Jie Fu

Bio: Jie Fu is an academic researcher from Northeastern University (China). The author has contributed to research in topics: Grain size & Volume fraction. The author has an hindex of 2, co-authored 2 publications receiving 55 citations.

Influence of phase volume fraction on the grain refining of a Ti-6Al-4V alloy by high-pressure torsion

Abstract: Using appropriate heat treatments, different volume fractions of the constituent phases were produced in a Ti–6Al–4V alloy. Thus, in Ti64-1 there was ∼85% of an equiaxed α-phase and ∼15% of a lamellar (α+β) microstructure and in Ti64-2 there was ∼48% of the α-phase and ∼52% of the (α+β) microstructure. These two alloys were processed by high-pressure torsion (HPT) at room temperature under an applied pressure of 6.0 GPa. Both materials showed increases in the microhardness and decreases in the grain size after HPT with a stabilization after about 10 turns. Higher hardness values and smaller grain sizes were attained in Ti64-2 thereby demonstrating that greater grain refinement is achieved when processing an alloy with approximately equal volume fractions of the constituent phases. In these experiments, the measured equilibrium grain sizes after 20 turns of HPT were ∼130 nm in Ti64-1 and ∼70 nm in Ti64-2.

Influence of phase volume fraction on the grain refining of a Ti-6Al-4V alloy by high-pressure

Abstract: a b s t r a c t A cold-rolled Ti-6Al-4V sheet was subjected to three different heat treatments prior to pro- cessing by high pressure torsion (HPT). Quantitative measurements revealed that the volume fractions were 70% equiaxedphase and 30% lamellar (� + �) (Ti64-1), 47% equiaxedphase and 53% lamellar (� + �) (Ti64-2) and 25% equiaxedphase and 75% lamellar (� + �) (Ti64-3) and the grain sizes of thephase were 7.0 ± 2 �m, 9.0 ± 1.5 �m and 9.5 ± 1.5 �m, respectively. The processing by HPT was performed at room temperature with a pressure of 6.0 GPa and a rotation speed of 1 rpm. Processing of the three heat treatment batches was conducted through a total number of revolutions, N, of 1/4, 1, 5, 10 and 20. The results show that the microhardness increases with increasing numbers of turns in HPT processing and for all three conditions stable microhardness values are reached after about 20 turns. The grain sizes after 20 turns of HPT were 115 ± 30 nm in Ti64-1, 85 ± 25 nm in Ti64-2 and 75 ± 15 nm in Ti64-3 so that the grain size decreases as the volume fraction ofphase decreases and the lamellar (� + �) increases.

The influence of defect structures on the mechanical properties of Ti-6Al-4V alloys deformed by high-pressure torsion at ambient temperature

Abstract: The high-pressure torsion method was employed to deform Ti-6Al-4V (TC4) alloy. The ambient temperature and high pressure were used to restrain the grain growth. Clear images showing the microstructure evolution of the deformed TC4 alloys were obtained using SEM, TEM and HRTEM. It was found that the HPT-deformed TC4 alloys contain a high density of dislocations and many defect structures. These dislocations were found to be generated on one or both sides of the elongated grains, and the dislocation lines were able to move across the elongated grains (mostly at ~60°) to form an uncondensed dislocation wall. Although deformation twins did not appear in the alloys deformed at intermediate strains (γ≤23.1), quantities of (10−12) tensile twins containing prismatic stacking faults were observed in the specimens deformed at a much larger plastic strain (γ≥157). The hardness-strain behaviors of the TC4 alloys were similar to those of pure Ti, which have a maximum hardness followed by a strain softening at large strains. In addition, the formation of the omega phase was suppressed due to the dissolution of substitutional Al and V. The alloy that received the highest levels of strain (γ~357) was found to have a nanoscale structure (~49.41 nm) with non-equilibrium GBs, as well as an increased microhardness (~424 HV) and yield strength (σ S ~960 MPa). The effects of these defect-structures on the mechanical behaviors of a TC4 alloy are mainly determined by their structures’ sizes according to Hall–Petch relationship. However, the effect of this mechanism reduces at large strains due to the existing high-dense dislocations and non-equilibrium grain boundaries.