Hot Working Research Articles

A comprehensive investigation on the effect of SiCp on microstructure and mechanical properties of Mg–5Sb-based hybrid composites

Microstructural development, strengthening mechanisms, and mechanical properties of the newly developed Mg–5Sb-xSiCp (x = 0, 1, 3, and 5) composites were studied in both as-cast and extruded states. The microstructures of composites were composed of α-Mg, in-situ Mg3Sb2, and SiCp phases. The cooling curves display that Mg3Sb2 intermetallics form as the primary phase. During solidification, the SiCp acts as heterogeneous sites for both α-Mg and intermetallics formation. The increase in SiCp content (from 0 % to 5 %) modified the as-cast grain size from 827 μm to 411 μm with the improvement of yield strength (YS) (74–97 MPa). Also, the SiC addition to as-cast facilitates the formation of a randomized texture and a significant reduction in intensity from 13.121 mrd to 6.301 mrd for SiC-Free and 5 wt% added MMCs, respectively. Grain refining and recrystallization are characterized by electron backscatter diffraction (EBSD) analysis. Grain refinement via SiCp and hot extrusion leads to substantial structural refinement, resulting in a decrease in grain size from about 411 μm down to 3.92 μm for MMC with 5 wt% of SiC. Consequently, the best combination of the ultimate tensile strength (UTS) (∼244 MPa) and total elongation (∼8.9 %) was obtained for the hot extruded composite containing 3 wt% SiCp. The prevailing strengthening mechanisms are supposed to be particle strengthening mechanism in the as-cast condition and coefficient of thermal expansion (CTE), Orowan, and Hall-Petch mechanisms in the as-extruded condition. Obviously, adding SiCp and employing hot working lead to significant increase in ultimate compressive strength (from 180 MPa to 321 MPa for 5 wt%).

Stress-induced intersecting stacking faults and shear antiphase boundary in Zr5Ge4 second phase precipitate embedded in Ge-modified Zircaloy-4

Secondary phase precipitates are vital to control mechanical, corrosion and irradiation response of the multiphase alloy systems. This work reports the mechanical response of an ordered complex intermetallic Zr5Ge4 precipitate during hot working of the experimental Zircaloy-4 modified with dilute Ge addition. Atomic scale insight is provided into the formation mechanism of straight and circular stacking faults and shear antiphase boundary in Zr5Ge4 precipitate. Two types of stacking faults, having displacement vectors 1/3[100] and 1/3[110] with small components along the c-axis, come across and form a distinct region on the (001) surface composed of a zigzag atomic arrangement different from the parent crystal. Besides this, a shear antiphase boundary along the Zr5Ge4/fcc-Zr interface is analysed and concomitant generation of nanotwins is evidenced by the streaking effect in the associated fast Fourier transform (FFT) pattern. By analysing the distortion and stacking faults in the surrounding fcc-Zr phase, comments are made on the role of external stresses in generating the aforementioned planar defects. The relative activity of two types of displacement vectors observed in Zr5Ge4 precipitate is discussed on the basis of the nature of the atomic bond.

Effect of hydrogen content on the high-temperature compressive deformation behavior and microstructure evolution of TC17 alloy

Thermo-hydrogen process (THP) has been an important research direction of the titanium alloy heat treatment process. However, the effect of THP on the thermal deformation behavior and microstructure evolution of TC17 alloy during hot compression has not been investigated. In this study, a series of isothermal compression experiments were carried out on hydrogenated TC17 alloy specimens in the temperature range covering the α+β phase region and β phase region of TC17 alloys with different hydrogen contents, to investigate the effect of hydrogen on the high-temperature flow behavior and microstructure evolution. The results show that the primary α phase of the hydrogenated TC17 alloy is significantly reduced. Observing the XRD pattern, the substitutional solution effect of hydrogen causes the β phase lattice to expand, resulting in a shift of the β phase toward a small angle as the hydrogen content increases. The flow stress shows a tendency to decrease and then increase with increasing hydrogen content. This is attributed to the softening effect of hydrogen on the α phase and the hardening effect on the β phase. This also leads to the deformation activation energy showing the same trend. When the hydrogen content increases to 0.4 wt%, the activation energy decreases to the lowest point by about 24 %. Finally, the appropriate hydrogen concentration can effectively reduce the destabilization region in the hot working map and expand the processing window of TC17 alloy.

