Effect Of Secondary Phase On Corrosion Resistance Of Titanium-Zirconium-Molybdenum Alloy

Titanium-zirconium-molybdenum(TZM)alloy is widely used in aerospace,power generation,nuclear reactor and other fields because of its high melting point,high strength,low linear expansion coefficient and good high temperature performance.At present,the research mainly focuses on the refinement and homogenization of the secondary phase to improve the comprehensive mechanical properties of the alloy.With the continuous application of TZM alloy,it has higher requirements for its performance in strong corrosion environment.However,only a few scholars have made preliminary studies on the electrochemical behavior of molybdenum alloy in seawater,acidic,alkaline and other corrosive environments.Little research has been done on the influence of secondary phase on the corrosion resistance and mechanism of the TZM alloys.It is necessary to study the effect of secondary phase on the corrosion resistance of TZM alloy in different corrosion environments in order to further expand the application of the alloy.TZM alloy and micro-nano TZM alloy were prepared by different powder metallurgy processes.The electrochemical corrosion behavior of Mo metal,TZM alloy and micro-nano TZM alloy in different corrosion environments was studied by potentiodynamic polarization.The corrosion morphology and secondary phase composition were characterized by scanning electron microscopy and energy spectrum.By comparing the polarization curves,AC impedance spectra,corrosion morphology and corrosion mechanism under same conditions,the influence of secondary phase on the corrosion resistance of TZM alloy was studied.On this basis,the influence of different size of the secondary phase on the corrosion resistance of TZM alloy was explored.The results show that the existence of secondary phase and the different size of secondary phase can change the impedance parameters and the corrosion mechanism.The secondary phase in TZM alloy is a mixture of Ti and Zr oxides and it is easy to form micro-galvanic couples with Mo matrix.The secondary phase acts as micro-cathode,which accelerates the corrosion of matrix and reduces the corrosion resistance of the alloy.When the content of alloying elements is constant,the secondary phase of micro-nano TZM alloy is smaller in size and larger in number,which is easier to form more pitting and corrosion holes.The corrosion resistance of micro-nano TZM alloy will be significantly reduced.Compared with TZM alloy,the micro-nano TZM alloy is suitable for the working environment with higher mechanical properties,and not suitable for the working environment with harsh corrosion conditions.