Yield Stress Values Research Articles

Comprehensive and Comparative Heat Treatment of Additively Manufactured Inconel 625 Alloy and Corresponding Microstructures and Mechanical Properties

This study examines and compares the microstructures, Vickers microindentation hardness, and mechanical properties for additively manufactured (AM) samples built by a variety of AM processes: wire arc AM (WAAM), electron beam powder bed fusion (EB-PBF), laser wire direct energy deposition (LW-DED), electron beam direct energy deposition (EB-DED), laser-powered direct energy deposition (LP-DED), and laser powder bed fusion (L-PBF). These AM process samples were post-processed and heat-treated by stress relief annealing at 1066 °C, HIP at 1163 °C, and solution annealing treatment at 1177 °C. The resulting microstructures and corresponding microindentation hardnesses were examined and compared with the as-built AM process microstructures and hardnesses. Fully heat-treated AM process samples were mechanically tested to obtain tensile properties and were also evaluated and compared. Principal findings in this study were that high-temperature heat treatment >1100 °C of AM process-built samples was dominant and exhibited recrystallized, equiaxed grains containing fcc {111} annealing twins and second phase particles independent of the AM process, in contrast to as-built columnar/dendritic structures. The corresponding yield stress values ranged from 285 MPa to 371 MPa, and elongations ranged from 52% to 70%, respectively. Vickers microindentation hardnesses (HV) over this range of heat-treated samples varied from HV 190 to HV 220, in contrast to the as-built samples, which varied from HV 191 to HV 304.

FexCo1-x alloy nanoparticles: Synthesis, structure, magnetic characterization and magnetorheological application

We present results concerning the synthesis of FexCo1-x (0 < x < 1) alloy nanoparticles (NPs) with different compositions by the chemical reduction technique and subsequent structural (XRD patterns), morphological (TEM images) and magnetic (VSM magnetometry) characterization. We have got excellent quality NPs in the cubic bcc structure showing a room temperature magnetization as high as 235 emu/g for the Fe66Co34 composition alloy. Powder of composition Fe47Co53 was used to fabricate a magnetorheological fluid (MRF) by using mineral oil as carrier liquid and Aerosil 300 as additive to control the viscosity of the fluid. This MRF showed a strong magnetorheological response with a superior performance under applied magnetic field up to 616.7 kA/m and good reversibility after demagnetization process. At that highest applied magnetic field, we determined a yield stress value of 2729 Pa, that competes well with the best ones reported in the most recent literature.

Quasi-Static Mechanical Properties of Post-Processed Laser Powder Bed Fusion Ti6Al4V(ELI) Parts under Compressive Loading

The Ti6Al4V structures in aircraft and biomedical industries are usually exposed to quasi-static loads. Therefore, understanding the quasi-static behaviour of this alloy manufactured by an additive manufacturing process is paramount. This paper documents an investigation of the quasi-static mechanical properties of various microstructures of heat-treated Ti6Al4V(ELI) parts manufactured by laser powder bed fusion (LPBF). The effects of different quasi-static strain rates on different microstructures of these samples and their strain hardening are also presented. The test samples were produced using an EOSINT M280 direct metal laser sintering (DMLS) machine and, thereafter, subdivided into three major groups, namely samples C, D and E, for high-temperature annealing at different heat treatment strategies. A universal hydraulic testing machine (UTM) was used to carry out tests at strain rates of 0.001 s−1, 0.005 s−1 and 0.1 s−1. The three forms of LPBF Ti6Al4V(ELI) were found to be sensitive to quasi-static strain rate, whereby values of yield and flow stresses in each form of alloy increased with increasing strain rate. The order of the strength at each strain rate from the highest to the lowest was found to be samples C, D and E. The effects of strain rate on flow hardening were found to be significant in samples C and insignificant in samples D and E.