Hot deformation characteristics and processing map analysis of Al-Zn/stainless steel particles-based composite

The hot deformation behavior of Al-Zn/martensitic stainless steel particles-based composite (Al-Zn/6 %SSp), was examined in this study. The composite was tested using isothermal compression at 200–350 °C/0.01–10 s−1 and a global strain of 0.5. From the results, it was noticed that the composite’s flow stress increased with strain rate increase and drop in temperature. The constitutive equation from the hot-worked composites resulted in an estimated activation energy of 226.27 kJ/mol, which was 58 % more than that for the self-diffusion of aluminum alloy (142 kJ/mol). These findings suggest dynamic recrystallization (DRX) as the dominant deformation mechanism, as confirmed from the microstructures of the hot worked samples mostly at high temperatures and strain rates. Work hardening was predicted to dominate the deformation process by the stress exponent (n) value of 10.36 (which exceeded 5), but this was inconsistent with the microstructural observations. Comparing the linear fitting of calculated flow stress data with the estimated flow stress yielded a correlation coefficient (R2) of approximately 0.97. This observation demonstrates an effective relationship involving the calculated stress with the computed stress value for the composite material that was fabricated. Based on the processing map analysis, the instability regime occurs at 200270 °C/0.01–10 s−1. The stable domain established was at 280–340◦C/0.01–10 s−1 which is most suitable for achieving the best microstructural conditions for enhanced service performance.

Hot Deformation Behavior and Workability of a New Ni–W–Cr Superalloy for Molten Salt Reactors

Hot Deformation Behavior and Workability of a New Ni–W–Cr Superalloy for Molten Salt Reactors

Delineating the role of dynamic and static recrystallization during hot working of nickel-based superalloy (IN600)

In the presented research, the dynamic working of nickel-based (IN600) superalloy was performed and the micro-mechanisms affecting the deformation behaviour were closely monitored, particularly the role of static and dynamic recrystallization. Hot deformation flow stress response indicated an increase in the true stress value with an increase in strain rate and decrease in temperature. The constitutive calculations indicated that deformation progressed mainly due to dislocation climb motion. The hot workability map indicated a peak power dissipation efficiency (PDE) of 0.39 in two working domains. The microstructural evolution in the hot deformed specimens depicted a consistent increase in dynamic softening at temperature ≥ 1000 °C, whereas, a steady decline in the extent of dynamic softening is observed with increase in strain rate from 0.01 s−1 to 1 s−1. The mechanism for microstructural evolution in this range (0.01–1 s−1) was identified as discontinuous dynamic recrystallization (DDRX). Moreover, at the highest strain rate of 10 s−1, a sudden surge in the recrystallization fraction was observed, which was attributed to the combined effect of DDRX and static recrystallization (SRX). Additionally, this study shows that the presence of twin boundaries (TBs) contributes to dynamic softening by serving as sites for nucleation of strain-free grains.

A New Lead-Free Copper Alloy CuAl8Fe5Ni4Zn4Sn1 for Plain Bearings and Its Strengthening Mechanisms

CuAl8Fe5Ni4Zn4Sn1 (OF 2238) is a new lead-free copper alloy for plain-bearing applications that was first officially presented in a scientific journal in 2020. Soon after its invention, the use of the alloy for connecting rod bushings in heavy-duty internal combustion engines was promoted and validated with customers. The aim of this article is to describe the material properties of the new alloy in more detail than previously and explain how the advantageous properties of CuAl8Fe5Ni4Zn4Sn1 are generated. At the beginning of this article, the general development trends in the field of copper alloys for sliding applications are presented, into which the new alloy from this publication can be classified. In the main part of this publication, the authors go through the production chain of CuAl8Fe5Ni4Zn4Sn and show how the entire manufacturing process contributes to obtaining a material with a combination of high strength, ductility and sufficient toughness. This starts with fine microstructures after casting, followed by homogenisation and refinement during hot extrusion and work hardening chiefly during cold drawing. What is most surprising, however, is the finding that a strong hardening effect can be achieved in the new alloy by precipitation of fine κ-phase at temperatures of about 400 °C and air cooling without prior solution treatment. These results make it clear that there is great potential for further material developments to support material efficiency and even to expand the application limits.

