Microstructural Evolution and Microhardness Variations in Pure Titanium Processed by High‐Pressure Torsion

Abstract

A grade 2 pure titanium with an initial grain size of %50 μm is processed by highpressure torsion (HPT) at room temperature under an imposed pressure of 6.0 GPa. The microhardness variations are examined and the results show that the disks are reasonably homogeneous after 10 turns of torsional straining. The microstructural evolution is systematically characterized by optical microscopy, X-ray diffraction, and transmission electron microscopy to provide information on the effect of shear strain on grain size and microstructure. The results demonstrate that the initial coarse structure is gradually refined from the edge to the center of the disk under the shear stress during HPT processing and an ultrafinegrained pure Ti is achieved with an average grain size of %96 nm after 10 turns. A model is developed by considering the formation of subgrain boundaries, twins, and high-angle grain boundaries for the grain refinement of pure Ti processed by HPT.

Microstructure Evolution and Mechanical Properties of AlCoCrFeNi2.1 Eutectic High-Entropy Alloys Processed by High-Pressure Torsion

“…As the XRD detection was conducted on the polished disk surface, the average level of varying shear strain in different regions along the radius direction for different HPT processes could be represented by the intensity of the diffraction peak of different phases, which was highly agreed with the previous research [24]. The average grain sizes of the samples were determined using XRD data analysis, revealing grain sizes of 171 nm, 161 nm, and 142 nm after undergoing HPT for 0.5 turns, 1 turn, and 3 turns, respectively, which was similar to the previous study [29]. However, as seen in Figure 3b, the diffraction peaks of HPT-treated samples were wider than those of the initial as-cast sample due to lattice strain induced by dislocation formation and grain size reduction [22,24].…”

“…This observation was consistent with the findings presented in the contour maps in Figure 5c-e. As shown in Figure 5c-e, the microhardness of the central region gradually increased with an increase in the number of turns, and according to previous reports, that was due to the heightened strain gradient introduced by HPT, leading to the generation of geometrically necessary dislocations (GNDs) [29,38]. With the number of revolutions reaching a certain level, the high microhardness zone progressively moved to the center until the microhardness reached saturation.…”

Microstructure evolution of pure titanium during hydrostatic extrusion

“…The deformation at higher strains is believed to be ruled by slip. Similar conclusions were drawn when microstructures of the ARB-ed [13], the HPT-ed [14] and the MDF-ed [15] titanium were examined.…”

“…Zherebtsov et al [30] declared that during low straining of pure titanium by means of the HE technique, twinning is to happen as demonstrated by a vast fraction of HAGBs and the existence of { 1010 }, { 1012 } and { 1123 } twins. Herein, the microstructure of a material deformed at the strain of 0.9 bore the stamp of twinning in shear-like bands, similar to these discovered in the HPTtreated titanium [14]. After all, it is commonly known that twinning generates a new orientation in a crystal by shear; thus, the observed bands are, indeed, its remains.…”

Microhardness and Microstructural Evolution of Pure Nickel Processed by High-Pressure Torsion

“…The present research shows that HPT is exceptionally excellent in producing very small grain sizes [19]. If the applied pressure is high and the number of turns is sufficient the HPT processing can be used to develop a uniform and reasonable microstructur throughout the disks: In this experiment, at room temperature, it is found for pure Ni tha a pressure of 6 GPa and more than five turns can achieve homogeneous grain refinemen The present research shows that HPT is exceptionally excellent in producing very small grain sizes [19].…”