Thermomechanical Processing Parameters Research Articles

Study on multi stage forging process with combination of different strain rate and temperature region in IMI685 aero engine compressor disc forging

IMI 685, a near alpha Ti alloy has been used in high pressure compressor discs for aero engine application due to its high strength to weight ratio and high creep resistance. Manufacturing process plays an important role in obtaining the required mechanical properties for the highly complex and critical products. The suitable manufacturing process is not available in open literature. Hence, in this paper non-isothermal approach of manufacturing compressor disc combining hydraulic press and pneumatic hammer at different temperature for different stages of forging has been explored. Mechanical and metallurgical analysis of processing in partial α-β/β temperature range resulted in higher creep resistance with acicular/needle alpha platelets with a basket weave structure. This experiment has proven that with a proper selection of thermo mechanical processing parameters (combination of different forging temperature and strain rates in forging sequence), required creep properties can be met with the non-isothermal processing route.

Strength-Ductility Synergy in High Entropy Alloys by Tuning the Thermo-Mechanical Process Parameters: A Comprehensive Review.

The strength–ductility trade-off is an eminent factor in deciding the mechanical performance of a material with regard to specific applications. The strength–ductility synergy is generally inadequate in as-synthesized high entropy alloys (HEAs); however, it can be tailored owing to its tunable microstructure and phase stability. Thermo-mechanical processing (TMP) allows the microstructure to be tailored to achieve desired strength–ductility combination. The additional attribute is evolution of texture, which also significantly influences the mechanical properties. This review presents a critical insight into the role of TMP to achieve superior strength–ductility symbiosis at room temperature in single-phase (FCC, BCC) and multiphase HEA. The role of overall processing strategy of HEAs encompassing rolling and subsequent annealing in relation to the evolution of microstructure and texture in have been discussed. Recently practiced severe plastic deformation processes have also shown promise in improving the strength–ductility combination. The relevance of these processes in the processing of HEAs has also been analysed. At the end, futuristic approaches have been elaborated to enable efficient as well as hassle-free process towards achieving the proficiency of strength–ductility in HEAs.

How the Thermomechanical Processing Can Modify the High Strain Rate Mechanical Response of a Microalloyed Steel.

The effects of thermomechanical processing (TMP) on the mechanical response of microalloyed steels subjected to dynamic loading conditions were examined. The deformation conditions in the thermomechanical laboratory rolling processes were selected on the basis of dilatometric tests. It allowed (with a constant value of total deformation) us to obtain microstructures with different compositions and morphology of the particular components. Several samples characterized by a particularly complex and unexpected representation of the obtained microstructures were selected for further research. Plastometric tests, i.e., compression and tensile tests, were performed under quasi-static loading with digital image correlation (DIC) analysis, and under dynamic loading on the Split Hopkinson Pressure Bar (SHPB) apparatus with strain rates of 1400 and 2000 s−1. Samples deformed in such conditions were subjected to microstructural analysis and hardness measurements. It has been observed that the use of various combinations of TMP parameters can result in the formation of specific microstructures, which in turn are the source of an attractive mechanical response under dynamic loading conditions. This opens up new possible areas of application for such popular structural materials which are microalloyed steels.

Influence of thermomechanical processing parameters on critical temperatures to develop an Advanced High-Strength Steel microstructure

A good selection of the thermomechanical processing parameters will optimize the function of alloying elements to get the most of mechanical properties in Advanced High-Strength Steels for automotive components, where high resistance is required for passenger safety. As such, critical processing temperatures must be defined taking into account alloy composition, in order for effective thermomechanical processing schedules to be designed. These critical temperatures mainly include the recrystallization stop temperature (T5%) and the transformation temperatures (Ar1, Ar3, Bs, etc.). These critical processing temperatures were characterized using different thermomechanical conditions. T5% was determined through the softening evaluation on double hit tests and the observation of prior austenite grain boundaries on the microstructure. Phase transformation temperatures were measured by dilatometry experiments at different cooling rates. The results indicate that the strain per pass and the interpass time will influence the most on the determination of T5%. The range of temperatures between the recrystallized and non-recrystallized regions can be as narrow as 30 °C at a higher amount of strain. The proposed controlled thermomechanical processing schedule involves getting a severely deformed austenite with a high dislocation density and deformation bands to increase the nucleation sites to start the transformation products. This microstructure along with a proper cooling strategy will lead to an enhancement in the final mechanical properties of a particular steel composition.