Failure mechanisms of multilayer TiN films based on mechanical properties of film and substrate

The poor adhesion, which is related to the mechanical properties of the substrate and film, leads to the film peeling off from the substrate and failure. In this study, TiN films with various structure were prepared on Ti6Al4V titanium alloy (TC4), 316L stainless steel (316L), 4Cr5MoSiV1 hot work die steel (H13), and W6Mo5Cr4V2 high-speed steel (W6) by adjusting the discharge currents using a hot-wire plasma-enhanced magnetron sputtering rig. The morphologies of the single-layer TiN films varied from loose to dense and ductile to brittle, and the nanohardness and elastic modulus increased as the hot-wire discharge current increased. The morphologies, nanohardnesses, and elastic moduli of the multilayer TiN films gradually approached those of the dense TiN single-layer films as the thicknesses of the top dense layers increased. The results, both by numerical simulation and experimental tests, revealed that the interfacial tensile stress and surface strain of a TiN/substrate system increased as the elastic modulus differences between TiN and its substrate increased, resulting in a serious TiN film elastic and plastic deformation asynchrony and poor film–substrate adhesion. The loose layer between the top dense TiN layer and its substrate acts as a buffer because the elastic modulus of the loose layer is in the middle, higher than that of the substrate but lower than that of the top dense layer. For TiN/TC4 or 316L with large differences in elastic moduli, loose/dense thickness ratios of 1:2 or 1:4 for the multilayer TiN films were sufficient to improve their adhesion. For TiN/H13 or W6, with small elastic modulus differences, a ratio of 1:4 was sufficiently large and may not be necessary.

Construction of hot processing map, dynamic recrystallization critical conditions and kinetic model of AZ61 alloy

Under temperature of 300–450 °C and strain rates from 0.003 s−1 to 1 s−1 and deformation of 70 %, hot compression experiments of AZ61 magnesium alloy were carried out on Gleeble-1500 test machine, to study its thermal deformation behavior. Based on the dynamic material theory model, a three-dimensional hot working map was obtained. Based on the work hardening rate curves inflection point, the critical strain model was built. Subsequently, the dynamic recrystallization kinetics model was constructed according to critical conditions. The findings showed that at low strain rates and high temperatures, materials with larger power dissipation factors exhibit better processability, and at high strain rates and low temperatures, materials are more prone to instability with the increase of strain. Considering the connection between peak strain εp and critical strain εc, it is observed that εc precedes εp, indicating that dynamic recrystallization occurs before reaching the peak strain. Based on the kinetics model, observed the dynamic recrystallization volume fraction curves follow a “slow-fast-slow” changing trend, exhibiting an “S” shaped growth, which was agreed with the kinetics curve in classical dynamics.

Hot deformation behaviors and microstructure characteristics of Cr–Mo–Ni–V steel with a banded structure

Abstract On a Gleeble-3800 thermal simulator, the hot deformation behavior of Cr–Mo–Ni–V steel was studied, with the designed deformation temperature varying from 900 to 1,200°C and the strain rate in the range of 0.01–10 s−1. It was observed that as the strain rate was increased and the hot working temperature was reduced, the flow stress of the experimental steel increased. The study also evaluated the safe parameters for deformation of the Cr–Mo–Ni–V steel in the hot working process, based on the established processing maps. It was found that the deformation temperature window varying from 1,050 to 1,150°C and the reasonable strain rate in the range of 0.01–1 s−1 are beneficial to the hot deformation of the steel. In this research, the effect of processing parameters of the hot working process on the microstructure evolution of the banded structure was also investigated. According to the research result, the banded structure in the steel remained visible under the conditions of a strain rate of 10 s−1 and the hot working temperature in the range of 900–1,200°C. However, it should be noted that the banded structure in the steel then gradually disappeared when the hot working temperature was increased to 1,200°C.

