The Interaction Mechanism Between The BaZrO₃ And The Titanium Melt And Its Doping Modification

Titanium and its alloys possess the high strength-to-weight ratio,the high resistant to corrosion,and the good mechanical properties at the elevated temperature,however,their wide application is limited by the high production cost.Seeking for a high stability refractory is the key technology to achieve the low-energy consumption and low cost prepration of induction melting of the titanium alloys.Recently,our group introduced the BaZrO₃ into the preparation area of the titanium alloys,the interfacial reaction between the titanium alloys and the BaZrO₃ crucible was dicussed by induction melting of the Ti Ni,Ti Fe and Ti Al alloys in the home-made BaZrO₃ crucibles,however,the interaction mechnism was sitll unstudied.This paper investigates the influence of titanium content on the interfacial reaction between the titanium melts and the BaZrO₃ crucible as well as the interaction mechanism,and the physical-chemistry theory model was set up.Moreover,the high stable oxide?CaO and Y₂O₃?was used as the additives for improving the thermodynamic stability of the BaZrO₃.A new CaO doped BaZrO₃ refractory was introduced to melting the Ti Al alloy,which had the high applicated prospect.In order to improve the hydration resistance of the CaO refractory for induction melting of the titanium alloys,various ratio of CaO/ZrO₂ samples were prepared to investigate the variation of the hydration resistance of CaO with the content of ZrO₂ aditive,and the mechanism of the modification was proposed.The detailed conclusions were shown as below:1.The BaZrO₃ refractory exhibited the good thermodynamic stability to the titanium melts,and no chemical reaction was achieved during melting the titanium alloys.Dissolution and erosion were the main mechanism responsible for the metal-crucible interaction.The dissolution amount of BaZrO₃ refractory in titanium melts proportionally increased with the increasing of the titanium content of melt due that the metal-crucible interaction was increased with increasing titanium content.The dissolution reaction of BaZrO₃ in the titanium melts TixNi?l?+?x/2?BaZrO₃?s??TixNi[?x/2?Zr,xO]?l?+?x/2?BaO?l? was determined.A serve damage phenomenon was appeared in the BaZrO₃ crucible after melting the alloys rich in titanium due to the significant crystal volume changed as the interaction product Ba O transform into BaCO₃ in the air.2.The Y-doped BaZrO₃ crucible was consisted of Ba2YZrO6-d and BaZr1-xYxO₃ after sintering at 1750 ? for 6 hours,and its grain sizes and relative density were apparently reduced by comparing with the BaZrO₃ crucible.After melting the Ti₁.5Ni alloy in the BaZrO₃ crucible,the crucible surface was uneven,and a little amount of BaZrO₃ refractory was attached to the metal after the metal separated from the crucible.However,the surface of the Y-doped BaZrO₃ crucible was even,and no attached layer was found after melting the Ti₁.5Ni alloy in the Y-BaZrO₃ crucible.After melting the Ti₂ Ni alloy in the BaZrO₃ crucible,a 270 ?m thick erosion layer and 50?m attached layer were observed.The thickness of erosion layer was only 45?m after melting the Ti₂ Ni alloy in the Y-doped BaZrO₃ crucible,and still no refractory was attached to the metal.3.The CaO doped BaZrO₃ refractory was prepared by using the mole ratio Ba O:ZrO₂:CaO=0.425:0.425:0.15.A part of CaO saluted into the BaZrO₃,in the sintering process,excessive CaO gathered together,and hindered the sintering of Ba_1-xCa_xZrO₃ grains,resulted in a large amount of big pores in the crucible.A precipitation behavior of CaO in the crucible wall was occurred,and this precipitation layer was mainly composed of CaO and Ba_1-xCa_xZrO₃ with about 70?m in thickness.By analyzing the interface reaction,the erosion thickness of BaZrO₃ crucible was about 270 ?m,no interfacial reaction was appeared between the titanium alloys and CaO doped BaZrO₃ crucible.4.The CaO doped BaZrO₃ refractory was prepared by using the mole ratio Ba O: ZrO₂:CaO= 0.465:0.465:0.07.During melting the Ti Al alloys in the CaO doped BaZrO₃ crucible,the Ba Al₂O₄ was generated and attached to the crucible surface.The microstructure of TiAl alloys was largely composed of lamellar ?₂+? with different orientations and small amount of bulk ? phase,and the oxygen concentration was about 0.108 wt.%,which was lower than that of the Ti Al alloys prepared by using the CaO and Y₂O₃ crucibles under the same melting condition.This may imply that the BaZrO₃ is a promising candidate of materials for the melting of TiAl alloys.5.Only CaZrO₃ was formed in CaO-ZrO₂ system which covered the surface and grain boundary of CaO samples with different contents of ZrO₂.The densification of the CaO refractory was promoted by addition of ZrO₂ due to the formation of Ca Zr O₃ by sintering;the relative density ratio first increased with the increased ZrO₂ additive,its value reached the top with 13 mol% ZrO₂ additive,then this value began to decrease with the further increase in the ZrO₂ additive.Meanwhile,when the ZrO₂ additive was 12 mol%,the AP was the lowest of about 0.75%.The sample with 12% ZrO₂ additive possessed the good hydration resistance;its weight additive stored after 56 days was less than 0.6 wt%.The contact interface of the Ti Ni alloy and CaO refractory was clear and no obvious Zr element appeared in the Ti Ni alloy after melting.The CaO with the ZrO₂ additive refractory could effectively prevent the erosion by the titanium melt.