Room Temperature Tensile Properties Research Articles

Research on the dislocation differences of CoCrFeMnNi with different local chemical orders during room temperature tensile test

More and more evidences show that local chemical order (LCO) plays an important role on the properties of materials. In this work, we for the first time clarified the effect of LCO on the room-temperature tensile properties of CoCrFeMnNi using hybrid molecular dynamics and Monte Carlo simulations. The results showed that three different chemical orderings (Co-Fe, Mn-Ni and Cr-rich ordering) were observed in the microstructure after MC cycles, which was consistent with the experimental results. Amongst them, the dislocations preferred to form in the Cr-rich region which has different lattice constant from other phases. The distribution and size of the Cr-rich region affected the density and distribution of the dislocations. These dislocation characteristics determined the mechanical properties of CoCrFeMnNi, so the mechanical properties can be controlled by adjusting the LCO.

Effect of Gradient Layer Number on Microstructure and Property of Laser Deposition TA15/Ti2AlNb Transition Zone

3 numerical models of laser deposited TA15/Ti2AlNb gradient composite structure were established to simulate the temperature variation of gradient composite structures with different gradient layers in different regions. Then TA15/Ti2AlNb gradient composite structures with different gradient layers were prepared by laser deposition technology. The microstructure, room-temperature tensile properties and microhardness of the deposited samples were observed by optical microscope, tensile testing machine, scanning electron microscope and microhardness tester. The results showed that as the number of gradient layers increased, the temperature in the deposition process of the transition zone increased, while the microstructure difference in the transition zone decreased gradually. As the number of transition layers increased, the tensile strength decreased, but the elongation after fracture increased. All the fracture locations were in the transition zone, and with the increasing of gradient layers, the fracture location gradually shifted to the Ti2AlNb side. The microhardness of the transition zone increased with the increasing of gradient layers. This study will provide reference for the optimization design of TA15/Ti2AlNb gradient composite structure.

Microstructure and Tensile Properties of a Cast Eutectic Al–Si–Cu Alloy Modified by Zr and V

Minor Zr and V were added individually and jointly to Al–12.5Si–1Cu alloy to develop heat-resistant aluminum alloys. The as-cast microstructure, room temperature, and high temperature (350 °C) tensile properties and the strengthening mechanism of the modified alloys were investigated. The results show that the rod-like (Al, Si)3Zr and hexagonal (Si, Al)2V precipitates are respectively found in the alloys with individually added Zr or V. At the same time, they were transformed into (Al, Si)3(Zr, V) and (Si, Al)2(V, Zr) when Zr and V were added together. Individually added Zr or V could change the eutectic silicon aspect ratio, but the largest effect was recorded for the combined addition 0.3 wt% Zr + 0.4 wt% V. The addition of Zr and V had no significant impact on the room temperature tensile strength of the alloys but improved the yield strength. Individual additions of Zr and V caused negligible improvements in high-temperature tensile strength of alloys tested. In contrast, the combined Zr + V additions resulted in the substantial improvement with tensile strength at 350 °C reaching 79.4 MPa, i.e. 89% higher than the base alloy. The analysis shows that the increase of eutectic silicon aspect ratio and the solution strengthening of trace V in eutectic silicon is the leading cause of improving high-temperature tensile strength. The brittle, blocky primary silicon, coarse rod-like (Al, Si)3(Zr, V), and hexagonal (Si, Al)2(V, Zr) precipitates are detrimental to high-temperature properties.

High-Density Deformation Nanotwin Further Improved Tensile Strength of Polycrystalline γ-TiAl-Based Intermetallic Alloy