The Impact of Hydration Level on Groundhandling Officer at Bandara Soekarno Hatta

Background: Groundhandling workers are workers who are exposed to heat for quite a long time. A work environment that exceeds tolerance limits can cause health problems such as dehydration and fatigue. Lestari (2016) in his research stated that a hot work environment that exceeds the Threshold Limit Value (TLV) can increase the risk of dehydration. Purpose: This research focuses on fatigue and the risk factors of fatigue, especially those caused by dehydration, without disregarding other risk factors among ground handling workers at Soekarno-Hatta Airport. Method: The method used in this research is an observational analytic approach with a cross-sectional design. The sampling technique employed random sampling with a sample size of 219 respondents consisting of ground handling workers working both inside buildings and on the apron. The measuring instruments used were specific gravity urine tests to determine hydration status and IFRC questionnaires to assess workers' physical fatigue status. Result: From the existing data it was found that the majority of respondenst experienced mild fatigue, namely 36,5% of the 219 respondents and others experienced severe fatigue 63,5%. With hydration status, most workers have good hydration status (euhydration), namely 70,3% and and some others experienced dehydration, namely 29,7%. The result of the analysis between hydration status and level fatigue showed 35,4% of respondents who werw dehydrated experienced severe fatigue, while 37% of respondents who were euhydrated/normohydrated experirienced severe fatgue. The results of the analysis test obtained was no relationship between hydratin status and fatigue level. The OR (Odd Ratio) shows a result or 0,932 meaning that respondents withs dehyration are protective factor of 0,93 times agains severe fatigue. Conclusion: The conclusion of this research is that good hydraton status can prevent fatigue in workers, especially those who work with direct heat exposure.

In Situ Study of Precipitates' Effect on Grain Deformation Behavior and Mechanical Properties of S31254 Super Austenitic Stainless Steel.

Grain boundary (GB) precipitation-induced cracking is a significant issue for S31254 super austenitic stainless steel during hot working. Investigating the deformation behavior based on precipitate morphology and distribution is essential. In this study, continuous smaller and intermittent larger precipitates were obtained through heat treatments at 950 °C and 1050 °C. The microstructure evolution and mechanical properties influenced by precipitates were experimentally investigated using an in situ tensile stage inside a scanning electron microscope (SEM) combined with electron backscatter diffraction (EBSD). The results showed that continuous precipitates at 950 °C had a stronger pinning effect on the GB, making grain rotation difficult and promoting slip deformation in the plastic interval. Continuous precipitates caused severe stress concentration near GB and reduced coordinated deformation ability. Additionally, the crack propagation path changed from transcrystalline to intercrystalline. Furthermore, internal precipitates were a crucial factor affecting the initial crack nucleation position. Interconnected precipitates led to an intergranular fracture tendency and severe deterioration of the material's plasticity, as observed in fracture morphology.

Effect of high temperature annealing on hot workability of Co40CrNiMo elastic alloy

Effect of high temperature annealing on hot workability of Co40CrNiMo elastic alloy

