Effects Of Melt Treatment On The Properties Of Ti-based Amorphous Alloys And Composites

Amorphous alloys have a short-range ordered and long-range disordered atomic structure that is different from crystalline materials.At present,the description of the microstructure of amorphous alloys is still controversial.It is generally believed that there are local ordered structures of various sizes in amorphous alloys.Amorphous composites introduces a certain volume fraction of crystalline phase into the amorphous matrix,and its microstructural characteristics are more complicated.It not only can maintain high strength,but also has good plastic deformation ability.At present,the influence of the rapid solidification behavior of high temperature melt on the structure and properties of amorphous alloys and composites remains to be further studied.Therefore,it is of great significance to explore the relationship between the preparation process--microstructure--properties of amorphous alloys and composites.In this paper,the effects of overheating and cyclic heating on the microstructure,thermal stability,and mechanical properties of amorphous alloys and composites are studied through melt treatment at different temperatures.In situ heating high-energy X-rays reveal the microstructure evolution mechanism of amorphous alloys and composites.The structural characterization and performance testing of the casting were carried out by various means,and the relationship between the melt treatment temperature and the composition,properties and structure was clarified,and the control of mechanical properties and thermal stability of amorphous alloys and composites were achieved.The amorphous alloys and composites were superheated by quartz crucible at 1373K,1573K and 1773K to obtain the castings at different casting temperatures.As the casting temperature increases,the plastic strain,crystallization activation energy,and oxygen content of the amorphous alloys gradually increase;the plastic strain of the amorphous composites gradually decreases,and the crystallization activation energy and oxygen content gradually increase.Oxygen distribution in amorphous alloys leads to increased hardness.In amorphous composites,as the casting temperature increases,oxygen gradually accumulates in ?-Ti,?-Ti shows an effect similar to that of oxygen absorption,and the hardness of both the amorphous matrix and the dendritic phase gradually increases.The effect of high temperature on the local ordered structure,the combined effect of oxygen inflow and cooling rate causes the mechanical properties and thermal stability of amorphous alloys and composites to change.By means of Y2O3 crucible,the amorphous alloy was heated for different times at 1073K,1173K,1273K,1373K and 1473K,and the amorphous composites was heated at 1373K,1473K,1573K and 1673K,and the castings with different microstructure,mechanical properties and thermal stability were obtained.When the amorphous alloys is cast below 1473K,the oxygen content hardly changes.When the amorphous alloys was cast 0 times and 5 times in the 1073K cycle,the Be2Ti phase precipitated,and both of them exhibited brittle fracture characteristics.The crystalline phase disappears when the casting temperature increases,and the amorphous alloys has a certain plasticity.The amorphous alloys obtained by casting at low temperature has high thermal stability.As the casting temperature increases,the thermal stability of the casting decreases.With the increase of the casting temperature of the amorphous composites,the oxygen content in the casting gradually increases,and the oxygen is gradually enriched in the dendrite phase.Oxygen causes the hardness of the amorphous matrix and ?-Ti to increase.The hardness of the dendrite phase even exceeds the hardness of the amorphous matrix under the heating conditions of 5 cycles of 1573K and 1673K.Amorphous composites have different microstructures due to changes in the oxygen content of the amorphous matrix and ?-Ti at different temperatures and cycle times,which has an effect on the initiation and nucleation of the shear bands,and eventually results in mechanical properties variety.The change of the volume fraction of crystalline phase during the casting of amorphous composites,the effect of oxygen on the amorphous matrix and crystalline phases,and the nucleation and growth of ?-Ti during crystallization,the combined effect caused its thermal stability to occur variety.At the same time,5 cycles of heating make the melt composition of amorphous alloys and amorphous composites more uniform,but at the same time,due to the liquid-phase insulation effect of amorphous composites,more oxygen is doped in the melt,resulting in the structure and large changes in performance.The in-situ heating high-energy X-rays were used to characterize the structure of amorphous alloys and composites.During the heating process of amorphous alloys,the internal microstructure of the alloy changed.In the heating process of amorphous composites,the expansion rate of the amorphous matrix and the ?-Ti is different,which results in that the amorphous matrix has a certain restraint effect on the crystalline phase,and the interaction between different crystal surfaces and the amorphous matrix results in the growth rate of different crystal surfaces is also different.