Evolution of Mechanical Properties and Microstructures with Equivalent Strain in Pure Fe Processed by High Pressure Torsion

Abstract

Pure Fe (99.96%) was processed by high pressure torsion (HPT) using disc and ring samples. When the microhardness and tensile properties are plotted against the equivalent strain, the individual properties fall well on unique single curves, level off at the equivalent strain of $40. At the saturated level, the tensile strength of 1050 MPa and the elongation to failure of 2% are attained. Transmission electron microscopy showed that a subgrain structure containing dislocations develops at an initial stage of straining. More dislocations form within the grains and the subgrain size decreases with further straining. At the saturation stage, the average grain size reaches $200 nm, the misorientation angle increases and some grains which are free from dislocations appear. It is suggested that at the saturation stage, a steady state condition should be established through a balance between hardening by dislocation generation and softening by recrystallization.

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

“…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. Considering the fact that the applied pressure of 0.6 GPa is lower than the yield stresses of 1 GPa for Fe and 0.8 GPa for Ti obtained by tensile testing, 7,16) there may be a critical pressure, P C , near the yield stress, below which the increase in the hardness is very slow or may be constant with respect to the equivalent strain.…”

“…1 for (a) Au, (b) Cu, (c) Pt, (d) Ni, (e) Fe and (f) Ti samples processed under different pressures in the range of 0.6-6 GPa. Here, the equivalent strain was calculated using the equation as described earlier 7,16,19) where the effect of slippage and thickness reduction during HPT was taken into account. Fig.…”

“…[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.…”

First-Principles Study of the Stability and Interfacial Bonding of Tilt and Twist Grain Boundaries in Al and Cu

“…3) This should be mainly caused by quite different behavior of dislocations due to different stacking-fault energies (SFEs) for Al (166 mJ/m 2 ) and Cu (45 mJ/m 2 ). 4) Recently, the origin of the different SFEs has been explained by the different bonding nature.…”

Effect of Initial Annealing Temperature on Microstructural Development and Microhardness in High‐Purity Copper Processed by High‐Pressure Torsion

“…However, with increasing number of turns, the microstructures usually evolve toward homogeneity and many metals exhibit a complete homogeneity at high numbers of turns. Materials showing this behavior include Al, [3,[8][9][10][11][12][13] Cu, [14][15][16] Ti, [17][18][19] Mg, [20][21][22][23] Fe, [24][25][26] Ni, [27,28] and numerous others metals and alloys. [29,30] Nevertheless, some materials show a different type of behavior when processed by HPT.…”