Effect of Mo content on Microstructure and Mechanical Properties of IN718 Alloy

Abstract

The effect of Mo content on microstructure and mechanical properties of IN718 alloy after standard heat treatment was investigated by means of optical microscopy(OM), scanning electron microscopy(SEM), transmission electron microscopy(TEM) and energy dispersive spectrometer(EDS). The results show that Mo significantly affects the intergranular precipitation. The amount of δ phase is decreased by the increase of Mo addition up to 4.00%. However, δ phase is inhibited thoroughly but Laves phase begins to precipitate at grain boundaries when Mo addition is higher than 5.50%, and the precipitation of Laves phase is increased by the increase of Mo content. Both the disk-shaped γ″ phase and spherical γ′ phase are precipitated in γ matrix grain in all of the alloys with the Mo additions ranging from 2.8% up to 7.5%, and there are no other second precipitates. Mo has no obvious effect on the number of the precipitation of γ″ phase and γ′ phase, but their sizes are decreased with the increase of Mo addition. Mo slightly reduces the tensile strength of IN718 alloy at room temperature and yield strength at 680 ℃. At room temperature, Mo addition lower than 5.5% has no evident effect on the tensile ductility, while the ductility is remarkably decreased when Mo addition is 7.50%. At 680 ℃, the ductility is enhanced gradually as Mo addition increases. Mo obviously improves the stress rupture life of IN718 alloy at 680 ℃ and 725 MPa. The life of the alloy with 7.50% Mo is about 1.5 times as long as that of the alloy with 2.8% Mo. Mo has no obvious effect on the tress rupture ductility.

Keywords

• IN718 alloy
• Mo
• microstructure
• mechanical properties