Hardness Evolution Research Articles

Cell structure and hardness evolutions of TPU foamed sheets with high hardness via a temperature rising foaming process

The foams based on TPU with high hardness were prepared by temperature rising foaming. The effects of hardness on thermal behavior, mechanical and rheological properties, gas solubility and diffusivity of TPU were discussed. It was found that TPU with higher hardness have lower CO2 solubility and smaller diffusivity. TPU foamed sheets with various expansion ratio and cellular morphology were fabricated using different foaming parameters. It was easier to prepare TPU foams with low density for TPU with higher hardness. At suitable foaming temperatures, foams with similar density but different cell sizes could be prepared by altering saturation pressures. Finally, the hardness of the foamed samples was systematically compared. It was demonstrated that the hardness of TPU foams was affected by foam density, resin hardness and cell structure.

Zirconia-based abradable coatings fabricated on single-crystal superalloy: Microstructure, residual stress and mechanical properties

Thermal sprayed ZrO2-based abradable coatings have shown great advantages in blade/shroud clearance control systems of aero-engine turbine components due to their good high-temperature stability and abradability. Dysprosia-stabilized-zirconia (DySZ) based Abradable Coating were deposited on the Ni-based single-crystal superalloy via atmospheric plasma spraying technique. Microstructure evolution behaviors of the ZrO2-based abradable coating and the substrate were examined after 1100 ℃ thermal cycling. Besides, variation of the residual stress of the top layer was measured by Raman spectroscopy. Nanoindentation tests were conducted on the polished cross-section samples to evaluate Young's modulus and hardness evolution behavior. Results indicated that the DySZ top layer exhibits superior phase stability and good thermal shock resistance during thermal cycling. Thermally Grown Oxide (TGO) layer, Inter-Diffusion Zone (IDZ), and Second Reaction Zone (SRZ) was detected with the prolongation of the heat treatment time. Correlation between the microstructure and residual stress, hardness, Young's modulus of the coating was discussed. This study aims to further understand the relationship between the coating evolution behavior and the service time.

Evolution of Microstructure and Hardness of the Nitrided Zone during Plasma Nitriding of High-Alloy Tool Steel

Plasma nitriding is widely used in various industrial applications to improve surface hardness and wear properties. Especially for tool steels, it is also used to improve the support and adhesion of diamond-like carbon (DLC) coatings. The properties of the nitrided zone produced by plasma nitriding are influenced by the applied process parameter, in particular temperature and time. However, for high-alloy tool steels, a deeper understanding of the underlying diffusion processes of the nitrogen and the interaction with the existing microstructure, as well as the effects on the case depth is still lacking. Therefore, in this study, specimens of high-alloy tool steel X153CrMoV12 were plasma nitrided at varying temperatures (480 °C, 520 °C, 560 °C) and treatment times (2 h, 4 h, 16 h). The resulting nitrided zones were investigated by optical and scanning electron microscopy (OM and SEM), depth-dependent glow discharge optical emission spectroscopy (GDOES), X-ray diffraction (XRD), and hardness measurements to characterize their microstructure, chemical composition, and hardness depending on the process parameters. The distribution of carbides (M7C3), e.g., chromium carbides, affects the diffusion of the nitrogen and the layer growth. An increase of temperature and duration leads to an increased layer thickness. The composition of the compound layer is, e.g., influenced by the process parameters: ε nitrides (Fe2–3N) occurred preferentially at lower temperatures, while γ′ nitrides (Fe4N) appeared mostly at higher temperatures. In order to investigate the influence of the carbides of the high-alloy tool steel on the nitriding process, a new methodology was developed by means of finite element analysis (FE), which makes it possible to analyze this influence on the development of the nitrogen concentration profile. This methodology makes it possible for the first time to map the heterogeneous nitrogen evolution and distribution.