Strengthening of TiAl-based intermetallic alloy is vital for its broader application, however, microstructural refinement through conventional processes is difficult to further strengthen this intermetallic alloy. Although high-density deformation nanotwin is expected to effectively strengthen it, there is still lack of in-depth understanding about the strengthening mechanism of high-density deformation nanotwin in TiAl-based alloy. Herein the microstructures, room-temperature (RT) tensile properties, tensile fracture behavior, and deformation mechanism of the Ti-45.5Al-4Cr-2.5Nb (at.%) master alloy (M. A.) as well as its continuous casting (C. C.) alloy and the heat-treated alloys were systematically investigated. After the C. C. alloy was annealed at 1250 °C for 2 hours, the volume fraction of (B2+γ) coupled structures in the original grains reached the minimum, the interlamellar spacing was markedly refined; besides, substantial Shockley partial dislocations and stacking faults were generated in γ phase. During RT tension, both the dominant deformation mechanisms of the M. A. and C. C. alloy were dislocation slip, while that of the 2h heat-treated alloy was changed into deformation twinning. High-density deformation nanotwins were generated in the γ phase (especially the γ lamellae) of the 2h heat-treated alloy, which improved the tensile strength of the M. A. by 79%. High-density deformation nanotwins can further strengthen TiAl-based alloy to a large extent, which is mainly attributed to the fact that their batch-to-batch generation in the polycrystalline TiAl-based alloy during tension could considerably relief the stress concentration in addition to effectively improving the work-hardening rate, thus making the work-hardening rate keeping stable.

In-Vitro Degradation of Hollow Silica Reinforced Magnesium Syntactic Foams in Different Simulated Body Fluids for Biomedical Applications

This article reports the mechanical and biocorrosion behaviour of hollow silica nanosphere (SiO2) reinforced (0.5–2 vol.%) magnesium (Mg) syntactic foams. Room temperature tensile properties’ characterization suggests that the increased addition of hollow silica nanospheres resulted in a progressive increase in tensile yield strength (TYS) and ultimate tensile strength (UTS) with Mg-2 vol.% SiO2 exhibiting a maximum TYS of 167 MPa and a UTS of 217 MPa. The degradation behaviour of the developed Mg-SiO2 syntactic foams in four different simulated body fluids (SBFs): artificial blood plasma solution (ABPS), phosphate-buffered saline solution (PBS), artificial saliva solution (ASS) and Hanks’ balanced saline solution (HBSS) was investigated by using potentiodynamic polarization studies. Results indicate that corrosion resistance of the Mg-SiO2 syntactic foam decreases with increasing chloride ion concentration of the SBF. Mg-1.0 vol.% SiO2 displayed the best corrosion response and its corrosion susceptibility pertaining to corrosion rate and polarisation curves in different SBF solutions can be ranked in the following order: ABPS > PBS > HBSS > ASS. The surface microstructure demonstrated the presence of a better passivated layer on the syntactic foams compared to pure Mg. The observed increase in corrosion resistance is correlated with intrinsic changes in microstructure due to the presence of hollow silica nanospheres. Further, the effect of corrosive environment on the degradation behaviour of Mg has been elucidated.

Designing thermal annealing to control mechanical performance of thermoplastic polyurethane elastomers

The use of thermoplastic polyurethane (TPU) films as a lightweight elastomer has grown continuously over the years due to their good mechanical properties and excellent chemical and corrosion resistance. Yet, the high-temperature mechanical performance of TPU elastomers needs to be improved for extending their application as metal counterparts. In this study, we design a facile post-processing thermal treatment (i.e. annealing) to control the mechanical performance of TPU films under a possible temperature rise during operation. For this purpose, the TPU films, prepared by compression molding of commercially available TPU granules, are annealed at different temperatures (i.e., 60, 120, and 180 °C) and times (i.e., 24 h and 1 week). The results reveal the effectiveness of annealing to enhance the creep behavior and storage modulus at high temperatures. In the meantime, the room temperature tensile properties of annealed samples remain almost unchanged, offering unique applications for the TPU elastomers often used at room temperature, while they may face a temperature increase up to a certain value during operation. The dual effect of annealing on structural evolution of TPUs (i.e., formation of new crystallites and slight rearrangement of hard segment rich domains) are also discussed through differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), small angle X-ray scattering (SAXS) characterizations, and atomic force microscopy (AFM).

