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In this paper, the effect of hot isostatic pressing (HIP) treatment on defects, microstructure, precipitated phases and mechanical properties of Udimet 720Li alloy formed by laser melting deposition (LMD) was investigated. The results showed that the internal microcracks of Udimet 720Li alloy formed by LMD were completely eliminated after HIP treatment, but a few small pores still existed, and the density of the sample were improved from 97.06 % to 99.97 %. Partial recrystallisation occurred in the as-deposited sample. After HIP treatment almost complete recrystallisation occurred, and the grain morphology changed from epitaxially grown columnar grains to equiaxed grains with a decreasement in grain size. After HIP treatment, the MC carbides in the sample were changed from granular to large-sized lumps. For the sample with hot isostatic pressing and heat treatment (HIP + HT), a large number of carbides dissolution, the carbides morphology became granular diffusely distributed in the grain. Meanwhile, the HIP treatment eliminated the γ/γ′ eutectic phases present due to solute segregation, and a large number of secondary γ′ phases were uniformly precipitated within the grain. After the HIP + HT treatment, the average size of the secondary γ′ phase decreased from 283.4 nm to 266.3 nm, and the quantity was significantly enhanced. The HIP treatment reduced the mechanical properties of Udimet 720Li alloy, the microhardness decreased from 480 HV to 404 HV and the tensile strength decreased from 1258 MPa to 1234 MPa, which was mainly related to the decrease in the number of γ′ phases and the increase in the size of carbides. After HIP + HT treatment, the room temperature tensile properties of the samples were enhanced (σ UTS = 1394 MPa, σ YS = 702 MPa, ε f = 18.33 %), which was mainly attributed to the precipitation of more small-sized secondary γ′ phases by heat treatment. [ABSTRACT FROM AUTHOR]

The effect of crystal orientation and heat treatment on microstructure and wear properties of Inconel 718 superalloy fabricated by laser directed energy deposition (LDED) were analyzed and compared with forged samples. Fully heat treated samples presented the lowest wear rate and better resistance to friction compared with other condition samples. The direct aging treated samples also had better wear resistance attributed to its microhardness and microstructure and were mainly abrasive wear with a large amount of wear debris and deeper scratches on the worn surface. As for the anisotropy of microstructure in LDED samples, the wear properties in different crystal orientations were different, and better wear performance was obtained in the section which is vertical to the deposition direction. • Anistropic microstructure leads to different wear resistance. • The solution of Laves phase and precipition of γ″ phase enhance the wear property. • Heat treatment can decrease the difference in wear property of differnt sections. [ABSTRACT FROM AUTHOR]

Effect of solution heat treatment on microstructure and electrochemical behavior was investigated for the electron beam smelted (EBS) 718 superalloy. The results imply that the solution heat treatment has a great influence on the precipitation behavior of EBS 718 superalloys and thus affects the electrochemical behavior. The increase of solution temperature gives rise to the solution of δ phase for both solution treated and aged EBS 718 superalloys. The 980 °C solution treated and aged EBS 718 superalloy exhibits the maximum content of the volume fraction of γʹʹ phase, in parallel with the highest lattice misfits. Further increase of solution temperature results in the precipitation of dispersively distributed γʹ particles. The pitting potential for the solution treated superalloys increases gradually with increase of solution temperature, and a similar behavior is observed for the aged superalloys with an exception of the alloy processed at 980 °C. The effect of solution temperature on the solution treated superalloys can be elucidated by considering the variation of the volume fraction and the size of δ precipitates. For the aged superalloys, the deterioration effect of Nb rich γʹʹ is obvious due to the tetragonal distortion and accompanying strain field in the nearby matrix. Higher solution temperature results in a uniform distribution of the nano-scale γʹ phase and smallest lattice misfits, with the highest apparent activation energy derived to be 52.86 kJ/mol. [ABSTRACT FROM AUTHOR]