Influence Of C, B And Y On Microstructure And Properties Of BT20Titanium Alloy

In this paper, BT20titanium alloy was selected as matrix alloy, and alloyingelements C, B and Y were added to this matrix alloy. WK-II-type non-consumabletungsten electrode arc melting with water-cooled copper crucible was used tofabricated BT20-C，BT20-B，BT20-Y，BT20-C-Y and BT20-B-Y titanium alloy. OM,SEM and electronic universal testing machine were used to research the influence ofalloying elements C, B and Y on the microstructure and properties of BT20alloy.Analysis of microstructures show that as C, B and Y are added to BT20titaniumalloy, TiC, TiB and Y2O3phases can be precipitated. When C content is less than0.2%, C will be solid-soluted in matrix alloy, so TiC can be observed. As C content ishigher than0.4%, eutectic TiC with strip morphology will be precipitated. As a smallamount of B is introduced into the alloy, TiB whisker with irregular shape can beobserved. Y2O3exhibits equiaxed morphology in BT20titanium alloy under thecondition that Y content is low. Increasing Y content leads to the formation ofstrip-like Y2O3phase. Introduction of the C, B and Y into BT20titanium alloy resultsin the refinement of β grain. The enrichment of C or B ahead the solid-liquidinterface of the β-Ti will lead to the formation of composition under-cooling, whichis the reason for the refinement of β grain. Y addition can change the melt properties,which can realize the β grain refinement. As C and Y are added in BT20titaniumalloy simultaneously, TiC and Y2O3phases can be precipitated. The presence of Y canrefine eutectic TiC. From the viewpoint of solidification process, TiC precipitatesfirst, and then Y2O3phase precipitates. Some Y2O3phases are attached to the TiCphase. When C and Y are added simultaneously, TiB and Y2O3phases can beobserved. Y2O3phase can grow on TiB whisker.The basic features of microstructure of BT20titanium alloy are not changedafter the addition of alloying elements C, B and Y. The microstructure is still basketmicrostructure. The addition of C or B into the alloy almost can not decrease αlamellar size, but can make α colony become unobvious. Effect of Y on α lamellarand α colony is greater than the influence of C or B. The addition of Y canremarkably refine α lamellar, and as Y content increases to1%, the average size of αlamellar decreases to about0.3μm.Addition of C or B all can enhance the yield strength and Webster Hardness ofBT20titanium alloy. With the increases of C or B content, compressive strength andcompressibility of BT20titanium alloy increase first and then decrease. When Ccontent is0.6%, compressive strength reaches to maximum, which is1607.3MPa. It should be noted that the increase in compressive strength is at the expense of ductility.In B modified BT20titanium alloy, as B content is0.1%, compressive strength andcompressibility all reach to their maximum, which are1545.3MPa and11.34%,respectively. With the addition of Y, the capacity of plastic deformation of this alloyis enhanced greatly. With0.1%Y addition, compressibility all reaches to13.11%.From the viewpoint of compressive properties, C alloying effect is better than Balloying. The influence of Y content on compressive properties of BT20+0.4C alloyand BT20+0.1B alloy is similar to the effect of Y on BT20titanium alloy.