【作者】 张勇；

【导师】 梁超平； 马运柱；

【作者基本信息】 中南大学 ， 工程（专业学位）， 2022， 硕士

【摘要】 钨是一种具有高密度、高熔点、高硬度和良好化学稳定性的难熔金属材料,被广泛应用于军事装备、航空航天及工业生产等领域。但是纯钨由于位错室温迁移率低,滑移派纳力大导致其具有明显的室温脆性。传统W-Ni-Fe合金的失效也是以W颗粒的穿晶解理断裂为主,因此改善W颗粒的本征脆性,对提升钨合金的强韧性具有重要意义。Ta、Re元素与W具有良好的晶格匹配性,且与W固溶后能降低位错运动阻力,从而改善W的本征特性。基于此,本研究从固溶改性的角度入手,采用固态合金化法制备W-Ta/Re合金粉末,创新性地以W-Ta/Re固溶体颗粒替代W颗粒作为烧结核心与Ni-Fe系共烧结,制备了90（W-Ta）-7Ni-3Fe与90（W-Re）-7Ni-3Fe合金。系统研究了固态合金化粉末组织物相演变规律,探究了预合金化Ta、Re添加对钨合金烧结组织、元素扩散、相转变以及力学性能的影响。主要研究结果如下:（1）W-Ta、W-Re粉末固态合金化过程经历粉末压延变形、破碎细化、冷焊断裂平衡几个阶段。使用硬质合金球磨罐与球磨珠,在转速300 rpm下,以无水乙醇为球磨介质,球料比10:1,球磨60 h后,可制备低引杂,元素分布均匀的W-20 wt.%Ta/Re固溶体粉末。（2）以预合金化W-Ta粉末为骨架制备出90（W-Ta）-Ni-Fe合金,揭示了W颗粒固溶与粘结相纳米析出的协同强化机理。90（W-Ta）-Ni-Fe合金在1450℃下烧结1 h可实现98%以上的相对密度。烧结升温过程中固溶的Ta从W-Ta颗粒中析出,与Ni发生共晶反应降低了液相形成温度。冷却过程中粘结相中发生包晶反应析出了纳米级针状Ni₃Ta相,改善了组织均匀性,提升了合金相对密度。Ta的固溶强化了W颗粒,析出的针状相强化了粘结相,使合金整体硬度上升。相较于传统直接添加,预合金化使合金界面失效转变为W颗粒穿晶解理与粘结相的韧性撕裂。（3）揭示了W-Re合金粉末与Ni-Fe系共烧结过程中的元素扩散与晶粒细化机制,成功制备出高强度90（W-Re）-Ni-Fe合金。合金最佳烧结工艺为1480℃下保温1.5 h。通过预合金化固溶的Re在烧结后主要仍保留于W颗粒中。少量进入粘结相的Re不与Ni-Fe发生相反应,而是形成了均匀的γ-（Ni,Fe,Re）固溶体。由于Re在粘结相中的固溶,抑制了W颗粒的溶解析出过程,使W颗粒平均晶粒尺寸由33.78μm缩小至12.67μm。90（W-Re）-Ni-Fe合金由于细晶强化与固溶强化的作用,在0—20 wt.%的添加范围内,随Re含量的增加合金强度先上升后下降,5 wt.%时强度达到1.05GPa。但合金失效模式由穿晶断裂转变为W颗粒与粘结相的界面失效,导致了韧性下降。图76幅,表19个,参考文献98篇更多还原

【Abstract】 Tungsten is a refractory metal with high density,high melting point,high hardness and good chemical stability.It is widely used in military equipment,aerospace and industrial production.However,pure tungsten has obvious room temperature brittleness due to low dislocation mobility at room temperature and large slip force.The failure of traditional W-Ni-Fe alloys is also dominated by the transgranular cleavage fracture of W particles.Therefore,improving the intrinsic brittleness of W particles is of great significance for improving the strength and toughness of tungsten alloys.Ta and Re elements have good lattice matching with W,and can reduce the resistance of dislocation motion after solid solution with W,thereby improving the intrinsic properties of W.Based on this,from the perspective of solid solution modification,W-Ta/Re alloy powder was prepared by solid-state alloying method.90（W-Ta）-7Ni-3Fe and 90（W-Re）-7Ni-3Fe alloys were prepared by co-sintering with Ni-Fe System with W-Ta/Re solid solution particles instead of W particles as sintering core.The microstructure and phase evolution of solid alloyed powder were systematically studied.The effects of pre alloyed Ta and Re on the sintering structure,element diffusion,phase transformation and mechanical properties of tungsten alloy were investigated.The main results are as follows:（1）The solid-state alloying process of W-Ta and W-Re powders goes through several stages:powder calendering deformation,crushing refinement and cold welding fracture balance.W-20wt.%Ta/Re solid solution powder with low impurity and uniform element distribution can be prepared by using cemented carbide ball milling tank and ball milling beads at 300 rpm,anhydrous ethanol as ball milling medium,ball material ratio of 10:1 and ball milling for 60 h.（2）90（W-Ta）-Ni-Fe alloy was prepared with pre alloyed W-Ta powder as skeleton.The synergistic strengthening mechanism of solid solution of tungsten particles and nano precipitation of matrix phase was revealed.90（W-Ta）-Ni-Fe alloy sintered at 1450℃for 1 h can achieve a density of more than 98%.The solid solution of Ta strengthens W particles,and the precipitated acicular phase strengthens the bonding phase,which increases the overall hardness of the alloy.During the sintering heating process,the solid solution Ta precipitates from W-Ta particles,and eutectic reaction occurs with Ni,which reduces the liquid phase formation temperature.During the cooling process,peritectic reaction occurs in the bonding phase,and nano acicular Ni₃Ta phase is precipitated,which improves the microstructure uniformity and the density of the alloy.Compared with the traditional direct addition,pre alloying changes the interface failure of the alloy into the ductile tearing of W particle transgranular cleavage and matrix phase,which increases the tensile strength of the alloy.（3）The mechanism of element diffusion and grain refinement in the co-sintering process of W-Re alloy powder and Ni-Fe system was revealed,and the high-strength 90（W-Re）-Ni-Fe alloy was successfully prepared.The optimum sintering process of the alloy is holding at 1480℃for 1.5 h.Re dissolved by pre-alloying is mainly retained in W particles after sintering.A small amount of Re entering the matrix phase does not react with Ni Fe,but forms a uniform phaseγ-（Ni,Fe,Re）solid solution.Due to the solid solution of Re in the matrix phase,the dissolution and precipitation process of W particles is inhibited,and the average grain size of W particles is reduced from 33.78μm to 12.67μm.The tensile strength and hardness of 90（W-Re）-Ni-Fe alloy were significantly improved due to fine grain strengthening and solid solution strengthening,and reached the highest strength of 1.05 GPa at 5 wt.%.However,the failure mode of the alloy changed from transgranular fracture to interface failure between W particles and matrix phase,resulting in the decrease of toughness.更多还原