Effect Of Initial Microstructure Research Articles

Effect of Initial Microstructure on the Temperature Dependence of the Flow Stress and Deformation Microstructure under Uniaxial Compression of Ti-407

In this study, the influence of initial microstructure and deformation temperature on the flow stress behavior and microstructural evolution of TIMETAL®407 (Ti-407) alloy are investigated. For this purpose, compression cylinders were β-annealed at 940 °C and then cooled to room temperature using furnace cooling, static air, and water quenching to promote three initial microstructures with different α lath thicknesses. The annealed cylinders were compressed isothermally in the range of 750 °C to 910 °C at a constant crosshead speed of 0.05 mm/s up to an engineering strain of −0.8. The resulting stress–strain curves are discussed in terms of the morphology and distribution of the α and β phases. It was found that flow stress is inversely proportional to deformation temperature for all initial microstructures. At the lowest temperatures, compressive yield strength was higher in water-quenched and air-cooled samples than in furnace-cooled specimens, suggesting that the acicular α-phase morphology obtained by rapid cooling could enhance mechanical strength by hindering dislocation motion. Two high-temperature flow regimes were determined based on the shape of the flow stress curves, indicating microstructural changes occurring during deformation. At higher temperatures, the effect of the initial microstructure is negligible as the primary α phase is transformed to the β phase at around 850 °C irrespective of the initial α-lath thickness.

The effect of thermomechanical welding on the microstructure and mechanical properties of S700MC steel welds

Grain refinement by plastic deformation during conventional TIG welding can help to compensate for the loss of mechanical properties of welded joints. The thermomechanical welding (TMW) tests were performed on S700MC steel with different combinations of TIG arc energy and high frequency hammering over three target cooling times (t8/5 = 5s, 15s, and 25s). Additionally, the effect of initial microstructures on the weld joint quality was analysed by testing three materials conditions: hot-rolled (as-received) and cold-rolled with 10% and 30% thickness reductions, respectively. The effects of plastic deformation and the mechanical vibration on the grain refinement were studied separately. Optical microscopy, electron backscattered diffraction, and Vickers hardness were used to characterise the weld microstructure heterogeneity. The weld width and depth and the mean grain size were correlated as the function of cooling time t8/5. The results show that the weld dimensions increase with increasing the t8/5. The weld microstructures transformed from the mixed martensite and bainite into mixed ferrite and bainite with increasing the t8/5 time, and the related mean grain size increased gradually. The TMW welds exhibit smaller grains compared to TIG welds due to the coupled effects of mechanical vibration and plastic deformation. The mechanical vibration contributes to weld metal homogenisation, accelerating TiN precipitation in the fusion zone. The proposed TMW process can refine the weld microstructure of S700MC steel, enhancing its mechanical properties.

Effects of Ultra-Low Temperatures on the Mechanical Properties and Microstructure Evolution of a Ni-Co-Based Superalloy Thin Sheet during Micro-Tensile Deformation.

With the development of product miniaturization in aerospace, the nuclear industry, and other fields, Ni-Co-based superalloys with excellent overall properties have become key materials for micro components in these fields. In the microforming field, size effects significantly impact the mechanical properties and plastic deformation behavior of materials. In this paper, micro-tensile experiments at room temperature and an ultra-low temperature were carried out to study the effects of initial microstructure and deformation temperature on the deformation behavior of Ni-Co-based superalloy thin sheets. The results show that as the ratio of specimen thickness to grain size (t/d) decreased from 8.6 to 2.4, the tensile strength σb decreased from 1221 MPa to 1090 MPa, the yield strength σs decreased from 793 MPa to 622 MPa, and the elongation decreased from 0.26 to 0.21 at room temperature. When t/d decreased from 8.6 to 2.4, σb decreased from 1458 MPa to 1132 MPa, σs decreased from 917 MPa to 730 MPa, and the elongation decreased from 0.31 to 0.28 at ultra-low temperatures. When t/d decreased from 8.6 to 2.4, the surface roughness of the specimen increased from 0.769 to 0.890 at room temperature and increased from 0.648 to 0.809 at ultra-low temperatures. During the microplastic deformation process of Ni-Co-based superalloy thin sheets, the coupled effects of surface roughening caused by free surface grains and hindered dislocation movement induced by grain boundary resulted in strain localization, which caused fracture failure of Ni-Co-based superalloy thin sheets.

