Microstructure and Mechanical Properties of HIP PM 718

Abstract

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 bj 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. L I'he consolidated materials are f~dl! dense and ha e verj fine and homogeneous n~icrostructures tj 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 for~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 po~~der 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 impro~ ed creep properties mith little loss in strength. During solutioning at 1800°F. no grain grouth nas obser~ ed. and \. eq 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.