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Superplastic Foaming of Titanium and Ti-6Al-4V

机译:钛和Ti-6Al-4V的超塑发泡

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Solid-state foaming of metals can be achieved by hot-isostatic pressing of powders in presence of argon followed by expansion of the resulting high-pressure argon bubbles at ambient pressure and elevated temperature. This foaming technique was first demonstrated by Kearns et al. [1] for Ti-6Al-4V, but is limited by its low creep rate and ductility, which lead to early cell wall fracture. We address these issues by performing the foaming step under superplastic conditions. Rather than using microstructural superplasticity (requiring fine grains which are difficult to achieve in porous powder-metallurgy materials), we used transformation superplasticity, which occurs at all grain sizes by biasing with a deviatoric stress (from the pore pressure) of internal stresses (from the allotropic mismatch during thermal cycling about the allotropic temperature range). As compared to control experiments performed under isothermal creep conditions, superplastic foaming under temperature cycling of unalloyed titanium and alloyed Ti-6Al-4V led to a significantly higher pore volume fraction and higher foaming rate.
机译:金属的固态发泡可以通过在氩气存在下对粉末进行热等静压来实现,然后在环境压力和高温下使所得的高压氩气气泡膨胀。 Kearns等人首先证明了这种发泡技术。 [1]对于Ti-6Al-4V,但受其低蠕变速率和延展性的限制,这会导致早期的细胞壁破裂。我们通过在超塑性条件下执行发泡步骤来解决这些问题。与其使用微观结构的超塑性(需要在多孔粉末冶金材料中难以获得的细晶粒),不如使用转变超塑性,该转变超塑性在所有晶粒尺寸上都通过偏应力(来自孔隙压力)的内应力(来自孔隙压力)而产生。在同素异形体温度范围内的热循环过程中的同素异形体不匹配)。与在等温蠕变条件下进行的控制实验相比,非合金钛和合金化的Ti-6Al-4V在温度循环下的超塑性发泡导致明显更高的孔体积分数和更高的发泡速率。

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