The Effect of Forging Variables on the Supersolvus Heat-Treatment Response of Powder-Metallurgy Nickel-Base Superalloys

Characterization of Plastic Flow Pertinent to the Evolution of Bulk Residual Stress in Powder-Metallurgy, Nickel-Base Superalloys

“…The occurrence of superplastic flow for LSHR (and, as will be discussed below, for IN-100) may seem surprising in view of the coarse gamma grain size (~15 to 20 lm) for the program materials. However, a comparison of the present results with those for the same alloys with gamma grain sizes of~2 to 3 lm [21] revealed an approximately two-orders-of-magnitude reduction in the strain rate at which the transition from PLC to superplastic flow had occurred. The observed trend noted here was thus at least qualitatively similar to the typical effect of grain size on the strain rate required for superplastic flow.…”

“…[17,18] The program materials were identical to those used in several previous investigations of the thermomechanical processing of PM superalloys. [19][20][21] The LSHR material consisted of 230-mm-diameter extruded billet produced by Special Metals (Princeton, KY). Its composition is given in Table I; its processing history is summarized in detail in References 19 and 20.…”

On the Evolution of Primary Gamma Prime Precipitates During High Temperature and High Strain Rate Deformation and Subsequent Heat Treatment in the Ni-Based Superalloy, RR1000

“…However, this method will also result in the exclusion of c grains sectioned far from their centroids and has limitations. [12] Therefore, in case of _ e ¼ 1 s À1 ; the intergranular incoherent c¢ precipitates are not delineated from c grains and for a collection of 479 grains, the average grain size is 1.46 lm, with a maximum of 5.4 lm and minimum of 0.5 lm and which includes averages of c and c¢ precipitates. In case of _ e ¼ 10 s À1 ; this becomes less reliable given the smaller distribution of grains, i.e., 145 grains and the marked increase in intragranular incoherent c¢ precipitates.…”

“…[2,[5][6][7][8][9][10] The evolution of the c¢ precipitate morphology is influenced by the stress, plastic strain, and most importantly the strain rate. [4,11,12] The 1st population termed as primary c¢ has the principal role of inhibiting grain growth during billet manufacture and forging by pinning the grain boundaries and are typically, 1 to 5 lm in size. [13] Thermomechanical operations carried out at temperatures where only these pinning particles are present in the microstructure (absence of secondary/tertiary populations, as they have lower solvus temperature compared to forging temperature) can be therefore carried out at decreased flow stresses.…”

“…[4,15] Furthermore, under such extreme deformation conditions, both the morphology and spatial occurrence of c¢ precipitates, i.e., inter/intragranular is determined by the strain rate. [12] The significance of studying the precipitate evolution under conditions of billet manufacture is key, since anomalous grain growth and existence of un-re-crystallized powder particles existing within the billet will affect both the flow stress and two-phase microstructure that evolves during forging, which can adversely affect the mechanical properties of the component. [1] Therefore,…”