Analysis on Deck Ship Conversion SPOB to LCT 234 GT Using Finite Element Method

Landing Craft Tank (LCT) is a sea transportation that serves to carry various types of cargo and heavy mining equipment and has a large size. In shipbuilding, the construction structure on the ship is not only designed to be able to accept the load from the cargo being transported but also must be able to withstand external loads caused by waves. With the modification of the Self-Propelled Oil Barge (SPOB) ship into a Landing Craft Tank (LCT), the calculation and planning process on the deck structure of the Landing Craft Tank (LCT) ship really needs to pay attention to the stress and strain strength in order to meet the safety factors that have been set in accordance with the applicable rules. This study aims to determine the maximum allowable stress value and the safety factor of the modified structure of the Landing Craft Tank (LCT) ship deck construction. The method used in this research is the finite element method. In this study uses 2 variations of the type of support "Tee Bar" and "Angle Bar". The results of this study the value of material deformation that occurs on the ship's deck with a variation of "Angle Bar" of 1.1497 mm and the value of material deformation that occurs on the deck of a ship with a variation of "Tee Bar" of 0.97269 mm. The maximum stress value acting on the ship's deck with the "Angle Bar" profile variation is 152.64 MPa and the maximum strain value is 0.00072686 mm/mm. The maximum stress value acting on the ship's deck for the "Tee Bar" profile variation is 147, 63 MPa and the maximum strain value is 0.000703 mm/mm. The value of the Safety Factor based on the criteria for the material on the ship's deck is obtained by comparing the yield stress value of the material and the maximum working stress must be greater than 1, then the deck construction with the variation of the "Angle Bar" profile is 2,326 and for the variation of the "Tee" profile type. Bar” 2,405 are categorized as safe. As for the Safety Factor based on BKI rules for the variation of the "Angle Bar" profile of 1,638 and for the variation of the "Tee Bar" profile of 1,693 it is categorized as safe. then the deck construction with the variation of the profile type "Angle Bar" is 2,326 and for the variation of the profile type "Tee Bar" 2.405 is categorized as safe. As for the Safety Factor based on BKI rules for the variation of the "Angle Bar" profile of 1,638 and for the variation of the "Tee Bar" profile of 1,693 it is categorized as safe. then the deck construction with the variation of the profile type "Angle Bar" is 2,326 and for the variation of the profile type "Tee Bar" 2.405 is categorized as safe. As for the Safety Factor based on BKI rules for the variation of the "Angle Bar" profile of 1,638 and for the variation of the "Tee Bar" profile of 1,693 it is categorized as safe.

Steady-State and Dynamic Rheological Properties of a Mineral Oil-Based Ferrofluid

In this study, nanoparticles were suspended in L-AN32 total loss system oil. The thixotropic yield behavior and viscoelastic behavior of ferrofluid were analyzed by steady-state and dynamic methods and explained according to the microscopic mechanism of magneto-rheology. The Herschel–Bulkley (H–B) model was used to fit the ferrofluid flow curves, and the observed static yield stress was greater than the dynamic yield stress. Both the static and dynamic yield stress values increased as the magnetic field increased, and the corresponding shear thinning viscosity curve increased more significantly as the magnetic field strength increased. The amplitude scanning results show that the linear viscoelastic region (LVE) is reached when the shear stress is 10%. The frequency scanning results showed that the storage modulus increased with the increase of the frequency at first. The storage modulus increased steadily at a higher frequency range, while the loss modulus increased slowly at the initial stage and rapidly at the later stage. In the amplitude sweep and frequency sweep experiments, the energy storage modulus and loss modulus are enhanced with the decrease of temperature. These findings are helpful to better understand the microscopic mechanism of magneto-rheology of ferrofluids, and also provide guidance for many practical applications.

