3-D observations of short fatigue crack interaction with lamellar and duplex microstructures in a two-phase titanium alloy
3-D observations of short fatigue crack interaction with lamellar and duplex microstructures in a two-phase titanium alloy
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DOI：
10.1016/j.actamat.2010.11.015
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发表时间：
2011-02-01
期刊：
影响因子：
9.4
通讯作者：
Preuss, M.
中科院分区：
文献类型：
--
作者：
Birosca, S.;Buffiere, J. Y.;Preuss, M.
采用同步辐射X射线显微层析术对粉末处理的Ti-6246中的短裂纹扩展进行了原位观察，以研究裂纹尖端与显微组织的相互作用。连同使用电子背散射衍射（EBSD）的事后分析，它是可能的，以确定一些微观结构的功能，影响裂纹扩展速率，引起裂纹分叉，裂纹桥接和裂纹偏转。以这种方式测试了具有不同微观结构的三个样品：层状、双相和显示层状和双相微观结构区域的异质微观结构。原位疲劳实验进行了最大应力为410 MPa和R = 0.1。三种显微组织显示出明显不同的短裂纹扩展速率，其中层状显微组织显示出最快的速率，而双相显微组织显示出最慢的速率。结果发现，层状显微组织开发一个更深的裂纹比双相显微组织，这是有关的显着的裂纹分叉发生在表面区域附近的层状，但不是双相显微组织。有人还发现，一个柱状层状显微组织创建一个相对平滑的裂纹前端，而篮子编织型显微组织迫使裂纹尖端的板条宽度尺度上的波动。观察到双相微观结构的细层状区域的裂纹桥接，这似乎阻碍了显著的裂纹分叉发生，但仍然提供了改善的裂纹扩展阻力，这解释了低裂纹扩展速率。在第三种显微组织中，由于显微组织的异质性，裂纹倾向于略微不对称地生长，导致中间生长速率。EBSD晶粒取向和Schmid因子分析的区域，包括裂纹显示，裂纹的路径是强烈的影响，由晶体取向的α层和晶粒。而在层状显微组织中，裂纹倾向于跨层状生长，有利于取向为基底滑移，在双相显微组织中，裂纹路径遵循有利于取向为棱柱滑移的初级α晶粒。有人建议，在层状显微组织中的基底取向的变化有关的要求α/β滑移转移的层状显微组织和伯格斯关系有利于在这种情况下的基底滑移。此外，在初级α中生长的裂纹倾向于在α晶粒内转向，并且在层状显微组织中看不到。初生α晶粒中的这种裂纹偏转可能进一步减缓裂纹扩展，并且可能与不同（11-20）平面的可用性有关，而基面在六方密排晶体中仅显示一个取向。皇冠版权所有（C）2010由爱思唯尔有限公司代表Acta Materialia Inc.出版。All rights reserved.
In situ observations of short crack growth in powder-processed Ti-6246 have been undertaken using synchrotron X-ray microtomography to investigate crack tip interaction with microstructure. Together with post-mortem analysis using electron backscatter diffraction (EBSD), it was possible to identify a number of microstructural features that affect crack propagation rates by causing crack bifurcation, crack bridging and crack deflection. Three samples with different microstructures were tested in this way: lamellar, duplex and a heterogeneous microstructure that showed regions of lamellar and duplex microstructure. The in situ fatigue experiments were carried out with a maximum stress of 410 MPa and R = 0.1. The three microstructures showed significantly different short crack propagation rates, with the lamellar microstructure displaying the fastest and the duplex microstructure the slowest rate. It was found that the lamellar microstructure develops a deeper crack than the duplex microstructure that is related to significant crack bifurcation taking place near the surface region in the lamellar but not duplex microstructure. It was also found that a columnar lamellar microstructure creates a relatively smooth crack front while a basket-weave-type microstructure forces the crack tip to undulate on the lath width scale. Crack bridging of the fine lamellar region of the duplex microstructure was observed, which seems to hinder significant crack bifurcation to occur, but still provides improved crack growth resistance that explains the low crack propagation rate. In the third microstructure the crack tended to grow slightly asymmetrically due to the heterogeneous nature of the microstructure, resulting in the intermediate growth rate. EBSD grain orientation and Schmid factor analysis of regions including the crack revealed that the crack path is strongly influenced by the crystallographic orientation of the alpha lamellae and grains. While in the lamellar microstructure the crack tends to grow across lamellae favourably orientated for basal slip, in the duplex microstructure the crack path follows primary alpha grains favourably orientated for prismatic slip. It is suggested that the change to basal orientation in the lamellar microstructure is related to the requirement of alpha/beta slip transfer in the lamellar microstructure and the Burgers relationship favouring basal slip in such a case. In addition, the crack growing in primary alpha tends to get diverted within the alpha grain and is not seen in the lamellar microstructure. This crack deflection in primary alpha grains might further slow down crack propagation and could be related to the availability of different (11-20) planes while basal planes only display one orientation in a hexagonal close-packed crystal. Crown Copyright (C) 2010 Published by Elsevier Ltd. on behalf of Acta Materialia Inc. All rights reserved.