Isothermal compression bonding mechanism and mechanical properties of WE43 magnesium-rare earth alloy

Isothermal compression bonding (ICB), or high temperature plastic deformation bonding, has become a prospective solid phase bonding technique without risk of casting defects in the joints compared to the conventional welding. In this study, a rare-earth magnesium alloy is subjected to the ICB process under a range of thermo-mechanical processing parameters. The results show that large grains and low grain orientation spread (GOS) values are observed in the bonding zone at high temperature and low strain rate, which leads to a lower bonding strength but a higher elongation (El). In the other cases (high strain rate or relatively low temperature & low strain rate), the grain size in the bonding zone is refined but the average GOS value increases, resulting in a stronger bonding strength but a weaker El. The former case belongs to a strong grain boundary sliding and thus the metallurgical bonding of the interfacial grain boundaries is enhanced while the latter is a DRX-dominated mechanism by the evaluation of stress exponent and apparent activation energy. In addition, the flow instability criterion is utilized to evaluate whether the ICB process is in a steady condition.

Effect of thermo-mechanical processing parameters on the dynamic restoration mechanism in an Mg-4Y-2Nd-1Sm-0.5Zr alloy during hot compression

Microstructure evolution and dynamic restoration mechanism of solution-treated Mg-4Y-2Nd-1Sm-0.5Zr alloy have been studied under three TMP parameters consisting of deformation temperatures (350–500 °C), strain rates (0.01–5 s−1), and strains (0.2, 0.4, and 0.8). A strong dynamic softening is observed in all stress-strain curves, even at higher strain rates (1 and 5 s−1) due to an adiabatic heating effect. Various stress-strain curves are applied to construct a processing map and develop an Arrhenius-type constitutive equation. With the prediction of the processing map, an optimal processing domain has been determined to be the temperature range 450–500 °C and strain rate range 0.01–0.1 s−1 at a strain of 0.8. The volume fraction of DRX grains is the largest in the corresponding domain of high temperature and low strain rate. For the effect of TMP parameters on the dynamic restoration, the discontinuous dynamic recrystallization (DDRX) and continuous DRX (CDRX) synergistic effect occur throughout the whole process at high temperature and high strain rate. In terms of high temperature and low strain rate, DDRX characteristics at a low strain and then the DDRX + CDRX synergistic effect is observed at a higher strain. Although the DRX process is weak at low temperature and low strain rate, deformation twins have occurred and provided nucleation sites for DRX grains.

The effect of crystallographic orientation and interfaces on thermo-mechanical softening of a martensitic steel

Thermo-mechanical softening forms the basis for hot working of metallic materials. In materials with hierarchical microstructures such as martensite, softening processes can be mediated or restricted by interfaces. In the present study, the operation of three distinct softening mechanisms in P91 martensitic steel during thermo-mechanical processing (TMP) has been investigated. The softening in the present case is found to arise from the interplay between microstructural strain, texture, and phase transformation. Further, softening characteristics vary with the TMP parameters. The manifestation of softening has been explored at the macroscopic, mesoscopic, and microscopic length scales. It has been found that each softening mechanism is differently mediated by the interfaces and is governed by local crystallographic orientation. Thermo-mechanical softening of martensite proceeds through orientation-dependent dynamic recrystallization. The role of specific interfaces in impeding this mechanism has been highlighted. In contrast, TMP of austenite proceeds through interface-mediated softening, combining the phenomena of recrystallization and phase transformation.

Process parameter influence on deformation and recrystallization textures in Al alloys

Mesoscopic changes take place during the entire thermomechanical processing (TMP) of polycrystalline metallic materials. Controlling the TMP parameters is of key importance since both microstructure and texture evolution of a particular technological step severely influence the final properties of a given product. This study is focusing on the crystallographic aspect of microstructural formation in Al alloys. The effect of straining level on the crystallographic texture evolution and texture-dependent properties is discussed. This contribution clearly demonstrates that the plastic stain ratio can be modified via TMP route. Implementation of relatively small deformation could account for improvement of anisotropy of plastic yielding, necessary for advanced deep drawing qualities.