Different methods for determining the yield stress of ferrofluids

The yield stress of ferrofluids has been a hot topic in their rheological studies, and it is still controversial which method could obtain the more accurate yield stress value. In this work, we used varieties of methods to obtain the yield stress of the ferrofluid, including steady shear and oscillatory shear. We obtained the static yield stress and dynamic yield stress of the ferrofluid by Herschel–Bulkley fitting of the flow curves measured by the controlled shear rate mode and the controlled shear stress mode, and found that at any magnetic field strength, the static yield stress was always significantly greater than the dynamic yield stress. We then performed oscillatory shear of the ferrofluid and determined the yield stress using three methods, where the yield stress value corresponding to the intersection of the storage modulus G′ and the loss modulus G″ is similar to the static yield stress value fitted by H-B at low magnetic field strength. The power law function and shear stress as a function of shear strain consistently gave the maximum value of the yield stress. Ultimately, we believe that which method is ultimately chosen depends on the practical application conditions of interest.

Yielding and K 0 Value Variation of Cemented Sand along a K 0 Path

The yield stress and the coefficient of lateral earth pressure at rest, K0, of soil are important parameters for geotechnical design. However, the effect of cementation on the values of yield stress and K0 of artificially cemented sand along a K0 path has not been fully studied, despite the common use of cement mixing for soil improvement. A series of consolidation tests of K0 on artificially cemented sand has been conducted using a plane-strain apparatus. The test results show that the value of K0 of cemented sand is very much affected by the amount of cementation; the lowest value of K0 in a K0 test corresponds to the yield stress provided by cementation. It is established in this study that the yield stress of cemented sand marks the start of a large amount of bond destruction. The value of K0 reduces exponentially with the increase in cement content. One important practical implication is that the lateral earth pressure at rest can be reduced by introducing cementation to soil. This study also shows that Jaky’s equation is no longer applicable for estimating the value of K0 of cemented sand, although it may still provide a rough estimate for clean sand. The value of K0 of cemented sand can be estimated using a combination of Jaky’s equation for clean sand and Jaky’s equation for cement content.

Effect of operational factors on reproducibility of yield stress measurement based on the vane method for cemented paste backfill

• Precise measure of yield stress is critical for CPB and vane method is widely used. • The reproducibility is subject to instrumental, analytical and operational influence. • Various vane positions, standing times and rotation speeds were tested. • A satisfactory reproducibility requires consistent preparation and operation. • A lower rotation speed facilitates a closer result to the true value. • Equilibrium time of 1 min and rotation speed of 0.1 rpm are suggested for CPB. Precise determination of yield stress with the desired reproducibility is critical for cemented paste backfill (CPB). An overview of the instrumental, analytical and operational factors was carried out to evaluate the key factors in CPB measurement using the vane method. Therewith the effects of vane inserted depth (10 to 40 mm), standing time (0 to 6 min), and rotational speed (0.05 to 5 rpm) were tested. The results show that an increased rotation speed or prolonged standing time leads to higher measured values and poorer reproducibility. The ESEM images indicate that larger yield stress values correspond to denser microstructures and the deterioration in structural homogeneity leads to pronounced deviation in results. Increasing the rotation speed enhances the role of viscous resistance and leads to an overestimation of yield stress. It is recommended that a consistent operation should be followed with the vane centered in the sample, resting for less than 1 min, and rotating below 0.1 rpm.

Microstructural and Mechanical Characterization of the Aging Response of Wrought 6156 (Al-Mg-Si) Aluminum Alloy

The impact of the artificial aging response on the microstructure and tensile mechanical properties of aluminum alloy 6156 was investigated. Specimens were artificially aged at three different artificial aging temperatures and for various holding times to investigate all possible aging conditions, including the under-aged (UA), peak-aged (PA) and over-aged (OA) tempers. Microstructural investigation as well as tensile tests were performed immediately after the isothermal artificial aging heat treatment. An almost 50% increase in yield stress (around 340 MPa) was noticed in the PA temper and this was attributed to the precipitation of β′ and Q′ phases, consistent with the modelling predictions. This high yield stress value is accompanied by high values of elongation at fracture (&gt;10%) that is essential for damage tolerance applications. The lack of large or interconnected grain boundary precipitates contributes to this high elongation. Slanted fracture was noticed for both UA and PA tempers, exhibiting a typical ductile and shear fracture mechanism. At the OA temper, coarsening of the precipitates along with broadening of the precipitate free zones resulted in a reduction in the strengthening effectiveness of the precipitates, and a small increase in the tensile ductility of approximately 12% was noticed.

