Microstructure And Mechanical Property Of Powder Metallurgy Brazing Of The Third Generation Single Crystal Superalloy

In order to realize the connection and repair of high temperature hot end parts,improve the brazing research system of the third generation single crystal superalloy,the third generation single crystal superalloy was brazed with the mixed powder filler made of JSSNi60A and the third generation single crystal superalloy powder at 1240?.The brazing time was set as 30 min and the gap was 200?m.The joints were subjected to post-weld heat treatment.The effects of particle size and proportion of high melting point alloy powder on microstructure and mechanical properties of brazed joints were studied.The microstructure evolution,element distribution and mechanical properties of brazed joints before and after heat treatment were analyzed,and the formation mechanism of brazed joint was elucidated.The joints were mainly composed of three parts:the filler alloy zone(FAZ),the interfacial bonding zone(IBZ)and diffusion affected zone(DAZ).The results showed that the FAZ was mainly composed of M₃B₂ boride,Cr B,Ni₃B and?+??eutectic,and the IBZ is composed of?matrix and uniformly precipitated??strengthening phase,but the size was smaller than those of the base metal.After heat treatment,the??phase in the interface junction zone was further refined into sphere,and the needle-like borides separated out in the DAZ.The width of the diffusion affected zone in joints decreased with the increase of the proportion of the alloy powder in the mixed filler.When the proportion of alloy powder reached 60%,the diffusion affected zone disappeared.In the joints,the melting point depressant element B mainly formed stable boride with W,Mo,Cr and other elements,precipitated in the center of the joints,and did not significantly diffuse to the base metal on both sides.The other element Si was distributed uniformly in the joints except boride,and only a small amount of Si diffused from the interface to the base metal.After heat treatment,the element diffusion in the joints was more uniform,a trace of B diffused to the base metal,and the element distribution in the most area of joints was the same as that in the base metal.Keeping the proportion of high melting point alloy powder in the mixed filler at 50%:when the particle size of alloy powder was no more than 177?m,obvious hole defects appeared in the joint;when the particle size of alloy powder was no more than 75?m or 44?m,complete welded joints could be obtained,but the microstructure of the joint was better when the particle size of alloy powder was more than 75?m.Keeping the particle size of high melting point alloy powder more than 75?m:when the proportion was 50%,the joint morphology was complete,the number and size of brittle phase were small,and the distribution was uniform.The microhardness and high temperature stress rupture properties of the joints with 30%,50%and 60%alloy powder were tested.The results showed that the hardness of IBZ was slightly higher than that of the base metal,while the hardness of FAZ decreased with the increase of the proportion of high melting point alloy powder.After heat treatment,the hardness of JSNi-75-7/3 joint and JSNi-75-5/5 joint decreased uniformity,but the hardness trend of JSNi-75-4/6 joint remained the same.The stress rupture life of the three kinds of joints at 980?/100MPa were 15 hours,34 hours and 0.6 hours respectively.When the proportion of high melting point alloy powder was 30%or 50%,the joint presented the mixed fracture characteristics of quasi cleavage fracture and microporous polymerization,and the cracks mainly started at the hard brittle phase;when the proportion was 60%,the fracture mainly started from the void defects.After heat treatment,the stress rupture life of the three kinds of joints at 980?/100MPa was 15 hours,14 hours and 4 hours respectively,showing the mixed fracture characteristics of quasi cleavage fracture and microporous polymerization.