Microstructure and hardness evolution of ERNiCrMo-3 deposited metal during aging at 750 °C

Microstructure and hardness evolution of ERNiCrMo-3 deposited metal during aging at 750 °C

Microstructural and hardness evolution of additively manufactured Al–Si–Cu alloy processed by high-pressure torsion

Nanostructured Al-9%Si-3%Cu alloy was achieved by direct metal laser sintering (DMLS) and then processed using high-pressure torsion (HPT) processing, which resulted in considerable grain refinement down to 60 nm associated with a substantial dislocation density up 6.2 × 1014 m−2 and a significant reduction in the porosity. Hardness measurements across the horizontal and vertical cross sections showed an improvement in the strength homogeneity for processed samples after 10 turns of HPT processing. These results indicate that a controllable ultrafine-grained microstructure can be achieved by employing additive manufacturing, followed by effective severe plastic deformation processing.

Numerical and experimental validation of gas metal arc welding on AISI 441 ferritic stainless steel through mechanical and microstructural analysis

Residual stresses and strains, distortions, heat-affected zone (HAZ), grain size changes and hardness variation during gas metal arc welding (GMAW), are fundamental aspects to study and control during welding processes. For this reason, numerical simulations of the welding processes represent the more frequently used tool to better analyse the several aspects characterizing this joining process with the aim to reduce lead time and production costs. In the present study, an uncoupled 3D thermo-mechanical analysis was carried out by two commercial finite element method (FEM) software to model an experimental single bead GMAW of AISI 441 at different processes set-up. The experimental HAZ and measured temperatures were used to calibrate the heat source of both the used numerical codes, then a validation phase was done to test the robustness of the two developed analytical procedures. One software was used to predict the residual stresses and strains and the distortions of the welded components, while in the second software, a user routine was implemented, including a physical based model and the Hall-Petch (H-P) equation, to predict grain size change and hardness evolution, respectively. The results demonstrate that the predicted mechanical and microstructural aspects agree with those experimentally found showing the reliability of the two codes in predicting the thermal phenomena characterizing the HAZ during the analysed welding process.

Experimental and modeling investigations of the non-isothermal and isothermal precipitations in an Al-Cu-Mg-Zr alloy with various pre-precipitation microstructures

The complex precipitation evolutions of Al-Cu-Mg alloys during both non-isothermal and isothermal thermal processes have been found to work on their mechanical properties and electrical resistivity. Modeling of the precipitation kinetics, electrical resistivity and strength evolution is therefore essential for optimizing heat treatment and processing of these alloys. In this work, in situ electrical resistivity monitoring during both non-isothermal and isothermal thermal processes and microstructural characterizations were conducted on an Al-Cu-Mg-Zr alloy with different pre-precipitation microstructures to provide fundamental insights of precipitation behaviors. The results showed that precipitation behaviors of Al-Cu-Mg-Zr alloy, such as the dominant strengthening phase, were highly dependent on pre-precipitation microstructures and thermal history. A time–temperature-microstructure-properties map was established to unravel precipitation characteristics and their strengthening functions. The maximum hardness was indicated to be attributed to the combined presence of Guinier–Preston–Bagaryatsky (GPB) zones and fine S (Al2CuMg) phase. Further, in situ electrical resistivity was used as the main input data to develop an improved model based on the classical Kampmann and Wagner type numerical model (KWN model). This integrated model could not only reveal precipitation kinetics but also well predict hardness evolutions of the studied alloy during non-isothermal and isothermal processes.

Microstructure, Texture, and Hardness Evolution of Cold-Rolled High-Purity Ti Sheet During Annealing at 350 °C to 550 °C

Microstructure, Texture, and Hardness Evolution of Cold-Rolled High-Purity Ti Sheet During Annealing at 350 °C to 550 °C

Surface evolution of Al–Si–Cu alloy in a high frequent pulsing oxyacetylene combustion

To understand the surface evolution in unsteady thermal environment of diesel engine, piston Al–Si–Cu alloy was ablated by a high frequent pulsing carburizing oxyacetylene combustion. The tested samples displayed good correlation with the characteristics of some bench tested pistons. As the loading cycles increased, the roughness slightly declined first and then rose sharply. Hardness evolution, micro-morphology, element and phase analysis suggested the surface roughness was mainly controlled by the thermal stress induced defects. And in combination with thermodynamics, the source of Al in surface deposited rimous carbon was ascertained to be chemical reactions between carburizing combustion and the Al–Si–Cu alloy.