Exploring Ho substituted Y-Fe-B nanocrystalline alloys and hot worked magnets

Aiming to balance the utilization of rare earth (RE) resources and develop Y-Fe-B based permanent magnets, Ho is employed as strategic substitution for enhancing the magnetic properties and thermal stability of nanocrystalline Y-Fe-B alloys. Ho substituting Y can enhance the coercivity of Y-Fe-B alloys while maintaining their excellent thermal stability. 30 at.% Ho substitution leads to an abnormal increase of remanence J r and (Y0.7Ho0.3)2Fe14B alloy exhibits good magnetic properties with remanence J r = 0.73 T, intrinsic coercivity H cj = 303 kA m−1, and maximum energy product (BH)max = 66 kJ m−3. High thermal stability with temperature coefficient of remanence α = −0.124%/K and temperature coefficient of coercivity β = −0.245%/K were obtained between 300–400 K. The results for RE-rich (Y1−xHox)2.5Fe14B alloys also show that the magnetic properties change with Ho content are similar to those of (Y1−xHox)2Fe14B alloys, but the coercivity is higher. In addition, nanocrystalline (Y0.5Ho0.5)2.5Fe14B magnets were prepared by hot-pressing and hot deformation process. Due to the lack of low melting point RE-rich phase, this alloy is difficult to be densified and deformed. The formation of high temperature RE2O3 and RE6Fe23 phases and the lack of continuously distributed RE-rich grain boundary phase are responsible for the poor texture of hot deformed magnet. The hot deformed magnet has the magnetic properties of J r = 0.50 T, H cj = 739 kA m−1, and (BH)max = 40 kJ m−3 together with high thermal stability. The micro-analysis demonstrated the chemical segregation of Y and Ho elements. Higher proportion of Ho than Y existed in main phase and grain boundary phase indicate excess Y were precipitated as Y-rich oxides.

Numerical analysis of the flow dynamics in Maxwell hybrid nanofluid flow with gyrotactic microorganisms over a permeable stretching surface with convective and zero-mass flux conditions: A comparative analysis

This study observes the 2-D flow of a Maxwell hybrid nanofluid flow on a permeable stretching surface containing Cu and CuO nanoparticles and gyrotactic microorganisms. The thermal convective and zero-mass flux constraints are adopted by incorporating a hot working fluid with a heat transfer coefficient and zero mass flow at the permeable sheet’s surface to investigate the heat transfer rate. This study is designed to present a comparative analysis of the nanofluid (Cu–water) as well as hybrid nanofluid (Cu–CuO/water) flows on a stretching sheet. Examining activation energy in water-based hybrid nanofluid flow offers important insights into the kinetics of chemical reactions, which in turn helps to optimize the features of the nanofluid and build more effective systems that use nanofluids for a variety of applications. The problem formulated initially is converted to dimension-free notation using appropriate variables for finding the numerical solution by incorporating the bvp4c MATLAB function. From the obtained results, it is found that the higher magnetic and porosity factors have declined the velocity profiles. Also, in the absence of porous media and magnetic field effects, the velocity distribution is highly affected when compared with the existence of these effects. It is observed that the velocity profiles of both nanofluids are dominant for Newtonian fluid in comparison to non-Newtonian fluid. Also, the thermal profiles of both nanofluids are dominant for non-Newtonian fluid in comparison to Newtonian fluid. The friction force of hybrid nanofluid is significantly influenced by the magnetic factor, porosity factor, and volume fractions of the solid nanoparticles when compared to nanofluid.

Mechanical and tribological properties of Ti1-xZrxB2 coatings deposited by magnetron sputtering on hot work steel

Low fracture toughness is a common problem encountered by many researchers in the application of pure TiB2 coatings. To improve their properties, a convenient and useful method is the use of doping, so this study proposes the deposition of TiB2 enriched with Zr on a steel substrate. The objective of the research was to investigate the impact of Zr addition to TiB2 coatings on both their mechanical and tribological properties. Four coatings with varying compositions (pure TiB2; TiB2 doped with 3, 6, and 10 at.% Zr) were deposited using magnetron sputtering from TiB2 and Zr targets. The coating structures were analyzed by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Nanoindentation, scratch test, and ball-on-disk test were used to determine the mechanical and tribological properties. In most cases, only two factors have a significant impact on the mechanical and tribological properties of the Zr-doped coating. Firstly, a change in the preferred orientation of the coating from (102)(111) to (100) results in increased hardness and wear resistance. Secondly, a reduction in crystallite and column size enhances ductility and fracture toughness by impeding or altering the direction of crack propagation. Based on the study, one can conclude that the optimal Ti1-xZrxB2 properties were obtained for 6 at.% Zr content.