Investigation of deformation behavior and microstructure evolution of a Ti-6Al-4V-0.5Ni-0.5Nb-0.05Ru alloy

(1) The dynamic deformation behavior and microstructure evolution of a new Ti-6Al-4V-0.5Ni-0.5Nb-0.05Ru alloy was studied in this paper. The constitutive model of the tested alloy was calculated, and a series of processing maps considering strain were constructed. The results revealed that the thermal activation energy of the tested alloy was 531.856 kJ/mol, which was lower than that of the Ti-6Al-4V-0.1Ru alloy. (2) The constitution model between peak-state flow behavior and TMP parameters can be expressed as ε̇=9.177×1021sinh0.0109×σp3.9086exp−531.856RT. The optimal thermomechanical process (TMP) parameter of the tested alloy was calculated to be in a temperature range of 940–1000 °C and a 0–1 s−1 strain rate, while the unstable region was in a temperature range of 930–990 °C and a 0.01–0.6 s−1 strain rate. Due to the rotation and deformation coordination of the large amount of equiaxed α phase and dynamic recrystallization α phase, the dynamic softening mechanism was a typical continuous dynamic recrystallization (CDRX) in the α + β phase region, and the dynamic recovery of the tested alloy occurred mainly in the β phase region.

Thermomechanical Treatment of Martensitic Stainless Steels Sheets and Its Effects on Their Deep Drawability and Resulting Hardness in Press Hardening

The deep drawability of three Martensitic Stainless Steels (MSS) alloys under conventional press hardening thermomechanical process conditions was investigated. The three alloys differ in the content of the main elements C and Cr. Firstly, the metallurgical properties of the alloys were determined, i.e., the phase mass fraction diagrams and the concentration of alloying elements in solid solution at the austenitic temperatures with help of the JMatPro® software version 7.0. Derived from this analysis, specific thermomechanical process parameters were defined to evaluate experimentally and numerically the hot sheet formability of the alloys during the deep drawing process. The hot deep drawability of the MSS alloys was experimentally assessed. The hot deep drawability was evaluated with the resulting maximum drawing depth values. In general, all three alloys developed very good formability at forming temperatures between 700 and 900 °C. However, they are susceptible to chemical composition, austenization temperature, dwell time, and flange gap. The hot formability behavior of the alloys as well as the resulting hardness showed very good concordance with the calculated metallurgical values. Finally, a numerical analysis was conducted using Simufact Forming® 15.0 software. The interval time during hot blank transfer to the tool determines the initial and final forming temperature. The effect of the time interval on the forming temperature was analyzed numerically and validated experimentally. It was also possible to determine the maximum level of plastic strain in the deep drawn cup.

Ensuring the strength and ductility synergy in an austenitic stainless steel: single- or multi-phase hetero-structures design

Heterogeneous microstructures have been proposed to optimize the mechanical properties in the respect of strength and ductility synergy in many alloy systems. In this work, the multi-phase hetero-structured microstructure consisting of fine grains and coarse grains where the ferrite is embedded in the vicinity of the nano-grains was obtained by regulating the thermomechanical processing parameters. A yield strength of 1.2 GPa which is more than two times higher than the coarse grained counterpart with less uniform elongation loss is achieved in the multi-phase hetero-structured steel. The microscopic load transfer in this complex microstructure is investigated by the in situ high energy synchrotron X-ray diffraction. The persistent strain hardening is ascribed to the hetero-deformation induced stress associated with the joint activation of transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects. As a comparison, the single-phase hetero-structured steel exhibits little lower strength but higher uniform ductility.

Extra-strengthening in a harmonic structure designed pure titanium due to preferential recrystallization phenomenon through thermomechanical treatment

The effect of thermomechanical processing (TMP), consisting of cold rolling followed by annealing, on the microstructure and mechanical properties of Harmonic Structure designed commercially pure Ti (HS–Ti) was studied. The TMP of HS-Ti led to the evolution of a peculiar preferentially recrystallized structure, localized in the Shell and Shell-Core interface regions. The underlying mechanism for such a unique microstructural evolution in the TMP HS-Ti has been proposed and discussed. The TMP treated HS-Ti specimens exhibited considerably higher strength values and comparable ductility with respect to its conventional homogeneous structured Ti (Homo-Ti) and as-sintered HS-Ti counterparts. The present work demonstrated that it is feasible to further enhance the superior mechanical properties of harmonic-structured materials through controlling the volume fraction and the grain size of the Core/Shell via controlling TMP parameters.

