Ge Peng

Processing Map of One Kind of Metastable β Titanium Alloy

In order to exploit the potential hot deformation ability of metastable β titanium alloy Ti-B19 the isothermal compression behavior was investigated by a Gleeble-1500 thermal simulator in the temperature range of 750–1000 °C at an interval of 50 °C and strain rate from 0.001 to 10 s−1. The results indicate that the flow stress of the alloy increases with increasing of the strain rate at a given temperature, and decreases with the increment of temperature at a given strain rate. The processing map for the alloy obtained at strain of 0.6 can be divided into three domains. The first is the one in the temperature range of 700∼800 °C and the strain rate range of 0.001–0.1 s−1, with a peak efficiency of 42% at about 750 °C and 0.01 s−1. The flow curves in this domain present a single peak or oscillation in the flow curves before continuous softening appears. The second is the one in the temperature range of 800–1000 °C and the strain rate range of 0.001–0.1 s−1, with efficiency from 29% to 36%. The flow curves in this domain present a single peak or oscillation in the flow curves before reaching steady state. Recrystallized structures can be found, which is a typical dynamic recrystallization zone. The third one is a flow instable domain at the temperature lower than 800 °C and the strain rate above 0.1 s−1, or at the temperature higher than 800 °C and strain rate above 10 s−1. The adiabatic shear bands (ASBs) and flow inhomogeneous zone of β phases can be observed.

Discontinuous Yielding in High Temperature Deformation of Ti-5553 Alloy

The discontinuous yield behavior of Ti-5Al-5Mo-5V-3Cr-0.5Fe alloys, a new metastable β titanium alloy, was tested at 800∼860 °C and in strain rate range of 0.1∼10 s−1 on a Gleeble-1500 thermal Simulation testing machine. Results show that discontinuous yielding appears at the highest strain rate (10 s−1), and the magnitude of discontinuous yielding increases with increasing of the temperature. The above mentioned phenomenon is in agreement with Johnston and Gilmans dynamic yield theory, that is to say, the discontinuous yield behavior is related to the sudden multiplication of a great quantity of mobile dislocations in the alloy.

Phase Transformation in a β-Ti Alloy with Good Balance Between High Strength and High Fracture Toughness

Abstract This article studies the phase transformation of the metastable β-Ti-Al-Mo-V-Cr-Zr alloy (Ti-1300) to disclose the morphological reason for its high strength and high fracture toughness. It has been found that its ultrahigh strength (ultimate tensile strength exceeds 1 400 MPa) owes mainly to the spheroidization of the α-phase, while the high fracture toughness (exceeds 81 MPa·m½) to the special lath-shaped α-particles. Compared to the needle-shaped second α-articles, the coarser lath-shaped ones remove the stress concentration at the lath tips and consequently benefit improvement of fracture toughness. The article also describes shape evolution of the α-particles during aging thermodynamically and kinetically, and suggests an optimized aging processing to achieve an ideal balance between high strength and high toughness for this alloy.

Relationship between Mechanical Properties and Microstructure in a New High Strength β Titanium Alloy

Abstract A new high strength titanium alloy containing elements Cr, Fe, Mo, W and Al was designed in order to achieve an excellent combination of ultra-high strength and good fracture toughness. Both the α/β and β heat treatment were introduced to study the effect of microstructure on mechanical properties of the alloy. The result shows that the alloy with α/β solution plus aging treatment is composed of mixture microstructures including a few equiaxed or short billet-like primary α phase and fine lamellar secondary α phase. The alloy has an excellent combination of ultra-high strength and good fracture toughness. The corresponding tensile strength exceeds 1400 MPa and fracture toughnesses KIC is up to 50.7 MPa-m1/2. Compared with the alloy after α/β heat treatment, the alloy with β region heat treatment presents representative Widmanstatten structure which has higher fracture toughnesses and lower strengths than the bimodal microstructure.