颗粒尺寸对钨铜合金组织性能及电弧烧蚀特性的影响

发布时间：2019-05-16 16:26

【摘要】：钨铜合金因其良好的导电、导热、耐电弧侵蚀性及抗熔焊性被广泛应用于触头材料、电极材料、航空航天用耐烧蚀材料。众所周知,粗晶材料有较好的高温性能,但细晶的钨铜合金具有分散电弧、耐电弧烧蚀性。针对不同应用场合的钨铜合金,本文采用不同粒度的钨粉并结合熔渗工艺制备出不同颗粒(晶粒)尺寸的CuW70合金。运用SEM、高温蠕变实验、模拟高压电弧烧蚀实验等探讨了颗粒尺寸对钨铜合金组织结构与相关性能的影响,同时利用第一性原理分析计算了不同颗粒尺寸CuW70合金的场发射电子能力,探讨了细晶钨铜合金耐电弧烧蚀性的电击穿机理。研究结果表明:(1)室温下,钨铜合金硬度和抗压强度随颗粒尺寸的增大而减小,电导率则随颗粒尺寸的增大而升高,当颗粒尺寸由0.52 μtm变为20.69 μm时,相对密度、硬度、抗压强度、电导率分别从 99.2 %、202 HB、1232.17 MPa、42.8 %IACS 变化为 97.5 %、179 HB、1116.31 MPa、44.6 %IACS;而高温下,粗晶粒的钨铜合金表现出良好的抗蠕变性能,随颗粒尺寸的减小合金的蠕变寿命变短,颗粒尺寸由0.52 μm变化到20.69 μuμm时,合金蠕变寿命由26.3 h提高到87.2 h。(2)室温下,试样的断口形貌为典型的解理断口形貌特征,断口以W-Cu界面断裂和W-W界面断裂为主;高温下,材料内部加热温度过高,削弱了钨相和粘结相铜的界面结合强度,同时,铜相断裂时所需剪切应力较钨相低,故裂纹容易在两相界面和铜相上产生,最终断口以W-Cu界面断裂和铜相延性断裂为主。.(3)同一击穿电压下,细晶钨铜合金相对于粗晶的首击穿烧蚀面积大,击穿坑多而浅,100次电击穿后,表面均有铜的飞溅沉积,出现大量的孔洞和裸露的钨骨架,颗粒越粗该现象越明显。细晶铜相分散,散热快,烧蚀面积大,烧蚀比较缓和;而粗晶合金铜相相对集中,烧蚀在此区域集中进行,最终导致铜相大量损失,烧蚀严重。(4)细晶比粗晶更耐电弧烧蚀,其机理一是细晶钨铜合金中铜相分布细小均匀,电弧不会在富铜区域聚集,而是均匀分布在阴极材料表面;二是细晶钨铜合金中W骨架致密,微小的铜滴可嵌在钨骨架中,使多次击穿后合金表面仍保持光滑平整,微凸起引发的场致电子发射几率减小,利于提高阴极材料的电击穿性能;三是细晶晶界的功函数降低,从而降低阴极温度和材料的蒸发,以此来减轻电弧烧蚀。(5)随外加电场增大,钨铜合金费米能级处态密度增大,外电场从0.087 Ha变化到0.12 Ha,态密度值从199.62 Ha增加到244.01 Ha。细颗粒钨铜合金耐电压强度高故外加电场强度大,态密度表示单位能量范围内的电子数,故细晶场发射电子能力强。细颗粒钨铜合金耐电弧烧蚀原因:一是细颗粒钨铜合金,钨相和铜相的均匀分布使势垒宽度变窄,电子易隧穿出固体表面,场发射电子能力强;二是内电场在钨铜晶界处形成,电子在晶界处聚积,电击穿容易在此发生,而细晶晶界较多,电子发射点在材料表面分散进行,使得试样烧蚀较轻。
[Abstract]:The tungsten-copper alloy is widely used in contact materials, electrode materials and aerospace-resistant materials because of its good conductivity, thermal conductivity, arc erosion resistance and resistance to fusion. It is well known that the coarse-grained material has good high-temperature performance, but the fine-grained tungsten-copper alloy has the advantages of dispersing arc and arc-resistance. The CuW70 alloy with different particle size (grain size) was prepared by using tungsten powder with different particle size and in combination with the infiltration process. The effect of particle size on the structure and related properties of the tungsten-copper alloy structure was discussed by means of SEM, high-temperature creep experiment and high-pressure arc ablation experiment. The first principle was used to analyze the field emission electron capability of the CuW70 alloy with different particle sizes. The electric breakdown mechanism of fine-grained tungsten-copper alloy is discussed. The results show that: (1) The hardness and compressive strength of the tungsten-copper alloy decreases with the increase of the particle size, and the conductivity increases with the increase of the particle size, and when the particle size is changed from 0.52. m to 20.69. m u.m, the relative density, hardness, compressive strength, The electrical conductivity changed from 99.2%, 202HB, 1232.17MPa, 42.8% IACS to 97.5%,179 HB, 1116.31 MPa and 44.6% IACS, respectively. The creep life of the alloy was increased from 26.3 h to 87.2 h when the particle size was changed from 0.52. m u.m to 20.69. m The internal heating temperature of the material is too high, the interface bonding strength of the tungsten phase and the bonding phase copper is weakened, and at the same time, when the copper phase is broken, the required shear stress is lower than that of