【作者】 刘文龙；

【导师】 孙本哲；

【作者基本信息】 东北大学 ， 材料物理与化学， 2020， 硕士

【摘要】 难熔金属通常是指钨(W)、钼(Mo)、钽(Ta)、铌(Nb)和铼(Re)五种过渡金属。由于钨及其合金具有熔点高、高温强度高、对液态金属腐蚀抗性强、良好的加工可塑性和较低成本等优势,这使其在高温服役环境下得到较好的应用。然而,近年来国防军工、航空航天、核工业等尖端科技领域的快速发展,对相关部件在超高温条件下服役强度和耐蚀性等性能提出了更高的要求。因此,有必要通过固溶强化、弥散强化、形变强化以及多种复合强化方式来提高钨合金的总体性能。碳化铪(HfC)是一种超高温、抗氧化的陶瓷材料,具有电热传导性良好和热膨胀小的优点,它是钨高温强化中最有效的第二相粒子。然而,HfC的强化效果是与其热稳定性和在钨基体中的尺寸与分布直接相关的。本论文以W-HfC二元体系和W-Re-HfC三元体系合金样品为研究对象,通过Re的固溶强化和HfC的弥散强化,来满足超高温服役性能要求。论文详细表征与研究合金的相组成及微观结构,重点分析各类第二相粒子的颗粒形状以及在钨基体上的分布情况,并探讨原始成分和制备工艺对合金微观组织结构的影响。研究发现,W-HfC二元合金体系由W基体和少量第二相粒子构成,其中,第二相粒子主要包括HfO2、W6C2.54和W2C类颗粒,初始碳源首先与W发生反应,生成了 W2C和W6C2.54,而HfH2中的Hf原子优先与O发生反应生成了 HfO2,仅有少量Hf原子进入到W2C类化合物中形成二次固溶体(W2-xHfx)C;在分别含 0.3 wt.%Hf 和 3.0 wt.%Hf 的两类 W-Re-HfC 三元体系中都观察到具有面心立方结构(FCC)的HfC第二相粒子,但颗粒尺寸较大;Re固溶到W基体中起到固溶强化作用,Re的加入降低了 Hf在W基体中含量,导致在基体晶界上形成部分HfC颗粒;在含有3.0wt.%Hf的三元体系中,HfH2和C反应生成HfC时,HfC内部分Hf原子和W原子发生了置换,从而形成Hf1-xWxC;过剩的Hf原子与不足的O形成了HfO2-x相。本论文研究对获得细小HfC第二相粒子以满足超高温的力学性能要求研究提供一定的理论依据。更多还原

【Abstract】 Refractory metals generally refer to five transition metals:tungsten(W),molybdenum(Mo),tantalum(Ta),niobium(Nb),and rhenium(Re).With many advantages including high melting point,high-temperature strength,strong resistance to liquid metal corrosion,good processing plasticity and low cost,W and its alloys have better application in high-temperature service environments.However,in recent years,with the development of advanced scientific and technological fields,such as defense military industry,aerospace and nuclear industry,the strength and corrosion resistance of relevant mechanical components under ultra-high temperature conditions are unable to meet requirements.Therefore,it is necessary to improve the overall performance of W and its alloys through solid solution,dispersion and deformation strengthening mechanisms,as well as multiple composite strengthening mechanism.Since hafnium carbide(HfC)is an ultra-high temperature and oxidation resistant ceramic material and has the advantages of good electrical and thermal conductivity and small thermal expansion,it has been an efficient second-phase strengthening particle in W and its alloys.Nevertheless,the strengthening effect of HfC is related closely to its thermal stability,size and distribution in W matrix.The W-HfC binary system and W-Re-HfC ternary system are considered as the research objects in this thesis.The solid solution strengthening of Re and the dispersion strengthening of HfC are used to meet the requirements of performance under ultra-high temperature conditions.The phase composition and microstructure of the two systems were characterized and investigated in detail.The morphology and distribution of various second-phase particles,as well as the effects of the original composition and preparation process on the microstructure of the alloy,were discussed and analyzed particularly in this thesis.It is found that that the W-HfC binary system is composed of W matrix and a small number of second-phase particles involving mainly HfO2,W6C2.54,and W2C-like particles.The initial carbon source reacts with W,leading to the formations of W6C2.54 and W2C-like particles.Meanwhile,the Hf atoms in HfH2 preferentially react with 0 to form HfO2,and only a small amount of Hf atoms is incorporated into the W2C lattice to form a secondary solid solution W2-xHfxC.In the two types of W-ReHfC systems containing 0.3 wt.%Hf and 3.0 wt.%Hf respectively,the HfC-like second-phase particle with a face-centered cubic(FCC)structure can be captured frequently.Unfortunately,the sizes of particle were large.Here,Re solid solution into W matrix plays a role in solid solution strengthening.The addition of Re into W matrix causes a decrease in solid solubility of Hf in W matrix,resulting in the formation of some HfC particles on the grain boundaries of W matrix.When HfH2 and C react to form HfC in the ternary system containing 3.0 wt.%Hf,some W atoms are also merged into HfC-like FCC structure and occupy the Hf-sites,bringing about an appearance of the secondary solid solution Hf1-xWxC.Additionally,the excess Hf atoms and insufficient O atoms form the HfO2-x phase.The research in this thesis provides a certain theoretical basis for obtaining fine HfC second-phase particles to meet the requirements of ultra-high temperature mechanical properties.更多还原