Effect of Ti addition on the thermal stability of nanocrystalline AZ61 Mg alloy

Nanostructured alloys possess exceptional desirable properties but suffer from low thermal stability, as a consequence of a high content of grain boundaries where the atoms are in non-equilibrium lattice positions. Here nanocrystalline Ti/AZ61 magnesium matrix composite (AZ61Mg-Ti) was annealed isothermally between 573 K and 723 K. Subsequently, the thermal stability was analyzed, taking nanocrystalline AZ61 alloy as the comparative object. After annealing at 723 K for 600 min, the average grain size of AZ61Mg-Ti was approximately 95 nm, much less than that for the annealed AZ61 alloy (~450 nm). And Ti particles with size of ~410 nm and nano scale Ti3Al particles with size of ~ 8 nm were uniformly distributed in magnesium matrix. The kinetics of magnesium grain growth for nanocrystalline AZ61Mg-Ti, was well interpreted by generalized parabolic grain growth model, D8−D08=kt. The activation energy (Eg) for grain growth was calculated to be 134 kJ/mol, being 42 kJ/mol higher than that for pure Mg. For Eg, the contribution rates of drag effect and pinning effect to improve thermal stability were calculated to be 62% and 38%, respectively. Hardness evolution of annealed samples was studied and with raising annealing temperature the downtrend for AZ61Mg-Ti was more gradual than for AZ61 alloy due to the effect of the non-thermal sensitive Ti particles and the restricted Mg grain growth. After annealing treatment at 723 K for 600 min, the hardness was 1.27 GPa, higher than that for the annealed AZ61 (1.13 GPa).

Effect of Shot Peening on the Surface Oxidation of P92 Steel in the Steam Environment at 600 °C

Abstract The effect of shot peening on oxidation behavior of P92 steel was investigated under the steam environment of 600 °C. Evolution of microstructure, hardness and residual stress under different air pressure of shot peening were discussed. On the shot peened surface, a stable hematite outer layer was detected by using scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) analysis. The increased oxidation resistance of hematite layer was ascribed to the increased outward diffusion of Cr and the decreased inward diffusion of oxygen. In addition, the role of residual stress in the oxygen diffusion was discussed.

Effect of nitrogen content on structural and mechanical properties of AlTiZrTaHf(-N) high entropy films deposited by reactive magnetron sputtering

There is a growing interest in the design of high entropy alloys due to their remarkable properties and applications in various fields such as aerospace, medical and automotive. AlTiTaZrHf(-N) high entropy metal-sublattice nitrides were deposited in various argon‑nitrogen gas mixtures on glass and silicon substrates. X-ray diffraction analyses reveal a transition from amorphous to an FCC single phase by increasing the nitrogen content. The films have compact or columnar morphology depending on the nitrogen flow rate. Energy dispersive spectroscopy analysis shows a decreasing of the matals content as the nitrogen flow rates ratio R N2 = N 2 /Ar + N 2 increases. XPS surface analysis reveal the formation of nitrides when the nitrogen is introduced. Evolution of hardness and Young's modulus are discussed and the maximum values are obtained for a flow rates ratio R N2 of 10% at 27.67 GPa and 205.56 GPa respectively. The same film reveals good tribological properties compared to other films. This work conclusively demonstrates that high entropy metal-sublattice nitrides can be generated in an efficient way with tunable properties. • Multicomponent AlTiTaZrHf(-N) deposited by reactive magnetron sputtering • Effect of nitrogen content on microstructure, mechanical properties and tribological performance studied • H and E are monitored by controlling the stoichiometric of N/Me.