Effect of initial microstructure on phase transformation and mechanical properties of Ti–3Al–5Mo–4Cr–2Zr–1Fe alloy

Phase transformation, microstructure evolution, and mechanical properties of Ti–3Al–5Mo–4Cr–2Zr–1Fe alloy were investigated during a continuous heating process. Three microstructures, specifically lath, duplex, and lamellar structures, were examined. The activation energies for phase transition in these structures were measured as 277, 220, and 193 kJ mol−1, respectively. The phase transition follows: For the lath structure, β transforms into αacicular (550–660°C), αacicular converts to β (660–785°C), αlath does to β (660–850°C); For the duplex structure, β transforms into αacicular (545–660°C), αacicular converts to β (660–770°C), αlath does to β (660–850°C); For the lamellar structure, β transforms into αsecondary (560–615°C), αsecondary converts to β (615–705°C), αlamellar dose to β (615–850°C). The lath and duplex structures exhibited favorable comprehensive properties compared to lamellar microstructure.

Effects of Initial Microstructure and Induction Heating Cycle on the Microstructure and Torsional Fatigue Performance of a Steel Containing 0.6 wt pct Carbon

Effects of Initial Microstructure and Induction Heating Cycle on the Microstructure and Torsional Fatigue Performance of a Steel Containing 0.6 wt pct Carbon

Effect of initial microstructures on microstructures and properties of extruded AZ31 alloy

The raw materials for extruded preparing magnesium alloy tubes were electromagnetic stirring (EMS) AZ31 magnesium alloy billets and conventional casting (CC) AZ31 magnesium alloy billets. According to the findings, the mechanical properties of the EMS extrusion tubes were far superior to those of the CC extrusion tubes. The key explanation was that the samples of EMS billet had variable initial grain sizes and twin boundaries, which provide additional nucleation sites for DRX nucleation during the extrusion process. With the increase of extrusion temperature and extrusion ratio, the elongation of the tube is further improved. During the extrusion process, the recrystallization mechanism changed from continuous dynamic recrystallization (CDRX) to discontinuous dynamic recrystallization (DDRX).

Microstructural and mechanical property evolution of Ar9+ ion irradiated Zr-based alloys – effect of initial microstructure and alloying addition

This work endeavours to bring out the role of initial microstructural features and alloying additions in the irradiation response of a material. Three Zr-based binary alloys, namely Zr-0.17 wt.% O, Zr-0.33 wt.% Sn and Zr-2.5 wt.% Nb, with starting microstructures exemplifying annealing, hot-extrusion and cold-pilgering operations, respectively, were selected. The alloys were irradiated at room temperature using 315 keV energy Ar9+ heavy ion. Depth-dependent microstructural evolution of the alloys upon irradiation was assessed through positron annihilation Doppler broadening spectroscopy and grazing incidence X-ray diffraction, while nanoindentation probed the mechanical behaviour. Irradiation responses of the alloys garnered in terms of S-parameter, coherently scattering domain size, microstrain, dislocation density and hardness were compared. The observed differences were rationalized on the basis of (i) starting microstructural attributes of the alloys, which posed as sinks to the irradiation-induced point defects, and (ii) impact of alloying additions on diffusion and annihilation of these defects.

Effect of Initial Microstructure on the High-Temperature Formability of STS 321 Alloy Using a Dynamic Material Model

General austenitic stainless steel has a problem with intergranular corrosion due to volatilizing chromium, which forms chromium carbide in a high temperature environment. By adding titanium as an alloying element, STS 321 stainless steel has excellent creep resistance and intergranular corrosion resistance at high temperatures, because the formation of chromium carbide is suppressed. It is important to find the optimal process conditions for STS 321 stainless steel used in the aerospace field, because high temperature processing is mainly applied, and defects or inhomogeneity of materials that occur during high temperature processing lowers the yield of products. In this study, to investigate the effect of the initial microstructure on the high-temperature deformation behavior of STS 321 stainless steel, a high-temperature compression test was performed on two types of STS321 alloys with different initial microstructures. The temperature range was set at 50°C intervals from 800°C to 1100°C, and the strain rate was set at 10-1/sec intervals from 1 × 100/ sec to 1 × 10-3/sec. Based on the experimental results, the thermal activation energy, which differed depending on differences in the initial microstructure, was calculated. In addition, by deriving flow stress and processing maps, the difference in energy dissipation efficiency depending on temperature and strain rate was explained, along with the initial microstructure and high-temperature deformation mechanism.

