热等静压Ti-47.5Al-2Cr-2Nb-0.2W-0.2B合金高温变形行为研究
发布时间：2019-04-02 06:47
【摘要】：钛铝合金因为具有密度低,高温强度高,抗蠕变和抗氧化能力强等特点,一直是航天和汽车行业应用材料研究的热门,但低延展率和较差的成型性能阻碍了其在工程上的进一步应用。粉末冶金等技术的引入很有效地解决成形难题,特别对于复杂制件近终成形,可以消除宏观偏析,对组织细化起到有效作用,而钛铝合金主要使用元素粉末法和预合金粉末法这两种方法。元素粉末法的特点是原料的成本较低(如HDH粉等),但不适用于热加工成形。预合金粉末法可以有效提高胚料的纯净度防止合金氧化,使合金具有高温超塑性。随着技术不断革新氩气雾化是制取高质量钛铝预合金粉末比较成熟的工艺,可以使粉末有较好的球形度,具有明显的快冷组织特征。在气雾化过程中,熔融液体被高速的气流打碎成极多较小的球形液滴,液滴在强对流作用下急剧冷却。尽管如此利用粉末冶金的方法制备的钛铝合金仍然存在微观缺陷,对成型后的材料的力学性能产生影响,研究表明热加工可以改善材料的组织分布,甚至提高材料的力学性能,所以有必要对粉末冶金钛铝合金热变形行为进行更深入的研究。目前的研究多集中在铸态钛铝合金粉末方面,而对钛铝合金预合金粉末方面的报道较少,尤其氩气雾化制备的预合金粉末研究几乎空白。由于制备工艺的不同胚料的组织性能也会有很大差异,因此对钛铝粉末合金热变形行为研究十分重要。本文基于氩气雾化预合金Ti-47.5Al-2Cr-2Nb-0.2W-0.2B合金粉末热等静压后的坯锭制成圆柱状试样,尺寸为φ8mm×12 mm,然后经过加工将两个表面打磨抛光至平整。在热力模拟实验机上进行热压缩模拟实验,探究该Ti-47.5Al合金高温变形行为,建立Ti-47.5Al-2Cr-2Nb-0.2W-0.2B合金本构方程,计算出激活能Q=~365.6 k J/mol,该方程的拟合相关系数和误差分别为0.98922和3.30415%,预测与实验结果一致性较好。结合形变组织研究观察了合金在1050-1200℃、应变速率0.001-0.5s-1粉末冶金Ti-47.5Al合金的组织变化,采用SEM,EBSD和TEM对热变形合金的微观组织演变进行了分析,发现材料中出现了细小的再结晶组织,并有层片结构留在变形组织中。同时,基于Prasad失稳准则以及动态DMM模型,最终建立了该合金变形过程中的加工图。基于所构造的加工图,该合金的最佳热加工窗口是在1080-1180℃的温度范围和0.001-0.1s-1的低应变速率。该研究中获得的结果为高温TiAl基合金零件的热加工及生产提供理论依据,为Ti-47.5Al合金热加工工艺起到指导作用。
[Abstract]:Because of its low density, high temperature strength, high creep resistance and oxidation resistance, Ti-Al alloy has been a hot research field in aerospace and automotive industry. However, low ductility and poor molding properties hinder its further application in engineering. The introduction of powder metallurgy and other technologies can effectively solve the forming problems, especially for the near-final forming of complex parts, which can eliminate macro-segregation and play an effective role in microstructure refinement. Titanium-aluminum alloy mainly uses two methods: elemental powder method and pre-alloyed powder method. Element powder method is characterized by low cost of raw materials (such as HDH powder, etc.), but is not suitable for hot-working forming. The pre-alloy powder method can effectively improve the purity of the embryo to prevent the oxidation of the alloy and make the alloy have high temperature superplasticity. Argon atomization is a mature process for producing high-quality titanium-aluminum prealloyed powder, which can make the powder have a better sphericity and have obvious fast-cooling microstructure characteristics. In the process of gas atomization, the molten liquid is broken into many smaller spherical droplets by high-speed airflow, and the droplets are cooled sharply under the action of strong convection. However, the Ti-Al alloy prepared by powder metallurgy still has micro-defects, which has influence on the mechanical properties of the molded materials. The research shows that hot-working can improve the microstructure distribution of the materials and even improve the mechanical properties of the materials. Therefore, it is necessary to study the hot deformation behavior of P / M Ti-Al alloy. Most of the researches are focused on as-cast Ti-Al alloy powders, but few reports have been reported on Ti-Al alloy pre-alloy powders, especially the study of pre-alloy powders prepared by argon atomization is almost blank. It is very important to study the hot deformation behavior of Ti-Al powder alloy because the microstructure and properties of different embryo materials are different. Based on the ingot of argon atomized pre-alloyed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy powder after hot isostatic pressing, a cylindrical sample was made. The size is 蠁 8mm 脳 12 mm, and the two surfaces are polished to level after machining. The high temperature deformation behavior of Ti-47.5Al alloy was investigated by means of thermal compression simulation experiment on a thermal simulation machine. The constitutive equation of Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy was established and the activation energy Q, 365.6 kJ / mol, was calculated. The fitting correlation coefficient and error of the equation are 0.98922 and 3.30415%, respectively. The prediction is in good agreement with the experimental results. The microstructure change of 0.001-0.5s-1 powder metallurgy Ti-47.5Al alloy at 1 050 鈩，
