alloy.In this thesis,8Crand 15Crferrite and its ODS alloywith good properties were prepared by mechanical alloying and spark plasma sintering process（SPS）.This research is of great significance to the development of fusionreactor structural materials.In this thesis,the average particle size,grain size,microstructure,elementdistribution,and phase structure of the powder particles during mechanical alloying were studied,the optimal ball milling time was determined,and the density andhardness of the SPS cured samples were further studied.,Element distribution and microstructure.The main results are as follows:（1）In the mechanical alloying process with a ball-to-material ratio of 10:1,a rotation speed of 300 rpm,and high purity argon gas protection,the cold welding effect of the ball mill dominates at the beginning,and the powder particle size gradually increases and the shape becomes Irregular flaky structure.After that,the crushing effect of theball mill began to dominate,the size of the powder particles gradually decreased,the flake structure gradually disappeared,and the shape tended to be regular and equiaxed.Finally,after 40 hours of ball milling,the crushing and cold welding no longer change significantly,and the size and shape of the powder particles reached a stable state.The grain size of the alloy powder and the effect of mechanical alloying also reached astable state after 40 h of ball milling.Therefore,40 h is the best mechanical alloying time under this experimental condition.（2）Discharge plasma sintering samples of 8Crand 15Crferrite and its ODS alloywith good performance were prepared by discharge plasma sintering process parameters with vacuum degree below 10 Pa,sintering pressure of 40 Mpa,maximum sinteringtemperature of 950℃and holding time of 5 min.It was found that the slight changes in the composition of the alloy powder and the changes in the mechanical alloying time did not greatly affect the densification degree of the SPS sample.The densificationdegree of the SPS sample mainly depends on the process parameters of spark plasma sintering.The difference in oxygen content in SPS samples with different ball milling time is very small,which shows that the high-purity argon gas protects the environment and effectively reduces the pollution of oxygen in the air.The hardness of the SPSsample increases continuously with the increase of the ball milling time,and finally no longer change significantly after 40 hours of ball milling.With the same ball milling time,the hardness of the 15CrSPS sample is greater than that of the 8CrSPS sample.This shows that the increase in Crcontent can increase the Vickers hardness of thematerial to a certain extent.（3）The grains in 40 h-8CrY powder are very fine,and after 40 hours of mechanicalalloying,a large number of dislocations are generated in 40 h-8CrY powder.（4）The grains of 8Crand 15Crferrite and their ODS alloys have a bimodaldistribution.The fine grain size is generally less than 500 nm,and the large grain size is generally greater than 1μm.The oxide dispersion strengthening phase in 8Crand 15CrSPS samples is mainly chromium oxide.In addition to Y₂O₃,the oxide dispersion-strengthened phases in 8CrY and 15CrY SPS samples also contain a small portion of large-scale chromium oxides.（5）There are a large number of oxide dispersion strengthening phases in 40h-8CrYand 40h-15CrY SPS samples.In 40h-8CrY,the average size of the oxide dispersion strengthened phase is about 40.2 nm,the numbe density is 1.65×10²⁰/m³,while in40h-15CrY,the average size of the oxide dispersion strengthened phase is about 31.9nm,and the number density is 3.98×10²⁰/m³.