Selective Laser Melting of Ni-based superalloys with combined precipitation- and oxide-dispersion-strengthening
Abstract
The general aim of the proposed project is to gain fundamental insights into the microstructure, oxide particle stability and mechanical performance of precipitation-strengthened and oxide-dispersion strengthened (ODS) superalloys consolidated by selective laser melting. We believe that the strengthening contributions by precipitates will be additive to that of the oxide dispersoids, within coarse, solidified grains that are more creep-resistant than fine grains. Powders from a mechanically-alloyed ODS nickel-based superalloy with simplified Ni-Cr-Al-Ti composition (and, time permitting, an aluminum-based Al-Sc superalloy) will be melted and solidified by selective laser melting (SLM) followed by a precipitation heat treatment to produce coherent Ll2-precipitates within the maaluminum-basedose the following fundamental research questions: - Do the very rapid material melting and solidification events occurring during SLM of ODS Ni superalloys prevent, or reduce, the four mechanisms associated with loss of oxide dispersoids (dissolution, coarsening, agglomeration and slagging, which are active when powders are slowly solidified), so that the SLM-processed microstructures will exhibit nearly unaltered oxide dispersoids? How is this related to the melt pool lifetime, which is a function of the laser processing parameters? - How do different oxide dispersoid species, yttria and alumina, with different reactivity and solubility with the melt and added in different amounts, chemically and physically evolve during SLM of ODS superalloys - Does the presence of oxide particles influence the microstructure formation during SLM of Ni superalloys? In particular, do the largest oxide particles act as nucleation sites for matrix grains, so that a fine grain structure can be created on solidification if desired to boost ambient- and intermediate-temperature yield strength? Can the finest oxide dispersoids be pushed by growing grains and accumulated at grain boundaries to prevent grain-boundary sliding during creep at elevated temperature? - How does the presence of oxide dispersoids in the matrix and at grain bounda1ies affect the nucleation and growth of LI2 precipitates during a subsequent solid-state heat treatment? In particular, are the dispersoids acting as nucleation sites for the L12 phase and thus included inherently or are they incorporated upon growth? - How do the two populations of particles - incoherent, strong, nanometric oxide dispersoids and coherent, shearable, sub-micron precipitates - impede matrix dislocation motion and achieve synergistic strengthening within the alloy ?
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 11, 2018
- Source ID
- W911NF1810129
Entities
People
- David C. Dunand
Organizations
- Army Contracting Command
- Northwestern University
- United States Army