Papers by Keyword: High Temperature Titanium Alloy

Abstract: In this paper, in order to explore the development of a titanium-based superalloy with a working temperature of 700°C to 750°C and good ductility at room temperature, using Ti+Al+Ti2AlNb ternary powder as the raw material, the temperature is 1200°C to 1300°C, 30MPa, 1.5h Directly mixed and sintered under hot pressing conditions, a new type of titanium-based superalloy (TiAl+Ti2AlNb) samples were prepared. The fracture morphology of hot-pressed sintered samples and tensile samples used scanning electron microscope (Scanning electron microscope, referred to as SEM) and Electron backscattered diffraction (EBSD) for observation. Discuss the room temperature tensile fracture behavior of a new type of high temperature titanium alloy Ti-Al-Nb, and lay a technical foundation for the development of a new type of high temperature titanium-based alloy with low brittleness at room temperature.

Abstract: A new type of near α high temperature titanium alloy of Ti-Al-Sn-Zr-Mo-Si-Er was studied. The samples with different primary α phase content were prepared by solid solution at 950 °C/1 h—1010 °C/1 h. The multi-step hot compression experiments were carried out by Gleeble-3500 in a sequence of upper region of α + β phase, then followed by lower region of α + β phase. The effects of primary α phase content and deformation temperature on the microstructure of the alloy were studied by means of true stress-strain curve and optical microscope. The results show that the content of primary α phase gradually decreases from 45.4% at 950°C to 0% at 1010°C. As the deformation temperature decreases from 940°C to 900°C, the content of α phase increases gradually from 65% to 94%, which is changed from dynamic recrystallization to deformed structure elongated along RD direction. It is found that the arrangement of α phase along RD direction is the longest at 920°C. With the increase of the deformation temperature in the multi-step high temperature region from 970°C to 990°C, the width of deformed α phase decreases from 3.64 μm at 970°C to 2.71 μm at 990°C. The optimized microstructure is composed of 20% primary α phase arranged along RD direction. This process has a certain potential in the process of hot deformation of the alloy. Key words: high temperature titanium alloy, primary α phase, multi-step hot deformation

Abstract: A new type of Ti-Al-Sn-Zr-Mo-Si series high temperature titanium alloy was prepared by a water-cooled copper crucible vacuum induction melting method, and its phase transition point was determined by differential thermal analysis to be T_β = 1017 °C. The influences of solution temperature on the microstructures and mechanical properties of the as-forged high temperature titanium alloy were studied. XRD results illustrated that the phase composition of the alloy after different heat treatments was mainly α phase and β phase. The microstructures showed that with the increase of the solution temperature, the content of the primary α phase gradually reduced, the β transformation structure increased by degrees, then, the number and size of secondary α phase increased obviously. The tensile results at room temperature (RT) illustrated that as the solution temperature increased, the strength of the alloy gradually increased, and the plasticity decreased slightly. The results of tensile test at 650 °C illustrated that the strength of the alloy enhanced with the increase of solution temperature, the plasticity decreased first and then increased, when the solution temperature increased to 1000 °C, the alloy had the best comprehensive mechanical properties, the tensile strength reached 714.01 MPa and the elongation was 8.48 %. Based on the room temperature and high temperature properties of the alloy, the best heat treatment process is finally determined as: 1000 °C/1 h/AC+650 °C/6 h/AC.

Abstract: The effects of pulse current on the tensile properties of high temperature titanium alloy Ti55 were investigated by pulse current assisted uniaxial tensile test under different electrical parameters. It was found that with the increase of peak current and pulse width, the tensile properties of Ti55 are significantly improved. At the same time, the pulsation effect of current on the mechanical properties of Ti55 was investigated. The results show that the tensile displacement of low pulsation group was higher, while the elongation of high pulsation group was higher. In order to explore the mechanism of pulsation effect of current, EBSD was adopted. The results indicated that high pulse current can significantly promote the dislocation movement and recrystallization. In addition, some macrozones was found in low pulsation group, which indicated that high pulsation current was more suitable for material forming than low pulsation current.

