Papers by Author: Yong Qing Zhao

Abstract: In this work the texture evolution of a near β Ti-3Zr-2Sn-3Mo-25Nb (TLM) biomedical titanium alloy in hot compression at different deformation temperatures from 750°C to 850°C has been investigated. The XRD examination shows that the samples of hot deformation consist of β phase only. The development of texture has been explained in terms of orientation distribution functions (ODFs) of α and γ fibres. Compared with cold compression of TLM alloy, the texture changes obviously with the increase of deformation temperature. The {111}<110> texture shows the feature that weaken firstly and then strengthen, while the {111}<112> texture shows an opposite tendency. Specifically, the prominent texture components change to the {111}<110> and {111}<112> at the deformation temperature of 850°C, which are the same texture type and the nearly level of orientation density with the starting materials.

Abstract: The damage and fracture behavior was researched in hot compression of as-cast Ti40 titanium alloy with single β phase. The main fracture modes consist of 45° shear fracture, inner cracking and longitudinal fracture on free-surface, which occur at 850°C/10s^-1, 900~950°C/10s^-1 and other deformation conditions respectively. Moreover, 45° transgranular cracking is the combination result of adiabatic shear bands due to local temperature rise and shear stress, the inner intergranular cracking is induced by the microvoids near the adiabatic shear bands propagted along grain boundry under shear stress, the surface longitudinal intergranular cracking is caused by the vaporization of oxide and function of hoop tensile stress. In addition, the material undergoes the complex fracture which has to be avoided or decreased in hot processing for obtaining satisfactory properties.

Abstract: Abstract. OM, XRD, SEM, EDS were used to test. and analyze the combustion products of TC4 and Ti40 alloys by layer-by-layer from reaction frontier to matrix The result shows that: titanium alloy can be divided into 4 sections, combustion surface (CS), molten zone (MZ), transitional zone (TZ) and influence zone (IZ). The CS is mainly consist of TiO₂, and with oxide of V. Cr₂O₃ and SiO₂ are detected on CS of Ti40. MZ of TC4 is in loose and porous state. There are lots of cracks and holes in the TZ and IZ; MZ of Ti40 is compact, between MZ and IZ there is a TZ which is rich of V and Cr, it can stop oxygen diffusing effectively. From the MZ to matrix, oxygen content reduces gradually, and oxide of Ti with different valence state is detected. Because of effect of oxygen, the hardness of the two alloy increase after combustion, increment of Ti40 is much greater than that of TC4.

Abstract: The superplastic forming and diffusion bonding (SPF/DB) of hydrogenated Ti-6Al-2.8Sn-4Zr-0.5Mo-0.4Si-0.1Y (Ti600) alloys were carried out in the temperature range of 1073-1213K under 1.5MPa gas pressure. The effects of hydrogen contents and diffusion temperature on welding-on ratio of SPF/DB and microstructure of interface and matrix in Ti600 alloy were investigated by OM and SEM. According to the experimental investigation, when the parameters of SPF/DB were as follows: T=860°C, P=1.5MPa and t=70min, the welding-on ratio of Ti600 alloy with hydrogen 0.5wt% was 100 percent. However, the physical contact of Ti600 alloy without hydrogen which was related to plastic forming could not occur. Moreover, the size and amount of voids at the diffusion bonding interface decreased and diffusion bonding quality improved gradually with the increase of hydrogen content and diffusion temperature, which was attributed to the decrease of phase transformation temperature and flow stress of plastic forming as well as the release of hydrogen. After SPF/DB, the recrystallization of joint grains through the interface was formed, and the matrix of hydrogenated Ti600 alloy changed.

Abstract: As the concept of aerospace design is changed, research objectives of titanium alloys also changed from high strength to high damage tolerance. High strength, high toughness titanium alloys with damage-tolerance have been investigated under the support of a national project since 2003. TC21 titanium alloy is the first Chinese-developed high strength, high toughness and damage-tolerance titanium alloy. The mechanical property of TC21 alloy is sensitive to solution temperature and aging temperature. The rods of TC21 alloy with the diameter of 20mm and 90mm possess good mechanical properties after solution at 900°C followed by aging at 600°C.

