Effect Of Element V On Microstructure And Properties Of DZ417G Superalloy

The DZ417 G superalloy with different V content was prepared by vacuum directional solidification technique.The V content of the alloy was 0.69%,0.96% and 1.04%,respectively.The effect of V element on DZ417 G alloy was investigated by means of micro-structure observation,phase composition analysis,creep test,tensile test and long-term aging;The carbide and ?' phase morphology of the different V content alloy was observed by the Scanning electron microscopy.The results showed that with the increase of the V content in the alloy,the carbide morphology in the alloy transformed from rod to block.The energy spectrum analysis of rod and block carbides show that there were more Cr,Al,Co element in the rod carbide and in the massive carbide the MC type carbide forming element Ti,Mo,V were more.With the increase of the V content in the alloy,the ?' morphology was almost unchanged,but the energy spectrum shows that the V content in the ? phase increases with the V content increasing in the alloy.The phase composition of the full heat-treatment alloy and the extracted ?' phase with different V content was analyzed by means of the XRD diffract meter.The results show that the ? matrix phase of the alloy is mainly composed of element Ni,Ti,Al and Ni,Cr,Co,Mo solid solution;the ?' phase is mainly composed of Ni3[Al,Ti],and the carbides are mainly composed of VC and [Ti,Mo]C based MC type carbides.The XRD diffraction peak of different V content alloy was studied by means of origin-peak-fitting,and then the lattice mismatch of the ?/?' phase was calculated.The results show that the ?/?' phase lattice mismatch was decreased with the increase of V content in the alloy.By means of middle and high temperature creep properties measurement of different V content alloy after full heat-treatment,the result shows that,with the increase of element V,the creep life of the alloy increases sharply.By means of adjusting the temperature and the stress during the creep process,the creep activation energy and the stress exponent was calculated,and the results show that the creep activation energy and stress exponent of the medium and high temperature increase together with the increasing of the V content.The crack initiation and propagation in the alloy were observed by means of the scanning electron microscopy,the result shows that carbide is the main source of cracks during medium and high temperature creep.The dislocation motion during high temperature creep was observed by means of the transmission electron microscopy,the result shows that the length of dislocation in the low V alloy is long,andthe deformation mechanism of the alloy is dislocations slipping in the ? matrix phase and climbing over the rafted ?' phase,while the deformation mechanism of the alloy is dislocations slipping in the ? matrix phase and shearing into the rafted ?' phase in the high V alloy,wherein the dislocations shearing into the rafted ?' phase are decomposed to form the configuration of the partial dislocation plus stacking fault.The tensile properties of different V alloy with full heat-treatment were tested at different temperatures,and the result shows that the tensile properties of high V alloy are better at room temperature;while the tensile properties of low V alloy are better at middle temperature,and the tensile properties of high V alloy were better at high temperature.The fracture morphology shows that a great amount of fine carbides appear in the low V content alloy and the carbides in the high V alloy is much bigger and fewer.At middle temperature,the slip traces in the low V content alloy are less than the ones in the high V content alloy.At high temperature,the fracture regions in the low V content alloy is smooth,and few dimples exist in these regions while much more dimples and a lot of slip traces exist in the high V alloy.By means of long-term aging to different V content alloys and observe the carbides morphology evolution,the influence of long-term aging on the morphology was investigated,the result shows that the carbides are decomposed,in which the rode carbides were decomposed and disconnected and the massive carbides are decomposed from the edge after long-term aging.The growth rate of the ?' phase increases with the element V rising in the alloy during long-term aging.At high temperature,the creep life of the 0.69% V alloy increases while the 0.96%V and 1.04% V alloys decrease after long-term aging.