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Enhancement of Strength and Fatigue Properties of Pure Titanium via Optimized ECAP Processing

通过优化 ECAP 工艺提高纯钛的强度和疲劳性能

基本信息

批准号：
17560620
负责人：
VINOGRADOV Alexei
金额：
$ 2.37万
依托单位：
Osaka City University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2006
项目状态：
已结题

项目摘要

Pure Titanium with the monotonic strength exceeding 1 GPa has been manufactured via multi-pass ECAP followed by forging and drawing. The role of processing factors such as ECAP route, number of passes and post-ECAP annealing on the structure and resultant mechanical properties and, particularly, in fatigue of metals and alloys has been investigated. The structure of ECAP-produced materials has been assessed by means of TEM and EBSD and X-ray analysis. It was shown that the structure difference between the samples produced by deifferent routes diminishes with increasing number of pressings. The processing route exerts little or no effect on both low-and high-cyclic fatigue properties, while the effect on the grain shape is very strong. Therefore, route A (no rotation of the working billet between subsequent passes) can be recommended for practical implementation. During severe plastic deformation to the effective strain of 8-30, the grain size is reduced to nanoscopic scale of 150-300 nm and the fraction of hghangle grain boundaries reaches of 65%, depending on the material, amount of imposed strain (number of ECAP pressings) and post-ECAP annealing. The improvement of fatigue properties in the high cycle regime has been demonstrated for many materials. For pure titanium the fatigue limit has reached 550 MPa after optimized severe plastic deformation processing and can be further improved by annealing. Hardening mechanisms were studied and it was shown that besides the Hall-Petch strengthening, the effect of dislocation accumulation on mechanical properties is significant. Furthermore, for precipitation hardenable materials the role of inclusion particles is important for structure stabilization and further enhancement of mechanical properties.

采用多道次等径角挤压、锻造和拉拔工艺制备了单调强度大于1 Gpa的纯钛。研究了ECAP工艺路线、道次数和ECAP后退火等工艺因素对组织和力学性能的影响，特别是对金属和合金疲劳性能的影响。用透射电子显微镜、电子背散射谱和X射线分析对ECAP制备的材料进行了结构分析。结果表明，不同路线得到的样品之间的结构差异随着压制次数的增加而减小。工艺路线对低周和高周疲劳性能的影响很小或没有影响，但对晶形的影响很大。因此，可推荐采用A路线(工作钢坯在后续道次之间不旋转)用于实际实施。在有效应变为8-30的剧烈塑性变形过程中，晶粒尺寸减小到150-300 nm的纳米尺度，六方晶界的比例达到65%，这取决于材料、施加的应变量(ECAP压力量)和ECAP后退火。许多材料在高周疲劳状态下的疲劳性能都得到了改善。对于纯钛，经过优化的大塑性变形工艺后，疲劳极限达到550 Mpa，并可通过退火进一步提高。研究了强化机制，结果表明，除Hall-Petch强化外，位错积累对力学性能也有显著影响。此外，对于沉淀硬化材料，夹杂物颗粒的作用对于稳定组织和进一步提高力学性能是重要的。