Some Slippage Issues in High-Pressure Torsion Using Cu and Ti Samples as an Example

Abstract

The effect of slippage during High Pressure Torsion (HPT) of technically pure Ti and pure Cu samples was investigated. The “joint torsion of the disk halves” method was used to evaluate the effect of slippage. It was shown that slippage starts already at the early stages of HPT. With a further increase in the number of revolutions n, the slippage effect increases, and no torsional deformation occurs after n = 5. The slippage effect is explained by analyzing the surface friction forces between the sample and the anvil. However, studies via TEM and XRD have shown that the structure of Ti samples after HPT at the investigated conditions is grinded to a nanocrystalline state. A structure is formed in Ti similar to that observed after HPT by other authors. The dislocation density increases with increasing HPT degree from n = 5 to n = 10 revolutions, despite slippage. Consequently, despite slippage at HPT at n ≥ 5, deformation still occurs. The following assumptions are made to explain the accumulated strain in the sample at HPT. It is assumed that the planes of the upper and lower anvil during HPT are at a slight inclination relative to each other. Computer modeling using the Deform 3D software package has shown that this leads to the accumulations of significant strain during HPT.

Slippage during High-Pressure Torsion: Accumulative High-Pressure Torsion—Overview of the Latest Results

“…Thus, after the preliminary HPT with n = 5, complete slippage was obs on the Ti specimen. As shown above (Figure 4a), the slippage effect was not so significant in the i stages (n = ¼) of the HPT of Cu [28]. However, we decided to investigate how the slip on Cu changes as the number of HPT revolutions increases.…”

“…The authors of the present paper have used the "joint HPT of two halves" method for the past 4 years to evaluate slippage on a number of metallic materials, see, e.g., [24][25][26][27]. It was shown that slippage on such a relatively mild material as copper was not so significant in the early stages of HPT [25,28]. However, during the HPT of such materials as mild steel (Fe-0.1% C), the Zr-1%Nb alloy, CP Ti, the β-Ti alloy, Ti-18Zr-15Nb, and the austenitic steel 316 (Fe-0.03C-17Cr-0.41Si-1.72Mn-0.01P-0.03S-12.9Ni-2.36Mo, wt.%) the slippage was revealed as follows [26][27][28]: samples of these materials received a certain degree of shear strain at the initial HPT stages, but significant slippage was observed already at the initial stages of HPT.…”

“…Moreover, the degree of deformation was not the same i ferent parts of the sample. However, in the case of the joint HPT of the Ti disk halves on anvils 20 mm in diameter having a groove with a depth of h = 0.5 mm (P = 6 GPa, room temperature), noticeable slippage already occurred at the initial stage of HPT-n = 1/4 [28].…”

“…It was shown that slippage on such a relatively mild material as copper was not so significant in the early stages of HPT [25,28]. However, during the HPT of such materials as mild steel (Fe-0.1% C), the Zr-1%Nb alloy, CP Ti, the β-Ti alloy, Ti-18Zr-15Nb, and the austenitic steel 316 (Fe-0.03C-17Cr-0.41Si-1.72Mn-0.01P-0.03S-12.9Ni-2.36Mo, wt.%) the slippage was revealed as follows [26][27][28]: samples of these materials received a certain degree of shear strain at the initial HPT stages, but significant slippage was observed already at the initial stages of HPT. However, the samples of these materials after HPT with n > 5, at further increase of n, did not lead to noticeable shear strain due to slippage.…”

“…In [28], slippage during the HPT of commercially pure Ti and Cu was additionally investigated. The results are detailed below.…”