Influence Of Plastic Deformation On Microstructure And Property Of Tungsten Alloys

Fusion energy is an important way for solving mankind’s energy demand in the future. One of the key issues for the application of fusion is the development of plasma facing materials (PFMs), which will be subjected to irradiation and heat fluxes. Tungsten (W) is considered as the most important candidate for PFMs due to its high melting point, high thermal conductivity, excellent high temperature mechanical properties and low deuterium/tritium retention, etc. However, serious brittleness limits its real application. It has been proven that plastic deformation and second phase doping can improve the brittleness of W. Besides, transient heat flux resistance and particle irradiation resistance also determine whether PFM meets the requirements of nuclear fusion devices. Particle irradiation resistance of W grain is related to the crystal orientation, thus the irradiation resistance of W can be improved by adjusting its texture characteristics. So pure tungsten (PW), W-1.0wt%La2O3 (WL10), potassium bubble doped tungsten (W-K) were prepared by plastic deformation. Then the microstructure, texture level, mechanical properties, especially the strength and ductile-brittle transition temperature (DBTT) as well as thermal conductivity were investigated. Subsequently, the transient heat flux resistance, texture characteristics were also characterized.Firstly, PW, WL10 samples with various reductions were prepared by unidirectional rolling. For PW, the 60% rolled sample exhibited the highest bending strength (1068 MPa), lowest DBTT (823-873 K), highest thermal conductivity (176.5 W/mK) and Charpy energy. For WL10, the 52% rolled sample showed the higher bending strength (1312 MPa), lowest DBTT (723-773 K), higher thermal conductivity (140.1 W/mK) and highest Charpy energy. Thus the optimal rolling reduction was 60% and 52% for PW and WL10, respectively. Rolled PW and WL10 with moderate deformation degrees not only ensured the grain refinement effect, substructure toughening effect but also avoided the brittle fracture induced by high textue level and microcracks. Then "swaging+rolling" technique was adopted to prepare the W-K. Fiber level (aspect ratio of fiber), texture level (volume fraction of main textures), microcracks, dynamic recrystallization and second phase were the main factors influencing the strength and toughness of W. The "swaged+rolled" W-K exhibited the lowest bending strength (856 MPa) and highest DBTT (923 K) due to the microcracks. The 52% rolled WL10 showed the highest bending strength (1312 MPa), lowest DBTT (723-773) and highest Charpy energy due to the few microcracks, lots of fine dynamic recrystallization grains and pinning effect on dislocation and grain boundary induced by La2O3 particles. The 60% rolled PW displayed the moderate bending strength (1068 MPa) and DBTT (823-873 K). Besides, compared with the 60% rolled PW, the "swaged+rolled" W-K exhibited higher Charpy energy, which was attributed to the possible dislocation pinning effect and annihilation effect of potassium bubbles.Afterwards, the transient thermal shock and fatigue performance of the 60% rolled PW,52% rolled WL10 and "swaged+rolled" W-K was evaluated by the electron beam in EMS-60. For PW, the cracking threshold was 0.22-0.44 GW/m2 and the melting threshold and recrystallization threshold were above 1.1 GW/m2. For WL10, the cracking threshold was below 0.22 GW/m2, the melting threshold was 0.66-0.88 GW/m2 and the recrystallization threshold were above 1.1 GW/m2. For W-K, the cracking threshold was 0.44-0.66 GW/m2, the melting threshold was above 1.1 GW/m2 and the recrystallization threshold was 0.44-0.66 GW/m2. In the case of thermal fatigue resistance, cracks occurred till 1000 cycles of 0.24 GW/m2 for PW and 100 cycles of 0.17 GW/m2 for WL10. W-K endured 1000 cycles of 0.44 GW/m2 without showing any signs of cracking instead of significant roughness and recrystallization. The best transient heat flux resistance of W-K may be caused by the dislocation pinning effect and possible annihilation effect of potassium bubbles. The worst transient heat flux resistance of WL10 can be attributed to its low thermal conductivity and decomposition, melting of La2O3.Finally, the effect of rolling manner, rolling reduction, doping La2O3 and recrystallization on the texture characteristics of W was investigated systemically. The results indicated that 1) compared with cross and clock rolled PW, the unidirectional rolled PW showed strong{100} texture and weak{111} texture.2) Dynamic recovery and dynamic recrystallization were the main factors influencing the texture evolution during the hot rolling process. Dynamic recovery intensified the{001}<110> texture of 72%,80% rolled PW and 43%,57%,72% rolled WL10. Dynamic recrystallization intensified the {001}<100> texture of 80% rolled PW and 72% rolled WL10.3) Recrystallization resulted in the rise of {100} texture for unidirectional and clock rolled PW and the drop of{111} texture for cross and clock rolled PW.