Analysis of Forging Cracks during Hot Compression of Powder Metallurgy Nickel‐Based Superalloy on Simulation and Experiment

Abstract

Hot compression tests on a newly designed hot extrusion Nickel-based powder metallurgy superalloy are conducted at various deformation conditions. The contact friction coefficient (f) between the die and forged part is determined as 0.30-0.40 by analyzing the results of simulation and the real experiment. A new coefficient B is introduced to evaluate the bulging levels and relate the value of f. The critical strains to prevent peripheral cracks are found to relate closely to the processing parameters. Thermally induced porosity and MC type carbides of grain boundaries are the primary mechanism for inducing cracks. Examinations on microstructure of cracking demonstrate that the cracks propagate along grain boundaries. A model is proposed to illustrate the formation of fractures during hot forging.

Failure behaviors and processing maps with failure domains for hot compression of a powder metallurgy Ni-based superalloy

“…However, lower strain rate results in more failure than a higher strain rate at 1050 C when −𝜀 𝑇 = 0.41. These observations are in line with the study of He et al [7], where it was reported that there existed a critical strain for the onset of failure and a lower strain rate caused the earlier failure. The result is also consistent with Zhang et al's study [9],…”

“…These defects will most likely induce deformation cracks in the P/M superalloy when reaching a threshold strain, leading to a narrow processing window. He et al [7] studied the forging cracks of a P/M Ni-based superalloy in the state of HEX condition, and found the existence of TIP and MC type carbides at grain boundaries accounted for the failure initiation through examining the microstructure evolution at different strains. They also employed dichotomy theory to determine the critical failure strains under different TMP conditions and found that the failure strain increased with the increase of temperature and/or strain rate.…”

“…As the crack formation is very sensitive to the TMP parameters (i.e., strain, strain rate, and temperature) [7,26], it would be of importance to examine the effects of processing parameters on the failure behaviors and establish a processing window that considers failure to guide the TMP of the superalloys. Traditionally, it is well established that the hot workability of an alloy could be evaluated by the processing maps based on the dynamic materials model (DMM) [27], which are comprised of the efficiency of power dissipation to delimit the region of good workability and flow instability to define the region where plastic instability will occur.…”

Optimizing the Thermomechanical Process of Nickel-Based ODS Superalloys by an Efficient Method

“…Generally, PPB are difficult to be broken and eliminated at low temperature, which facilitates the crack nucleation and propagation during thermal consolidation [17]. The microcrack along the PPB are mainly caused by local stress concentration [18,19]. With the increase of consolidation temperature, the thermal activation of the material increases, the atomic diffusion rate accelerates, and the kinetic energy of the atoms increases, weakening the binding force between atoms, the softening effect of the material becomes obvious.…”

Quasi-static hot deformation behavior of a novel third-generation Ni-based powder metallurgy superalloy

“…6 Moreover, their thermal plasticity was relatively poor at high temperature and therefore made them hard to be severely deformed. 5,7 Hence, defects such as cracks and flow instabilities were easy to occur during hot processing 8,9 and the processing window of the Ni-based P/M superalloys might be comparatively narrow. 10 That might be the reason why improving processing methods of the Ni-based P/M superalloys is of great importance and worthy of a thorough investigation now.…”