Effect Of Element V On Microstructure Of DZ125 Superalloy

The DZ125 columnar superalloys with V content of 0.3%,0.6%and 0.9%were prepared by vacuum directional solidification technique,and the microstructure and property of DZ125 superalloys were investigated by means of observation,phase composition analysis,creep property test and high temperature thermal exposure.The microstructures of carbides,?'phase,?phase and?+?'eutectic phase of as-cast and heat-treated alloys with various V contents were observed by scanning electron microscopy.The results showed that with the increase of V content,the carbides shape changed from the sheet into granular first,and then transformed into a acicular.The morphology did not changed of?'phase,?phase and?+?'eutectic phase,but the energy spectrum analysis shows that the V content increases with the increase of V content in the alloy.The?'phase of the alloy was extracted by electrolysis method,and the X-ray diffraction of as-cast and heat-treated alloys and their?'phase with various V content were carried out.The results showed that the?phase of the alloy is mainly composed of element Ni,Ta,Hf,Cr,Co,W,Mo,Ti and Al,the?'phase was mainly Ni₃[Al,Ti]and the carbides were mainly MC type.The lattice constants of?phase and?'phase were measured and the?/?'lattice mismatch degree was calculated.With the V content increase in the alloy,the lattice constants of?phase and?'phase decreased first and then increased,and the?/?'lattice mismatch degree also decreased first and then increased.After heat treatment,the creep properties of DZ125 alloy with various V content showed that with the increase of V content,the creep life of the alloy increased first and then decreased slightly,the creep activation energy and apparent stress index also increased first and then decreased slightly.When the V content is low in the alloy,the dislocation mainly traversed through the?'phase.When the V content is high,the dislocations slided into the second phase in the matrix.The high temperature thermal exposure of DZ125 alloy with various V content was carried out for 3000h,with the increase of V content,the transformation rate of MC carbide into M₂₃C₆ carbide gradually accelerated.The sheet carbides started to decompose from the edge,and the acicular carbides break down,?'phase growth rate accelerated first and then dropped sharply,TCP phase appeared earlier,the number gradually increased,and then gradually back to the solution.Creep property test was got on,with the high temperature thermal exposure,when the V content is less,the creep life began to decrease after 1000 h,and decreased to about one-third when it reached 2000h.When the V content is high,the creep life began to decrease after 2000h,and decreased to about one-third when it reached3000 h.When the V content is too high,the creep life decreased very slowly.During the high temperature creep,the?+?'eutectic phase is the main cradle of the crack in the alloy in the heat-treated state.After high temperature thermal exposure,the crack will germinate firstly on the M₂₃C₆ carbide,and extend along the grain boundary.Then appeared at the eutectic?+?'phase,and growth extend along the larger eutectic weaknesses and broken carbide or grain boundary,until the occurrence of fracture.After the high temperature creep rupture,the microstructure of the fracture corresponds to the elongation of the material.The dimple size and number larger,the smaller the slip trace,the better of the plasticity.