Directional Solidification Behavior Of Ti-6Al-4V Alloy And Ti-TiBw Composites

Titanium alloys and titanium matrix composites have high specific strength,specific modulus,high temperature resistance,corrosion resistance and other excellent properties,which have been widely used in aviation,aerospace,energy,chemical industry and other fields.With the rapid development of science and technology,the research of new titanium materials and their composites with excellent comprehensive properties has attracted great attention.Directional solidification technology can significantly improve the microstructures,thereby improving properties of anisotropic materials in specific directions.It has important effects on material properties for distribution of TiBw whiskers and orientation relationship between TiBw and matrix in TiB whisker to reinforce Ti matrix composites.Based on this,the idea of preparing TiBw whisker reinforced Ti matrix composites by directional solidification technology is proposed in this paper,and on this basis,we studied the effects of directional solidification on the microstructure and properties of the alloy.In this paper,The directional solidification behavior of pure Ti(TAI),Ti-6A1-4V(TC4)alloys and Ti-TiBw composites was studied by Bridgman directional solidification method.The effects of directional solidification parameters on the microstructures of TA1,TC4 and Ti-TiBw composites were systematically analyzed by means of metallographic microscope(OM),scanning electron microscopy(SEM)and electron backscatter diffraction(EBSD).XRD and EBSD were used to investigate the microstructures and orientation behavior of the above materials,revealing the influence of drawing rate on the solidification structure,explaining the directional solidification growth behavior of the above materials under different conditions,and studying the interaction between matrix and reinforcement phase of TiBw reinforced Ti matrix composites during directional solidification.The main results are as follows:It was found that with the decrease of drawing rate,the effect of drawing rate on the preferential growth of primary dendrite was gradually enhanced,in the orientation zone of TA1 pure titanium.When drawing rate was reduced to 5 ?m/s,the primary dendrite growth along drawing direction was basically realized in the directional region.The change rule of crystal orientation was qualitatively studied by analyzing the relative peak intensity of XRD diffraction pattern.In Ti-6Al-4V alloy,it is found that the primary dendrite directional growth is achieved at 5?m/s,and the alloying elements Al and V have little influence on the primary dendrite directional growth.The microstructures in different regions of the samples changed obviously,due to the influence of temperature gradient during directional solidification.In the directional region,the transverse grain boundary is eliminated.Complex solid-state phase transformation occurs in the crystal,and the matrix alpha lamellar structure is distorted and fragmented,eventually forming equiaxed structureIn Ti-TiBw composites,the evolution of TiBw whiskers under directional solidification mainly occurs in the undissolved transition zone.In this region,TiBw whiskers fragmented and aggregated in the primary grain boundary layer in the original extruded material are fully fused and grown under directional solidification conditions,and the directional growth of TiBw whiskers is realized.Combined with EBSD and XRD analysis,it was found that the phase difference between adjacent grains decreased in the undissolved transition zone,the grain orientation changed,and the matrix structure showed strong texture orientation.