| The ferrous powder metallurgy parts are widely used in the automotive,machinery,household appliances,military and the other fields.Fabrication of high performance ferrous powder metallurgy material has been the development direction of the ferrous powder metallurgy and research focus.Among the common elements of C,Cu,Ni,Mo used in ferrous PM materials for alloyed strengthening,molybdenum owns excellent solution strengthening effect,forms carbides to enhance strength and increase hardenability.Therefore,in this dissertation,Mo coated Fe powders were prepared by chemical coating method,then mixed with other elements powders,the sintered materials were obtained after pressing and sintering.The properties and microstructure and the influence mechanism of molybdenum in the matrix have been explored.The effects of addition forms,addition amount of molybdenum,warm compaction and heat treatment on the properties of Mo-containing ferrous PM materials were compared.The present works focus on the developments of ferrous PM materials with optimized microstructure and high mechanical properties.The main results and innovations are as follows:In order to improve the properties of ferrous sintered materials and the distribution uniformity of Mo element,the chapter 2 of this dissertation prepared Mo coated Fe powders by different preparation processes.The optimized reduction temperature is700?.The Mo element was introduced into the Fe-2Cu-1Mo-0.8C powder mixtures by elemental powders and Mo coated Fe powders,respectively.After pressing and sintering,the sintered materials were obtained.The effects of the two molybdenum introduction forms on the microstructure and mechanical properties of the sintered materials were investigated.The experimental results show that compared with elemental powders,the apparent density and flow ability of Fe-2Cu-1Mo-0.8C powder mixtures prepared with the addition of Mo coated Fe powders increases by0.22 g/cm~3 and 2.14 s/50 g,respectively.The density of the sintered materials prepared by Mo coated Fe powders is 7.26 g/cm~3,which compacted at 800 MPa and sintering at 1150?for 90 min.Compared with the sintered sample prepared by the elemental powders,the tensile strength and hardness from Mo coated Fe powders were increased by 32 MPa and 4.7 HRB,respectively.Because the addition amount of alloying element has effect on the microstructure and properties of the ferrous PM material,in chapter 3 of this dissertation,Fe-2Cu-x Mo-0.8C(0,0.5 wt.%,1 wt.%,1.5 wt.%,2 wt.%)sintered materials were prepared by Mo coated Fe powders with different molybdenum contents.The effect of molybdenum content on the microstructure and properties of sintered materials was investigated.The results show that when the addition amount of molybdenum increases from 0 to 1 wt.%,the density of the sintered samples increases.When the molybdenum content is 1 wt.%,the sintered sample has less cleavage in fracture surface,and owns better ductility,with smooth surface.The performance of the sintered samples reaches the best,the density,tensile strength and hardness of the sintered samples are 7.20 g/cm~3,511 MPa and 97.1 HRB,respectively.When the molybdenum content increase to 2 wt.%,the density and mechanical properties of sintered samples begins to decrease.The density and mechanical properties of ferrous materials can improved by warm compaction and heat treatment,in chapter 4 of this dissertation,Fe-2Cu-1Mo-0.8C material was treated by warm compaction and heat treatment.The influence of Mo addition forms on the warm compaction behavior of the powder mixtures,and influence of heat treatment on the microstructure and properties of materials was explored.The experimental results show that the green density increases from 7.20g/cm~3 to 7.29 g/cm~3 at 700 MPa by warm compaction.After heat treatment,the hardness of the sintered samples prepared by Mo coated Fe powders increases from103.5 HRB to 37.7 HRC,and the tensile strength increases from 654 MPa to 912MPa. |
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