Effect of Hot Deformation Parameters on the Grain Size of Wrought IN718

Abstract

Superalloy IN71 8 is one of the most important aero-materials. It has been widely used to manufacture turbine discs and other important components. Because the microstructure and mechanical properties of IN7 18 forgings are highly sensitive to metallurgical technology and thermomechanical processing(TMP), it is very difficult to control every step of TMP to obtain most favorable mechanical properties and microstructures in IN7 18 forgings. In recent years, more and more attention has been paid to the hot deformation behavior and computer simulation of TMP of superalloy IN718. However, up to now, any perfect model suitable for manufacturing turbine discs has not been found. To set up such a model, it is necessary to formulate the relationship between grain size and hot deformation parameters after a constitutive relationship has been developed. In the present work, isothermal constant speed compression tests of superalloy IN718 were conducted using a computer-controlled MTS machine with temperatures from 960°C to 1040"~, initial strain rates from O.OOls-' to 1.0~~' and engineering strain from 0.1 to 0.7. The deformed specimens were immediately quenched in water to retain the deformation microstructures. The effect of hot deformation parameters on the grain size was analyzed. A formula was developed to express the relationship between grain size and deformation temperature, strain rate and strain.

An Integrated Approach to Relate Hot Forging Process Controlled Microstructure of IN718 Aerospace Components to Fatigue Life

“…The demand of simultaneously characterizing the grain-shape based microstructure of plane metallographic sections possessing uniformly distributed grains and bimodal microstructure can not be reached by considering just the average ASTM grain size. The microstructural formation which includes grain boundary morphology and δ-phase behavior influences forged superalloy 718 fatigue life in major ways [1][2][3][4][5][6]. Therefore, a two-parametric alternative method was developed in a previous work to gain additional grain shape information [7].…”

“…If it is necessary to determine the endurable number of load cycles at a given local load situation; defined by the stress amplitude σ a ; one can minimize the load cycle error by using a function handle to the MSEA-fatigue function shown in equation (3). The displayed pseudo code complies with the Matlab syntax.…”

The structural evolution of superalloy ingots during hot working

“…The effects of hotworking temperature, strain, strain rate, and initial grain size have been investigated to determine their influence on processed grain size. [13][14][15][16][17][18][19][20][21] Dynamic, metadynamic, and static recrystallization occur during processing. Dynamic recrystallization occurs during the actual deformation; whereas under metadynamic recrystallization conditions, the partially recrystallized grain structure observed right after deformation transforms to a more fully recrystallized structure by growth of recrystallization nuclei formed during deformation.…”

An Integrated Approach to Relate Hot Forging Process Controlled Microstructure of IN718 Aerospace Components to Fatigue Life

“…it is necessary to determine the endurable number of load cycles at a given local load situation; defined by the stress amplitude σ a ; one can minimize the load cycle error by using a function handle to the MSEA-fatigue function shown in equation(3). The displayed pseudo code complies with the Matlab syntax.…”