Influence of the temperature and pressure on densification, physical and mechanical properties of Inconel 718 produced by Hot Pressing

Abstract

This work aims to study the influence of hot-pressing (HP) sintering conditions (temperature and pressure) on Inconel 718 (Inc718) powders densification, microstructural, fracture mode and hardness properties. The sintering conditions included temperatures of 1000, 1068 and 1150 ºC and pressures of 50 and 60 MPa for a dwell time of 60 min. Fracture mode and the grain morphology were assessed by scanning electron microscopy (SEM). The grain size (GS) of the compacts increased with increasing HPed temperature and the fracture mode changed from intergranular dominant fracture to fully dimple ductile fracture. The microstructure features were characterized by X-ray diffraction (XRD) analysis. The results showed that intermetallic precipitate originated from the Inconel 718 powders were retained in the sintered specimens considered. The chromium Carbides ( ) were formed at 1068ºC but were eliminated when HPed at and above 1150ºC and 60 MPa once they tend to dissolve when increasing temperature. The hardness results revealed that the sintering Inconel 718 powders at 1000 ºC is not enough to promote the proper densification and so the optimum hardness results. For higher temperature (1068 and 1150 ºC) the hardness results decrease from 292 to 283 HV with increasing HP temperature (for 60 MPa) due to the dissolution of chromium carbides ( ). The pressure conditions also influenced powder’s sintering but did not reveal a pronounced difference in densification and hardness results. Further investigations must consider a wide range of pressure values as well a deeply study on the microstructure features on particle grain boundaries.