Lap joining of aluminum 5052 to copper by optimum friction stir spot welding process

In the present study, lap joints of dissimilar 5052 aluminum alloy and pure copper were fabricated by friction stir spot welding process. The work was aimed to find simultaneous effect of parameters such as tool rotary speed (1000, 1500, and 2000 rpm) and dwell time (5, 10, and 15 s) on lap shear force (LSF), hardness, and microstructure evolution. Also, statistical models of the quality characteristics were developed to understand which parameter has dominant effect on quality characteristics. Research findings showed that to obtain sound joints with high lap shear strength, tool rotary speed of 1500 rpm and dwell time of 15 s should be selected. It provides sufficient heat input for mechanical interlocking and prevents the formation of coarse and thick intermetallic compounds (IMCs) in the stir zone. On the other hand, to achieve maximum hardness, 2000 rpm tool rotary speed should be chosen to provide enough heat for formation of intermetallic compound and 10 s dwell time should be used to prevent enough time for microstructure refining. Moreover, from the statistical analyses, it was found that dwell time and tool speed are the significant factors for lap shear strength and hardness, respectively. In order to attain simultaneous maximum strength and hardness, tool speed of 1630 rpm and dwell time of 14 s should be used. In such condition, lap shear strength of 1980 N and hardness of 78 V are achieved with desirability of 86%.

Hard gluon evolution in the last stage of the bottom-up thermalization

The study of how fast thermalization in heavy ion collisions occurs has been one of the central topics in the heavy ion community. In the weak coupling picture this thermalization occurs from ‘the bottom up’: high energy partons, formed early in the collision, radiate low energy gluons which then proceed to equilibrate among themselves, forming a thermal bath that brings the high energy sector to equilibrium. In this scheme we apply a model on parton energy loss to discuss the effects of medium expansion on the thermalization problem and estimate the average transverse momentum diffusivity for thermalization in a Bjorken expanding medium.

Correction to: Quantitative Nanostructure and Hardness Evolution in Duplex Stainless Steels: Under Real Low-Temperature Service Conditions

Correction to: Quantitative Nanostructure and Hardness Evolution in Duplex Stainless Steels: Under Real Low-Temperature Service Conditions

Surface integrity of new dry-electropolishing technology on WC-Co cemented carbides

This study is focused on WC-Co dry-electropolished by DryLyte® technology that allows to obtain corrosion-free surfaces with a roughness below 9 nm. The main goal behind this research is to investigate the surface integrity trying to correlate the remanent microstructure after different dry-electropolishing times as a function of the hardness and elastic modulus evolution though massive nanoindentation. The quality of the surface has been evaluated by using advanced characterization techniques and the mechanical response treated by using the statistical methodology proposed by Ulm and Constantinides. To sum up, a close correlation is observed between the residual microstructure and the surface integrity in terms of hardness and elastic modulus maps.

The UV/Optical Peak and X-Ray Brightening in TDE Candidate AT 2019azh: A Case of Stream–Stream Collision and Delayed Accretion

Abstract We present and analyze the optical/UV and X-ray observations of a nearby tidal disruption event (TDE) candidate, AT 2019azh, from ∼30 days before to ∼400 days after its early optical peak. The X-rays show a late brightening by a factor of ∼30–100 around 200 days after discovery, while the UV/opticals continuously decayed. The early X-rays show two flaring episodes of variation, temporally uncorrelated with the early UV/opticals. We found a clear sign of X-ray hardness evolution; i.e., the source is harder at early times and becomes softer as it brightens later. The drastically different temporal behaviors in X-rays and UV/opticals suggest that the two bands are physically distinct emission components and probably arise from different locations. These properties argue against the reprocessing of X-rays by any outflow as the origin of the UV/optical peak. The full data are best explained by a two-process scenario, in which the UV/optical peak is produced by the debris stream–stream collisions during the circularization phase; some shocked gas with low angular momentum forms an early, low-mass “precursor” accretion disk that emits the early X-rays. The major body of the disk is formed after the circularization finishes, whose enhanced accretion rate produces the late X-ray brightening. Event AT 2019azh is a strong case of a TDE whose emission signatures of stream–stream collision and delayed accretion are both identified.

