Effect Of Ni Content On Micro Structure And Mechanical Properties Of Co-Al-W Based Superalloy

The ?' phase with L12 face centered cubic structure is similar to that of Ni based superalloy which has been found in Co-Al-W based superalloy.However,compared with Ni based superalloy,the ?' phase in Co-Al-W based alloy can not exist stably at higher temperature.As alloying is an effective way to improve the structure and properties of the alloy,it is estimated that the addition of Ni element can promote the properties of the alloy.However,the development time of cobalt based superalloys is relatively short,and has less related research.Therefore,in this paper,four new Co-Al-W-based superalloys with different Ni contents(20/25/28/30wt.%),which are strengthened by ?' phase,are taken as the research objects to observe the micro structure of as cast,as solid solution and as effective condition for analyze.At the same time,the hardness test,tensile test and creep test were carried out to analyze the influence and mechanism of Ni content on the mechanical properties of the alloy The results showed that there were y phase,?' phase,?-(CoAl)phase and solid solution phase based on Co3Ta in the as cast alloy.With the increase of Ni content,the cubic degree of ?/?' phase in as cast and heat-treated alloys increased.After solution treatment,the number of ?' phases in the alloy increased.During aging,the transformation from ?' phase to Co3W phase took place.With the increase of aging time,the ?' phase will all changed to Co3W phase.After aging treatment,the morphology of the alloy ?' phase with low Ni content changed from round to irregular,and the alloy ?' phase with high Ni content changed from regular to directional,all of which produce coarsening behavior.After heat treatment for 4h,?' phase dissolved and merged.When the content of Ni element in the alloy was the highest,the ?' phase merged the most and the volume fraction increases the most.The hardness of the alloy increased with the increased of Ni content in the alloy.The higher the content of Ni element,the better the tensile strength and yield strength of the alloy.When the content of Ni element was the most,the hardness and plasticity of the alloy were the worst.In the creep experiment,when the content of Ni element was more than 25wt%,the creep life of the alloy had a significant increase.The alloy formed a raft structure parallel to the tensile stress under 1000?/137MPa.The higher the content of Ni element,the better the raft extent and the better the creep property of the alloy.