Texture-dependent dwell fatigue response of titanium

ABSTRACT

This study investigates heterogeneity in the deformation of an annealed sheet of commercially pure titanium (cp-Ti), its variation with loading direction and its influence on dwell fatigue response. Cp-Ti sheet with a typical cold rolling texture was deformed, along its rolling direction (RD) and transverse direction (TD), to the same strain level in tension. Higher level of grain boundary sliding in TD led to increased surface roughness (30% higher) in TD when compared to RD. Whereas, the higher extent of grain boundary-affected zones in TD resulted in a higher level of strain gradient, as evident from higher Kernal Average Misorientation values observed in TD. The reason for the higher extent of grain boundary sliding and formation of grain boundary-affected zones in TD samples was higher compatibility issues in TD. This work proposes a criterion defining the compatibility of a boundary. This criterion, which is based on the c-axis deviation of constituent grains with respect to the loading axis and the geometric compatibility of slip systems, is demonstrated to define the compatibility of a boundary completely. Using this criterion, a higher fraction of incompatible boundaries is identified in TD. Moreover, the markedly superior dwell fatigue response of RD samples when compared to TD is partly attributed to the lower heterogeneity in the nature of deformation in the former. Furthermore, textures with less damage prone grain boundaries and hence better dwell fatigue resistance is also proposed. Taken together, the present work underlines the principal role of crystallographic texture on the mechanical behaviour in general and dwell fatigue in particular.

KEYWORDS:

• Cp-Titanium
• deformation heterogeneity
• grain boundary-affected zones
• grain boundary sliding
• dwell fatigue

Acknowledgements

The authors would like to thank Prof. Satish V Kailas, Mech. Eng. Dept, IISc Bangalore, for providing the fatigue testing facility. They thank Mr. Rajneesh, Research Assistant, Mech. Eng. Dept., IISc Bangalore, for his assistance during fatigue testing experiments and Dr. Samarth Chanagiri, Advanced facility for microscopy and microanalysis, IISc for his help in TEM lamella preparation. The authors are grateful to Dr. Sumeet Mishra, University of Manchester, for many useful discussions. They are also thankful to the Department of Science and Technology (DST-FIST), India, for the financial support.

Disclosure statement

No potential conflict of interest was reported by the author(s).