Design,Thermal Shock Resistance And Corrosion Resistance To Melting Metal Properties Of Y₂O₃-W Graded Materials

The material selection of crucible which is used to smelt metal and high temperature alloy is the key to influence its purity.Although the corrosion resistance and high temperature stability make yttrium oxide?Y2O3?widely used in the field of high temperature alloy melting crucible materials,the poor mechanical properties and thermal shock resistance limit its development and industrial applications.Tungsten?W?and Y₂O₃ have good chemical compatibility at high temperature,meanwhile Y2O3-W composites have many excellent performanc,such as high thermal conductivity,low thermal expansion coefficient and excellent thermal shock resistance,etc.Considering the advantages and disadvantages of W and Y2O3,this paper designs and makes Y2O3-W gradient materials which is used to smelt metal and high temperature alloys.A series of Y₂O₃-W composite materials with gradient change of Y₂O₃ content were prepared by the pressureless sintering and hot pressing sintering process.In order to determine the reasonable sintering process of Y₂O₃-W gradient material,the phase,microstructure and mechanical properties of Y₂O₃-W composites prepared by different sintering processes were studied by using X-ray diffraction?XRD?,scanning electron microscope?SEM?,three point bending,single edge notched beam method and so on.The influence of Y₂O₃ content on the thermal physical properties of Y₂O₃-W composites was studied by means of 402C DIL thermal expansion instrument and LFA 457 laser thermal conductivity analyzer.According to the measured data of mechanical properties and thermal properties of Y₂O₃-W composites,the size and distribution of transient and steady-state thermal stress Y₂O₃-W gradient materials with different component distribution index in the process of preparing are simulated by using ANSYS finite element analysis software,further guide and optimize the design of gradient layer composition and layer thickness of the gradient materials.A series of Y₂O₃-W gradient materials were prepared,the material that meets the service condition of the crucible is optimized by testing the mechanical properties of the material,and the cyclic thermal shock resistance and corrosion resistance are evaluated.The results shows that the densification and mechanical properties of Y2O3-W composites prepared by pressure-less sintering at 1900?gradually decrease with the increase of Y₂O₃ content.The Y₂O₃-W composites prepared by hot-pressing sintering at1600?could achieve almost complete densification when the volume fraction of Y₂O₃ is more than 40%.The mechanical properties of Y₂O₃-W composites prepared by hot pressing sintering at 1600?are all higher than that prepared by pressure-less sintering at1900?.Compared with the microstructure and mechanical properties of Y₂O₃-W composites made by different methods.The hot pressing sintering process at 1600?could be a reasonable sintering process for preparation of Y₂O₃-W graded materialsThermal expansion coefficient of Y₂O₃,W and Y₂O₃-W composites prepared by hot pressing sintering at 1600?increased linearly with increasing temperature.The thermal expansion rate of the material decrease with increasing the Y₂O₃ content,while the thermal expansion coefficient of the material increases at the same temperature.The thermal conductivity of these several materials decreases with the temperature increase.The materials with higher contents of Y₂O₃ have lower thermal conductivity at the same temperature.According to the measured mechanical properties and thermal properties of Y₂O₃-W composites during sintering,the thermal stress finite element simulation results show that intact Y₂O₃-W graded materials may be successfully fabricated when the first layer in Y₂O₃-W graded material which contact with molten is pure Y₂O₃,number of layers?n?is 9and composition distribution index?p?is 0.1.In addition,when the first layer is Y₂O₃-W composites with volume content of Y₂O₃ is 95%and 90%,n is 9 and p is 0.3,the intact Y₂O₃-W graded materials also could be smoothly fabricated.In a series of Y₂O₃-W graded materials which were fabricated by hot pressing at 1600?,the three kinds of Y₂O₃-W graded materials above-mentioned are all in good condition.The guiding significance of finite element simulation results is verified.The facture models of graded materials are typical brittle fracture.However,the flexure strength of Y₂O₃-W graded material is only 218.5MPa when pure Y₂O₃ as the first layer,it means that this kind of material is not suitable for crucible material.When 95 vol.%and 90 vol.%Y₂O₃-W composites as the first layer of graded materials,the residual strength of the two graded materials decreases to 131.8 MPa and 131.2MPa after40 cycles of thermal shocks at 1200-1600?,respectively.Simultaneously the residual strength retention rate decreases to 42.2%and 39.8%,respectively.After 20 cycles of water quenching at 25?-425?,the residual strength of the two materials decreases to 124.6MPa and 150.5MPa and the residual strength retention rate decreases to 39.8%and 45.6%respectively.It is proved that the two graded materials can meet the requirements of high temperature alloy melting crucible materials.With the extension of the corrosion,the line corrosion rates of Y₂O₃ and Y₂O₃-W composites containing 95 vol.%and 90 vol.%Y₂O₃ are gradually reduced and the anti-corrosion performance of Y₂O₃-W composites increases with increasing the Y₂O₃ content in 1200?-1400?cerium molten.The corrosion activation energy of Y₂O₃ and Y₂O₃-W composites containing 95 vol.%and 90 vol.%Y₂O₃ is 395 kJ/mol,356 kJ/mol and 198kJ/mol,respectively.Furthermore,the corrosion resistance against melting metal mechanism of Y₂O₃-W composites were researched.