The Study Of The Influence Of Elementary Minor Additions On The Microstructures And Properties Of Ti-based Amorphous Matrix Composites

Due to its unique long-range disordered structure,Ti-based amorphous alloy has excellent properties such as high specific strength,large elastic limit,good corrosion resistance,so it has potential application values in aerospace,biomedical and other fields.However,the weak glass-forming ability and the room-temperature brittleness of Ti-based amorphous alloys limit its applications.In order to improve their plasticity at room temperature,researchers have prepared amorphous composites by introducing a second phase.Not only is the plastic deformability of Ti amorphous composites enhanced by B2 phase,but also the pronounced work-harding phenomenon can be observed because of the the martensitic transformation of B2 phase during the deformation,which eliminates the work-softening effect of amorphous alloy.But the precipitated B2 phases are large in size and unevenly distributed,which is not conducive to improving further improving its mechanical properties.Ta and Mo,which can be used as stabilizers of metastable phase B2,can improve the glass forming ability(GFA),change the microstructure and increase the room-temperature plasticity.In this paper,Ti-based amorphous alloy composites with the precipitation ability of B2 phase were selected as the matrix alloy.By adding Ta and Mo with 0-3%atomic percentage respectively,the changes of the composite structure and properties after minor additions and the influence of added elementary content on the microstructure and properties were studied in detail.By using X-ray diffraction(XRD)and scanning electron microscope(SEM),the effect of Ta or Mo minor addtions on microstructure of Ti-based bulk metallic glass composite have been discussed.The results show that,with increasing Ta content,the distribution and morphology of the cubic B2 phase have been changed from big platelike distribution to spherical granular distribution,with the volume fraction of B2phase decreasing and the volume fraction of amorphous phase increasing.But with minor addtions of Mo,the crystal precipitates have not only B2 phase,but also other crystal phase.It has been studied about the effects of Ta or Mo minor addtions on the glass-forming ability(GFA)and thermal properties of Ti-based bulk metallic glass composite by using differential scanning calorimetry(DSC).The results show that with increasing Ta content,the thermal stability of the supercooled liquild and the GFA of Ti-based bulk metallic glass composite and the whole amorphous thin ribbons have been improved.According to the calculation results of equivalent atomic size differences(?),mixing enthalpies(?H_mix)and equivalent electronegativity differences(??),the negative mixing enthalpies(?H_mix)and equivalent atomic radius size differences(?)are decreasing,but the electronegativity(??)is increasing.The improvement of electronegativity,which can increase the attraction between atoms,form some atomic pairs and inhibit the diffusion of atoms during the solidification of alloy melt,will facilitate the formation of amorphous alloy.So the improvement of glass-formation ability is mainly due to the increase of electronegativity.But its GFA of the amorphous thin ribbons by minor addtions of Mo has been decreased.According to the calculation results of the electronic criterion?h,it is caused by the decrease of?h.The compression tests at room temperature by the electronic universal testing machine have indicated that,with increasing Ta content,Ti-based bulk metallic glass composites have showed a lower plasiticity,but the yield strength increases obviously.This is related to the increase of the volume fraction of the amorphous phase.