Preparation And Properties Of In-situ NbC Particle Reinforced Iron Matrix Composites

With the progress of science and the development of modern industrial technology,the requirements for material properties are higher and higher.A single material can not meet the requirements of modern industry.In order to meet the requirements of new materials,particle reinforced composites（PPMC）has become a research hotspot at home and abroad.Firstly,Nb₂O₅was evenly dispersed in Fe matrix by mechanical activation method,and then particle reinforced iron matrix composites were prepared by microwave sintering process.In this thesis,iron matrix composites were prepared by mechanical activation method and microwave sintering process.The microstructure and mechanical properties of the materials were studied.The main research work is as follows:（1）to explore the effects of different ball milling time and sintering temperature on the microwave carbothermal reduction of Nb₂O₅.（2）Iron matrix composites were prepared by mechanical activation and microwave sintering,and their mechanical properties and microstructure were analyzed.（3）The effects of adding trace alloying element La and Nb₂O₅ with different mass fractions on the mechanical properties and microstructure of iron matrix composites were investigated.The following conclusions are drawn:（1）The degree of microwave carbothermal reduction of Nb₂O₅ is related to the ball milling time and sintering temperature.From the weight loss rate,it can be seen that the weight loss rate increases gradually with the extension of ball milling time and the increase of sintering temperature,indicating that the reduction degree of Nb₂O₅ increases gradually.Combined with the scanning electron microscope（SEM）and energy spectrum（EDS）of the powder after ball milling,it can be seen that with the extension of ball milling time,C particles will be gradually refined and evenly dispersed in Nb₂O₅,It is conducive to the reduction reaction.According to the XRD,SEM,EDS and XPS of the sintered powder,Nb₂O₅ has been basically reduced to Nb C when sintered at 1200℃and ball milled for 20h.When ball milled for 30h and microwave sintered at 1400℃,metal niobium can be reduced.（2）When preparing ball milled powder of iron matrix composites,with the extension of ball milling time,the powder yield of ball milled powder gradually decreases,the particle size gradually decreases,the specific surface area gradually increases,and the particles gradually homogenize.When the sintering temperature is low,the particle size of ball milled powder has a great influence on the mechanical properties of iron matrix composites.With the increase of sintering temperature,the mechanical properties of iron matrix composites are gradually affected by the basic sintering state of iron body and the existence form of various components in iron matrix.The maximum density of iron-based composites is 7.827g/cm³ when ball milling for 20h and sintering at 1400℃.When sintering temperature is 1300℃and ball milling time is 20h,the mechanical properties of iron-based composites are the best,with hardness of 688HV and flexural strength of 536MPa.（3）After adding different mass fractions of La into iron matrix composites,the mechanical properties of the materials increased first and then decreased.A small amount of La can effectively increase the bonding ability between Nb C particles and iron matrix.When 0.3%is added,the mechanical properties of the material are the best,and the hardness and flexural strength are 958HV and 833MPa respectively.Because the iron matrix itself is affected by the content of C,the addition of different mass fractions of Nb₂O₅ has a greater impact on the hardness and flexural strength of the iron matrix composites.When 10%Nb₂O₅ is added,the mechanical properties of the materials reach the best,and the hardness and flexural strength are 960HV and 578MPa respectively.