TC17 alloy is a near β-type alloy with excellent comprehensive properties. Its nominal composition is Ti-5Al-2Sn-2Zr-4Mo-4Cr (mass fraction,%). The alloy can be forged in the α + β phase region or Forging is performed in the β phase region. It not only has high strength, hardenability and fracture toughness, but also has good heat stability, high fatigue performance and good hot workability. Since the 1970s, it has gradually entered the field of aeronautical manufacturing due to its excellent performance, and is used as a compressor plate and other forgings on high-thrust engines. Researchers have studied the effect of forging temperature on the bright spots of TC17 titanium alloy through three forging temperatures.
The test uses Φ140mm TC17 titanium alloy bar. The microstructure of the bar is an equiaxed α phase uniformly distributed on the β matrix, and the α phase content is about 50%. The material used in the experiment measured the phase transformation point (α + β / β) of the alloy by metallographic method from 880 to 900 ℃.
The billet is deformed by about 60% on the 2500T fast forging machine at three temperatures of 950 ° C, 850 ° C and 830 ° C, and forged into Φ90mm bars. The low-power microstructure inspection was carried out on the bars produced by the three forging temperatures, and the distribution of bright spots in the low-power microstructure was observed. Observe the microstructure on the OLYMPUS GX71 metallographic microscope, analyze the bright spots by means of energy spectrum (EDS) analysis and microhardness test, etc. After treatment at ℃ / 8h. AC, the mechanical properties and metallographic structure of the bar are tested.
The forging temperature determines the structure and properties of the titanium alloy. The β-phase transformation during the β-phase forging of the titanium alloy is a phase transformation process that must be experienced. However, if it is a two-phase forging, the β-spot is a structural defect that is not allowed to appear. . Through reasonable forging temperature selection, β spots can be effectively avoided.
Existing studies have shown that the larger the beta spot area, the greater the impact on room temperature tensile properties and low cycle fatigue properties. The United States stipulates that the maximum area of the beta spot in the Ti-10V-2Fe-3A1 alloy is 0.762mm × 0.762mm, and Russia ’s regulation on the maximum area of the beta spot in the Ti-5553 alloy is 0.75mm × 0.75mm, which is less than the specified value Spots have little effect on mechanical properties.
For near-beta forged TC17 titanium alloy products, the uniformity of deformation and the rate of deformation should be controlled as much as possible to avoid the formation of beta spots due to excessive local temperature rise. The study reached the following conclusions:
- (1) The uneven composition of the micro zone is the essential factor that causes the plaque of the TC17 titanium alloy, and the forging temperature is the main inducer of the formation of the plaque. Produced at 30 ° C below the phase transition point, β spots will appear in the bar at low magnification. This is because the distribution of the components in the micro area is not uniform, resulting in the transition temperature of this area being lower than that of the matrix area, which causes the local temperature to exceed the phase transition point earlier during forging, thereby forming β spots. Production at 50 ℃ below the phase transition point can effectively avoid the occurrence of β spots.
- (2) The area of β spot appeared in the study is about 0.35mm × 0.30mm. The local small area of β spot has no great influence on the overall mechanical properties of TC17 titanium alloy bar, which can meet the requirements of use.