Analysis of Low-power Tissue Bright Spots of TC17 Titanium Alloy Bars

Analysis of Low-power Tissue Bright Spots of TC17 Titanium Alloy Bars

TC17 alloy is a near-β alloy with excellent comprehensive performance. Its nominal composition is Ti-5Al-2Sn-2Zr-4Mo-4Cr (mass fraction, %). The alloy can be forged in the α+β phase region. Forging is carried out in the β phase region. It not only has high strength, hardenability and fracture toughness, but also good heat resistance stability, high fatigue performance and good hot workability. Since the 1970s, it has gradually entered the aerospace manufacturing industry with its excellent performance, and has been used as a forging on compressors and higher thrust engines. Researchers used three forging temperatures to study the effect of forging temperature on low-powered tissue spot of TC17 titanium alloy

The test used a Φ140mmTC17 titanium alloy bar. The bar microstructure is uniformly distributed on the β matrix with an equiaxed α phase, and the α phase content is about 50%. The experimental material was measured by the metallographic method to determine the phase transition point (α + β / β) of the alloy was 880 to 900 ° C.

The billet was deformed by about 60% on a 2500T fast forging machine at three temperatures of 950 ° C, 850 ° C and 830 ° C, and forged into a rod of Φ 90 mm. The rods produced at the three forging temperatures were subjected to low-magnification inspection to observe the distribution of bright spots in low-magnification tissues. Microstructure observation was carried out on an OLYMPUS GX71 metallographic microscope, and the bright spots were analyzed by means of energy dispersive spectroscopy (EDS) analysis and microhardness testing, and the bars were subjected to 840 ° C / 2 h. AC + 800 ° C / 4 h. WC + 630 After °C/8h.AC treatment, the mechanical properties and metallographic structure of the bar were examined.

The forging temperature determines the microstructure and properties of the titanium alloy. The β-phase transformation during the β-phase forging process of the titanium alloy is a phase transition process that must be experienced, but if it is in the two-phase forging, the β-species are not allowed to appear. . By reasonable forging temperature selection, β spot generation can be effectively avoided.

Previous studies have shown that the larger the beta speckle area, the greater the effect on room temperature tensile properties and low cycle fatigue properties. The maximum area of ​​β-spots in Ti-10V-2Fe-3A1 alloy in the United States is 0.762mm×0.762mm. The maximum area of ​​β-spots in Ti-5553 alloy in Russia is 0.75mm×0.75mm, which is less than the specified value β. Spots have little effect on mechanical properties.

For the near-β forged TC17 titanium alloy products, the uniformity of deformation and the deformation rate should be controlled as much as possible to avoid the formation of β-spots due to excessive local temperature rise. The study draws the following conclusions:

(1) The heterogeneity of the micro-region is the essential factor causing the β-spot of TC17 titanium alloy, and the forging temperature is the main predisposing factor for the formation of β-spot. Produced at 30 ° C below the phase transition point, different degrees of beta plaque will appear in the low-fold structure of the bar. This is because the distribution of the composition of the micro-region is not uniform, resulting in a transition temperature lower than that of the matrix region in the region, causing the local temperature to advance beyond the phase transition point in the forging, thereby forming a beta spot. Production at 50 ° C below the phase transition point can effectively prevent the generation of beta plaques.

(2) The area of β-plaques appearing in the study is about 0.35mm×0.30mm, and the local small-area β-spots have no significant influence on the overall mechanical properties of TC17 titanium alloy bars, which can meet the requirements for use.