Micro-Incremental Forming of Ultra-Thin CP Titanium Thin Sheets: Effect of Microstructure and Crystallographic Bulk Texture

A low aspect ratio poses a significant challenge in micro-forming processes due to pronounced anisotropy and size effects. Micro-incremental sheet forming (mu -ISF) is an emerging micro-forming technique with significant potential due to its adaptability and enhanced formability. The current study investigates the forming behavior of 50, 100, and 200 mu m commercially pure titanium ultra-thin sheets into a conical shape using mu -ISF. Optimal mu -ISF process parameters were optimized by an orthogonal array design. The effect of tool diameter and step depth on forming forces, surface roughness, and microstructure evolution were analyzed. The novelty of this work is to deform ultra-thin sheets using mu -ISF and establish a non-linear trend in forces with the sheet thickness, attributed to the dominance of the size effect (thickness-to-grain size (T/D) ratio). Surface roughness also showed a dependence on the T/D ratio across different sheet thicknesses, and a superior surface finish was obtained with the larger tool diameter and smaller step depth. These observations were explained by a detailed microstructural characterization at the center region of the deformed samples using electron backscatter diffraction and X-ray techniques. The microstructural analysis revealed that twinning-specifically, tensile < 1<overline>21<overline>0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{1 }2\overline{1 }0$$\end{document}> and compressive < 11<overline>00\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1\overline{1 }00$$\end{document}>, was predominant in all the deformed samples. Misorientation was found to decrease with increasing step depth, likely due to a reduced number of overlaps at greater step depths. Textural analysis indicated a transition from 'A' and 'D' texture components to 'B' and 'E' components, and vs, driven by twin formation. The wall angle limit revealed a tearing-type fracture in all the sheet thicknesses, and the wall angle limit increased with an increase in sheet thickness.