Room-temperature stretch formability, tensile properties, and microstructures of precipitation hardenable Mg–6Zn-0.2Ca (mass%) alloy sheets micro-alloyed with Ce or Y

We have investigated room-temperature stretch formability, age-hardening behavior, tensile properties, and microstructures of Mg–6Zn-0.2Ca-0.3Ce and Mg–6Zn-0.2Ca-0.4Y (mass%) alloy sheets. In hot-rolled and solution-treated sheets, (0001) planes of most grains split into both rolling and transverse directions, resulting in large Index Erichsen values of 7.6 ± 0.5 mm and 7.7 ± 0.2 mm, respectively. The Y-containing sheet shows lower age-hardenability than the Ce-containing alloy sheet; however, the Y addition led to a significant grain refinement, suppressing the ductility loss after peak aging. This results in the improved balance of strength and ductility in the Mg–6Zn-0.2Ca-0.4Y alloy sheet, and subsequent peak-aging led to high 0.2% proof stresses of 228 ± 1 MPa and large elongation to failure of 19 ± 1% along the rolling direction. Quasi-in-situ EBSD analysis of texture development during a solution treatment indicated that twinning-mediated recrystallization mainly contributes to the texture weakening in the high-alloyed Mg–Zn–Ca based alloy sheets.

Discontinuous precipitation leading to nano-rod intermetallic precipitates in an Al0.2Ti0.3Co1.5CrFeNi1.5 high entropy alloy results in an excellent strength-ductility combination

The phenomenon of discontinuous precipitation (DP) leading to the formation of nano-rod FCC (γ) + L12 (γ’) colonies, has been typically considered deleterious for mechanical properties. However, the present study shows clear evidence that substantially large fractions of FCC + nano-rod L12 microstructure within a thermo-mechanically processed high entropy alloys (HEA) or complex concentrated alloys (CCA) of composition Al0.2Ti0.3Co1.5CrFeNi1.5, formed via recrystallization coupled with discontinuous precipitation, can lead to an excellent combination of room temperature strength and ductility. The extent of thermomechanical processing can be engineered to modify the phase transformation pathway from homogenous L12 precipitation to discontinuous L12 precipitation in the same HEA. This predominantly FCC + nano-rod L12 microstructure exhibits a yield stress ~1.4 GPa, ultimate tensile strength ~1.6 GPa, and tensile ductility of ~14%, making it one of the best combinations of room temperature tensile properties for FCC-based HEAs, that have been reported to date, as well as better than current generation wrought nickel base superalloys. A high yield strength of the order of ~1 GPa is also retained to a temperature of 500 °C in this alloy. However, at higher temperatures (>550 °C), the DP microstructures exhibit a rapid decline in strength and become less competitive as compared to microstructures consisting of homogeneously precipitated L12 within the FCC matrix.

Body-centered-cubic martensite and the role on room-temperature tensile properties in Si-added SiVCrMnFeCo high-entropy alloys

We present a new class of metastable high-entropy alloys (HEAs), triggering deformation-induced martensitic transformation (DIMT) from face-centered-cubic (FCC) to body-centered-cubic (BCC), i.e., BCC-DIMT. Through the ab-initio calculation based on 1st order axial interaction model and combined with the Gibbs free energy calculation, the addition of Si is considered as a critical element which enables to reduce the intrinsic stacking fault energy (ISFE) in SixV(9-x)Cr10Mn5Fe46Co30 (x = 2, 4, and 7 at.%) alloy system. The ISFE decreases from -30.4 to -35.5 mJ/m2 as the Si content increases from 2 to 7 at.%, which well corresponds to the reduced phase stability of FCC against HCP. The BCC-DIMT occurs in all the alloys via intermediate HCP martensite, and the HCP martensite provides nucleation sites of BCC martensite. Therefore, the transformation rate enhances as the Si content increases in an earlier deformation range. However, the BCC-DIMT is also affected by the phase stability of FCC against BCC, and the stability is the highest at the Si content of 7 at.%. Thus, the 7Si alloy presents the moderate transformation rate in the later deformation range. Due to the well-controlled transformation rate and consequent strain-hardening rate, the 7Si alloy possesses the superior combination of strength and ductility beyond 1 GPa of tensile strength at room temperature. Our results suggest that the Si addition can be a favorable candidate in various metastable HEAs for the further property improvement.

