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首页> 外文学位 >Effects of thermal and mechanical processing on microstructures and desired properties of particle-strengthened copper-chromium-niobium alloys.
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Effects of thermal and mechanical processing on microstructures and desired properties of particle-strengthened copper-chromium-niobium alloys.

机译：热处理和机械加工对颗粒增强的铜铬铌合金微结构和所需性能的影响。

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Ternary Cu-Cr-Nb alloys, particularly Cu-8 Cr-4 Nb (in at.%), have demonstrated good thermal stability as well as high strength and high conductivity at low and high temperatures. This behavior—due to the insoluble and strong Cr2Nb intermetallic phase that forms from the 2:1 Cr/Nb ratio—has put Cu-Cr-Nb alloys at the forefront as the next-generation particle-strengthened Cu alloys for aerospace applications. The initial powder material, produced by Ar-gas atomization, has a bimodal size distribution of Cr2Nb precipitates. Primary Cr2Nb precipitates, formed congruently from the melt, are typically ∼1 μm in size, and secondary Cr2Nb particles, precipitated from atomized solid solution, are typically 30–200 nm in size. This study provides the first detailed examination of the stability and strengthening effects of these particles in Cu-Cr-Nb alloys. Extruded Cu-8 Cr-4 Nb exposed to temperatures of up to 1323 K for up to 100 hr sustained a drop in strength of only 25–30%.; This investigation also revealed that the primary particles, usually situated at grain boundaries and triple points, provide a direct grain boundary pinning effect, and moreover, an indirect, grain boundary strengthening effect, but virtually no Orowan strengthening effect. The secondary Cr2Nb particles, typically found within grains (and to a lesser extent, at grain boundaries), do provide Orowan strengthening. For extruded material, it was established that grain-boundary strengthening (Hall-Petch effect) accounts for about two-thirds of the overall strength of material, with Orowan effects essentially contributing the remainder. The proven thermal stability, strengthening effects and, more importantly, strength retention, was the driving force to further improve upon these attributes via microstructural refinement of Cu-Cr-Nb alloys.; Mechanical milling (MM) of Cu-4 Cr-2 Nb and Cu-8 Cr-2 Nb produced an increase in hot pressed Vickers hardness of 122% and 96%, respectively. However, MM also inadvertently produced a corresponding decrease in electrical conductivity of ∼33% for both alloys. The increase in hardness was more due to Cu grain-size refinement than to second-phase particle-size refinement. The drop in conductivity was due to second-phase particle-size refinement, which increased both particle/matrix interfacial area and solute solubility. This novel detailed study also proved the enhanced stability of mechanically processed Cu-4 Cr-2 Nb. Hot pressed 4 hr-milled Cu-4 Cr-2 Nb experienced a 30% increase in conductivity with only a 22% drop in hardness when annealed at 1273 K for 50 hr. Such changes were largely due to an increase in dispersed-particle size (decrease in solute and interfacial electron scattering) and Cu grain size (reduced Hall-Petch effect), respectively. (Abstract shortened by UMI.)
机译：三元Cu-Cr-Nb合金，特别是Cu-8 Cr-4 Nb（原子％），在低温和高温下均表现出良好的热稳定性以及高强度和高电导率。这种行为-由于由2：1 Cr / Nb比形成的不溶性强Cr 2 Nb金属间相，使Cu-Cr-Nb合金成为下一代粒子居于首位。航空航天应用的高强度铜合金。氩气雾化生产的初始粉末材料具有Cr 2 Nb沉淀物的双峰尺寸分布。由熔体一致形成的一次Cr 2 Nb沉淀物的大小通常约为1μm，而从雾化的固溶体中沉淀出来的二次Cr 2 Nb颗粒的大小通常为30尺寸为–200 nm。这项研究提供了对这些颗粒在Cu-Cr-Nb合金中的稳定性和增强作用的首次详细检查。挤压的Cu-8 Cr-4 Nb暴露在高达1323 K的温度下长达100个小时，其强度仅降低了25％至30％。该研究还表明，通常位于晶粒边界和三点处的初级粒子提供直接的晶粒边界固定作用，此外，还提供间接的晶粒边界强化作用，但实际上没有Orowan强化作用。 Cr 2 Nb次级颗粒通常在晶粒内（且在较小程度上在晶界处）发现，确实提供了Orowan增强作用。对于挤压材料，已经确定，晶界强化（Hall-Petch效应）约占材料总强度的三分之二，而Orowan效应则主要贡献了其余部分。业已证明的热稳定性，增强作用以及更重要的是强度保持力，是通过对Cu-Cr-Nb合金进行微观组织细化而进一步改善这些属性的驱动力。 Cu-4 Cr-2 Nb和Cu-8 Cr-2 Nb的机械铣削（MM）使得热压维氏硬度分别提高了122％和96％。但是，MM也会无意中使两种合金的电导率相应降低约33％。硬度的增加更多是由于铜晶粒细化而不是第二相粒度细化。电导率的下降归因于第二相粒度的细化，这增加了颗粒/基质的界面面积和溶质的溶解度。这项新颖的详细研究还证明了机械加工的Cu-4 Cr-2 Nb具有增强的稳定性。在1273 K退火50 hr后，热压4 hr碾磨的Cu-4 Cr-2 Nb的电导率增加30％，而硬度仅降低22％。这种变化主要是由于分散粒径的增加（溶质和界面电子散射的减小）和铜晶粒尺寸的增加（霍尔-Petch效应降低）所致。 （摘要由UMI缩短。）

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