Effects of initial microstructure on creep properties of Mg-8Gd-2Y-0.5Zr alloys

Effects of initial microstructure on creep properties of Mg-8Gd-2Y-0.5Zr alloys

Effect of Initial Microstructure on the Plastic Deformation Bonding of Ti64 and Ti17

Effect of Initial Microstructure on the Plastic Deformation Bonding of Ti64 and Ti17

Effects of Initial Microstructure on the Low-Temperature Plasma Nitriding of Ferritic Stainless Steel

AISI 430 ferritic stainless steel with different initial microstructures was low-temperature plasma nitrided to improve its hardness and wear resistance in the present investigation. The microstructure and properties of the low-temperature nitrided layers on stainless steel with different initial microstructures were studied by an optical microscope, X-ray diffractometer, scanning electron microscope, microhardness tester, pin-on-disk tribometer, and electrochemical workstation. The results show that the low-temperature nitrided layer characteristics of ferritic stainless steel are highly initial-microstructure dependent. For the ferritic stainless steel with a solid solution and annealing treatment, it had the best performance after low-temperature plasma nitriding when compared with the stainless steel with other initial microstructures. The nitrided layer thickness reached 34 μm after nitriding at 450 °C for 8 h. The phase composition of the low-temperature-nitrided layer consisted mainly of a nitrogen “expanded” α phase (αN) and iron nitrides (Fe4N and Fe2–3N). The hardness of the nitrided layer could reach up to 1832 HV0.1. Moreover, the wear and corrosion resistance of the nitrided layer on the solution and annealing treated ferritic stainless steel could be improved at the same time.

Microstructure-sensitive modeling of high temperature creep in grade-91 alloy

Predicting the effects of microstructure on high-temperature creep responses of steel components is critical to minimize the risks of failure and maximize economic viability in the energy sector. In this work, a recently developed advanced mechanistic constitutive model is employed to study the effect of microstructure on the creep responses and to rationalize experimentally reported variability in the performances of grade-91 alloy. Hundreds of experimental creep tests from the literature are used to assess the predictability of the model. The model proposed is shown to accurately predict the steady-state creep rates and also the less commonly considered, yet important, primary-to-secondary transients for a wide range of creep conditions. Further, the model is capable of extrapolating the creep response of grade 91 alloy even outside of the calibration regime. Using this model, the roles of initial microstructure described in terms of grain size, dislocation density, and precipitate content, on the creep responses are investigated. The effect of initial microstructure on the steady-state creep rates and creep-strain is found to vary with stress and temperature. Grain size plays a significant role in the low-stress creep, where the diffusional creep is dominant. On the other hand, the effects of dislocation densities and precipitate content are significant in the dislocation-plasticity-dominated high-stress and temperature regimes. Furthermore, by comparing model predictions against a large experimental creep database, it is found that variability in the creep responses can be rationalized on the basis of differences in the initial microstructure. Overall, this work provides a robust pathway for microstructure-aware engineering design, verification, and validation of metallic components for energy applications.

Grain size-dependent phase-specific deformation mechanisms of the Fe50Mn30Co10Cr10 high entropy alloy

The present work reports the effect of initial microstructures (i.e., the material annealed at 600 °C (A600) with the fine grain single FCC phase vs. the material annealed at 900 °C (A900) with the coarse grain FCC/HCP dual phase) on deformation mechanisms, damage resistance, and mechanical properties of the Fe50Mn30Co10Cr10 HEA. The strength of A600 is higher than A900, and the ductility of both materials is similar with the total elongation exceeding 50%. A900 shows a higher strain hardening rate than A600 below 0.2 true strain, which could be attributed to simultaneous deformation accommodation from the FCC/HCP dual phase. The FCC grains mainly exhibit deformation-induced HCP phase transformation while the HCP grains show multiple deformation mechanisms, i.e., various slip modes (Shockley partial dislocations, perfect dislocations, extended dislocations, and dislocations present on prismatic planes), the HCP to FCC reverse transformation, the formation of kink bands. The strain hardening rate of both materials is similar above 0.2 true strain, which could be related to higher TRIP kinetics of A600 than A900. The A600 shows the refinement of the crack size due to its fine size of grains and HCP phase. The superior damage resistance could lead to the large ductility of A600 even in the presence of the non-recrystallized areas in its initial microstructure. The present work could provide microstructure design solutions for metastable HEAs with superior strength-ductility combination and damage resistance.

