Microstructure And Properties Of DD6 Single Crystal Superalloy At Different With Drawing Rates

Nickel-based single crystal superalloys are an important structural material widely used in the manufacture of aeroengine hot end components,especially turbine blades.Although the single-crystal superalloy adopts advanced preparation process and heat treatment process,the grain boundary is eliminated,and the high-temperature performance is greatly improved.However,there are still various degrees of microporosity and homogenization-pore defects in the high-temperature alloy.The microscopic pores destroy the continuity of the matrix,and it is easy to cause stress concentration during the loading process,which seriously jeopardizes the mechanical properties and service life of the superalloy.Therefore,it is urgent to carry out the formation mechanism and control method of microscopic pores in single crystal alloys,and to reserve technical reserves for the preparation of high quality single crystal superalloy blades.In this paper,a second-generation single-crystal superalloy developed in China containing 2% Re was independently researched.The single-crystal superalloy test rod was prepared by high-rate solidification method,and the influence of withdrawing rate on the solidification structure of single crystal was studied.Three extraction rates were selected as 30?m/s?80?m/s and 150?m/s,respectively.Subsequently,high-temperature solid solution was carried out to study the influence of solution temperature and time on the solid solution homogenization-pores and segregation of alloying elements.Then carry out standard heat treatment and long-term aging to study the effect of long-term aging temperature on the stability of the tissue.Finally,the hot isostatic pressing,high temperature and low cycle fatigue,analysis of the influence of heat treatment and hot isostatic pressing on the alloy structure,especially the fatigue properties,are intended to provide technical support for the application of the alloy.The main findings are as follows:(1)As the withdrawing speed increases,the primary dendrite spacing decreases,The microscopic porosity first decreases and then increases,the eutectic content increases,the segregation of the main elements increases,and the size of the ?' phase decreases.At a moderate drawing rate,the deviation from the(001)orientation reaches 4°,and the alloy orientation is better.The solid-liquid line of the alloy did not change significantly with the withdrawing rate.(2)Solution treatment can significantly change the segregation of the alloy elements,and the eutectic disappears.After high temperature solid solution,the main element segregation ratio is similar.With the solution time prolonged,the solid solution micro-pore increase significantly.After 1320? / 6 h treatment,the micro-pore content can reach 0.4%,which is an order of magnitude higher than the as-cast state.(3)The hot isostatic pressure significantly reduces the microscopic porosity and eutectic content in the as-cast microstructure.After hot isostatic pressing,the ?' phase increases in size,the degree of cubication decreases,and the ? matrix channel becomes wider.The hardness of the alloy is reduced by the formation of carbides during hot isostatic pressing.(4)Long-term aging tissue coarsening at 980?,long-term aging at 1050 ? will produce a large number of TCP phase,seriously impairing tissue stability.(5)Hot isostatic pressing + standard heat treatment will reduce the high temperature and low cycle fatigue performance of DD6,mainly due to the precipitation of carbide,recrystallization and local initial melting.