the tungsten phase, so that the crack can be easily generated on the two-phase interface and the copper phase, and the final fracture is mainly caused by the fracture of the W-Cu interface and the ductile fracture of the copper. (3) Under the same breakdown voltage, the area of the fine-grained tungsten-copper alloy with respect to the first breakdown and ablation area of the coarse crystal is large, the breakdown pit is more and shallow, and after 100 times of electrical breakdown, the surface all has the splashing and deposition of copper, a large number of holes and a bare tungsten skeleton appear, and the more coarse the particles are. The fine-grained copper phase is dispersed, the heat dissipation is fast, the ablation area is large, the ablation is relatively mild, and the copper phase of the coarse-crystal alloy is relatively concentrated, and the ablation is concentrated in the region, so that the copper phase is greatly lost and the ablation is serious. (4) the fine crystal is more resistant to arc ablation than the coarse crystal, the mechanism is that the copper phase in the fine-grained tungsten-copper alloy is fine and uniform, the arc does not collect in the copper-rich region, but is uniformly distributed on the surface of the cathode material; the W-framework in the fine-grained tungsten-copper alloy is compact, and the tiny copper drops can be embedded in the tungsten skeleton, The surface of the alloy after multiple breakdown is still smooth and flat, the field electron emission probability caused by the micro-bump is reduced, and the electric breakdown performance of the cathode material is facilitated; and thirdly, the work function of the fine crystal grain boundary is reduced, so that the cathode temperature and the evaporation of the material are reduced, so that the arc ablation is reduced. (5) With the increase of the applied electric field, the state density of the Fermi level of the tungsten-copper alloy is increased, the external electric field changes from 0.087Ha to 0.12Ha, and the state density value is increased from 0.62Ha to 244.01 Ha. The fine-grain-tungsten-copper alloy has high voltage-resistant strength, and the applied electric field intensity is large, and the state density indicates the number of electrons in the unit energy range, so that the fine-grain field emission electronic capacity is strong. the reason for arc ablation of the fine-particle tungsten-copper alloy is that the uniform distribution of the fine-particle tungsten-copper alloy, the tungsten phase and the copper phase makes the width of the barrier narrow, the electrons are easily tunneled out of the solid surface, the field emission is strong, the second is that the internal electric field is formed at the grain boundary of the tungsten copper, and the electrons are accumulated at the grain boundary, The electrical breakdown is easy to take place, and the fine crystal cell is more, and the electron emission point is dispersed on the surface of the material, so that the ablation of the sample is light.
【学位授予单位】：西安理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.411

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