Effect of Cu addition on overaging behaviour, room and high temperature tensile and fatigue properties of A357 alloy

Abstract The aims of the present work are to evaluate the overaging behaviour of the investigated Cu-enriched alloy and to assess its mechanical behaviour, in terms of the tensile and fatigue strength, at room temperature and at 200 °C, and to correlate the mechanical performance with its microstructure, in particular with the secondary dendrite arm spacing (SDAS). The mechanical tests carried out on the overaged alloy at 200 °C indicate that the addition of about 1.3 wt.% Cu to the A357 alloy enables to maintain ultimate tensile strength and yield strength values close to 210 and 200 MPa, respectively, and fatigue strength at about 100 MPa. Compared to the quaternary (Al−Si−Cu−Mg) alloy C355, the A357−Cu alloy has greater mechanical properties at room temperature and comparable mechanical behaviour in the overaged condition at 200 °C. The microstructural analyses highlight that SDAS affects the mechanical behaviour of the peak-aged A357−Cu alloy at room temperature, while its influence is negligible on the tensile and fatigue properties of the overaged alloy at 200 °C.

Microstructural and Tensile Properties Anisotropy of Selective Laser Melting Manufactured IN 625.

The present study was focused on the assessment of microstructural anisotropy of IN 625 manufactured by selective laser melting (SLM) and its influence on the material’s room temperature tensile properties. Microstructural anisotropy was assessed based on computational and experimental investigations. Tensile specimens were manufactured using four building orientations (along Z, X, Y-axis, and tilted at 45° in the XZ plane) and three different scanning strategies (90°, 67°, and 45°). The simulation of microstructure development in specimens built along the Z-axis, applying all three scanning strategies, showed that the as-built microstructure is strongly textured and is influenced by the scanning strategy. The 45° scanning strategy induced the highest microstructural texture from all scanning strategies used. The monotonic tensile test results highlighted that the material exhibits significant anisotropic properties, depending on both the specimen orientation and the scanning strategy. Regardless of the scanning strategy used, the lowest mechanical performances of IN 625, in terms of strength values, were recorded for specimens built in the vertical position, as compared with all the other orientations.

Improving room-temperature stretch formability of a high-alloyed Mg–Al–Ca–Mn alloy sheet by a high-temperature solution-treatment

Various solution-treatments were applied on a rapidly solidified and subsequently rolled Mg-7.50Al-1.07Ca-0.17Mn (mass%) alloy sheet, and a room-temperature stretch formability, tensile properties, microstructures, and textures of the solution-treated sheets have been investigated. Although the solution-treatment at 400 °C gives high strengths, the sheet shows poor room-temperature stretch formability with the Index Erichsen value of 4.8 mm due to densely dispersed second phase particles. Also, the particles tend to distribute to the rolling direction, leading to limited elongation to failure of 11.0% along the transverse direction. The solution-treatment at higher temperature leads to the sparse and relatively uniform dispersion of the particles. This results in the significant improvement in the room-temperature stretch formability and ductility. The Index Erichsen increases to 6.8 mm by the solution-treatment at 450 °C for 4 h, and the sheet shows large elongation to failure of 19.1% and 17.1% along the rolling and transverse directions, respectively. The sheet also exhibits high strengths and in-plane isotropic properties, tensile strength over 320 MPa and 0.2% proof stress of ~180 MPa could be obtained due to fine grain structure with the average grain size of 9.5 μm.

Microstructure, mechanical properties, and corrosion resistance of friction stir welded Mg-Al-Zn alloy thick plate joints

Mg-Al-Zn (AZ31) of 10-mm thick plates were subjected to friction stir welding (FSW) using a conventional tool (CT) and bobbin tool (BT), respectively. The microstructure, room temperature tensile properties, dynamic compressive mechanical properties, and corrosion resistance of the base metal (BM) and various regions of the friction stir welded joints were investigated systematically. The mean grain size, dislocation density, and precipitate distribution in the various regions of the friction stir welded joints were various due to different thermal cycle and plastic deformation. Compared with the CT, a relatively more homogeneous microstructure, a larger number of high-density dislocations and precipitates were produced in the various regions of the joint prepared by the BT due to higher thermal cycle and strain rate. As a result, the friction stir welded joint prepared by the BT exhibits excellent tensile properties and dynamic compressive mechanical properties, and outstanding corrosion resistances compared to those of the CT. In addition to slight changes in tensile properties and dynamic compressive mechanical properties, the corrosion resistance of the joint prepared by the BT was significantly improved compared to the BM. FSW with BT was suggested to be the optimal method to weld AZ31 alloy thick plate.

