Study of the hydrogenation effect on the structure and flattening of tubular samples of PT-7M titanium alloy

Abstract

In this work, we analyze the effect of hydrogen embrittlement on the performance of PT-7M titanium alloy products. The above examples show that PT-7M titanium alloy products with a high hydrogen content are prone to cracking, the probability of their destruction increases. In the initial state, the samples were annealed in vacuum at 680 о. Hydrogenation of the samples was carried out by the diffusion method at room temperatures to concentrations of 0.002, 0.005 and 0.01 % (by mass) in a Siverts laboratory setup. The hydrogen content in the samples was determined on a highly sensitive G8 Galileo gas analyzer. To assess the effect of hydrogen embrittlement on the plastic properties and tendency to crack formation, the samples were tested for flattening. The structural state of the alloy was analyzed, which showed that hydride phases were observed to increase with increasing hydrogen concentration. The effect of structural changes in the alloy on the microhardness was studied. The X-ray diffraction analysis also showed the presence of hydride precipitates in the PT-7M alloy. Using the CAE ANSYS engineering complex, a numerical simulation of the stress-strain state of samples was carried out during a flattening test. The simulation results showed that the maximum stresses during flattening exceed the tensile strength. One of the reasons for the hydride phase precipitation is high stresses, which is also confirmed by the results of flattening tests and metallographic analysis: in local zones with an increased level of stresses in the material structure, a higher concentration of the TiHx hydride phase. Flattening tests also showed that the cause of cracking during flattening testing is the presence of brittle hydrides in the structure of the material: cracks are formed by the destruction of hydride phases. In the initial state and with a low hydrogen content (up to 0.002 mass %) no cracks were found in the samples. Thr research was conducted within the framework of the grant RNF No. 19-19-00332 "Development of scientifically substantiated approaches, hardware and software facilities for monitoring of damage of construction materials, based on the artificial intellect approaches to provide safe operation of technical objects in the Arctic conditions".