Influence of thermomechanical processing parameters on microstructural evolution of a gamma-prime strengthened cobalt based superalloy during high temperature deformation

Recent reports on γ′-L12 strengthened cobalt base superalloys showed the potential of this class of alloys to replace nickel-base superalloys for high-temperature applications. The studies on thermo-mechanical processing behavior of these new class of alloys are limited. Thus, the present study investigates the thermo-mechanical processing behavior of Co-30Ni-10Al-2Nb-4Ti-12Cr (all in at. %, referred to as Co10Al2Nb) γˈ strengthened cobalt base superalloy at different conditions of temperature and strain rates. The high temperature uniaxial compression tests were carried out using Gleeble 3800® in the temperature range of 1298–1448 K and the strain rate range of 0.001 to 10 s-1. The flow curves exhibited three distinct flow behavior characteristics: work hardening, softening, and steady state. Microstructures of deformed samples revealed the presence of fine strain-free dynamic recrystallization (DRX) grains in lower strain rate regime (0.001 to 0.1 s-1) and flow localization features like shear bands, cracks along the grain boundary in high strain rate regime (especially at 10 s-1) for all the temperatures. The strain rate sensitivity (m) map along with instability ( ξ(ε˙)) map revealed two distinct domains, one with m ~0.15 to 0.3 (0.001 to 1 s-1), and other domain with m < 0.13 ( >1 s-1) for the temperature range studied. DRX was observed to be the main restoration process at m ~ 0.15 to 0.3, whereas the flow localization was dominant at m < 0.13. The microstructure at different strain levels revealed that discontinuous dynamic recrystallization (DDRX) was the prevalent deformation mechanism for the present alloy. The strain field distribution obtained from the FEM simulation for different deformation conditions correlated with DRX microstructure evolution was also presented.

Simulation of Technology for the Production of Axisymmetric Parts for Gas Turbine Engines Made of Heat Resistant Alloys by Means of Reeling under Superplastic Conditions

Shaping by means of reeling under the conditions of superplasticity using specialized reeling mills is a promising technology for manufacturing axisymmetric parts of gas turbine engines (disks and hollow shafts) based on heat-resistant alloys. Mathematical simulation is an efficient method for determining the energy and thermomechanical parameters of the technological process. This paper describes a methodology for constructing a finite element model for the reeling of parts under the conditions of superplasticity, as well as the results of simulation by the example of making a disk and a hollow shaft of heat-resistant alloys. The technique proposed can be used in developing a technology and equipment design for reeling axisymmetric parts (disks, hollow shafts) based on heat-resistant alloys under superplastic conditions.

Development of a Flow Localization Band and Texture in a Forged Near-α Titanium Alloy

This work investigated crystallographic textures and the features of a flow localization band in a forged Ti6242S billet. The flow localization band experienced a large strain and grains within it were elongated under shear stress. The main macrotextural components were made up of (11 2 ¯ 0)/&lt;10 2 ¯ 0&gt;, &lt;0002&gt;/axial direction, and a static recrystallization texture (11 2 ¯ 0)/(3 3 ¯ 02), which can be explained by motion of a prismatic &lt;a&gt; slip system and a newly proposed method of projection. Finally, three types of macrozone, each with a sharp defined texture were observed and subsequently, it was demonstrated that the formation of macrozones was only connected with parameters of thermomechanical processing and was independent of variants selection.

Thermomechanical process route to achieve high fracture toughness in Ti-17 forgings for high temperature applications

Mechanical properties of Ti-17 are typically strongly influenced by different thermomechanical process parameters such as applied strain, cooling rates and heat treatment temperatures and times. A variation of theses parameters allows the optimization of material properties. Today Ti-17 is mainly used for aero engine applications, where a high strength and good low cycle fatigue properties are needed up to 450°C. For structural parts damage tolerance properties are the main focus and therefore fracture toughness and fatigue crack propagation are the main driving factors for the design. In large forgings such as aero structural parts, the tempering cross section generally varies significantly, which makes it extremely challenging to achieve uniform properties in each area of the forging especially in case of low buy-to-fly ratio. The aim of this work is to develop a robust thermomechanical processing route for large Ti-17 die forgings with complex geometry and high fracture toughness requirements. Hand forging trials with four different thermomechanical processing routes resulting in a lamellar microstructure have been performed and their strength and fracture toughness properties were studied. In addition, one die forging using a promising process route was manufactured and strength and fracture toughness were compared with values typically achieved for Ti6-4.

