Microstructure and Properties of Ti-1023 Titanium Alloy Rods
Ti 1023 Titanium Bar is widely used in aerospace field. This paper introduces the use of 650 mm Ti-1023 titanium alloy ingot produced by Xinjiang Xiangrun to produce 160 mm bar through multiple forging deformations through the "high-low-high-low" process. The macroscopic, microstructure and mechanical properties of the bar were compared and analyzed, and the results showed that: the bar showed uniform fuzzy grain macroscopically, the microstructure was a uniform two-phase region processing structure, and the equiaxed primary α phase was evenly distributed on the β matrix; after heat treatment , The mechanical properties and ultrasonic detection of the bar meet the requirements of relevant standards.
Ti 1023 Titanium Bar is a high-strength and high-toughness near-β titanium alloy with high reliability and low cost. The nominal composition is Ti-10V-2Fe-3Al. The advantages of small size, low forging temperature and strong stress corrosion resistance can meet the design requirements of high reliability and low manufacturing cost, so it is widely used in the aerospace field.
1. Experiment
In the experiment, a total of 2 t of 0A-grade small particle sponge titanium and multi-element master alloy were fed and smelted three times in a vacuum consumable electric arc furnace to prepare a ?650 mmTi1023 titanium alloy ingot. The main component (mass fraction, %) V was 9.0%~11.0 %, Fe is 1.6%~2.2%, Al is 2.6%~3.4%, and the rest is Ti, which meets the requirements of GJB1538. After cutting the riser, cutting the bottom, and sawing the center of the ingot, samples were taken at the head, middle, and tail of the axial outer circle (Figure 1), and at the 9 o'clock position of the cross section (Figure 2), and the main components were tested by atomic emission spectrometry. The content of alloying elements (Al, V, Fe) and other impurity elements.
An appropriate amount of sample block was cut from the head of the Ti-1023 titanium alloy ingot, and the transformation temperature of the α+β phase/β phase was measured by metallographic method as 805~810°C. The overall ingot is processed and forged using the "high-low-high-low" process route, and a 45/50MN fast forging machine is used to open the billet in the single-phase area (β-phase area), and finally forged into a 160 mm finished bar.
According to the GJB1538 standard, the microstructure and mechanical properties of Ti-1023 titanium alloy rods are cut from 160 mm rods along the longitudinal direction to cut 20 mm thick sample pieces and 80 mm long sample rods for various performance tests. R state, β spot (785°C×1.5 h WC+530°C×8 h AC) and solution aging (775°C×1.5 h WC+540°C×8 h AC) after treatment on the flat end face of the 20 mm thick specimen Using ICX41M metallographic microscope to observe the structure morphology and take metallographic photos. After the 80 mm long sample bar is heat-treated in a muffle furnace at 775°C×1.5 h WC+540°C×8 h AC, the horizontal and vertical samples are cut at D/4 of the sample sheet with a H-5550K semi-automatic band saw The billet is machined into a mechanical performance test sample according to the standard requirements, and the tensile test of the mechanical performance at room temperature is carried out on it, and the tensile test is measured on a CMT5205 tensile testing machine. At the same time, contact ultrasonic non-destructive testing is carried out on the finished bars.
2. Results and analysis
2.1. Analysis of the chemical composition of the ingot
According to the product sampling requirements, samples were taken at 9 points in the longitudinal head, middle, tail and cross section of the ingot surface to detect the content of main alloy elements in different parts. The test results showed that the chemical composition of the ingot met the requirements of relevant technical standards. In particular, the test results of the content of impurity elements (C, N, O, H) at the head and tail of the longitudinal surface all meet the requirements of the standard range, indicating that the ingot has a high degree of purity.
During the vacuum consumable arc smelting process of the ingot, there is the element Fe that is prone to segregation, and the inhomogeneous composition or segregation may occur during the ingot smelting. According to the titanium alloy phase diagram and alloy solidification theory, under normal solidification conditions, alloy elements with a segregation coefficient k≥1 are not prone to segregation, unless the alloy elements and intermediate alloys are not sufficiently homogenized during the smelting process; the segregation coefficient k< 1 alloy elements, even if the alloy is uniform in the molten state, there is still a certain difference between the solid phase composition and the liquid phase composition at the same temperature during solidification, and the element content in the liquid phase is always higher than that in the solid phase, which leads to casting Ingots tend to segregate in the middle and head.
Overall, the chemical composition of the main alloying elements in the Ti-1023 titanium alloy 2 t grade ingot is evenly distributed and the purity is good, all of which meet the technical requirements of the ingot. Process control and other aspects are reasonable and feasible.
2.2. Microstructure and Morphology Analysis of Bars
Forged state (R state) photographs of Ti-1023 titanium alloy cut from the head and tail of the 160 mm bar for surface corrosion.
Adopt 4500 t fast forging machine with large tonnage pressure, adopt "high-low-high-low" process route for multi-fire forging ingots, fully break the as-cast grains, and use reverse forging for billets to improve forging penetration of billets properties, making the structure of the bar more uniform. The forging process utilizes the processing characteristics of slow grain growth when the β matrix of the near β alloy is rapidly completed recrystallization, so that the metal grains are repeatedly broken, sub-grains merge and grow, and grain boundary migration process, the final bar The structure tends to be uniform, which lays a good foundation for the uniform structure and good performance of the bar.
Cut transverse samples of different regions (edge, D/4 and core) from the bar sample sheet corresponding to the position of the head of the ingot, observe the R state and its microstructure after solid solution and aging heat treatment ,
2.3. Detection results of bar β spots
The equilibrium distribution constant of Fe element in Ti-1023 titanium alloy is 0.3, which has a great tendency of segregation. The main reason for the formation of β spots in Ti-1023 titanium alloy is that the local segregation and enrichment of "Fe" alloy materials causes the β transformation temperature of this part to drop compared with that of the matrix, resulting in the formation of Fe-rich areas that do not contain primary α-phase or have relatively rare α-phase content. Areas, namely β spots, β spots can seriously affect the plasticity and low cycle fatigue life of the alloy.
The uneven composition of Fe in TB6 alloy ingots is the "innate" factor for the formation of β spots, and the subsequent thermal processing and heat treatment processes are the "acquired" factors that affect the formation of β spots. According to the heat treatment process in GJB1538, 785 ℃×1.5 h WC+530 ℃×8 h AC were selected to prepare rods. Observation of the bar shows that there is no abnormal phenomenon in the bar on the macroscopic appearance; while the content of the equiaxed primary α phase in the microstructure is about 15%, which meets the standard requirement of the primary α phase content of more than 10% in GJB1538.
3 Conclusion
(1) The titanium alloy ingot produced by smelting 0A grade small particle sponge titanium and multi-element master alloy has good composition uniformity, and the ingot meets the standard requirements.
(2) The ingot is forged with multiple fires using the "high-low-high-low" process to prepare bars with high-magnification structure, low-magnification structure, and ultrasonic flaw detection that meet the requirements of the GJB1538 standard.
(3) By adopting a suitable heat treatment process, the strength of the rod has little difference in the horizontal and vertical directions, the uniformity of each point is good, and the mechanical properties can meet the requirements of the GJB1538 standard.
