Hydrogen Induced Microstructure Evolution And High-temperature Deformation Behavior Of TC18 Titanium Alloy

TC18 titanium alloy is widely used in aerospace field because of its high strength and good hardenability,but its low plasticity and high processing cost greatly limit its application level.Hot hydrogen treatment technology provides an effective way to improve the hot working performance of two-phase titanium alloy.In order to explore the effect of hot hydrogen processing technology on microstructure evolution and thermal deformation behavior of near β titanium alloy TC18,the phase transformation,microstructure and thermal deformation of TC18 titanium alloy induced by hydrogen were studied in this paper.It provides a theoretical basis for clarifying hydrogen alloying of TC18 titanium alloy.Firstly,TC18 titanium alloy with hydrogen content of 0～0.8wt.% was obtained by solid-state hydrogen storage.The effect of hydrogen element on the phase transition temperature of TC18 was obtained by differential scanning calorimetry.The effect of hot hydrogen treatment on the phase composition and phase transformation behavior of TC18 titanium alloy was analyzed by X-ray diffraction.The transformation process of solid phase during hydrogen storage and cooling was revealed.The microstructure observation and hydride calibration of TC18 titanium alloy with hydrogen were carried out.The homogeneity of alloy structure was verified and the order of hydride precipitation was determined,which provided the basis for the selection of hot hydrogen treatment and hot deformation process of titanium alloy.Then,the effects of deformation temperature,strain rate and hydrogen content on the high temperature deformation behavior of TC18 titanium alloy were systematically studied by the method of thermal simulation compression test.The softening and strengthening mechanism of TC18 titanium alloy with hydrogen was explored and its concentration range of optimal hydrogen content was determined.The constitutive equation of high temperature deformation of hydrogen free and hydrogen containing TC18 titanium alloys were established,and their hot working diagram was drawn,which provided the basis for the selection of alloy process parameters.The effects of thermal deformation parameters and hydrogen content on the microstructure of the alloy were analyzed by observing the microstructure and simulating the damage condition of the alloys.Finally,dehydrogenation of hydrogen TC18 titanium alloy was carried out by vacuum annealing.The uniform and dense two-phase microstructure was obtained which is conducive to the further improvement of the alloy properties.The results show that the addition of appropriate hydrogen element can reduce the hot working temperature and instability risk of the alloy,which is of great significance for the selection of the technical parameters of the hot hydrogen processing of TC18 titanium alloy,saving the cost of hot processing.