Influence Of Heat Treatment On Microstructure And Properties Of C, B And Y-refinced BT20Titanium Alloy

In this paper, BT20-C，BT20-B，BT20-Y，BT20-C-Y and BT20-B-Y titaniumalloys were produced by non-consumable tungsten electrode arc melting withwater-cooled copper crucible. A variety of heat treatment processes were performedon theses titanium alloys. OM, SEM and electronic universal testing machine wereused to research the influence of heat treatment on the microstructures and propertiesof BT20titanium alloy refined by C, B, and Y.Analysis of microstructures show that the evolution behaviors of TiC, TiB andY2O3in C, B, and Y-refined BT20alloy are completely different during heattreatment. After β heat treatment, the granulation effect of TiC occurred and TiC cansolute in the alloys. TiB shape does not change under this heat treatment. Y2O3wasre-precipitated and exhibit equiaxed morphology.After air-cooled from β phase field, the microstructures of BT20titanium alloyare lamellar microstructure with basket feature, although the alloying elements addedare different. α lath size almost does not vary with the content of alloying elements.After furnace cooling, α phase evolves into equiaxed morphology in C and B alloyedalloys. This is mainly atributed to the presence of TiC and TiB. In Y alloyed alloy, αphase exhibits lamellar morphology and the size of α lath decreases with the increseof Y content. After air-cooled from the α+β phase field, the microstructures arecomposed of primary α phase and tranfored β phase. The feature of primary α phaseis mainly dependence on alloying elements and heat treatment temperature. Afterfurnace cooling, α phase exhibits lamellar morphology. After the addition of C and Yor B and Y, the evolution behaviors of the microstructures of the alloys are similar tothose with single additon of C or B, respectively.After air cooling or furnace cooling from β phase field, BT20-0.4C, BT20-0.1Band BT20-0.2Y own excellent comprehensive mechanical properties. After furnacecooling, the compressive strength, yield strength and compressibility of BT20alloywith addition of0.4%C are1576MPa,1003.5MPa and19.37%, respectively. Calloyed BT20alloy exhibits higher mechanical properties than B or Y alloyed alloysafter heat treatment. The influence of Y content on compressive properties andVickers hardness of BT20+0.4C alloy and BT20+0.1B alloy is similar to the effect ofY on BT20titanium alloy. Comprehensive mechanical properties obtained by β heattreatment are better than those by α+β heat treatment and Comprehensivemechanical properties obtained by furnace cooling process are better than those by aircooling process. Compressibility of those alloys can reach about20%in the preferred compositions after furnace cooling.