Abstract: The Ti-6.5Al-2Sn-4Zr-1.5Mo-2Nb-0.25Fe-0.2Si (wt%) alloy is a novel two-phase high temperature alloy for short-term application. The effects of different heat treatments on the microstructure and mechanical properties were investigated through electron probe microanalysis (EPMA), optical microcopy (OM), scanning electron microscope (SEM), electron backscattered diffraction (EBSD) and tensile tests at room temperature and 650°C. Subjected to the annealing treatment at α+β region (1010 °C/2 h, FC to 990 °C+990 °C/2 h, AC), the microstructure was composed of bimodal structure, which consists of equiaxed primary α (α_p) phase and lamellar transformed β (β_t) structure. As a strong β stabilizer, the content of Fe in α phase is much less than that in β phase. Annealing at β region (1040 °C/2 h, AC) resulted in the formation of widmannstatten structure, consisting of coarse raw β grain and secondary α phase precipitated on the β grain. With respect to the tensile property, different heat-treated alloys obtained similar strength. However, widmannstatten structure was characterized by lower plasticity, with the elongation only half that of bimodal structure. The fracture characteristics at room temperature for the alloy with bimodal structure and widmannstatten structure are dominated by ductile fracture and cleavage fracture, respectively.

Abstract: The effect of the primary α content and precipitate on the creep resistance of a high-temperature titanium alloy with a small amount of Hf addition were studied. The microstructures with different primary α contents were prepared by the heat treatment of 920~1010 °C /1 h+700 °C/5 h, and the creep test (600 °C/150 MPa/100 h) was carried out. The interaction between the precipitation phase and the dislocation configuration was analyzed. The results showed that with the increase of solution temperature, the volume fraction of primary α phase decreased from 44.9% at 920 °C to 0% at 1010 °C, and the steady state creep rate of the alloy decreased from 60.60×10^-4%/h to 3.72×10^-4%/h, indicating that the creep property was significantly improved with the decrease of solution temperature. The basket structure with optimal creep resistance was obtained under the heat treatment of 1010 °C/1 h+700 °C/5 h. It is believed that during the high temperature creep test, the precipitated α₂ phase and the hafnium-containing silicide hinder the dislocation motion in α crystal and the phase boundary, thereby improving the creep resistance of the alloy.

Abstract: The microstructures and mechanical properties of a new type near α high temperature titanium alloy Ti-6.5Al-2.5Sn-9Zr-0.5Mo-0.25Si-1Nb-1W-0.3Re (wt. %) (denoted as TA6.5) were investigated. It was observed that the microstructure of forged TA6.5 mainly consisted of deformed lamellar α phase, small amount of equiaxed α phase, and residual β phase, exhibiting high strength and comparatively low elongation. Three different heat treatments processes were performed on forged TA6.5. The results showed that all heat treated alloys displayed high tensile strengths, and the values of strength parameters were almost unchanged with the increasing solution temperature, ascribing to the combination effects of decreasing primary α phase and increasing contents and widths of secondary α phase and lamellas. The tensile elongations of heat treated alloys tested at 650 °C decreased slightly with the increasing solution temperature, which is due to the increased width of secondary α lamellas and the generation of coarse grain boundary α phase. TA6.5 treated in the process of 990 °C/1 h/AC+700 °C/4 h/AC exhibited excellent comprehensive mechanical properties, i.e. the ultimate tensile strength of 829 MPa, yield strength of 707 MPa and elongation of 18.73% respectively.

Abstract: A near-α high temperature titanium alloy, Ti-6Al-2.5Sn-4Zr-0.7Mo-0.30Si, was produced with various Y contents from 0 to 0.7wt% by arc-melting technique to study the influence of Y on its microstructure and mechanical properties. It was found that small amount of Y obviously refines the grain size of Ti-6Al-2.5Sn-4Zr-0.7Mo-0.30Si alloy. SEM and TEM observations revealed that Y-containing phase precipitated at the β grain boundary in the form of Y2O3 particles. Hardness and compression tests performed at room temperature revealed the strengthening effect of Y.