Physical and 3D Printing Properties of Arrowroot Starch Gels.

This paper aims to investigate the physical and 3D printing properties of arrowroot starch (AS), a natural biopolymer with many potential health benefits. Scanning electron microscopy images showed that AS granules had mixed spherical and elongated geometries, with average sizes of 10.5 ± 2.5 μm. The molecular weight of AS measured by gel permeation chromatography (GPC) was 3.24 × 107 g/mol, and the amylose/amylopectin ratio of AS was approximately 4:11. AS has an A-type crystal structure, with a gelatinization temperature of 71.8 ± 0.2 °C. The overlap concentration (C*) of AS in aqueous solutions was 0.42% (w/v). Temperature-dependent dynamic rheological analyses of 10% to 30% (w/v) AS fluids showed that the storage modulus (G’) reached the maximum values around the gelatinization temperatures, while the yield stress (τy) and flow stress (τf) values all increased with the increase in AS concentration. The printing accuracy of AS gels was found to be associated with the interplay between the G’ values and the restorability after extrusion, determined by the three-interval thixotropy tests (3ITT). The optimum 3D printing condition occurred at 20% (w/v) AS, the nozzle diameter of 0.60 mm, the printing speed of 100 mm/s and the extrusion speed of 100 mm/s. Our research provides a promising biopolymer to be used in the design of novel personalized functional foods.

Experimental Study Regarding the Mechanical Behavior of PPR Pipes

The PPR pipes are more and more used in different industrial applications, due to their multiple advantages compared with the conventional metallic pipes. The experimental study presented in this article, was conducted in two directions, analyzing the behavior of welded PPR pipes and also the behaviour of unwelded PPR pipes exposed to different aggressive environments. In the second investigation, the PPR pipes were immersed in different chemically active environments as gasoline, sodium hypochlorite (NaClO), water + sodium hypochlorite (NaClO)-20% NaClO volume concentration, for a period of 3 weeks (21 days), in order to reveal the influence on the mechanical properties of the PPR pipes. The examination was made by using both visual inspection and tensile and bending tests. The investigations made have led to the conclusion that the presence of sodium hypochlorite do not affect the mechanical properties of PPR pipes, unlike the gasoline which significantly decrease the yield stress value. For the welded PPR pipes it was found that they failed at pressures of about 180 bar. Although the optimal welding parameters, recommended by the manufacturer, were modified (maintenance time), the only sample that failed in the welded joint was the one with the most acute misalignment and the shortest welding time. However, the sample withstood high pressures, reaching about 55% of the burst pressures obtained for welded pipes with the recommended welding parameters. The need to conduct such studies derived from the fact that most of the information regarding the behavior of PPR pipes is provided by the manufacturers and there is insufficient information in the scientific literature.

Tensile-compressive asymmetry in extruded AZ31B rod and its effect on Profilometry-based Indentation Plastometry (PIP)

This paper concerns Tensile-Compressive Asymmetry (TCA) in a Mg-based alloy. Strong TCA is in general unusual, but previous publications have indicated that it can arise with the AZ31(B) alloy (in extruded rod or rolled plate form), such that there is a factor of up to two between yield stress values obtained by testing the same sample (in the same direction) in tension and in compression. This is confirmed in the present work. It has also been previously established that this effect is associated both with strong crystallographic texture and with the plasticity involving at least some deformation twinning. It is thus more likely with hexagonal metals, such as Mg, since their lower crystallographic symmetry (compared with cubic metals) favours this type of deformation. The microstructural evolution, and operative deformation mechanisms, that give rise to the observed TCA effects are investigated in detail here and at least most of the observed mechanical characteristics are rationalised. Finally, the Profilometry-based Indentation Plastometry (PIP) methodology for inferring stress-strain curves from indentation tests is applied to this material. As expected, full TCA characteristics cannot be obtained via PIP, but it is shown that there is a well-defined relationship between curves inferred in this way and the full set of uniaxial test outcomes.

Experimental Study of Aluminium Joint Plate Between AA5052 with AA5083: Application on Hull Vessel Material

Generally, the planning of the material arrangement of the aluminum hull plate is always carried out at an early stage to obtain a material formation that has good economic value. One of the strategies used to obtain economic value in shipbuilding is the use of various grades of plate material. The grade of aluminum material that is often used on ships is the 5xxx series. Where this series has many grades that can be used as ship hull material options. The price difference for each grade of aluminum material for ships is a very influential variable on the economic value of shipbuilding. However, before being applied to shipbuilding, it is necessary to test the feasibility of aluminum plate connections with variations in plate grade. The aim is to provide clear information regarding the technical feasibility of selecting material grades. Therefore, in this study, a simulation will be carried out to test the strength of the plate connection with variations in the grade of aluminum material using the experimental method. The plate joint test is carried out using only the Tensile test in the laboratory with reference to the ASTM rules. The grades of aluminum plate materials used are 5052 and 5083. Connection formations are between 5052-5052, 5083-5083, and 5052-5083. From the test results, the largest average yield stress value is 202.34 N/mm 2 at the variation 5083-5083, the maximum average ultimate stress value is 261.70 N/mm 2 at the variation 5083-5083. For the variation of the 5052-5083 plate connection, it still has a yield stress value that is greater than the basic yield stress of the material, namely 142.97 N/mm 2 . Where the percentage value of the achievement level of yield strength is 113.6% of the basic yield stress value of the material based on BKI rules. However, in achieving the ultimate stress value, it is still lower than the ultimate basic stress of the BKI rules standard material, which is 193.88 N/mm 2 . Where the percentage value of the level of ultimate strength achievement is 70.5% of the ultimate basic stress value of the BKI rules standard material.

Ab initio point defect calculations for structural properties of a model austenitic steel alloy

We present first-principles density functional theory calculations of atomic properties relevant to the material strength of an austenitic (face-centered-cubic) steel alloy, ${\mathrm{Fe}}_{0.70}{\mathrm{Ni}}_{0.12}{\mathrm{Cr}}_{0.18}$. While alloys in this class appear nonmagnetic macroscopically because their local magnetic moments are disordered, significant deviation from experiment can result when calculating properties using nonmagnetic calculations or magnetically ordered calculations. To overcome these difficulties, in this paper we employ a magnetic sampling method with spin-polarized density functional theory to approximate magnetically disordered states by averaging over several static configurations. Using this approach, we calculate elastic and point defect properties, which are then used to evaluate the dominant solid-solution strengthening contribution to the yield strength. Moreover, since the local composition can interact with strain fields, whether externally applied or induced by dislocations, diffusion can give rise to local changes in mechanical properties. We therefore calculate contributions to the vacancy-mediated diffusivity from the formation and migration terms in the activation energy, and the harmonic-transition-state-theory prefactor which depends on the vibrational states of the initial and transition states. While the prefactor is very sensitive to noise and therefore only loosely constrained by our calculations, the activation energies and yield stress values obtained from paramagnetic calculations are in good agreement with available experimental results.

Quantitative insights into rheology of self-crosslinking dialdehyde carboxymethyl cellulose/collagen solution: A comprehensive experimental and modelling investigation

Rheological behaviors (fluid type, thixotropy, viscoelasticity and deformation resistance) of self-crosslinking dialdehyde carboxymethyl cellulose (DCMC)/collagen solutions were comprehensively investigated and quantitatively modelled. The formation of self-crosslinking bonds gave rise to the enhancement of entanglements among collagen molecules and aggregates, resulting in the improvement of collagen solution's mechanical properties. The collagen solution was typical pseudoplastic fluid with shear-thinning behavior, and DCMC did not alter its flow behavior; therefore, the flow curves for all samples could be well simulated by Ostwald-de Waele and Carreau models. However, the viscosity and pseudoplasticity increased, and the effect of DCMC became more pronounced at higher DCMC/collagen ratios. Similar upward variation was observable for thixotropy, detected by the increased area of hysteresis loops from 20.947 to 219.978 Watts/m3. Additionally, the negative values of apparent yield stress and flow index below 1 from Herschel–Bulkley model confirmed that the DCMC/collagen solutions remained pseudoplasticity without yield stress. The viscoelasticity was examined based on dynamic frequency sweep and creep–recovery measurement and then simulated using Leonov model, Burger model and a semi-empirical model, respectively. The increases in elastic moduli and proportion of recoverable compliance reflected the self-crosslinking DCMC/collagen solutions had stronger elasticity and exhibited more resistance to deformation than the native collagen solution. Nevertheless, the more complicated structures of the DCMC/collagen solutions required more time to recover after removing external force. These data can be directly applied to the utilization of DCMC/collagen solutions, whilst also provide a basis for the prediction of printability or spinnability of collagen-based materials.

An Experimental Investigation of the Effects of Fly Ash and Nano Titanium Dioxide (n-TiO2) Usage as Viscosity Modifying Agents(VMAs) in Cement-Based Grouts on Rheological Parameters.

The effects of n-TiO2 additions at different amounts by mass (0.0%, 0.3%, 0.6%, 0.9%, 1.2% and 1.5%) on rheological properties (plastic viscosity and yield stress) of cement-based grouts incorporated with fly ash as mineral additive at different constitutes (0%-for control purpose, 5%, 10%, 15%, 20%, 25% and 30%) were investigated by analysis of experiments in this study. To prepare all samples, w/b ratio was defined as 1.0. To prevent sedimentation of TiO2 nanoparticles in free water and to supply uniform distribution of TiO2 nanoparticles in water with help of removing of these nanoparticles from each other, Ultrasonication method was applied by using a Horn type Ultrasonic Homogenizer in this experimental study. All experimental viscosity values of the cement-based grout samples were also obtained by using Coaxial Rotating Cylinder Rheometer test machine. Modified Bingham analytical model was used to investigate on this study for reference grout samples because of it shows dilatant (shear-thickening) flow behavior. Test results show that plastic viscosity values of the grout samples obtained by addition of FA remarkably decrease with rising amount of n-TiO2. Yield stress of fresh grout mixtures increases with respect to increase amount of FA content in all grout mixtures with different proportions of n-TiO2. the usage of FA as a mineral additive in cement-based grouts has improved the yield stress value of the samples. Since n-TiO2 has such a low specific surface area, the water requirement of the grout matrix tends to increase. Therefore, this situation causes increasing of cohesion. The developed ANNs model has been able to predict the plastic viscosity and yield stress of cement-based grouts containing TiO2 nanoparticle doped fly ash with very low error rates and high accuracy

Study on the influence of surface roughness on wall slip effect (in rheological measurement) of magnetic fluid

Magnetic fluid is a new type of smart material, and its rheological properties have always been a hot research topic, and how to measure quickly and accurately is also a research difficulty, among which wall slip is one of the important influencing factors. In this work, we studied the effect of wall slip on the flow curve and yield stress of the magnetic fluid. To this end, we used multiple rheometer rotors with different surface roughness. The flow curves of two magnetic fluids with different viscosities were drawn, and the Herschel-Bulkley model was used to fit them to determine the yield stress. In addition, a forced shear oscillation test was carried out on the magnetic fluid. We found when using a rotor with a smooth measuring surface to measure the flow curve of the magnetic fluid, the shear stress of magnetic fluid is underestimated at low shear rates. At the same time, the fitted values of yield stress of various roughness measurement surfaces were similar and greater than those of smooth measurement surfaces. From an engineering point of view, the fitting values of non-smooth measurement surfaces were more reliable. Affected by the wall slip, the storage modulus curve of the magnetic fluid often dropped suddenly during the frequency sweeping oscillation process. By changing the surface roughness of the measuring rotor, the wall slip during the oscillation sweep process was effectively restrained. The research results will have certain guiding significance for the study of the state of the solid–liquid interface junction in applications such as magnetic fluids sealing and lubrication.

Rheological behavior of gel polymer electrolytes: yield stress and viscoelasticity

In redox flow batteries (RFBs), semi-solid flow cells incorporate solid particles in the same medium than the electrolyte in the form of slurry to increase energy efficiency. However, rheological properties of the fluid hosting the solid particles need to favor particle stability and pumping process within the RFB. In this study, the materials used to formulate a gelled polymer electrolyte (GPE), which will be used as a suspending fluid for dense zinc microparticles in a zinc slurry-air RFB, were analyzed. It was found that when using polyacrylic acid and attapulgite gelling agents together, a yield stress behavior was obtained. This satisfactory result was accomplished even in harsh alkaline conditions (pH > 14), representative of the battery operation conditions in which the chemical stability of gelling agents is threatened. Yield stress values were obtained by fitting experimental data to the Herschel-Bulkley model, and results were compared to those obtained by creep tests. Results indicate that the GPEs presented in this study are good candidates to host zinc microparticles for a zinc slurry-air RFB.Graphical abstract

Evaluation of a Uniaxial Powder Tester and Comparison with an Annular Shear Tester

Bulk flowability measurement of particulate systems for quality control and product development purposes requires a fast, repeatable, accurate and affordable characterization approach. In the present study, two versions of the recently developed Freeman Technology Uniaxial Powder Tester (UPT) are compared to the Schulze Ring Shear Tester and the Johanson Hang-Up Indicizer. The UPT instruments were found to have excellent repeatability in measurements of uniaxial unconfined yield stress and compressed bulk density across a broad range of materials. Amongst the testing devices investigated in this study, the computer-controlled Advanced UPT (AUPT) instrument showed higher repeatability than the Manual UPT (MUPT) and the Johanson Indicizer. The Schulze Ring Shear Tester (RST) had slightly better repeatability than the AUPT, but there were a few situations in which its automated software did not produce a value of unconfined yield stress, resulting in a need to manually process the data. For most of the test cases, the AUPT measured a higher value of uniaxial unconfined yield stress than the MUPT. This was attributed to the stress relaxation that the powder bed experiences in the MUPT, where the consolidation stress is not automatically maintained on the sample. The AUPT measured lower values of unconfined yield stress compared to the Schulze RST for all the cases in this study. This is a well-recognized occurrence as the Schulze RST and other biaxial testers, in contrast to the AUPT, brings the sample to the critical consolidation state before measuring the shear strength. The AUPT produced its flow function data in about half the time as the Schulze RST.

Microstructural engineering of medium entropy NiCo(CrAl) alloy for enhanced room and high-temperature mechanical properties

This work demonstrates the development of a strong and ductile medium entropy alloy by employing conventional alloying and thermomechanical processing to induce partial recrystallization (PR) and precipitation strengthening in the microstructure. First, the cold working of homogenized alloy resulted in a highly deformed microstructure. On annealing at 700 °C, B2 ordered precipitates heterogeneously nucleate on the highly misoriented sites. These B2 promotes particle stimulated nucleation (PSN) of new recrystallized strain-free grains. The migration of recrystallized grain boundaries leads to discontinuous precipitation of L12 ordered regions in highly dense lamellae structures. We also observe near-spherical L12 precipitates in the non-recrystallized grains. Atomic-scale compositional analysis reveals a significant amount of Ni confined to the Phase Boundary (PB) regions between B2 and L12 precipitates, indicating Ni as a rate-controlling element for coarsening the microstructure. On 20 h of annealing, the alloy comprises a composite microstructure of recrystallized and non-recrystallized grains, B2 particles at the grain boundaries (GBs), and coherent L12 precipitates inside the grains. The microstructure results in a 0.2% yield stress (YS) value of ∼1060 MPa with ∼25% elongation at ambient temperature and retains up to ∼910 MPa at 670 °C. Examination of deformed microstructure reveals excessive twinning, formation of stacking faults, shearing of L12 precipitates, and accumulation of dislocations at around the B2 precipitates and GBs attributed to high strain hardening of the alloy.