I. Experimental Process From the perspective of the basic characteristics of materials, TC21 titanium alloy will undergo a series of changes when it is solution - treated at different phase region temperatures. Specifically, the TC21 titanium alloy bars of specific specifications are subjected to multi - pass plastic processing and fine treatment. According to its phase transformation point, the solution temperatures such as 910 - 1010 °C are accurately set, followed by water - cooling treatment, and then the alloys after solution treatment at different temperatures are comprehensively tested and analyzed.
II. Influence on Microstructure
Changes in Microstructure Morphology The test results show that the change of solution temperature has a significant impact on the microstructure morphology of TC21 titanium alloy. Phase Analysis It can be known from the XRD patterns that whether the solution temperature is in the single - phase region or the two - phase region, the α″ - phase will be precipitated in the alloy structure. During the solution process, due to the fast cooling rate, a large undercooling degree will be generated, which makes the alloy elements in the structure have no time to orderly diffuse during cooling, resulting in the β - phase transforming into the α′ - phase in the form of shear.
III. Influence on Mechanical Properties
Trends of Strength and Plasticity The strength of the alloy first increases and then decreases with the increase of the solution temperature, while the plasticity continuously decreases.
Fracture Morphology and Fracture Mode in Different Phase Regions When the solution temperature is in the two - phase region, the tensile fracture morphology of the alloy is mainly dimples, and the fracture mode is ductile fracture; when the solution temperature reaches the single - phase region, the tensile fracture morphology is mainly rock - like, and there are a small number of small - sized dimples, and the fracture mode becomes brittle fracture.
IV. Analysis of Specific Mechanisms
When the Solution Temperature is Low When the solution temperature is low, the content of primary α - phase in the structure is high, which helps to improve the structural parameters of the microstructure, optimize the deformation behavior of the structure, promote the sliding of the cross - slip system, increase the structural coordination, so that the alloy has good plasticity.
When the Solution Temperature Increases As the solution temperature rises to the single - phase region, the primary α - phase completely disappears, and coarse β - grains appear. Dislocation movement and grain boundary slip are effectively inhibited, the deformation resistance increases, and the alloy plasticity becomes worse. At the same time, the fine needle - like α' - phase and α" - phase in the structure have a large hindrance to slip during the tensile process, are prone to stress concentration, which makes the alloy strength increase; after the primary α - phase completely disappears, the structural coordination performance is greatly reduced, a large number of α' - phase and α" - phase are precipitated, and it is difficult for dislocations to pass through the α/β - phase interface, resulting in a large number of dislocation pile - ups at the interface, causing non - uniform deformation in micro - regions and slip bands, easily forming micropores and growing rapidly, causing the tensile specimen to enter the yield stage prematurely, and finally making the alloy strength decrease.
In conclusion, the solution temperature is crucial for the microstructure and mechanical properties of TC21 titanium alloy. Clarifying the tissue evolution law that the increase of solution temperature promotes the decrease of primary α - phase, the equiaxialization and the increase of needle - like α - phase in TC21 titanium alloy until the disappearance of primary α - phase in the single - phase region, determining the trend that the alloy strength first increases and then decreases with the solution temperature and the plasticity continuously decreases, and accurately judging the characteristics of ductile fracture in the two - phase region and brittle fracture in the single - phase region, and explaining the transformation of fracture mechanism from the perspective of tissue change can provide key performance data for the optimization of heat treatment process parameters of TC21 titanium alloy, provide a solid theoretical basis for the failure analysis and application of the alloy, and has important practical significance for promoting the wide application of TC21 titanium alloy in aerospace and other fields.