en Research Paper Research Paper <span style="font-size:11pt"><span style="line-height:200%"><span style="font-family:Calibri"><span new="" roman="" style="font-family:" times=""><span style="background-color:#ffffff;">Phase transformations and the evolution of hardness during elevated-temperature annealing of Inconel 718 superalloy manufactured by the laser powder bed fusion (L-PBF) were investigated. The microstructural evolution, elemental analysis, phase formation, and hardening were characterized by scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and Vickers indentation test, respectively. </span></span><span new="" roman="" style="font-family:" times=""><span style="background-color:#ffffff;">It was observed that the effect of annealing treatments is directly governed by the annealing parameters (i.e. time and temperature), for which the hardness measurement as a fruitful and convenient tool can reveal this effect. The increase of the hardness, which was obtained by the annealing (aging) treatments at the temperature range of 800-900 &deg;C, indicated precipitation of </span></span><span style="font-size:11.5pt"><span style="line-height:200%"><span new="" roman="" style="font-family:" times=""><span style="background-color:#ffffff;">the Ni</span>_{<span style="background-color:#ffffff;">3</span>}<span style="background-color:#ffffff;">Nb &gamma;˝ strengthening phase</span></span></span></span><span new="" roman="" style="font-family:" times=""><span style="background-color:#ffffff;">; </span><span style="background:yellow"><span style="background-color:#ffffff;">while owing to the coarsening of precipitates as a results of overaging at this temperature range, the hardness decreased. For instance </span></span></span><span style="font-size:11.5pt"><span style="background:yellow"><span style="line-height:200%"><span new="" roman="" style="font-family:" times=""><span style="background-color:#ffffff;">the length and aspect ratio of precipitates in the aged sample at 800 &deg;C for 1 h is 67.14 nm and 0.32, respectively; while these values in the aged sample at 800 &deg;C for 8 h is 78.34 nm and 0.44, respectively.</span></span></span></span></span><span style="font-size:11.5pt"><span style="line-height:200%"><span new="" roman="" style="font-family:" times=""><span style="background-color:#ffffff;"> On the other hand, </span></span></span></span><span new="" roman="" style="font-family:" times=""><span style="background-color:#ffffff;">the decrease of the hardness at temperatures of 950 and 1000 &deg;C was attributed to the decrease of dislocation density in conjunction with the </span></span><span style="font-size:11.5pt"><span style="line-height:200%"><span new="" roman="" style="font-family:" times=""><span style="background-color:#ffffff;">Ni</span>_{<span style="background-color:#ffffff;">2</span>}<span style="background-color:#ffffff;">Nb</span></span></span></span><span new="" roman="" style="font-family:" times=""><span style="background-color:#ffffff;"> Laves phase dissolution. Hence, it is crucial to determine the annealing parameters according to the required microstructure and properties.</span></span><span style="font-size:11.5pt"><span style="line-height:200%"><span style="font-family:"Times New Roman""></span></span></span></span></span></span> Nickel-based superalloys,Additive manufacturing,Aging heat treatment,Homogenization treatment,Precipitation strengthening 1 8 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-911-1&slc_lang=en&sid=1 Sajad Ghaemifar sajad.ghaemifar@gmail.com 1800319475328460018159 1800319475328460018159 No School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran Hamed Mirzadeh hmirzadeh@ut.ac.ir 1800319475328460018160 1800319475328460018160 Yes School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran