Room Temperature Tensile Behavior Research Articles

The Role of Molybdenum on Room Temperature Tensile Behavior of Recrystallized Fe30Mn5Al1CxMo Lightweight Austenitic Steels

The Role of Molybdenum on Room Temperature Tensile Behavior of Recrystallized Fe30Mn5Al1CxMo Lightweight Austenitic Steels

Elucidating the role of stress-induced martensite on the tensile behaviour of metastable β Ti-10V-2Fe-3Al alloy

Stress-induced martensitic transformation (SIMT) during loading in metastable alloy systems result in strength-ductility enhancement via transformation-induced plasticity (TRIP). The present study aims to investigate the influence of stress-induced martensites (SIM) on the tensile behaviour of metastable β Ti-10 V-2Fe-3Al (Ti-1023) alloy. The solutionized, and thermo-mechanically processed (i.e., cold rolling and annealing at 820 °C for 5 to 30 min) condition of Ti-1023, with single β phase microstructure, has been considered. The β grain size of solutionized Ti-1023 was ~625 μm, while the thermo-mechanically processed Ti-1023 was in the range of ~48 μm to ~106 μm as function of annealing time. The room temperature tensile behaviour of considered samples show SIMT, which results in strength enhancement (~7.5%), along with an increase in the trigger stress (~30%) as a function of β grain size (i.e., ~48 μm to ~625 μm). However, the % strain to failure show a significant decrease. A detailed microstructural characterization indicates the relation of SIM formation capability with β grain size. For finer β grain size, SIM displays a pronounced embrittling effect on the Ti-1023 tensile behaviour. Fracture surfaces show distinct regions with lath morphologies, which are further confirmed by surface as well as cross-sectional transmission electron microscopy (TEM) of the tensile fractured surfaces, illustrating the embrittling effects induced by SIM. In comparison, the dislocation-induced plasticity regions in the surrounding remnant β matrix result in dimple morphology. Thus, the coupling of enhanced martensite transformability, with reduced grain size, and the eventual decrease in martensitic laths spacing (i.e., from ~48 μm to ~7 μm), increase the density of martensite/matrix interfaces and the embrittling action. This results in pronounced dislocation pileups and formation of multiple martensitic variants facilitating premature failure by micro-void nucleation (at the martensite/matrix interface), growth and coalescence mechanism. The observations suggest that grain boundary engineering be optimized in order to fully exploit SIM's potential in enhancing the strength-ductility relation in Ti-1023 alloy.

Room and elevated temperature tensile and fatigue behaviour of additively manufactured Hastelloy X

Quasi-static tensile and stress-controlled high cycle fatigue tests of solution heat-treated (SHT) Hastelloy X manufactured by electron beam powder bed fusion (PBF-EB) and laser-based power bed fusion (PBF-LB) process were performed at room temperature and 750 °C. Post-fabrication SHT was ineffective in overcoming the microstructural anisotropy observed within as-built specimens, with the grains still maintaining its columnar architecture along the build direction. A significant drop in ductility was observed in tensile specimens tested at 750 °C, which was attributed to the carbide precipitation and grain boundary sliding. Upon investigating the influence of microstructural evolution as a function of test duration, a significant increase in precipitation was observed with an increase in test duration. A notable decrease in the fatigue strength was observed at elevated temperature. The long columnar grain structure within vertically build PBF-EB specimens was found to offer higher resistance against fatigue at 750 °C, owing to its reduced grain boundary area perpendicular to the loading direction. The corresponding fatigue damage mechanisms were investigated via fractographic analysis of the fracture surfaces and longitudinal cross-sections of the fractured specimens. Irrespective of the build orientation and test conditions, the fatigue cracks that resulted in final failure were found to initiate from the specimen surface. Also, the grain boundary precipitates were found to result in intergranular cracking during elevated temperature fatigue tests.

The Effect of Strain Rate on Hydrogen-Assisted Deformation Behavior and Microstructure in AISI 316L Austenitic Stainless Steel.

The influence of strain rate in the interval of (10-5-10-3) 1/s on room temperature tensile behavior, dislocation arrangement, deformation mechanisms, and fracture of austenitic stainless steel AISI 316L electrochemically charged with hydrogen was investigated. Independently on strain rate, hydrogen charging provides the increase in the yield strength of the specimens due to a solid solution hardening of austenite, but it slightly influences deformation behavior and strain hardening of the steel. Simultaneously, hydrogen charging assists surface embrittlement of the specimens during straining and reduces an elongation to failure, which both are strain rate-dependent parameters. Hydrogen embrittlement index decreases with increase in strain rate, which testifies the importance of hydrogen transport with dislocations during plastic deformation. The stress-relaxation tests directly confirm the hydrogen-enhanced increase in the dislocation dynamics at low strain rates. The interaction of the hydrogen atoms with dislocations and hydrogen-associated plastic flow are discussed.

Effect of Uniaxial Pre-strain on Room Temperature Tensile and Creep Behavior of Aluminum Alloy AA2219-T87 for Propellant Tanks of Satellite Launch Vehicles

Effect of Uniaxial Pre-strain on Room Temperature Tensile and Creep Behavior of Aluminum Alloy AA2219-T87 for Propellant Tanks of Satellite Launch Vehicles

Effect of Boronizing and WC Coating on the High Temperature Mechanical Behavior of AISI 321 Stainless Steel

In the current paper, the effect of two different coating techniques of boronizing and tungsten carbide (WC) coating on the room and high temperature tensile behavior of the AISI 321 stainless steel were investigated. Consequently, the fracture morphology observations were conducted via scanning electron microscopy (SEM) to inspect the variation of fracture mechanisms after implementing different coating methods. The results of tensile tests at room temperature revealed that despite boronizing reduced the yield strength of the sample due to the softening and grain growth at high coating temperature, the dispersion of boron particles improved the work hardening and ductility of boronized AISI 321. In contrast, the strain to failure of the WC coated sample was decreased due to the fast fracture of the ceramic WC layer at both room and high tensile tests. Furthermore, results of SEM revealed that particle decomposition occured on the fracture surface of the boronized 321 stainless steel represented by dispersed boron particles on the edges of the dimples after failure at high temperature.

Plasticity and brittleness of the ordered βo phase in a TNM-TiAl alloy

In order to identify the reasons for the brittleness of a TNM-TiAl alloy (Ti51.05Al43.9Nb4Mo0.95B0.1 in at.%), the plastic deformation behaviour of the ordered βo phase is investigated. The corresponding powder was densified by Spark Plasma Sintering to produce a near lamellar microstructure made of γ/α2 lamellar colonies surrounded by γ and βo grains. Then, the room temperature tensile behaviour is studied by carrying out tensile tests and additional in-situ straining experiments in a transmission electron microscope (TEM). The TNM alloy exhibits a limited ductility, with the fracture surface of test specimens showing cleavage facets along lamellar interfaces. In addition, the βo grains contain nano-precipitates of the ωo phase and deform plastically by <111> superdislocations dissociated into two superpartial dislocations separated by an antiphase boundary. These dislocations glide in {011} planes and are observed to be localized into pile-ups, which is related to the ωo strengthening precipitation within the βo grains. This localised hardening behaviour leads to stress concentration in grain boundaries which is assumed to be responsible for delamination along lamellar interfaces in neighbouring lamellar colonies.

Effect of Boronizing on the High Temperature Mechanical Behavior of Inconel 625

Inconel 625 is a frequently used material specifically in the exhaust and piping components of gas turbine engines, because of its good corrosion resistance even at high temperatures. In this work, the effect of boronizing on the room and high temperature tensile behavior of Inconel 625 alloy was investigated. According to the room temperature tensile test results, yield strength (YS) and ultimate tensile strength (UTS) of the samples reduced after boronizing. This strength reduction may be attributed to the softening of the material throughout the boronizing process at a high temperature of 1100°C. On the other hand, ductility of the Inconel 625 samples decreased. At elevated temperature, the yield strength of the boronized sample significantly reduced because of the possible decomposition of boron particles throughout tensile straining at elevated temperatures. Consequently, the fracture morphology observations revealed that the main fracture mechanism of both coated and uncoated conditions at high temperature was ductile fracture represented by coarse and deep dimples.

Interplay of austenite and ferrite deformation mechanisms to enhance the strength and ductility of a duplex low-density steel

Advanced low-density steels have been highlighted recently due to reduced weight and their superior mechanical properties due to various deformation mechanisms. This study investigates room temperature tensile behavior and the dominant deformation mechanisms of a ferrite-based duplex low-density steel. The present steel was subjected to a thermo-mechanical process including 70% cold rolling at ambient temperature and subsequent annealing at 1200 °C for 3, 5, and 10 min duration times. Room temperature tensile tests were carried out at 0.01s−1 strain rate. The Electron backscatter diffraction (EBSD) analysis on the deformed specimens demonstrates that the deformation induced martensite transformation in austenite, and deformation twinning in ferrite are synergistically responsible for the obtained high strength and ductility in this material. Transformation induced plasticity (TRIP) mechanism in austenite is found as the dominant deformation mechanism in specimens annealed for 3 min, while twinning induced plasticity (TWIP) in ferrite along with the dislocation gliding are characterized for specimens annealed for longer time (i.e., 5 and 10 min).Deformation twins are found to form in large ferrite grains with high Schmid factor, while dislocation gliding was dominant in smaller grains.

Study on Tensile Fracture Behavior of New Type High Temperature Titanium Alloy Ti-Al-Nb at Room Temperature

In this paper, in order to explore the development of a titanium-based superalloy with a working temperature of 700°C to 750°C and good ductility at room temperature, using Ti+Al+Ti2AlNb ternary powder as the raw material, the temperature is 1200°C to 1300°C, 30MPa, 1.5h Directly mixed and sintered under hot pressing conditions, a new type of titanium-based superalloy (TiAl+Ti2AlNb) samples were prepared. The fracture morphology of hot-pressed sintered samples and tensile samples used scanning electron microscope (Scanning electron microscope, referred to as SEM) and Electron backscattered diffraction (EBSD) for observation. Discuss the room temperature tensile fracture behavior of a new type of high temperature titanium alloy Ti-Al-Nb, and lay a technical foundation for the development of a new type of high temperature titanium-based alloy with low brittleness at room temperature.

The effect of strain rate on deformation-induced α′ phase transformation and mechanical properties of a metastable β-type Ti–30Zr–5Mo alloy

The effect of strain rate on stress-induced α′ phase transformation and room temperature tensile deformation flow behavior of a metastable β-type Ti–30Zr–5Mo alloy at strain rates ranging from 3 × 10−5 to 103 s−1 was investigated. The trigger stress for α′ phase transformation increases from 190 to 632 MPa with the strain rate increasing from 3 × 10−5 to 103 s−1, while the transformed volume of α′ phase decreases at the same time. The true strain at which stress-induced α′ phase transformation occurs also increases from 0.01 to 0.035 with the strain rate increasing from 3 × 10−5 to 103 s−1. Ultrahigh strain hardening rate of 8.7 GPa is observed at the strain rate of 3 × 10−5 s−1 due to the stress-induced α′ phase transformation. At a high strain rate of 103 s−1, the planar slip bands also form during deformation, indicating that the deformation becomes more localized with increasing strain rate. The ultimate tensile strength increases from 722 to 853 MPa with increasing the strain rate from 3 × 10−3 s−1 to 101 s−1 without sacrificing the elongation to fracture. The improved mechanical properties are attributed to the dislocation hindering mechanism of short-range obstacles associated with the stress-induced α′ phase transformation during deformation, and the adiabatic temperature rise caused by the deformation.

Influence of prior deformation temperature on strain induced martensite formation and its effect on the tensile strengthening behaviour of type 304 SS studied by XRDLPA

Type 304 stainless steel is a metastable austenitic stainless steel that undergoes strain induced transformation from austenite to α′ martensite during deformation at room temperature. Role of prior deformation, by rolling at room temperature and at 200 °C (a temperature at which the strain induced martensitic transformation does not occur), on the subsequent room temperature tensile deformation behaviour of the austenite phase is investigated. The changes in dislocation density of the parent phase and the volume fraction of the martensite formed due to deformation were estimated by X-ray diffraction line profile analysis of data obtained from Beam Line - 12 of the Indus 2 synchrotron. The contrast caused by dislocations in the austenite phase has been addressed using the modified Williamson-Hall method. The character of dislocations changes from screw to edge above a critical equivalent strain of ~0.14. The influence of martensite formation on the increase in dislocation density in the austenite phase is confirmed from XRDLPA. An alternative approach to determine dislocation density is proposed which is independent of elastic constants of the material and is found to correlate well with the values determined by the Williamson-Smallman approach. The results obtained from XRDLPA are corroborated with EBSD analysis. It is also seen that the composite strength of the steel, which has undergone different levels of deformation, is related to the changes in dislocation density of austenite and volume fraction of martensite based on Taylor's equation enabling correlation of structure-property.

Room temperature tensile deformation behavior of a Ni-based superalloy with high W content

K416B Ni-based superalloy with high W content has good high temperature properties and low cost, which has a great development potential. To investigate the room temperature tensile property and the deformation feature of K416B superalloy, tensile testing at room temperature was carried out, and optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to analyze the deformation and damage mechanisms. Results show that the main room temperature tensile deformation features of the K416B nickel-based superalloy are dislocations slipping in the matrix and shearing into γ′ phase. The <110> super-dislocations shearing into γ′ phase can form the anti-phase boundary two coupled (a/2)<110> partial-dislocations or decompose into the configuration of two (a/3)<112> partial dislocations plus stacking fault. In the later stage of tensile testing, the slip-lines with different orientations are activated in the grain, causing the stress concentration in the regions of block carbide or the porosity, and cracks initiate and propagate along these regions.

On the room-temperature tensile deformation behavior of a cast dual-phase high-entropy alloy CrFeCoNiAl0.7

The microstructure and room-temperature tensile deformation behavior of the cast CrFeCoNiAl0.7 high-entropy alloy (HEA) were studied in details. The cast HEA consisted of a dual-phase structure of 77. 3 vol. % face-centered-cubic (FCC) phase plus 22.7 vol.% B2 phase, and exhibited excellent room-temperature tensile properties with a high yield strength of 876 MPa, ultimate tensile strength of 1198 MPa and a relatively large elongation to fracture of ∼9 %. Dislocations gliding in the FCC phase governed the plastic deformation at the early stage of room-temperature tensile, and disordered dislocations were to form dislocation walls as the deformation proceeded. With further increase in strain to a high level, the stacking faults were generated through the dissociation of the geometrically necessary dislocations, serving as the potential heterogeneous nucleation sites for the deformation twins.

Microband-Induced Plasticity in a Nb Content Fe–28Mn–10Al–C Low Density Steel

Novel Fe–28Mn–10Al–C–0.5Nb low-density steel was developed and the room temperature tensile behavior in the solid solution state and the microstructure evolution process during plastic deformation were studied, aiming to clarify the dominant deformation mechanisms. The results show that the developed steel was fully austenitic with a low density of 6.63 g/cm3 and fairly high stacking fault energy of 84 MJ/m2. The present fully austenitic Fe–28Mn–10Al–C–0.5Nb low-density steel exhibited an excellent ultimate tensile strength of 1084 MPa and elongation of 37.5%; in addition, the steel exhibited an excellent combination of strength and ductility (i.e., the product of strength and ductility (PSE) could reach as high as 40.65 GPa%). In spite of the high stacking fault energy, deformed microstructures exhibited planar glide characteristics, seemingly due to the glide plane softening effect. The excellent combination of strength and ductility is attributed to plasticity induced by microbands and leads to the continuous strain hardening during deformation at room temperature. Moreover, the addition of Nb does not change the deformation mechanism and strengthening mechanism of Fe–Mn–Al–C low-density steel, and can optimize the mechanical properties of the steel.

In situ high-energy X-ray study of deformation mechanisms in additively manufactured 316L stainless steel

A key structural material planned to be used in the core of the Transformational Challenge Reactor is the additively manufactured 316L stainless steel (AM 316L SS). While the deformation of conventionally-manufactured 316 SS have been extensively studied, the deformation mechanism of AM 316L SS is less known. Here the room-temperature tensile behavior of AM 316L SS was studied in situ using high-energy X-ray diffraction and X-ray tomography. Diffraction yielded the lattice strains and the dislocation densities of the AM 316L SS, which were compared to those of a conventionally processed 316H SS. It was found that while the conventional 316H SS had three distinct deformation stages, namely stage II athermal hardening, stage III dynamic recovery, and stage IV, the AM 316L experienced only the stages III and IV after an initial transitional period. The plastic instability stresses (PIS), i.e. the true ultimate tensile strength, were nearly the same in both materials. The AM 316L had very low dislocation barrier strength throughout the plastic deformation, which, in combination with the invariant PIS, explained its high dislocation storage capability and the attractive combination of strength and ductility. Tomography revealed morphological changes of the built-in pores in the AM 316L during deformation and fracture, and it was concluded that large pores close to the surface might have significant roles in the necking stage.

Microstructure and mechanical behaviour of an advanced powder metallurgy nickel base superalloy processed through hot isostatic pressing route for aerospace applications

An advanced powder metallurgy (P/M) nickel-base superalloy envisaged for aerospace applications is realized through hot isostatic pressing (HIPing) of inert gas atomized powder. Extensive characterization of the microstructural features at different scales by employing optical microscopy, SEM-EBSD and transmission electron microscopy (TEM) divulged multi-modal distribution of γʹ precipitates within austenitic γ-FCC matrix phase in the as-HIPed condition. Investigation of prior particle boundary precipitates (PPBs) through TEM and Electron Probe Micro Analysis (EPMA) techniques revealed the dominance of metallic oxides and MC type carbides. The suitability of the advanced P/M superalloy for realizing near-net shape components by Direct-HIPing for short duration aeroengine rotating components is assessed by evaluating the room temperature and elevated temperature tensile behaviour as well as stress-rupture life in the service temperature regimes. The yield strength and the ultimate tensile strength of the present alloy at 650 °C are found to be 850 MPa and 1275 MPa respectively combined with 28% of ductility which is comparable to those of the similar class of superalloys in service. On the other hand, the as-HIPed superalloy exhibited minimum 1000 h of stress rupture life around service temperatures and bettered the stress rupture life of wrought superalloy IN718 alloy showing its potential for fabrication of near-net shape components for aerospace applications.

Cold-workable refractory complex concentrated alloys with tunable microstructure and good room-temperature tensile behavior

A novel non-equiatomic NbTaTi-based refractory complex concentrated alloy (RCCA) capable of being cold-rolled up to a reduction in thickness of over 90% directly from the as-cast state is studied. Instead of conventional heat-treatment at temperatures greater than 0.8Tm for long durations, the excellent cold-workability in this RCCA allows for tunable microstructural features, including fine-grained, coarse-grained, and heterogeneous lamella (HL) structures, through proper heat-treatment at relatively lower temperatures for shorter duration. By tailoring microstructures, balanced tensile properties are achieved in this RCCA, through back-stress strengthening of HL structures. This study demonstrates an energy-saving and efficient way to fabricate high-performance RCCAs.

Non-contact strain evaluation for miniature tensile specimens of neutron-irradiated F82H by digital image correlation

• Non-contact strain evaluation by DIC using speckle patterns of surface flaws was applied and reliability of the technique was demonstrated. • Room temperature tensile behavior of Japanese RAFM, F82H, irradiated to ∼70 dpa at 573 K was preliminarily evaluated. • No possible irradiation-induced change of the elastic properties in both axial and transverse directions for irradiated F82H was demonstrated. The small specimen tensile test is commonly used as the basic test to evaluate the irradiation effect on the strength of fusion structural materials after irradiation, and a lot of attempts were made to qualify the data obtained by small size specimen, but the specific attention on the evaluation of strain were not satisfactory given. This study therefore aims to propose a novel non-contact strain measurement technique, based on digital image correlation (DIC) method, for reduced-activation ferritic/martensitic (RAFM) steel, e.g., F82H, as the leading candidate structural material of fusion in-vessel components in Japan. A flat rectangular miniature specimen, e.g., SS-J3 type, was adopted to evaluate non-irradiated and neutron-irradiated tensile properties. In the proposed DIC, very tiny surface machining flaws were recognized by the DIC computation program and utilized to set several pairs of the gauge end points with a fixed gauge length. In case of the room-temperature test, it was clearly demonstrated that this procedure could provide more precise and reliable data compared with the previous approach of the single-scan measurement under floated gauge length. Superior linearity was achieved and recognized DIC points of concern were traceable during the entire period of the test. By applying this technique, superior high-dose stability of elastic properties of F82H was first demonstrated.

Failure Analysis of Unidirectional Ceramic Matrix Composite Lamina and Cross-Ply Laminate under Fiber Direction Uniaxial Tensile Load: Cohesive Zone Modeling and Brittle Fracture Mechanics Approach

The current research work presents the computational micromechanical analysis of the room temperature tensile failure behavior of unidirectional (UD) and cross-ply (0/90) ceramic matrix composites (CMCs). For computational micromechanical analysis, three-dimensional (3D) representative volume element (RVE) and multi-fiber multilayer RVE (M2 RVE) models are generated that are representative of the lamina and the laminate under investigation. The RVE and M2 RVE models are generated by replicating the fiber distribution, and the placement of the fibers observed in a microscopic image of an actual CMC laminate. The generated RVE models consist of the discrete representation of individual constituent phases of the CMC such as fibers, interphase, matrix, and the fiber–interphase interface region. Under the applied external tensile load, the fiber–interphase interface interactions are modeled using the cohesive elements that follow the bilinear traction separation law. The matrix, fiber, and interphase materials failure behavior is captured using a brittle cracking model. In order to validate the proposed numerical methodology, the predicted average stress–strain curve at the UD laminate level is compared to the experimental stress–strain curve reported in the literature. In addition, the observed different phases in the predicted stress–strain curve are validated with the literature data. Using the proposed numerical methodology, a detailed local stress–strain and damage analysis leads to an observation that the so-called ductile stress–strain behavior (kink in the stress–strain curve) of a CMC UD laminate under uniaxial fiber direction tensile loads is mainly caused by the matrix damage initiation. Apart from the SiC material properties such as strength and fracture energy, it is also observed that the RVE size influences the average strength and failure strain predictions using computational micromechanics.