Microstructure and Mechanical Properties of HIP PM 718
Superalloys 718, 625, 706 and Various Derivatives (2001)
1 his paper explores ad\ antages of ponder ~netallurgical (Plh4) processing of Alloj 7 18 using gas atomization and hot isostatic pressing (HIP). To e1,aluate the effect of different processing parameters on HIP PIAM 718. pouders uith lou and standard carbon lelels were produced b j nitrogen and argon atomization. A small amount of Mg mas added to one heat to imestigate the possibilitj of improving elevated temperature properties. The Mg-treatment is a necessitj to obtain good creep properties.
... d creep properties. L I'he consolidated materials are f~dl! dense and ha\ e verj fine and homogeneous n~icrostructures t j pica1 for fullj dense PIM alloj s. Yield strength lelels range from 140 to 170 ksi at room te~npesature. and from 1 15 to 145 ksi at 1200°F. \I hile tensile ductilities range f o r~n 19 to 15 and 9 to 24%. respectivelj . Different heat treatments mere ebaluated. since the standard heat treatment for cast and l~rought 71 8 led to hea\;4 decoration of prior p o~~d e r particle and grain boundaries. \\hich resulted in 10% ductilitj. especially at 1200°F. Creep rupture properties mere elaluated at 1200°F and 100ksi. Depending on heat treatment. time to rupture Lvas as high as 170 hrs. Higher solution temperatures resulted in n~icrostructures uith less grain boundarq decoration. better d~lctilities and i m p r o~ ed creep properties mith little loss in strength. During solutioning at 1800°F. no grain grouth n a s o b s e r~ ed. and \. e q limited grain grou-th %as obser~ ed during heat treatments at temperatures up to 2200°F. Taking into account the relath el) lou le\ els of precipitate forming elements. the strength levels are still fairlj good. Superalloys 718. 625. 706 and Various Derivatives Edited b! E.A. L~r i i i ThlS ( P h s XIinerals. &letals (9: Matsrials Societ) ). 2001