| Titanium alloy has excellent comprehensive mechanical properties.It is widely used in aerospace,marine and civil applications.However,the high preparation cost limits the promotion and application of titanium alloy.The main reasons for the high production cost include two aspects:First,the traditional titanium alloy contains more metal components such as V and Cr.These metal resources are scarce resources and expensive in China.If China's resource-rich base metal element is used instead of V,it can reduce the cost of raw materials for titanium alloy production,which is also the starting point for low-cost titanium alloy composition design.On the other hand,the existing titanium alloys are based on the Kroll method to prepare titanium sponge first,which has the disadvantages of high energy consumption,high pollution,high production cost,etc.Therefore,it is another way to reduce the cost of titanium alloy preparation to develop a new process of low cost and clean preparation of titaniumAt present,the industrial preparation methods of titanium and titanium alloy powder mainly include:hydrogenation dehydrogenation method and atomization method,the above methods are all made of sponge titanium of Kroll method,so it is impossible to fundamentally overcome the shortcomings of Kroll method.There are also defects such as high requirements on equipment,complicated process,and high processing cost.Electrochemical reduction and metal thermal reduction methods for the preparation of metal titanium and titanium alloy green clean production technology have not gone out of the laboratory.Aiming at the technical problems existing in the production process of existing titanium and titanium alloy powders,the research group proposed a new idea of preparing Ti-5Al-2.5Fe alloy powder by multi-stage deep reduction method.Firstly,TiO2,Fe2O3 and AI are used as raw materials,Mg is a reducing agent.Self-propagation rapid reduction is carried out to obtain a primary reduction-reduction product mainly composed of low-valent titanium oxide which is primary reduction.Then the primary reduction product is formulated with an appropriate amount of calcium.The reducing agent is subjected to deep reduction deoxidation to obtain a deep reduction product which is multi-stage deep reduction.Finally,the deep reduction product is subjected to dilute hydrochloric acid leaching to remove impurities.The by-products such as MgO and CaO are removed.The sample is dried and filtered to obtain Ti-5Al-2.5Fe powder.The main conclusions of the paper are follows:(1)Thermodynamic analysis results show that the adiabatic temperature of the primary reduction reaction system is>2000 K,higher than the thermodynamic criterion of 1800 K,no matter Mg or Ca are used as reductant,indicating that the actual reaction system could self-sustain in the self-propagating mode.MgTiO3,MgTi2O5,Mg2TiO4,Al2TiO5,MgAl2O4,FeTiO3,Fe2TiO4,FeAl2O4,Fe2MgO4 and other by-product phases may be generated when the metal Mg is used as the reducing agent for primary reduction.However,Ti,Fe and AI in the by-product phases can be reduced to metal elemental substances by Ca in the process of deep reduction.TiO,Ti2O and other low-priced titanium oxides generated by primary reduction reaction can also be reduced to metal Ti by Ca in depth reduction.(2)Primary reduction experiments show that the primary reduction products are mainly composed of TiO,Ti2O and a small amount of Ti6O phase.As Mg/TiO2 increases from 1.6 to 2.4,the oxygen content in the primary reduction product gradually decreases from 29.10%to 11.10%.As the sample preparation pressure increases from 0 MPa to 40 MPa,the oxygen content in the primary reduction product gradually decreases from 28.40%to 18.20%.The increase of the initial atmospheric pressure contributes to the progress of the reduction reaction,and as the reaction atmosphere pressure is increased from 100 Pa to 0.2 MPa,the oxygen content in the primary reduction product is lowered from 25.40%to 15.50%.The suitable process conditions for the primary reduction process are:the dosing amount of Mg is stoichiometric equivalent,the sample preparation pressure is 10 MPa,and the initial reaction atmosphere pressure is 0.1 MPa,and the oxygen content in the primary reduction product prepared at this time is 15.60%.(3)Direct reduction of primary reduction products(refers to direct reduction of primary reduction products by acid leaching).The results show that as the amount of Ca increases from 100%to 500%,the oxygen content in the deep reduction products decreases firstly.The increase was reduces from 5.65%to 0.35%and then increases to 0.65%.As the reduction temperature increases from 800? to 1100?,the oxygen content in the deep reduction product decreases from 0.72%to 0.20%.As the reduction time is extended from 2 h to 6 h,the oxygen content in the deep reduction product decreases from 0.44%to 0.29%.The direct reduction suitable reduction conditions are:the primary reduction product mass to calcium mass ratio of 15.0:14.1,the reduction time is 5 h,and the reduction temperature is 1100?.The chemical composition of the alloy powder prepared under these conditions is:Ti91.59%,A15.47%,Fe2.64%,O0.20%,Mg0.03%,Ca0.07%.It meets the composition requirements of Ti-5Al-2.5Fe alloy.(4)The results of deep reduction after primary acid reduction by acid leaching show that the oxygen content in the deep reduction product decreases from 0.39%to 0.23%with the increase of the amount of Ca.As the reduction temperature increases,the oxygen content in the deep reduction product decreases from 1.45%to 0.19%.As the reduction time prolonges,the oxygen content in the deep reduction product decreases from 0.37%to 0.24%.The reduction conditions of the primary reduction product after acid leaching are as follows:the primary reduction product(after acid leaching)and the calcium mass ratio are 1:1.25,the reduction time is 3 h,and the reduction temperature is 1100?.The chemical composition of the alloy powder prepared under these conditions is:Ti92.39%,A14.88%,Fe2.46%,O0.19%,Mg0.02%,Ca0.06%.It meets the composition requirements of Ti-5Al-2.5Fe alloy. |
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