Papers by Author: Yun Lian Qi

Abstract: Effects of extrusion temperature and heat treatment process on the microstructure and mechanical properties of Ti-1300 titanium alloy tube billets were studied by tensile testing and microstructure observation, and the relationship among the thermal processing technique and microscopic structure and mechanical properties of the billets were also investigated. The results showed that the transverse structure of Ti-1300 alloy after extrusion in the a+b two-phase region was uniform and fine. And the longitudinal structure could be seen that the extrusion processing streamline was broken uniformly. Ti-1300 alloy extruded at a+b two-phase has a good match of the strength and ductility, and the ductility of two-phase extrusion is obviously better than that of β single-phase extrusion, especially for the reduction of area.

Abstract: Microstructure and dislocations were observed for Ti-600 alloy crept at the temperature of 600°C with the stress of 200MPa and 300 MPa. The results indicate that more precipitation phases could be found both in β phases and at phase boundaries for the alloy after creep tests, and the width of the phase boundary become broader obviously. Also more dislocations could be seen at or around the precipitation phases for the alloy crept at 600°Cwith the stress of 200MPa. Dislocation density is rather big in some regions, dislocations aggregate in precipitation phases, phase boundaries and sub-grain boundaries. Some tangled dislocations or regular arranged dislocations could also be found around precipitation phases. Condensed three-dimensional dislocation meshes could be found in the alloy crept for the alloy crept at 600°Cwith two stresses. For the alloy crept at 600°Cwith the stress of 200MPa, faults originated from boundaries of α lamellar could be found in α lamellar. Some of these faults extend to boundaries of α lamellar, and some stop or end off in α lamellar. While for the alloy crept at 600°Cwith the stress of 300MPa, dislocation tend to arrange in dislocation walls, form bamboo-like structure along the direction of α lamellar, which would expand and penetrate the whole grain of elongated dislocation walls, and at last stop at grain boundaries.

Abstract: The deformation behavior in isothermal compression of Ti-5Al-4Mo-2Cr-4Zr-2Sn-1Fe alloy was investigated at the deformation temperature of 800°C, 850°C, 900°C, 950°C and 1000°C, the strain rate of 0.01s^-1, 0.1s^-1, 1.0s^-1 and 10.0s^-1, and the height reduction of 70%. The flow stress increases rapidly with the increasing of strain at the beginning of deformation. When the strain exceeds a certain value, the flow stress begins to decline and becomes steady. With the increasing of deformation temperature and decreasing of strain rate, the steady stress and peak stress decrease significantly. The effect of strain on the processing maps of Ti-5Al-4Mo-2Cr-4Zr-2Sn-1Fe alloy is obvious. As the strain increases, the instable region moves towards high temperature and high strain rate area. Meanwhile, the contour of efficiency of power dissipation becomes more and more intensive, and the region with high efficiency of power dissipation reduces. Strain rate of 0.01s^-1 and deformation temperature of 900°C are the optimum processing parameters for Ti-5Al-4Mo-2Cr-4Zr-2Sn-1Fe alloy forging under strain of 0.3.

Abstract: Creep tests were carried out on one kind of near alpha titanium alloy named after Ti-600 alloy at the temperature of 650°C, and with the stresses of 150MPa, 200MPa, 250 MPa, 300 MPa and 350 MPa, respectively. The alloy ingot was conventionally forged and rolled to diameter 18mm bars. The creep samples were cut from the rolling bars and were solutioned at 1020°C for 1 h, air cooling, then aged at 650°C for 8 h, air cooling (STA). Steady state creep rate and the stress exponent n at different stresses were calculated for the alloy. Threshold stress σ₀ was introduced to get the true stress exponent p. Creep deformation mechanism was also investigated. The results indicated that the steady state creep rate will increase with the rise of stress, and the creep time will also be shortened at the same time. At 650°C, the threshold stress is 83.8MPa. The value of n and p is 7.7 and 3.3 respectively for the alloy crept at lower stress region (150-200MPa); and which is 2.1 and 4.7 respectively for the alloy crept at relatively higher stress region (200-350MPa). Constitutive equations of steady state creep rate were also established for the alloy crept at 650°C. The creep deformation for the alloy is controlled by dislocation slipping at lower stress region, and which is mainly controlled by dislocation climbing and subordinately controlled by dislocation slipping at higher stress region.

Abstract: The effects of extrusion temperature and heat treatment on the microstructure and mechanical properties of beta-CEZ titanium alloy tube blank were studied with an emphasis on the relationship between the heat processing technique and microscopic structure. The results show that the extruded tube blank of beta-CEZ titanium alloy at alpha-beta phase has better tensile strength and plasticity match, and the ductility of the alpha-beta phase extrusion is obviously better than that of the single beta-phase extrusion, especially the reduction of area. When the extruded tube is heat treated at 830°C and 860°C solid solution, with the increase of aging temperature, the strength of tube decreases and the plasticity increases. When the aging temperature is up to 600°C, the reduction of area of the tube increases obviously. When the extruding tube is aged at 550°C and 600°C, the strength of the tube increases and the plasticity decreases with the increase of the solid solution temperature. The titanium alloy of beta-CEZ is extruded below the phase transition point after low temperature solid solution and high temperature aging treatment, which can achieve good microstructure and performance matching. The tensile strength is greater than 1250MPa, the elongation is more than 15%, and the reduction of area is more than 40%. The microstructure was a fine and uniform equiaxed structure.

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.