| Tungsten and its alloys are an excellent refractory metal material,which plays an important role in aerospace,military and nuclear industries.However,pure tungsten still has some problems,such as low-temperature brittleness and recrystallization brittleness,which limit its application range.Therefore,the key to solve the above problems is how to improve the high-temperature strength and reduce the ductile-brittle transition temperature.The results show that doping the second phase particles can inhibit the growth of tungsten grains and improve its properties.At present,rare earth oxides（Y2O3,La2O3）are widely used as doping phases,but their melting points are relatively low,and they are easy to agglomerate and grow in the preparation process.In view of the higher melting point and hardness of Zr O2,this topic selects doped fully stable cubic zirconia（YSZ）to strengthen tungsten alloy.As Zr O2 is easy to change crystal form with temperature,fully stable cubic zirconia（YSZ）can be obtained at room temperature only by adding stabilizer.In this paper,W-YSZ tungsten alloy was prepared by liquid phase doping method.The microstructure and interface relationship in the preparation process were characterized.The hot deformation behavior of the alloy at high temperature was studied,and the effects of rotary forging and annealing on the microstructure and properties of the alloy were analyzed.The irradiation damage and oxidation resistance of W-YSZ alloy were tested.The specific research results are as follows:（1）Yttria stabilized zirconia（YSZ）powder was prepared by hydrothermal method.When the mass ratio of Zr O2to Y2O3is 4:1,zirconia is cubic phase,and excessive doping of Y2O3 can not only stabilize Zr O2,but also refine grain size.Zirconia doped tungsten alloy powders with different crystal forms were prepared by liquid phase doping.When oxygen was doped with stable cubic Zr O2,the grain size of tungsten alloy was the smallest.W-1.5wt.%YSZ alloy was prepared by different sintering methods,among which tungsten alloy obtained by vertical melting sintering had the best comprehensive properties.The interface of W/Zr O2 is well bonded,and the mismatch degree of W（110）and Zr O2（002）is 12%,which is semi-coherent.（2）Adding zirconia and rotary swaging can improve the mechanical properties of tungsten alloy at room temperature.After multi pass rotary swaging,the diameter of tungsten alloy bar is reduced from 9 mm to 5 mm,which are named D9 W-YSZ alloy and D5 W-YSZ alloy respectively.The maximum compressive strength of D5 W-1.5YSZ alloy at room temperature is 2235 MPa and the failure strain is as high as 50.5%.The addition of Zr O2 can delay the recrystallization of tungsten alloy during annealing and inhibit grain growth.When the annealing temperature is lower than 1200℃,the compressive strength of tungsten alloy remains unchanged and the toughness increases.According to the changes of grain structure and hardness after annealing,the recrystallization temperature range of W-1.5YSZ is 1400～1500℃,which is higher than that of pure tungsten.（3）Based on Arrhenius model,the relationship between flow stress,strain rate and deformation temperature of W-1.5YSZ alloy was established.According to the stress-strain curve and microstructure changes,it is considered that the main recovery mechanisms of W-1.5YSZ alloy are dynamic recrystallization（DRX）and dynamic recovery（DRV）.Below 1400℃,DRV plays a leading role in deformation.When the temperature rises to 1400℃,DRX appears in tungsten alloy.The deformation mechanism and instability mechanism of W-1.5YSZ alloy were analyzed by using the obtained hot working diagram,and the hot working process parameters were optimized.（4）The tensile strength and toughness of W-1.5YSZ alloy are improved compared with pure tungsten.At 200℃,the ultimate tensile strength of tungsten alloy is 21.5%higher than that of pure tungsten.At 400℃,the elongation of tungsten alloy is 28.2%higher than that of pure tungsten.Compared with the tungsten materials reported in the literature,the W-1.5YSZ alloy prepared in this subject has a lower DBTT,between 100-150℃.（5）The C-ion irradiation and oxidation resistance of tungsten alloys were studied.W-1.5YSZ alloy added with the second phase has less surface etching under the same irradiation conditions,so it has better anti ion irradiation ability than pure tungsten.With the increase of irradiation dose,the dislocation ring density in pure tungsten increases slowly,while that in W-1.5YSZ alloy increases first and then decreases.This is because W-1.5YSZ has smaller grain size and more grain boundaries,which can effectively absorb some point defects caused by irradiation and reduce the dislocation density.Therefore,after ion irradiation under the same conditions,the size and number of dislocation rings produced by W-1.5YSZ alloy are smaller.The oxidation degree of W-1.5YSZ alloy deepens with the increase of temperature and time.At 400℃,there is still a large amount of W on the surface of W-1.5YSZ.When the oxidation temperature is 800℃,the surface has been completely oxidized,and the reaction product is mainly m-WO3.According to the mass change curve and morphology analysis after oxidation,the oxidation resistance of W-1.5YSZ is better than that of pure tungsten at high temperature.In conclusion,in order to meet the application requirements of tungsten alloy inaerospace,nuclear energy and other industrial fields and solve the problems of low-temperature brittleness and irradiation brittleness of tungsten alloy,YSZ reinforced tungsten alloy was prepared by liquid phase method,which reduced the DBTT of the material and improved its comprehensive mechanical properties.This paper provides some ideas and theoretical guidance for the development and application of new tungsten alloys. |
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