High-pressure torsion using ring specimens

Universal Plot for Hardness Variation in Pure Metals Processed by High-Pressure Torsion

“…However, a different type of the curve was obtained in Al (99.99%) such that the hardness initially increases with increasing strain and, after taking a maximum, decreases to a constant level. 14,22) The mechanism for this unusual softening in pure Al was reported elsewhere due to fast recovery. 22) For the case of Fe and Ti after processing at 0.6 GPa, the equivalent strain of 80 appears to be insufficient to reach the steady state and it was confirmed that the hardness level was still lower even after N ¼ 20 corresponding to equivalent strain up to 370.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12] The HPT has been applied to a wide range of metallic materials including ductile metals such as Al, 2) Cu, 3) Ni 4,5) and Fe, 6,7) and relatively hard and low ductile metals such as Ti, 8) Zr, 12) Mg, 9) Mo 10) and W. 11) The HPT is generally used with thin disc 1,13) or ring samples. 14) Using discs and/or rings, earlier reports showed that the hardness variation is represented by a unique function of the equivalent strain in Al, 14) Cu, 15) Fe, 7) Ti 16) and Zr.…”

Microstructural Evolution in Pure Aluminum in the Early Stages of Processing by High-Pressure Torsion

“…This result matches earlier results plotted for aluminum of the same purity where the datum points were extended to strains of >40 using ring samples. 31,34) The scatter in the points visible in Fig. 4 at equivalent strains in the range of 2{7 is attributed to the inhomogeneous development of the microstructure when processing thin disks by HPT.…”

“…13) More recently this same approach was used to interpret hardness data obtained in the processing by HPT of both disk and ring samples. 27,[31][32][33][34][35] In order to make use of this analytical approach in the present investigation, it is first noted that the thicknesses of the HPT disks are reduced in HPT processing and this reduction generally increases with increasing numbers of turns. 25) In this investigation, the sample had an initial thickness of 0:85 mm and this was reduced to 0:80 mm on application of the applied pressure and it was further reduced to 0:76 mm after one turn of HPT.…”

“…14) Third, the hardness values saturate at equivalent strains above 7 as revealed in this investigation and in experiments with ring samples. [31][32][33][34][35] …”