稀土Y掺杂W-Ni-Fe复合粉末与合金制备过程中稀土Y赋存状态研究

【作者】 彭石高；

【导师】 范景莲；

【作者基本信息】 中南大学 ， 粉体材料科学与工程， 2008， 硕士

【摘要】 高密度钨基合金具有一系列优异的物理、力学性能,在军用和民用领域中具有不可替代的作用。细化钨晶粒组织可以提高高密度钨合金的性能,细晶钨合金材料已成为当今世界研究的热点之一。制备纳米/超细粉末和控制合金晶粒长大是制备高性能细晶钨基合金材料的核心,添加微量元素制备超细粉末、细化合金组织已成为一个重要研究方向,本论文针对添加稀土元素Y制备纳米级W-Ni-Fe复合粉末及其合金进行了较系统、较深入的研究,为进一步深入研究稀土改性高密度钨基合金提供一定的理论与实验基础。实验采用喷雾干燥法制备不同Y含量W-Ni-Fe前驱体粉末,经煅烧后采用两步还原工艺进行还原,研究稀土Y对纳米/超细复合粉末物相组成与变化规律的影响。结果表明:经600℃煅烧后稀土Y与W结合生成了复合氧化物相Y₂W₃O₁₂,这种复合氧化物相在低于600℃氢气气氛下还原时非常稳定,在温度达到700℃时,复合氧化物相Y₂W₃O₁2)中的部分钨被还原,Y含量为5%时含稀土相为Y₂WO₆,Y含量为10%和20%时,含稀土相为Y₂WO₆和Y₆W₂O₁₅。而W-Ni-Fe复合粉末的颗粒长大机理主要是由钨还原过程中的化学气相迁移所控制,随还原过程的进行,所生成的水蒸汽逐渐增多,钨的氧化物与水蒸汽化合成易挥发的水合物WO_x·nH₂O（一般认为是WO₃·H₂O）,而后通过气相迁移,沉积在低价氧化钨或金属钨粉的颗粒表面,导致颗粒长大,由于稀土Y的复合氧化物相的存在,阻止了还原过程中钨的氧化物与水蒸汽化合生成易挥发水合物WO₃·H₂O的生成速度和含量,从而减少了其气相迁移,有效地阻止了粉末颗粒的长大。当稀土元素质量百分数在0-20%范围内变化时（占90W-7Ni-3Fe复合粉末的质量百分数）,随着稀土元素含量的增大,还原粉末越细。深入研究了稀土元素Y在合金中的分布和存在形态以及对纳米粉90W-Ni-Fe合金组织和性能的影响,较好地解释了稀土元素Y与合金性能和显微结构的关系。稀土Y以Y₂O₃的形式存在于合金中,随着Y含量的增加,钨晶粒越细。添加0.4%稀土元素Y后,试样液相烧结温度降低,少量稀土Y可以增加钨晶粒的穿晶解理断裂,改善合金的延性,并对W晶粒起到了有效的细化作用。随着稀土Y含量的增加,在合金中会出现富Y区域,且稀土Y成梯度从远离钨颗粒点向钨颗粒边缘区域递减。稀土含量过多,合金性能下降。更多还原

【Abstract】 High-density tungsten-based alloys with a series of excellent physical, mechanical properties, plays an irreplaceable role in the field of military and civilian. Refinement of tungsten grain organizations can increase high-density tungsten alloy performance, fine-grained material tungsten alloy has become one of the hot study spots in today’s world. The core of preparation high-performance fine-grained material tungsten-based alloys is preparation Nano / ultra-fine powder and control alloy grain growth. Add trace elements of ultra-fine powder, refined alloys has become an important research direction,this paper conducts a more systematic, more specially studies about the preparation of nano-W-Ni-Fe composite powder and alloy against add Y , which is further modified in-depth study of rare earth high-density tungsten-based alloys provide a theoretical and experimental basis.The method of Spray-dried is used to prepare W-Ni-Fe precursor powder with add different content Y in this experimental. Reducing the precursor powder by a two-step reduction process. the composite powder phase composition and changes in law with adding rare earth Y is studied . The results show, the rare earth Y and W formed by complex oxides phase Y₂W₃O₁₂ after calcined at 600℃. The complex oxides are very stable during hydrogen reduction of less than 600℃. When the temperature reaches 700℃, some tungsten in complex oxides phase is reduced, the rare earth phase is Y₂WO₆ with adding Y content of 5% , the rare earth phase is Y₂WO₆ and Y₆W₂O₁₅with adding Y content of 10% and 20%. Air phase transfer which mainly resulted in growth of particles during reduction was put forward. With the increasing of vapour produced during reduction, volatile WO_X·nH₂O was easy synthesized by tungsten oxide and vapour WO_X·nH₂O deposited in surface of oxide tungsten with lower chemistry value or metal tungsten powder and resulted in growth of particles. Adding rare earth Y were put forward in order to inhibit growth of particles in this paper. When adding rare earth elements Y, Complex oxides phase formed and adsorbed on surface of metal tungsten particles or tungsten oxide particles. The rate of producing volatile WO_X·nH₂O was prevented from synthesizing of tungsten oxide and vapour, then air phase transfer was decreased. Growth of powder particles were hold back. When the rare earth element content changes from 0 wt% to 20 wt%, with the increasing of the rare earth elements content, the Particle sizeof the composite powder improved distinctly.In-depth study the distribution and morphology of the rare earth element Y in the alloy ,and explain the relationship between the rare earth element Y and the properties and microstructure of alloy. Rare earth element Y formed by Y₂O₃ in the alloy, With the increase of the rare earth element Y, the grain of tungsten decreased. Add rare earth element Y 0.4wt%, the liquid phase sintering temperature lower, a small amount of rare earth Y can increase the grain size of tungsten transgranular cleavage fracture and improve the ductility alloy, and has played an effective grain refinement. With rare earth Y increasing, the Y-rich region in the alloy appears, and rare earth Y-gradient from the tungsten particles from the point of tungsten particles to the brink of regional decline. Excessive content of rare earth ,the properties of alloy decreased.更多还原