Effect of microstructural and environmental variables on ductility of austenitic stainless steels

Austenitic stainless steels are used extensively in harsh environments, including for high-pressure gaseous hydrogen service. However, the tensile ductility of this class of materials is very sensitive to materials and environmental variables. While tensile ductility is generally insufficient to qualify a material for hydrogen service, ductility is an effective tool to explore microstructural and environmental variables and their effects on hydrogen susceptibility, to inform understanding of the mechanisms of hydrogen effects in metals, and to provide insight to microstructural variables that may improve relative performance. In this study, hydrogen precharging was used to simulate high-pressure hydrogen environments to evaluate hydrogen effects on tensile properties. Several austenitic stainless steels were considered, including both metastable and stable alloys. Room temperature and subambient temperature tensile properties were evaluated with three different internal hydrogen contents for type 304L and 316L austenitic stainless steels and one hydrogen content for XM-11. Significant ductility loss was observed for both metastable and stable alloys, suggesting the stability of the austenitic phase is not sufficient to characterize the effects of hydrogen. Internal hydrogen does influence the character of deformation, which drives local damage accumulation and ultimately fracture for both metastable and stable alloys. While a quantitative description of hydrogen-assisted fracture in austenitic stainless steels remains elusive, these observations underscore the importance of the hydrogen-defect interactions and the accumulation of damage at deformation length scales.

Effect of Heat Treatments on Microstructural Evolution and Tensile Properties of 15Cr12MoVWN Ferritic/Martensitic Steel

In this study, the phase transformation temperature of 15Cr12MoVWN ferritic/martensitic steel was determined by differential scanning calorimetry to provide a theoretical basis for the design of a heat treatment process. An orthogonal design experiment was performed to investigate the relationship between microstructure and heat treatment parameters, i.e., normalizing temperature, cooling method and tempering temperature by evaluating the room-temperature and elevated-temperature tensile properties, and the optimum heat treatment parameters were determined. It is shown that the optimized heat treatment process was composed of normalizing at 1050 °C followed by air cooling to room temperature and tempering at 700 °C. Under the optimum heat treatment condition, the room-temperature tensile properties were 1014 MPa (UTS), 810.5 MPa (YS) and 18.8% (elongation), while the values are 577.5 MPa (UTS), 469 MPa (YS) and 39.8% (elongation) tested at 550 °C. The microstructural examination shows that the strengthening contributions from microstructural factors were the martensitic lath width, dislocations, M23C6, MX and grain boundaries of prior austenite grain (PAG) in a descending order. The main factors influencing the tensile strength of 15Cr12MoVWN steel were the martensitic lath width and dislocations.

Investigation on high-temperature mechanical properties of Al–7Si–0.6Mg alloy by wire + arc additive manufacturing

The room temperature and high temperature tensile properties of Al–7Si–0.6Mg alloy prepared by wire arc additive manufacturing have been investigated. The results show that the strengthening phase gradually coarsens and the eutectic silicon phase does not grow and agglomerate, meanwhile, the tensile strength and yield strength of the alloy gradually decrease with the increase of temperature. The high-temperature properties of the alloy are better than that of cast alloy. With the increase of temperature, the fracture of the alloy changes from ductile transgranular fracture to intergranular fracture.

The Effect of Electrolytic Hydrogenation on Mechanical Properties of T92 Steel Weldments under Different PWHT Conditions.

