Large strain deformation and ultra-fine grained materials by machining

Microstructures of Cutting Chips of SUS430 and SUS304 Steels, and NCF 750 and 6061-T6 Alloys

“…The approximate shear strain (γ) in the central part of the chip specimens was calculated by the following equation. Swaminathan et al 15) confirmed that for two-dimensional cutting the shear strain calculated by the above equation was close to the value experimentally obtained by the high-speed image analysis on the chip of OFHC copper. A rough estimation of shear strain was also made using the above equations for a chip specimen of the Inconel X-750 alloy (γ ≈ 3) produced under the non two-dimensional cutting condition in the previous study.…”

“…However, application of these techniques is limited to relatively low-strength materials. T. L. Brown et al 14) and S. Swaminathan et al 15) proposed a low-cost cutting process for production of nanostructured metals and alloys with very high hardness. A large shear strain (γ ) up to ~20 can be imposed on chips by a single cutting process.…”

“…This method is also applicable to the high-strength materials. Using the selected area electron diffraction patterns of thin films with a transmission electron microscope (TEM), S. Swaminathan et al 15) found that the change from elongated sub grain structure to nano-scale equiaxed grain structure occurs at a shear strain of ~13 in the chip specimens of the OFHC Cu. Based on the similar analysis using a TEM, M. Ravi Shankar et al 16) concluded qualitatively that there exists a small region containing high angle boundaries in the chip specimens of the 6061-T6 alloy deformed to a shear strain (γ) up to 3.2 or 5.2.…”

Effect of strain rate in severe plastic deformation on microstructure refinement and stored energies

“…Chip formation by machining emerged as our choice of method for severe plastic deformation because of its versatility to impart large range of strain and strain-rate in a single deformation pass in a range of material systems [19][20][21][22][23][24][25]. This allowed us to scan across wide ranges of strainrate (~10 1 -10 3 /s) and strains while still creating fully-dense bulk samples that were still large 5 enough for reliable thermal and mechanical analysis.…”

“…We used a machining configuration as shown in Figure 1, with a depth of cut (DOC) value, which determines the width of the samples, as 3mm and feed rate (f), which determines the thickness of the undeformed chip, as 0.17mm. This configuration where the width is much larger than the undeformed chip thickness offers a plane-strain simple shear configuration for imposing SPD across a range of strains, strain-rates and temperature values [19,22,26].…”