Effect Of Heat Treatment And Alloy Composition On Microstructure And Property Of Ni-base Superalloy K4169

The composition of Ni-base superalloy K4169 is similar to that of American Inconel718 alloy.It has excellent fatigue resistance,good oxidation resistance,high strength and good corrosion resistance in the temperature range of-252~650?.It is used in nuclear power chemical industry,aerospace,mechanical metallurgy and other key materials.However,the as-cast structure of K4169 alloy has serious segregation.When used for a long time above 650?,the strengthening phase ?? will transform to the brittle phase ?,resulting in a decrease in the mechanical properties of the alloy and severely limiting its scope of use.Therefore,this paper took K4169 alloy as the research object.The influence of heat treatment and the change of alloy element content on the microstructure and mechanical property of K4169 superalloy was investigated by using optical microscopy,scanning electron microscopy,transmission electron microscopy observation and tensile testing.The following main conclusions were drawn:(1)With the increase of Al and Mo content,the alloy held at 1095? for 2h can obtain better homogenization effect.However,with the increase of Nb content,the alloy still retains a large number of Laves phase after homogenization.(2)When the Mo content increases to 5.05% or the Al content increases to 1.3%,the ultimate tensile strength of the alloy treated at 955? are slightly higher than those treated at 1130?.However,when the content of Nb increases to 8.9% or the content of Al increases to 2.1%,Al and Nb elements will further dissolve into the matrix at 1130?,so a large number of strengthening phases are precipitated in the aging process to improve the strength of the alloy.(3)As the aging temperature increases from 620? to 720?,the strength of the standard composition alloy increases by 40.9%,but the elongation decrease by 29.1%The strength increases by 24.5% in the temperature range of 670~720?,which is higher than that in the temperature range of 620~670?(16.4%).(4)After standard heat treatment,with the increase of Al content from 0.5% to2.1%,the content of ?? phase gradually decreases from 2.89% to 0.32%.When Al content increases to 2.1%,the size of strengthen phase increases sharply,the ?? phase increases from 14.3nm and 3.2nnm to 78.6nm and 11.6nm in the length and width directions,respectively,and the ?? phase increases from 12.9nm and 12.7nm to 80.4nm and 73.5nm in the length and width directions,respectively,leading to the decrease of strength and elongation.With the increase of Mo content from 3.05% to 5.05%,the mechanical properties of the alloy have no obvious change.With the increase of Nb content from 4.9% to 8.9%,the content of Laves and ? phase increases,which significantly reduces the elongation of the alloy.At the same time,the content of ??phase increased,and the precipitation of the ?? phase is hardly observed.