Preparation Of Iron-based Bulk Metallic Glass And Its Plasticization Research

Fe-based Bulk metallic glasses,which are characterized by high strength,high hardness,high elasticity,and low material cast and other excellent performance,However,limited plasticity at room temperature and poor glass forming ability,which hinders their widespread use and mass production as a new high-strength structural materials.Therefore,developing a new kind of Fe-based metallic glass or Fe-based metallic matrix composite which possess the high strength,good room temperature plastic and good glass forming ability became a top-hot and meaningful subject.In this dissertation,according to the analyses of the compositional characteristics of Fe-based metallic glasses can be divided into three types: Fe-P-C system,Fe-B system and Fe-C-B system.Comparing with other two systems,the Fe-P-C system bulk metallic glass has good plasticity in the room temperature and high toughness.While the Fe-C-B system bulk metallic glass has good glass forming ability.In order to improve the plasticity in the room temperature and glass forming ability of Fe-based bulk metallic glass,we proposes micro-alloying to improve the plasticity of the single amorphous phase bulk metallic glass and developing the Fe-based metallic glass matrix composite reinforced with in-situ formed different size of ductile ?-Fe dendrite phase to enhance the Fe-based bulk metallic glass in room temperature.Based on reasonable designed the composition and structure,we choose the Fe-Mo-P-C system bulk metallic glass as the primary composition,which has better performances in the Fe-P-C system bulk metallic glass.By adding different content of B element to increase the glass forming ability and the plasticity in the room temperature.In the same time,we also select the Fe77Mo5P9C7.5B1.5 as the primary composition,which already be proved can precipitate the micrometer ?-Fe dendrite phase.And we hope it can precipitate the nanometer ?-Fe phase by adding different content of Cu element,use this method to preparation the Fe-based metallic glass matrix composite reinforced with in-situ formed micrometer-nanometer sized ductile ?-Fe phase to enhance the plasticity in the room temperature.The microstructures was systematically studied by X-ray diffraction(XRD),scanning electron microscope(SEM),and transmission electron microscopy(TEM).The thermal stability was studied by differential scanning calorimetry(DSC).The mechanical properties was tested by mechanical properties tester.The main conclusions are summarized as follows:1 B element has a strong inhibitory effect on ?-Fe phase,and also inhibits Fe-P phase Fe-C phase.A small amount addition of B element could effectively enhance the glass forming ability of the Fe-P-C system bulk metallic glass.However,However,an excessive of B element addition resulted the precipitation of Fe-B phase,which reduced the glass forming ability.2 With the content of the B element in sample increase,the mechanical properties are decrease.And the glass transition temperature Tg and the activation energy of glass transition Eg are both increased.Indicating that the mechanical properties and the glass transition temperature and the activation energy of glass transition has a certain internal relationship.Likely that a low glass transition temperature and a low activation energy of glass transition are generally associated with a high plasticity at room temperature.3 with the addition of B element,the average thermal expansion coefficient from room temperature to the Tg-DIL of glassy alloys ?g,and the average thermal expansion coefficient above the Tx-DIL of crystalline alloys ?c shows a tendency to increase first and then decrease,meanwhile the different value ?? of ?g and ?g also shows a tendency to increase first and then decrease.It is also shows that ?? is proportional to the glass forming ability.And the sample which has larger supercooled liquid region,when temperature above the glass transition temperature Tg,the shrinking length of sample will be more.Moreover,with the increase content of B element in the sample,the fragility parameter m of the samples will be decreased,which means that the sample became strong from fragility,which representative with the addition of B element,the glass forming ability is enhanced.From this work,a link among the average thermal expansion coefficient ?g,the viscosity of the supercooled liquid,the fragility parameter m and glass forming ability of Fe-based bulk metallic glass was established.In general,the alloys with large ?g,much scatter viscosity in the supercooled liquid and low fragility m,were suggested to have a large glass forming ability.4 with addition different content of Cu element,we found that the micronmeter sized dendrites ?-Fe will growing larger with the increased content of Cu element,resulting in the mechanical properties decreased.We found that when the content of Cu element was 0.1 at.%,The plasticity in the room temperature was the best.At the same time,the micronmeter and nanometer sized ?-Fe will hinder the shear band developing,cause the speed of shear band into crack slow down,meanwhlie inducing produce the branch of shear band and changing the direction of shear band development,Therefore can increasing the plasticity of sample in the room temperature.