Study On The Glass Forming Ability And Properties Of Fe-Zr-B Based Metallic Glasses

Currently,Fe-based metallic glasses(MGs)are the most widely used amorphous alloy materials,and this kind of MGs has been mainly applied for soft-magnetic and wear-resisting corrosion-resistant materials.Therefore,developing new functional Fe-based bulk metallic glasses(BMGs)is important to expand the application fields of MGs.In this work,base on the benefical effect of B and Zr elements,which have small and large atomic size respectively,on the glass forming ability(GFA),Fe-Zr-B BMG systems with high content of Fe and Cr,respectively,have been developed.Novel Fe-Cr-Zr-B based amorphous coating has also been prepared.In this work,the relation between metastable transition in solidification process and GFA of Fe-B based alloys has firstly been analyzed.According to the occupation tendency of transition metals with large atomic radii in Fe23B6 structure,quaternary Fe77B1gTixZr5-x(1?x?4)BMGs have been successfully developed by adding 5%content of Ti and Zr into near-eutectic Fe82B18 alloys.These MGs exhibit good soft-magnetic properties.For example,Fe77B18Ti4Zr1 alloy shows the saturation magnetization(Bs)of 1.41 T.To obtain Fe-based BMGs with better soft-magnetic properties,the addition amount of Zr in Fe-B-Si alloys was adjusted and optimized.A series of Fe-based BMGs with high Fe content and low Zr content was designed and prepared.All these MGs exhibit high Bs over 1.5 T.Especially,Fe77.7B15.5Si5Zr1.8 alloy exhibit high Bs of 1.60 T and low coercive force of 4.3 A/m.By the addition of Zr into near-eutectic Fe-Cr-B alloys,new Fe-Cr-Zr-B based BMGs with high Cr and B contents has been successfully developed.Furthermore,it has also been found that the addition of Mo could markedly improve the GFA and expand the BMG forming area.The mechanical properties tests have proved that the new developed Fe-Cr(Mo)-Zr-B BMGs possess ultrahigh compressive strength and micro-hardness.The compressive strengths of Fe57Cr10Mo7Zr8B18 and Fe57Cr12Mo5Zr8B18 BMGs,reach 3857 and 4020 MPa,respectively.All the tested Fe-Cr(Mo)-Zr-B BMGs show high micro-hardness over 1100 HV.It has been also found that increasing Cr or Mo content is advantageous to improve the hardness.The micro-hardness values of Fe38Cr40Mo2Zr8B12 BMG with high Cr content and Fe42Cr18Mo17Zr8B15 BMG with high Mo content reach up to 1397 and 1394 HV,respectively.Electrochemical and immersion tests were designed to examine the corrosion properties of the Fe-Cr(Mo)-Zr-B BMGs in 1 M HCl at room temperature.It was found that there exists a specific Cr-controlling active-passive transition in Mo-free Fe92-x-zCrxZr8Bz BMGs.When the Cr content is less than 25%,the BMGs was active in the solution;while the BMGs with Cr content above 25%could be spontaneously passivated in the same solutions.However,the addition of 2%Mo could remarkablely decrease this Cr threshold.By investigating the evolution of oxide films in the alloy surfaces,it was found that the sudden change of Fe3+/Fe2+ratio at the 25%Cr content should be responsible for the corrosion-resistance transition.Moreove,the active-passive transition still played certain role in Mo-doped BMGs.When the Cr content in Fe90-x-zCrxMo2Zr8Bz BMGs is below 25%,the primary oxide film was not protective enough in 1 M HC1.Severe atomic selective dissolution occurred on the alloy surface,which promoted the chemical reactions between Mo and solution.Then the generated Mo6+ oxides accelerated the passivation.When the Cr content exceeds 25%,due to the high protectiveness of primary oxide films,much weaker atomic selective dissolution happened on the alloy surfaces before the alloys were passivated in the solution.Thus Mo6+ oxides were unlikely to be generated.These results indicate different mechanisms of passivation for the two series of BMGs.Moreover,highly vitrified powders with the selected Fe54Cr18Mo2Zr8B18 alloy was synthesized by using gas atomization technology.And entirely vitrified coating with thickness of about 350?m and density of 97.2%was fabricated on 304 stainless steel(304 SS)by using hypersonic flame spraying technology.The amorphous coating exhibited high bonding strength over 55.3 MPa,which is the highest among the reported bonding strengths of Fe-based amorphous coatings.The Fe54Cr18Mo2Zr8B18 amorphous coating exhibited high micro-hardness of 1150 HV,which is obviously larger than that of commercial Fe44Cr16Mo16C1836 amorphous coating or 304 SS.Thus the new Fe54Cr1gMo2Zr8B18 amorphous coating possess excellent wear resistance.The abrasion tests prove that the wear volume of the new Fe54Cr18Mo2Zr8B18 amorphous coating is only 64.2%of that for commercial Fe44Cr16Mo16C18B6 amorphous coating,and 39.0%of that for 304 SS.Moreover,the electrochemical tests prove that the new Fe54Cr18Mo2Zr8B18 coating possess better corrosion resistance than commercial Fe44Cr16Mo16C18B6 amorphous coating and 304 SS in 1 M HCl solution at room temperature.