The results show that after 1190~ 1200℃/120-160 MPa/3-4h HIP and 1180℃/4h+ 980℃/6h heat treating, the mid-temperature mechanical properties including the tensile and rupture-stress as well as the low cycle fatigue of the fine grain cast K403 alloy were improved greatly. At the same time,the high temperature stress rupture property was about equal to conventional cast.
Adding 0.022% phosphorus separately and adding both 0.022% phosphorus and 0.011% boron to direct aging IN718 (DA718) alloy can greatly improve its stress rupture properties, at 650 ℃ under 700 MPa, the stress rupture lives reach up to over 200% and 280% respectively, while the ductility of the later alloy decreased slightly.
However,α phase is unstable during the period of solid solution heat treatment at 1260℃ or thermal exposure at 1100℃ because of its solid solution or transformation to blocky M_6C carbides which result in a deterioration of the stress rupture properties of alloys at elevated temperature.
By means of a pretreatment at 1150℃ for 8h, Ni5Hf phase can be eliminated and therefore the final solution treatment temperature can be raised nearly 50℃ which brings about a homogenezing effect and further increase in the stress-rupture properties of the alloy at 1040℃.
Tensile and stress-rupture properties have been measured for the investment cast and directionally solidified (DS) alloy.
Tensile and stress-rupture properties, and fracture behaviour were observed to vary between the central and the outer portion of the forged stock.
Three alloy chemistry variants, with 0.17C/0.02B, 0.06C/0.1 B and 0.03C/0.2B (wt%) have been investment cast and investigated for microstructure, heat-treatment, tensile properties, stress-rupture properties and hot corrosion resistance.
However, the tensile ductility and the stress-rupture properties are considerably degraded.
A coincident irradiation-induced deterioration in stress-rupture properties may be associated with intergranular γ' and phosphorus.