In the present work, the effects of electrolytic hydrogen charging of T92 steel weldments on their room-temperature tensile properties were investigated. Two circumferential weldments between the T92 grade tubes were produced by gas tungsten arc welding using the matching Thermanit MTS 616 filler material. The produced weldments were individually subjected to considerably differing post-welding heat treatment (PWHT) procedures. The first-produced weldment was conventionally tempered (i.e., short-term annealed below the Ac1 critical transformation temperature of the T92 steel), whereas the second one was subjected to its full renormalization (i.e., appropriate reaustenitization well above the T92 steel Ac3 critical transformation temperature and subsequent air cooling), followed by its conventional subcritical tempering. From both weldments, cylindrical tensile specimens of cross-weld configuration were machined. The room-temperature tensile tests were performed for the individual welds’ PWHT states in both hydrogen-free and electrolytically hydrogen-charged conditions. The results indicated higher hydrogen embrittlement susceptibility for the renormalized-and-tempered weldments, compared to the conventionally tempered ones. The obtained findings were correlated with performed microstructural and fractographic observations.

Evolution of microstructure and room temperature tensile properties in aluminum‐bearing high strength steel processed by ultrafast cooling

AbstractAn aluminum‐bearing high strength steel with relatively high precipitation hardening was fabricated by lowering coiling temperature to 627 °C. The influence of coiling temperature on microstructure evolution and precipitation behavior was comprehensively investigated by means of scanning electron microscopy, electron back‐scatter diffraction and transmission electron microscopy. Both yield strength and tensile strength can be increased by around 100 MPa through decreasing coiling temperature to 627 °C, whereas there is nearly no deterioration in ductility. In addition, The grain boundary precipitation of (Fe, Cr, Mn)xCy‐type carbides can be effectively suppressed by lowering coiling temperature. Regardless of coiling temperature, both interphase precipitation consisting of curved and planar shape and random precipitation can be observed. Moreover, the sheet spacing can be refined from 29 nm–47 nm to 18 nm–27 nm by lowering coiling temperature from 721 °C to 627 °C. This small sheet spacing provides a greater precipitation hardening. Compared with a coiling temperature of 721 °C, the precipitation hardening can be increased by around 100 MPa for a coiling temperature of 627 °C.

Effect of Microstructure Control on the Mechanical Properties of Hot Worked TiAl Alloy

The microstructure and mechanical properties of a newly developed, β-phase containing TiAl alloy have been studied through hot working and post heat treatment to enhance room temperature ductility and strength. The controlled microstructures hadthree types of structure, fully lamellar, nearly lamellar and duplex, and were produced by cyclic heat-treatment in a single α region and (α+γ) region after a hot-forging process in high temperature (α+β) region. As a result of the room temperature tensile test, the fully lamellar structure exhibited a tensile strength of 622 MPa and ductility of 0.62%. The duplex structure had a tensile strength of 787 MPa and ductility of 1.22%, while the nearly lamellar structure showed a tensile strength of 880 MPa and ductility of 1.76%. In the room temperature tensile test, the nearly lamellar structure exhibited excellent tensile strength and ductility. The strength and ductility were increased by decreasing grain size and β / B2 phase fraction. The newly developed TiAl alloy showed higher tensile values compared with the previous TiAl alloys. The relationship between microstructure and room temperature tensile properties of the newly developed β-phase containing TiAl alloy was examined, and the best approach for hot working and post heat-treatment to obtain the most balanced mechanical properties was proposed.

Effect of the microstructure evolution on the high-temperature strength of P92 heat-resistant steel for different service times

Grade 92 heat-resistant steel is an important material for ultra-supercritical units. The degradation of the P92 properties affects the safety of structural components during long-term service. In this paper, the microstructural evolution of P92 depending on different service times was quantitatively studied using scanning electron microscopy and transmission electron microscopy. The effect of each strengthening mechanism on the strength of P92 is discussed. The results show that the dimensions of M23C6 and Laves phases increase with increasing service time, but the growth rate of the Laves phase is higher than that of M23C6 and the size of MX carbonitrides remains almost unchanged. The width of the martensite lath increases from the initial 350 nm–750 nm after 70,000 h of service. The dislocation density significantly decreases and then stabilizes with increasing service time. The high- and room temperature tensile properties worsen and then stabilize during long-term service. The thermal yield stress of P92 during service was calculated. The results show that the high-temperature strength of P92 steel is mainly affected by lath and dislocation hardening during the initial service time; as the service time increases, the strengthening mechanism transforms into lath and precipitate hardening.