Formation of Microcrystalline Structures and Superplastic Properties of Nickel Based Alloys

Formation of Nanocrystalline Structure Upon Severe Thermomechanical Processing and Its Effect on the Superplastic Properties of Nickel Base Alloys

“…Bulk samples (40-80 mm in diameter and 10-12 mm long), were generated with MC, SMC and NC structures on 100 and 630 ton-force presses using severe thermomechanical processing (STMP) by MF on flat dies over the range of deformation temperatures 1100-600 °C (EP962, alloy 718) [13][14][15][16]. The powder PDS-1 (Ni-10.1Cr-7.5W-6.8Al-1.2Y20 3) alloy was produced by mechanical alloying and was in the form of 22 mm diameter rod from which the samples were machined [14].…”

“…The microstructure of precipitation hardened alloys 718 and EP962 in the initial state is completely recrystallized and coarse-grained with grain sizes of 40-80p,m. The TEM studies of microstructures o f these alloys [13,15] have shown that within the alloy 718 matrix grains there are coarse 5-phase plates, between which there is a uniform dispersion of coherent disk-type y"-phase precipitates (Figure 1a). In the EP962, partially coherent precipitates of y'-phase, 0.5p,m in size [11], are observed within the grains (Figure 2a).…”

“…Such structures can be produced using severe plastic deformation (SPD) technique, such as multiple forging (MF) [8 10]. There is presently a substantial interest to the generation of such structural states and the study o f their physical and mechanical properties [7][8][9][10][11][12][13]. However, there have been few previous studies of the formation of SMC and NC structures in complex nickel base alloys and the effect of these structures on SP behavior.…”

Deformation Mechanisms and Microstructural Evolution of ? + ?' Duplex Aggregates Generated during Thermomechanical Processing of Nickel-Base Superalloys

“…One is a dispersion of particles in the matrix, and the other is the equiaxed + duplex aggregates. + duplex structures are usually generated during certain thermomechanical processing (TMP) procedures, meanwhile, their extraordinary hot working plasticity and flow softening effect have long been known [11,12]. Nonetheless, the characteristic deformation mechanism of the + duplex structure has not yet been evaluated comprehensively.…”

“…However, the grain refinement process during TMP is usually combined with a topological transformation in the -two-phase configuration, i.e., from the dispersion to the + duplex. In addition, the topological transition of the twophase relationship inevitably leads to a change in the deformation mechanisms, which has not been well elaborated [11][12][13][14]. The difference between the flow behavior of the dispersion and the + duplex means that the flow stress is no longer a single-valued function of major state variables (i.e., temperature and strain rate) in the subsolvus temperature region because the topological features act as an extra variable [11,13].…”