Prediction of forming limit diagrams using machine learning

Measuring forming limit diagrams (FLDs) is a time consuming and expensive process. Data-driven and artificial intelligence approaches have been used to facilitate finding relationships between alloy composition, and manufacturing processing conditions with mechanical properties of materials. Machine learning (ML) methods are a promising route to predict FLD of aluminium alloys that are increasingly used in automotive structural applications. In the present work, we developed a machine learning (ML) based tool to establish the relationships between alloy composition / thermomechanical processing route to the material’s FLD, which is a measure of formability. Measured FLDs of various 5XXX and 6XXX aluminium alloys along with their chemical composition and thermomechanical processing parameters like homogenization, hot and cold rolling parameters etc. and the respective mechanical properties like n and r values were manually curated and stored in a database. A two-stage ML model was trained on this database. In the first stage, the minimum and maximum points of the minor strain were predicted using a feature set incorporating chemical composition, thermomechanical processing parameters, and n and r values using support vector regression (SVR). In the second stage, the predicted minor strain in the first stage was used as input in addition to the same feature set to predict the major strain using gradient boost regression (GBR). The trained ML model successfully predicted FLDs with R2 value above 0.93. To study the impact of the difference between a predicted and a measured FLD on stamping simulation results, finite element simulations of a cross die were performed. The difference in draw depth of the cross-die using the predicted FLD and the measured FLD was between 5 to 10%. The current results show that ML can be a viable way for predicting FLDs.

Performance Analysis of Non–Oriented Electrical Steel with Optimum Texture for High–Speed Traction Motors

The magnetic properties of non–oriented electrical steel (NOES) vary significantly with respect to the microstructure and crystallographic texture of the final steel sheets, which, in turn, are highly dependent upon the thermomechanical processing parameters used during hot rolling, cold rolling and annealing. This paper performs an exploratory performance analysis of NOES for use in high–speed traction motors, emphasizing the importance of obtaining an appropriate crystallographic texture to achieve the desired magnetic properties by controlling the annealing temperature and holding time. A 3.2% Si NOES annealed at 860°C for 24 hours after hot rolling can result in reduced core losses after cold rolling and final annealing. This material was chosen for the performance analysis of a laboratory scale high–speed, high–power traction motor (45 kW, 10,000 rpm) using finite element analysis (FEA). The motor using the NOES is compared to that using a commercially available grain–oriented electrical steel (GOES) to highlight the feasibility and advantages of NOES for high–speed motor applications. In addition, the motor performance using the NOES is compared to that using commercial NOES to understand the scope of improvement obtained by optimizing the microstructure and texture of the steel sheet.

Effect of Thermomechanical Parameters on Grain Growth and Recrystallization during Grain Boundary Engineering of Austenitic Stainless Steel

Grain boundary engineering has been attracting attention as an effective method to prevent intergranular corrosion of austenitic stainless steel and Ni based alloys. It has been considered that grain growth and recrystallization play important role in evolution of grain boundary character distribution during thermomechanical process. However, systematic researches to examine the effect of thermomechanical process parameters on grain growth and recrystallization have not been performed. In this study, grain boundary character distribution of 304 austenitic stainless steel after thermomechanical process with various parameters was analysed by electron backscatter diffraction (EBSD). Grain boundary character distribution was mainly affected by the reduction ratio of cold rolling. Abnormal grain growth was observed in the specimen with small reduction ratio (3%). Length ratio of coincident site lattice (CSL) boundaries was drastically increased to 86% in the 3% cold rolled and annealed specimens from 67% in the base material. On the other hand, normal grain growth was observed in thermomechanical processed specimens with slightly higher reduction of cold rolling (5%). In these specimens length ratio of CSL boundaries did not exceed 80%, which is required to disconnect the random boundary networks and to improve intergranular corrosion resistance effectively. Detailed analysis of grain boundary character distribution has shown that disconnection of random boundary networks was achieved by formation of annealing twins during abnormal grain growth.

Effect of thermomechanical processing on microstructural evolution in precipitation strengthened ferrite steel

The present study is focused on processing simulation in Gleeble® to understand the effect of thermomechanical processing parameters, especially thin-slab casting rolling (TSCR) process, on the ferrite grain structure and precipitation in a nano-precipitation strengthened ferritic steel. The double-hit compression test confirmed that heavy deformation in the range of 900–850 °C can accumulate sufficient strain in deformed austenite that is required to achieve significant ferrite grain refinement. Subsequent simulation of conventional hot-strip mill processing route showed fully ferritic microstructure upon isothermal holding at and above 650 °C (for coiling simulation). Holding at lower temperatures (≤ 600 °C) generate pearlite and bainite, which are undesirable for formability. Finally a TSCR-type of processing schedule is applied maintaining a constant deformation temperature (870 °C) and isothermal holding temperature (650 °C) to understand the effect of equalization entry temperature (Teet). A low equalization entry temperature (900 °C) was found to be beneficial to generate fine ferrite grains with fine precipitates during processing by TSCR route which is a novel finding.