| With the increasing demand for oil resources,the depth of oil and gas well mining has gradually increased.Titanium zirconium niobium-based shape memory alloys have broad application prospects as downhole tool materials due to their unique functional characteristics,excellent mechanical properties,and corrosion resistance.However,the corrosion resistance of titanium zirconium niobium-based shape memory alloys in downhole environments has not received sufficient attention.In this article,the corrosion resistance of titanium zirconium niobium-based shape memory alloys studied by simulating downhole environments,combining electrochemical testing and micro-characterization instruments,and exploring the effects of element composition and heat treatment process.The study on the effect of Nb content on the corrosion resistance of Ti-30Zr-x Nb(x=7,10,13 at.%)alloys shows that Nb element can improve the surface characteristics of the passivation film of Ti-30 Zr alloy.As Nb content increases,the corrosion resistance of the alloy first increases and then decreases.The main reason is that with the increase of Nb content,the grain refinement of the alloy is obvious.When the composition exceeds the solubility limit,twinning and defects such as dislocation pile-up increase,and a large number of uneven energy positions are produced.As a result,it is found that the corrosion resistance of Ti-30Zr-10 Nb alloy is better than that of other compositions.The results of studying the effect of annealing temperatures of600°C,700°C,and 800°C on the corrosion resistance of Ti-19Zr-11Nb-2Ta alloy show that as the annealing temperature increases,the grain size first decreases and then increases,and the corrosion resistance of the alloy first increases and then decreases.The main reason is that the higher temperature leads to more vigorous atomic movement in the crystal structure,which diffuses to the interface and merges into larger grains.Coarser grains cause stress concentration in the alloy,which damages the integrity of the alloy,forms corrosion points,and is easy to adsorb corrosive media,promoting corrosion.As a result,it was found that the alloy annealed at700°C had the best corrosion resistance compared to other annealed alloys.The immersion results in simulated downhole environments showed that the maximum average corrosion rates of Ti-30Zr-x Nb(x = 7,10,13 at.%)and Ti-19Zr-11Nb-2Ta shape memory alloys were 0.0046mm/a and 0.0048mm/a,respectively,which were both considered mild corrosion according to the NACE SP0775-2013 national standard.The relevant results lay the theoretical foundation for developing high-temperature-resistant titanium,zirconium,and niobium shape memory alloy tools suitable for corrosive underground environments. |