本文编号：2452349
[Abstract]:Because of its low density, high temperature strength, high creep resistance and oxidation resistance, Ti-Al alloy has been a hot research field in aerospace and automotive industry. However, low ductility and poor molding properties hinder its further application in engineering. The introduction of powder metallurgy and other technologies can effectively solve the forming problems, especially for the near-final forming of complex parts, which can eliminate macro-segregation and play an effective role in microstructure refinement. Titanium-aluminum alloy mainly uses two methods: elemental powder method and pre-alloyed powder method. Element powder method is characterized by low cost of raw materials (such as HDH powder, etc.), but is not suitable for hot-working forming. The pre-alloy powder method can effectively improve the purity of the embryo to prevent the oxidation of the alloy and make the alloy have high temperature superplasticity. Argon atomization is a mature process for producing high-quality titanium-aluminum prealloyed powder, which can make the powder have a better sphericity and have obvious fast-cooling microstructure characteristics. In the process of gas atomization, the molten liquid is broken into many smaller spherical droplets by high-speed airflow, and the droplets are cooled sharply under the action of strong convection. However, the Ti-Al alloy prepared by powder metallurgy still has micro-defects, which has influence on the mechanical properties of the molded materials. The research shows that hot-working can improve the microstructure distribution of the materials and even improve the mechanical properties of the materials. Therefore, it is necessary to study the hot deformation behavior of P / M Ti-Al alloy. Most of the researches are focused on as-cast Ti-Al alloy powders, but few reports have been reported on Ti-Al alloy pre-alloy powders, especially the study of pre-alloy powders prepared by argon atomization is almost blank. It is very important to study the hot deformation behavior of Ti-Al powder alloy because the microstructure and properties of different embryo materials are different. Based on the ingot of argon atomized pre-alloyed Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy powder after hot isostatic pressing, a cylindrical sample was made. The size is 蠁 8mm 脳 12 mm, and the two surfaces are polished to level after machining. The high temperature deformation behavior of Ti-47.5Al alloy was investigated by means of thermal compression simulation experiment on a thermal simulation machine. The constitutive equation of Ti-47.5Al-2Cr-2Nb-0.2W-0.2B alloy was established and the activation energy Q, 365.6 kJ / mol, was calculated. The fitting correlation coefficient and error of the equation are 0.98922 and 3.30415%, respectively. The prediction is in good agreement with the experimental results. The microstructure change of 0.001-0.5s-1 powder metallurgy Ti-47.5Al alloy at 1 050 鈩，
本文编号：2452349
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