Investigation of Energy Consumption and Surface Roughness in Hot Work Tool Steel (DIN 1.2367) and Cold Work Tool steel (DIN 1.2550)

Investigation of Energy Consumption and Surface Roughness in Hot Work Tool Steel (DIN 1.2367) and Cold Work Tool steel (DIN 1.2550)

Dynamic globularization behavior of the dual-phase TiZrV medium entropy alloy during hot working

Globularization is an advantageous way to improve the formability of dual-phase materials. Dynamic globularization behavior of the TiZrV medium entropy alloy (MEA) with dual-phase was investigated at the temperature range of 500 ℃ ∼ 700 ℃ and strain rate of 0.1 s-1 ∼ 10 s-1 by the double-cone compression test. The finite element software was used to simulate the hot compression process of the double-cone specimen. Transmission electron microscope (TEM) was used to study the deformation microstructure features. The double-cone test can produce a wide strain range and corresponding deformation microstructure. The highest globularization ratio of 72.4% was obtained under the strain of about 0.88 at 500 ℃ and 10 s-1. The hot deformation mechanism map in the temperature range of 500 ℃ ∼ 700 ℃ and the strain range of 0.2 ∼ 1.2 at 10 s-1 was constructed by combining the double-cone test with finite element simulation. The hot deformation mechanism map is divided primarily into two parts. At 500 ℃, in the strain region of 0.2 ∼ 0.88, the deformation mechanism is dynamic recovery (DRV), and in the strain region of 0.88 ∼ 1.2, the deformation mechanism is dynamic recrystallization (DRX). It is considered that DRX plays a key role in dynamic globularization of the TiV phase during hot working and its production is summarized.

Effect of initial grain size on hot deformation behavior and recrystallization mechanism of Al-Zn-Mg-Cu alloy

Grain size is industrially important for improving mechanical properties and formability. In order to investigate the effect of grain size on the hot workability and deformation mechanisms, Al-Zn-Mg-Cu alloys with different initial grain sizes, 241.2, 100.4 and 48.4 μm, were subjected to hot compression tests. Using the established constitutive equation, the rheological behavior is described and the influence of the initial grain on the thermal deformation behavior is analyzed. Electron back-scatter diffraction (EBSD) analysis was used to study the dynamic recrystallization (DRX) mechanisms of Al-Zn-Mg-Cu alloys with different initial grain sizes. The microstructures obtained under various deformation conditions were analyzed. The results show that decreasing the initial grain size enhances both the peak stress and the activation energy for thermal deformation. Meanwhile, the dynamic recrystallization mechanism varies depending on the initial grain size. Continuous dynamic recrystallization (CDRX) is the primary DRX nucleation mode for coarse-grained alloys. Nonetheless, discontinuous dynamic recrystallization (DDRX) is predominant for alloys with fine grains.

İndüksiyonla sıcak işlemin Si3N4 ve grafen takviyeli Al6061 matrisli kompozitlerin mekanik ve tribolojik özelliklerine olan etkisi

Yapılan bu çalışmada indüksiyonla sıcak presleme ve toz metalürjisi yöntemleri ile Al6061 matrisli Si3N4 (ağırlıkça %1-12) ve grafen (ağırlıkça %0,15-0,45) takviyeli kompozitler üretilmiştir. Üretilen kompozit malzemelerin yoğunluğu, sertliği, basma dayanımı, aşınma direnci, mikroyapısı ve faz yapısı sırasıyla incelenmiştir. Yapılan testler sonucunda en yoğun mikroyapı, en iyi mekanik ve tribolojik özellikler Al6061-%9Si3N4-%0.15grafen kompozit yapıda elde edilmiştir. Yürütülen ısıl işlem çalışmaları neticesinde ise; sinterleme sonrası indüksiyonla sıcak preslenmiş numunelerin mekanik ve tribolojik özelliklerinin yalnızca sinterlenmiş kompozitlere kıyasla ~%37’ye varan oranlarda iyileştiği tespit edilmiştir.