The Effect Of TI On The Microstructure And Mechanical Property In Re-Containing Single Crystal Superalloys

In order to investigate the effect of Ti content(0,0.5,1wt%) in single crystal superalloys containing rhenium, as-cast state microstructure, structural evolution during heat hreatment and long term aging and stress rupture properties were studied by optical microscope, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), three-dimensional atom probe (3DAP), and differential scanning calorimetry (DSC). Moreover, the impact of Ti content on the alloy was studied in theory by using the Thermo-Calc and Materials Studio software. The main conclusions can be drawn as follows:With the increasing of Ti content, the volume fraction ofγ/γ′eutectic was enhanced and the arrangement regulation of dendrite was decreased within the as-solidified microsture of three alloys. The incipient temperature, liquidus and solidus of the alloys all dropped. A small amount of MC carbides were found in the interdendritic region of three alloys.After full heat treatment, theγ/γ′eutectic in alloy A and alloy B completely disappeared, but there wasγ/γ′eutectic in the interdendritic region undissolved. With the enhancing of Ti content, the size ofγ′phase enhanced and the cubic degree ofγ′phase decreased. A small quantity of acicularμphase was precipitated in alloy C. Three-dimensional atom probe analysis show that the partition behavior of alloying elements inγandγ′phase were significantly influenced by Ti element addition. Mo, Cr, Re and some other element was apt to partition intoγphase. because the partition ratio changed with the Ti cotent increasing, the absolute value of mismatch betweenγandγ′phase enhance. By first-principles calculations, Ti decreases the formation energy for Re element inγphase.During long-term aging process at 1093℃, the morphology ofγ′phase evolves from small cubic to large and irregular shape then to raft. With the increasing of Ti content, the trend of raft advances, the rafting time of three alloys begin with 200h,100h and 50h. Moreover, Ti can accelerate the precipitation ofμphase obviously. The quantity ofμphase increases in alloy A with the extension of time, while in alloy B and C theμphase conserned, theμphase increase until 500h aging treatment ,but theμphase decrease after 1000h aging treatment.The stress rupture lives decrease with the increase of Ti content under the tests condition of 982℃/248MPa and 871℃/552MPa. The analysis show that the stress ruptures mechanism of three alloys is microvoid coalescence fracture. However, Ti can improve the elongation to some extent.γ′phase regulation was reduced andμphase was increased with the increasing of Ti in fracture samples at 982℃/248MPa. Under the condition of 871℃/552MPa, some crack initiate in the interface between carbide andγphase.