Tensile properties and constitutive model of ultrathin pure titanium foils at elevated temperatures in microforming assisted by resistance heating method
Tensile properties and constitutive model of ultrathin pure titanium foils at elevated temperatures in microforming assisted by resistance heating method
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DOI：
10.1016/j.matdes.2014.06.039
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发表时间：
2014-11-01
影响因子：
8.4
通讯作者：
Yang, Ming
中科院分区：
文献类型：
--
作者：
Zheng, Qiu;Shimizu, Tetsuhide;Yang, Ming
纯钛（Ti）通常用于生物医学设备和植入物中的微型零件。微成形是一种很有前途的微小零件制造技术。由于微成形过程中尺寸效应的存在，材料流动呈现出非均匀性，工艺参数表现出较大的离散性。热辅助微成形是解决这些问题的有效方法。为了提高加热速度，将电阻加热方法引入微成形工艺中。为了设计有效的电阻加热辅助微成形工艺，需要确定电流与材料流动应力之间的关系，为此，本研究开发了一套电阻加热辅助微成形拉伸试验系统。通过高温单轴拉伸试验研究了0.05 mm厚纯钛箔的拉伸性能。拉伸试验在相对于轧制方向的不同角度（0度、45度和90度）下、在从室温（298 K）到723 K的各种温度下以及在从10（4）到10（1）s（1）的不同应变速率下进行。为了有助于电阻加热辅助微成形工艺的设计，讨论了温度和电流密度对纯钛箔材料性能的影响。基于Fields Bachofen（FB）方程，建立了一个描述非晶纯钛在不同成形条件下流变应力的本构模型。电流密度对加工硬化和应变速率敏感性的影响包括在推导的本构模型。计算结果与实验结果吻合较好，验证了所提出的电阻加热辅助微成形本构模型的可行性。(C)2014爱思唯尔有限公司版权所有。
Pure titanium (Ti) is often used for microparts in biomedical devices and implants. Microforming is a promising technology for the manufacture of microparts. Owing to the occurrence of size effects in microforming, the material flow is nonhomogeneous and the process parameters exhibit considerable scattering. Heat-assisted microforming is an effective process for solving these problems. To improve the heating rate, the resistance heating method has been introduced into the microforming process. To design an effective resistance-heating-assisted microforming process, the relationship between the electric current and the flow stress of the material should be determined.To achieve this, a tensile testing system incorporating the resistance heating method is developed in this study. The tensile properties of 0.05-mm-thick pure Ti foils are investigated by performing uniaxial tensile tests at elevated temperatures. The tensile tests are carried out at different angles (0 degrees, 45 degrees, and 90 degrees) relative to the rolling direction, at various temperatures from room temperature (298 K) to 723 K, and under different strain rates from 10 (4) to 10 (1) s (1). To contribute to the design of the resistance-heating- assisted microforming process, the effect of the temperature and electrical current density on the material properties of ultrathin pure Ti foils is discussed. A constitutive model based on the Fields-Bachofen (FB) equation is derived to describe the flow stress of ultrathin pure Ti under different forming conditions. The effect of the electrical current density on the work hardening and strain rate sensitivity is included in the derived constitutive model. The good agreement between the calculated and experimental results confirms the feasibility of the proposed constitutive model for resistance-heating- assisted microforming. (C) 2014 Elsevier Ltd. All rights reserved.