Effect of nickel addition on enhancing nano-structuring and suppressing TRIP effect in Fe40Mn40Co10Cr10 high entropy alloy during high-pressure torsion

The present work unravels the effect of nickel (Ni) addition on the deformation mechanism and hardness evolution in a Fe40Mn40Co10Cr10 high entropy alloy (HEA) during high-pressure torsion (HPT) processing. For this purpose, two variants of the high entropy Cantor alloy, with compositions (atomic%) Fe40Mn40Co10Cr10 (Ni0 alloy) and Fe35Mn35Co10Cr10Ni10 (Ni10 alloy) were selected. The study revealed a transition in the predominant plasticity mechanism with addition of Ni from TRIP in Ni0 to dislocation slip in Ni10 alloy. Such transition of plasticity mechanism was the direct consequence of an increase in the free energy of phase transformation, ΔGγ→ε towards a more positive value with Ni addition. Interestingly, the Ni10 alloy showed a greater extent of nano-structuring than the Ni0 alloy with nearly three-fold refined grain sizes, that is, lesser than 30 nm in Ni10 alloy and ∼90 nm in Ni0 alloy. Furthermore, a 3–4 times higher dislocation density was observed in the FCC phase of the Ni10 alloy compared to that in the transformed HCP phase in the Ni0 alloy for any given HPT processing conditions. These differences in mechanism(s) of deformation and the extent of nano-structuring manifested as a greater ability of Ni added Ni10 alloy to harden itself during HPT. The present study suggests that a large fraction of hard HCP phase originating from TRIP effect in the Ni0 alloy has a lower hardening ability than the high dislocation density and nano-structuring in the Ni10 alloy.

Fabrication of hybrid nanocrystalline Al–Ti alloys by mechanical bonding through high-pressure torsion

This study demonstrates an approach of utilizing high-pressure torsion (HPT) to fabricate a novel hybrid material by the direct bonding of Al and Ti disks at room temperature under a compressive pressure of 6.0 GPa and with increasing numbers of HPT turns up to 50. Detailed structural observations revealed the formation of a multi-layered nanostructure in the edge regions of the disks with a grain size of ∼30 nm. X-ray diffraction (XRD) and selected area electron diffraction (SAED) confirmed the presence of three intermetallic compounds, AlTi, Al3Ti and Ti3Al, in the layered structures. Processing by HPT led to the formation of a hybrid nanocomposite with exceptional hardness (over 300 Hv) in the edge regions of the disks. Special emphasis was placed on understanding the evolution of hardness in the hybrid material. The investigation demonstrates a significant opportunity for using HPT processing to deepen the knowledge on diffusion bonding and mechanical joining technologies as well as for fabricating new and valuable hybrid nanomaterials.

Evolution of microstructure and hardness in shell moulded impeller casting

ABSTRACT To remain competitive in this growing field of the manufacturing industry, there is a need to reduce the lead times in the development of a component. The virtual simulation environment tool can be utilised for minimising production time as well as assure defect-free casting. This technique is based on heat transfer and volumetric calculations for prediction of possible defects. In this paper, analysis of automobile impeller casting is explored. The modelling of the casting and feeding system is done using the CATIA software. The CAD model of the impeller is imported into the simulation environment for solidification simulation. The simulation is performed using SolidCAST software which is based on the Finite Difference Method. The simulations are performed to ensure proper feeding for achieving sound casting. The melting trials are performed in jobbing foundry. The hardness and microstructure analysis of simulated and experimental casting is performed so as to correlate. The section thickness and cooling rates in casting were analysed and used for formulating hardness and microstructure in the experimental castings. The statistical predictions based on simulated and experimental results are presented for formulating Brinell hardness and amount of pearlite phase in particular section of shell moulded ductile iron casting.