Hot ductility behavior of AD730™ nickel-base superalloy

Abstract

Hot ductility of the newly developed AD730 TM nickel-base superalloy was investigated in the temperature interval 1050-1240°C. The nil strength and nil ductility temperatures were determined by hot tensile testing using the Gleeble TM 3800 weld thermal simulation method. The influence of heating rate, representing the weld thermal cycle, on hot ductility behavior of the alloy was also investigated. The microstructure and the fracture mode of samples were examined by optical and scanning electron microscopy. The influence of heating rate on the extent of grain boundary liquation and void formation was determined and it is shown that the significant ductility loss near the NDT point could be related to the reduction of surface tension at the grain boundary-matrix interface. In addition, the contribution of hard precipitates, such as grain boundary MC carbides, voids, and cavities as other damage mechanisms responsible for ductility loss at high temperature, are discussed.

The high-temperature strength and plastic properties of Incoloy 800HT and Invar 36 alloys

“…The solidus temperatures of 1,358 °C and 1,439 °C were determined for the Incoloy 800HT and Invar 36 alloys, respectively. The determined nil-strength temperatures are lower than the solidus temperatures of both investigated alloys, which corresponds to the results of the works [4,6].…”

“…For an experimental examination of the strength and plastic properties at high temperatures it is suitable to use uniaxial tensile tests or torsion tests to a rupture of a tested specimen [1][2][3]. By using of universal plastometers of the Gleeble type it is possible to determine (among other things) the nil-strength temperature and nil-ductility temperature of the investigated metal material [4][5][6][7][8][9]. The nil-strength temperature NST (°C) is defined as a temperature associated with a loss of all strength of metal due to the melting of grain boundaries.…”

“…The nil-ductility temperature NDT (°C) corresponds to a temperature at which the ductility of the material is equal to zero (achieving of 100 % brittleness). The value of the nil-ductility temperature NDT (°C) can be determined by using of tensile tests with a direct heating to the deformation temperatures [4,[7][8][9].…”

Grain size and misorientation evolution in linear friction welding of additively manufactured IN718 to forged superalloy AD730™

“…As a result, different macro-and microstructural characteristics are to be expected near the weld line region, on either side of the weld. Considering that the dissolution temperature of the strengthening phases in IN718 (γ‫°039=״‬C, γ‫׳‬ =970°C, and δ=1020°C) [28,29] are lower than in AD730 TM (γ‫°0021=׳‬C) [25,30], more material will be ejected from the weld region of as-SLM-IN718 (and H-SLM) into the flash at a lower temperature than for AD730 TM .…”

“…IN718 is a high strength superalloy extensively used for blade applications in gas turbines due to its good weldability and excellent resistance to cracking [20][21][22]. AD730 TM is a Ni-based alloy recently developed by Auber & Duval Company as a new forged Ni-based superalloy for turbine disk applications, and its mechanical properties are comparable to those of other Ni-based superalloys such as Waspaloy, Udimet720 and IN718Plus [13,14,[23][24][25].…”