Hydrogen Embrittlement of Titanium Sheet under Multiaxial Deformation Paths.
MICHIGAN TECHNOLOGICAL UNIV HOUGHTON DEPT OF METALLURGICAL ENGINEERING
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The ductility of commercially pure titanium sheet containing either 60, 630, or 980 wt ppm hydrogen has been investigated over deformation paths ranging from uniaxial to equibiaxial tension. Based on measurements of fracture strains measured locally from grids, the data show a decrease in ductility with increasing hydrogen content as the degree of biaxiality of the tensile strain increases. Thus hydrogen embrittlement of Ti sheet depends on deformation path, being the most severe under equibiaxial straining. The embrittlement occurs even though hydrogen has no significant effect on the room temperature yielding and flow behavior of Ti in either uniaxial or balanced biaxial tension. Quantitative metallography indicates that void nucleation is due to hydride fracture and occurs at comparatively small strains in plane strain and equibiaxial deformation. An analysis shows that the strain-induced fracture of the hydrides appears to obey a critical normal stress criterion, the stresses being caused by a the inhomogeneity of strain between the matrix and the particles and b the maximum principal stress within the matrix. Calculations show that only the latter changes significantly with loading path, and this is primarily due to the strong degree of plastic anisotropy in the Ti sheet.
- Metallurgy and Metallography