Abstract: Effects of thermal exposure on low cycle fatigue behavior of Ti600 alloy were investigated by LSCM, SEM and TEM. The results demonstrated that both the NTE specimens and the TE specimens showed the cyclic softening, within a total strain amplitude range from ±0.45% to ±1.00%. Since the α2 phase precipitated in the αp phase during thermal exposure, the resistance of fatigue crack propagation of αp phase could be increased by the precipitation of α2 phase. Therefore, the low cycle fatigue (LCF) lives of Ti600 alloy after thermal exposure were longer than those without thermal exposure, at the same total strain amplitude.

Abstract: The effects of the process parameters on the deformation behavior of Ti14 alloy have been investigated by compressive tests, at temperature between 1000°C and 1150°C and with strain rates from 5×10-3 S-1 to 5S-1. The results revealed that deformation temperature and strain rate have significant effect on the peak flow stress, the flow stress decreases. The response time required by deformation was affected by the strain rates and liquid fraction was done by the temperature. At higher temperature, transforms deformation mechanism was changed from sliding between solid particles to flow of liquid incorporating solid particles by the change of the liquid fraction.

Abstract: The recent shift in the design focus for aeroplanes from strength to damage tolerance has led to a subsequent shift in the focus of Ti alloy research. China first started to research Ti alloys with damage tolerance from the year 2000. The first product stemming from this research is a Ti alloy with high strength, high toughness and damage tolerance (TC21). TC21 exhibits high strength (UTS  1100MPa), high fracture toughness (K1c  70MPa.m1/2) and a low crack propagation rate (da/dN being similar to Ti-6-4 with  annealing). Another Ti alloy, named TC4-DT, has also been produced. It has moderate strength, along with high toughness and damage tolerance (UTS  900MPa, K1c  70MPa.m1/2, da/dN being similar to Ti-6-4 with  annealing). Both TC21 and TC4-DT are now undergoing rapid development, with the former alloy also being applied to a full scale aeronautical application. Both TC21 and TC4-DT have promising futures in the industry. They will be the main Ti alloys with damage tolerance utilised in the Chinese market.

Abstract: The superplastic tensile deformation behavior and structural evolution of two kinds of α+β titanium alloys were investigated in this paper, one is a new high strength high toughness Ti alloy with damage tolerance called TC21, and the other is a new superplastic Ti alloy so called Ti-SP2500. The results indicated that TC21 alloy has good superplasticity at the temperature from 720
to 960
and with the strain rate of 5.510-5s-1∼1.110-2s-1. On the optimal superplastic condition, the maximum elongation is over 1300%. During the superplastic tensile deformation, the dynamic recrystallization occurs in deformation zone of the specimens and the superplasticity is improved. Ti-SP2500 alloy has good superplasticity at the temperature from 720°C to 800°C and with the strain rate of 6.67 10-4s-1∼1.1110-2s-1. The maximum elongation for Ti-SP2500 alloy will exceed 2200% at 780°C with the strain rate of 5.5610-3s-1. Its superplastic deformation mechanism is controlled by grain boundary sliding, and the grain deformation and dislocation creep has the coordinating action.

Abstract: Tensile and high cycle fatigue (HCF) property for TiC particle reinforced titanium matrix composite has been studied in this paper. The results indicated that the composite possessed favorite comprehensive properties. The tensile properties for the composite are superior to that of the common high temperature titanium alloys, e.g. IMI834, Ti-1100. Smooth axial fatigue tests were taken at a frequency of 76Hz with a load ratio R of 0.06 and –1, respectively. And HCF strength for the composite at ambient temperature is 595MPa and 494MPa, respectively.