Research And Experiment Optimization Of TA15Titanium Alloy During Superplastic

Titanium and Titanium alloy have the low density, high intensity, the good hightemperature performance, corrosion resistance, are importantly application value andwidely development prospect in aviation, aerospace, chemical industries, vehicleengineering, biomedical engineering. However, its high deformation resistance, coldforming crack easily, low rate of finished products, limited their application.Superplastic forming technology can break through this defect, especially for processingcomplicated shape parts. In recent years, superplastic forming techno-logy (SPF) for preparing titanium alloy with excellent comprehensive properties, hadbecome a hot research direction. At present, the study mainly focuses on thedeformation mechanism of superplasticity, and superplastic has a lot of influence factors,people often through comparison and orthogonal method to get the best deformationconditions, the lack of systematic research.Therefore, this paper studied about near-TA15alloy by the optimization studyof superplastic deformation factors, get optimal deformation temperature, strain rate andgrain size. The influence of deformation conditions on the superplastic deformationbehaviorin the process of deformation, microstructure evolution, andfracture mechanism of superplastic deformation was studied.Results are summarized as follows:1. Analysis on the microstructure and mechanical properties of TA15titanium alloy rawmaterial. The results and conclusions are as follows:Microstructure of TA15titanium alloy is uniform, fine, mainly is the andβ phases, phase transition temperature is991℃. At room temperature and high temperature(500℃) of TA15titanium alloy has a very high yield strength and elongation,compared with the tensile properties at room temperature, tensile strength decreaseswhen high temperature tensile, but its elongation increases.2. Experiment optimization of superplastic, analysis of the evolution of TA15titanium alloy during superplastic deformation, study of technological parameters ofTA15titanium alloy superplastic deformation behavior. The results and conclusions areas follows:(1) In850℃,900℃,950℃deformation temperature and1×10-4S-1,5.5×10-4S-1,1×10-3S-1strain rate of TA15alloy during superplastic tensile obtained good elongation.(2) Through response surface regression fitted equation, the model of basic a linearrelationship between predicted values and the real value, can represent the experimentalresults very well. The calculated optimal superplastic tensiledeformation conditions for4.6μm grain size,890.7℃deformation temperature and3.74×10-4S-1strain rate, the biggest elongation was916.2%.(3) From the true stress-strain curve, TA15titanium alloy under differenttemperature and strain rate deformation curve shape similarity. Basically we could seestrain hardening, strain softening and strain hardening, strain softening three differentstages of dynamic balance. During deformation, the hardening and the softeningcompeted each other, realized for the traditional steady-state superplastic flowcharacteristics.3. Studied the fracture mechanism of superplastic deformation, discusses thedeformation process parameters(grain size,deformation temperature, strain rate)on theinfluence of superplastic tensile behavior. The results and conclusions are as follows:As TA15alloy, deformation in the process of superplastic tensile deformationtemperature, strain rate and grain size have larger influence on fracture surfacemorphology, and the experimental design conditions within the scope of localmacroscopic plastic deformation. Tensile samples after a great extend gradually stretchinto a filament and finally happen neck fracture, thus can obtain larger elongation.TA15alloy tensile deformation at different deformation temperature, strain rate grainsizeunder, the sample fracture will appear different sizes round or oval plastic fracture pits-dimple, fracture was ductile fracture...