Effect of intercritical heat treatment process on the microstructure and mechanical properties of low alloy structural steels with residual element tin

ABSTRACT The intercritical heat treatment process is considered a novel technology to solve the mismatch of strength and toughness of low alloy steel containing residual elements. In the present study, the effects of initial microstructure and intercritical quenching temperature on microstructural morphology, mechanical properties and fracture appearance of the experimental tin-bearing steel have been investigated. The results show that, under the same intercritical quenching and tempering (IQ-T) heat treatment parameters, the initial microstructures of bainite and ferrite (B-F) and complete martensite (M) yield different ferrite morphologies, block and strip-like ferrite, respectively. It is found that after IQ-T process, the tensile strength of the steel containing 0.09% tin with B-F as initial microstructure is 1061 MPa, but the impact energy value is only 26 J; while the steel with M has achieved the combined properties of high strength and excellent toughness, and the optimal intercritical quenching temperature is 770°C.

Effects of initial microstructure on the aging behavior and subsequent mechanical properties of Ti–Nb–O titanium alloy

Effects of initial microstructure on the aging behavior and subsequent mechanical properties of Ti–Nb–O titanium alloy

Correction to: Effect of Initial Microstructure and Strain Rate on the Hot Deformation Behavior of ATI425 Alloy in Two-Phase α/β Region

Correction to: Effect of Initial Microstructure and Strain Rate on the Hot Deformation Behavior of ATI425 Alloy in Two-Phase α/β Region

Effect of Initial Microstructure and Strain Rate on the Hot Deformation Behavior of ATI425 Alloy in Two-Phase α/β Region

Effect of Initial Microstructure and Strain Rate on the Hot Deformation Behavior of ATI425 Alloy in Two-Phase α/β Region

Cutting edge radius effect on the surface integrity of orthogonal turned aluminium alloy Al6082 with different initial microstructure

In the present study, the combined effect of initial microstructure and relative tool sharpness (RTS) on the surface integrity of aluminium(Al6082) alloy has been investigated. Orthogonal turning is carried out on as-received and heat-treated specimen with group of edge radiused tools. Surface roughness and micro hardness have been evaluated with respect to number of turns for varying RTS value. Results indicate that the workpiece material adhesion on the tool has significantly influenced the surface roughness. In addition, below the critical RTS, the surface integrity is greatly influenced by the grain size of the material.

Microstructure and Mechanical Properties of Dual‐Phase Steels by Combining Adjusted Initial Microstructures and Severe Plastic Deformation

Herein, the effects of initial microstructure in combination with the severe plastic deformation on the developed microstructures and mechanical properties of dual‐phase (DP) steels are investigated. DP steels are produced by an intercritical annealing from the preliminarily heat‐treated samples with different initial microstructures. The constrained groove pressing (CGP) process is additionally applied before the final intercritical annealing step. It is found that the martensitic and tempered martensitic microstructures lead to DP steels with a good balance of strength and elongation because of finer and more uniformly dispersed martensitic islands. The ferrite/pearlite banded initial microstructure is not a proper choice for intercritical annealing as all mechanical properties become worse. The CGP can be employed before intercritical annealing for refining microstructure and enhancing damage tolerance of DP steels. Nevertheless, the impacts of the CGP process on the resulted strength of DP steels are obviously different depending on the initial microstructures. The amounts, sizes, and distributions of dimples and cleavage facets on the fracture surfaces of DP steels correlate well with the corresponding microstructures and tensile characteristics.

Effect of initial microstructure on graphitization behavior of Fe–0.55C–2.3Si steel

In this study, the effect of the initial microstructure (i.e., ferrite + pearlite or martensite) on the graphitization behavior and microstructural evolution during heat treatment of a hot-rolled medium-carbon, high-silicon steel (Fe–0.55C–2.3Si) is investigated. When a sample consists of ferrite and pearlite, its microstructure gradually changes to ferrite and graphite during heat treatment via the decomposition of pearlite and the formation of graphite particles. In the sample with a martensite microstructure, the phase transformation occurs in the following step: martensite → ferrite + cementite → ferrite + graphite. Although the graphitization process of the martensite sample is more complex than that of the ferrite + pearlite sample, the graphitization rate is substantially faster in the former owing to more abundant grain boundaries and triple junctions that act as nucleation sites for graphite. When the initial microstructure changes from ferrite + pearlite to martensite, the graphite completion time significantly reduces from 16 to 2 h at 650 °C and from 6 to 0.5 h at 700 °C. After complete graphitization, the average size and number density of graphites in the martensite sample are respectively smaller and higher than those in the ferrite + pearlite sample. The rate of hardness decrease (i.e., material softening) during heat treatment is also faster in the martensite sample. These results demonstrate that changing the initial microstructure from ferrite + pearlite to martensite is an effective means to accelerate the graphitization behavior and acquire a graphitized steel with uniformly distributed fine graphite particles.