Benchmarking mean-field models available in commercial FE software in application to two-blow forging of IN718 alloy

This paper analyses the potential of standard mean-field models available in commercial FE software Deform®, Forge® and QForm® for a microstructural prediction during multistage forging process of Inconel 718 at conditions close to industrial ones. The special set of experimental trials including heating, forging, reheating and final forging were conducted on 5 MN hydraulic press with detailed measurements of temperature distributions, timings and forging parameters. The microstructure distribution was investigated after each stage of the process (optical and EBSD) and compared with the predictions obtained in three softwares. Standard and optional capabilities as well as limitations and challenges of the models were investigated, and some improvement ideas were proposed

On the applicability of JMAK-type models in predicting IN718 microstructural evolution

Nickel-based superalloys are widely used in the aerospace sector for their mechanical properties, which are directly related to the microstructural and physical properties of these materials. JMAK-type models have been applied to this class of superalloys for the prediction of microstructural evolution phenomena such as recrystallisation. However, these models often lack a clear range of applicability. The majority of the successful applications normally address rather idealised processes (relatively slow forging, simple geometry). However, the industrial production environment generally involves complex strain paths and thermal histories. Thus, there arises the question of whether the JMAK-type models can be applied to such cases. This paper’s research focus is to investigate the applicability of JMAK-type models for such processes. To do this, screw press forging of disks was used to validate the in-built JMAK-type model of Inconel 718® available in DEFORMTM. In particular, the applicability of the model was examined using a comparison between the results from simulation and from metallographic analysis. At first, the appropriateness of the JMAK outputs in describing the observed microstructures was investigated and then quantitative results were evaluated. The model’s outputs were found to be insufficient in describing the observed microstructural states and additional parameters were deemed necessary. The model’s predictions ranged from a broadly good match, for which the model could be calibrated with a proposed new methodology, to a qualitative mismatch that highlights the limits of the model’s applicability

The occurrence of ideal plastic state in CP titanium processed by twist extrusion

This paper deals with the analysis of strength and plastic characteristics of commercially pure (CP) titanium as a function of equivalent plastic strain accumulated during Twist Extrusion (TE) process. It is shown experimentally that multipass TE leads to the saturation of the following characteristics of the material: yield stress, reduction in area, elongation to failure, and uniform elongation. This fact indicates the occurrence of an ideal plastic state in the processed material. The threshold value of accumulated plastic strain for ideal plastic behavior of CP titanium during TE is defined. The strain state and mechanical properties of CP titanium billets processed by TE are studied. An explanation for the hardening on the axis of a billet during TE is offered. The analysis of deformation modes on the billet axis during TE and High Pressure Torsion is carried out. It is shown that the differences in strain state on the axis are caused by the difference in symmetry of these processes

The effect of initial grain size on formability of AZ31B magnesium alloy during I-ECAP

The goal of this work was to investigate formability of AZ31B magnesium alloy during incremental equal channel angular pressing (I-ECAP). Square billets were processed using different routes of I-ECAP at temperatures varying from 125 °C to 250 °C. The billets were obtained from commercially available coarse-grained, hot-extruded rod and fine-grained, hot-rolled plate. A strong influence of the initial microstructure on processing temperature was reported. Fine-grained samples were successfully processed at 200 °C, while coarse-grained ones must have been heated up to 250 °C to avoid fracture. A gradual temperature decrease with subsequent passes allowed successful pressing at 150 °C. Processing using various routes of I-ECAP showed that a billet rotation before the last pass had strong influence on mechanical properties. The results of experiments were plotted on the diagram of allowable processing temperature for AZ31B. It was found that the relation between the minimum temperature in I-ECAP and the initial grain size could be described by a logarithmic equation

Applicability of JMAK-type model for predicting microstructural evolution in nickel-based superalloys

The question of the prediction of microstructural transformation over a wide range of temperatures and strain rates is important for the simulation of industrial hot forging processes, especially those focused on net-shape forging. A large spectrum of microstructural models, from the simplest empirical and phenomenological forms to more complex physics-based ones were developed during last century; some of them were embedded into commercial software. However, in spite of some successful implementations, the problem of the robust prediction of microstructure development in the real multi-operational industrial processes remains in general unsolved. Complex models often suffer due to high computational cost, possible mathematical instability and ill-defined calibration techniques. Simple models are easier for practical use but, due to the nature of the simplifying assumptions, have a limited range of validity, which is almost never specified. JMAK-type models are one of the examples of the relatively simple mathematical model forms popular for the description a number of metallurgical processes. One of them is recrystallisation, which is one of the dominating mechanisms in the hot working of metals. In this paper, the wellknown family of 718 nickel-base superalloys and a range of forging trials of different levels of complexity were used to analyze the applicability of the JMAK-type models