Effect Of Trace Elements On Interstitial Phase Of Nickel Base Superalloy

The nickel base superalloy has high temperature reep resistance,oxdiation resistance,corrosion resistance and good phase stability.The alloy can work in severe environment and has good comprehensive property.Nickel based superalloy materials are widely used in aerospace,aviation,transportation,metallurgy and other fields.As the alloy works in the environment of high temperature and high pressure,the grain boundary is brittle.It is necessary to improve the negative effect by adding the appropriate grain boundary strengthening element.In this experiment,a single variable method was used to keep the same elements and change the content of B,Y and W.The effect of alloy elements on the precipitation of nickel base superalloy was studied.Three heat treatment methods were carried out to investigate the effect of heat treatment on the precipitation of nickel base superalloy.SEM,TEM,XRD and other test methods were adopted in the study.The results show that the B elements are mainly distributed in grain boundaries in the form of M3B2 boride or are concentrated in grain boundaries in the form of single substance.When the content of B element is 0.006%⁰.020%,the lattice constant of?/??increases with the increase of B content,and the?/??mismatch also increases,and the yield strength and tensile strength of the alloy at 1000?at high temperature increase.When the content of the B element is 0.020%⁰.025%,the lattice constant of?/??decreases,while the mismatch of the alloy decreases,and the yield strength and fracture strength of the alloy decreases.When the Boron contains 0.020%,the yield strength and ultimate strength of the alloy are the hightest.When Y content is 0.013%,M3B2 only can be formed in the alloy when B content exceeds 0.015%.The Y element has no obvious influence on the morphology of the enhanced phase.When the content of Y is 0.010%,the yield strength and ultimate strength of the alloy are the highest.The increase of Y content can promote the formation of M₂₃C₆ carbide and M3B2 boride.The Y element can be counterate with the harmful element S to form spherical YS compounds,reducing the harm of the elements to the alloy.When the W content is 3.5%⁵.0%,the tensile elongation and yield strength of the as cast alloy increase with W content.When the content of W is 5.0%⁶.0%,the elongation and yield strength decrease.When the W content in the alloy is 5.0%,the elongation and strength of the alloy are the best.When the W content is 3.5%⁵.0%,the?/??misfit of the as-cast alloy increases as the W content increases,and the?/??misfit increases to 5.0%W.When the W content reaches 6.0%,the mismatch decreases.After different heat treatment of the as-cast alloy,the type,number,and morphology of the precipitated phases have changed significantly.The behavior of MC degradation to M₂₃C₆ was evident in the three stage heat treatment samples.In the as cast state,the strengthening phase of the alloy is coaser,showing a regular cube shape,and the?/??mismatch degree is also larger.After aging treatment at 1100?/4h,the alloy has dual mode size and the mismatch degree decreases.A large number of small??are distributed within the matrix channel between large??.The two stage heat treatment 1220?/4h+air cooled+870?/24h+air cooled strengthened the phase particles to regular cube shape,and the?/??mismatch decreased compared with the as cast state.1220?/4h+air cooling+1050?/4h+air cooling+870?/24h+air cooling also presents the dual mode size phase,of which the shape of large??is horseshoe,and??is small spheroid,and the number is far less than the number of direct aging.The mismatch degree of?/??is the smallest in three heat treatment systems after three stage heat treatment.The main types of grain boundary interstitial phases are MC and M₃B₂.After three stage heat treatment,the alloy has the highest yield strength and breaking strength.The second is the two stage heat treatment,while the strength of the heat treatment with high temperature direct aging is only slightly higher than that of the as cast state.