Department of Metallurgical & Materials Engineering

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The present work systematically investigates the influence of crystal orientation on deformation response of quasi-single crystal zinc using nanoindentation. Both Berkovich and cono-spherical indenters were used to extract the quantitative information as well as to elucidate the deformation mechanisms with crystal orientations. The Young's modulus of zinc was highly anisotropic and increased as orientation changed from basal (38 ± 2 GPa) to prismatic (103 ± 6 GPa) orientation. Deformation mechanisms, such as slip, twinning and formation of sub-structure were explained by using slip trace analysis and a combination of variety of characterization techniques, such as atomic force microscopy (AFM), optical microscopy (OM), scanning electron microscopy (SEM), and orientation imaging microscopy (OIM). Influence of crystal orientation on twinning load, extent of pile-up/sink-in and indent morphology has been discerned. Changing the orientation from basal to prismatic not only increased the pile-up height/sink-in depths but also resulted in their anisotropic behavior, which were further correlated with twinning and type of slip systems activated. © 2020

World University root node

Materials Science and Engineering A

Effect of crystal orientation on indentation-induced deformation behavior of zinc

This paper reports on the dissolution of δ-ferrite in the weld fusion zone using post-weld normalizing and tempering (PWNT) and its effect on mechanical properties. The autogenous gas tungsten arc welding (GTAW) was used to prepare double-sided welded joints of P92 steel. After welding, post-weld heat treatment (PWHT) at 760 °C for 2 h and post-weld normalizing at 1050 °C for 1 h followed by tempering at 760 °C for 2 h were performed. The morphology, composition, structure, and hardness of δ-ferrite are verified. The effect of PWHT and PWNT on mechanical properties is also observed. In as-welded and PWHT conditions, the retention of δ-ferrite was observed while the dissolution of δ-ferrite was confirmed after PWNT. In the PWNT condition, uniform microhardness across the welded joint, increased ductility, and increased Charpy toughness of weld fusion zone (almost equal to as received material) were achieved. Dissolution kinetics of δ-ferrite is quantified using Thermo-Calc for Scheil's solidification calculation and DICTRA for calculating diffusion coefficients of Cr and W at 1050 °C in austenite. © 2020

Dissolution of δ-ferrite and its effect on mechanical properties of P92 steel welds

Formation of Laves phase in creep strength enhanced ferritic steel is investigated using re-austenitization and tempering treatment. The as-received material is exposed to 620°C for 4560 h aging, and then re-austenitizated at 1050°C for 1 h, and followed by tempering at 760°C for different times (2 and 4 h). After re-austenitization and tempering, the dissolution of Laves phase is observed while grain size and microhardness have not changed significantly. A model is suggested to quantify the dissolution of W-containing Laves phase. Thermo-Calc is used to predict driving forces for precipitation of Laves and M23C6 phases. © 2020, © 2020 Institute of Materials, Minerals and Mining.

Materials Science and Technology (United Kingdom)

Dissolution of laves phase by re-austenitization and tempering of creep strength enhanced ferritic steel

The present study investigates the orientation dependence of deformation-induced martensite (DIM) transformation in carbide-free bainitic steel using experimental macrotexture analysis and crystal plasticity-based modelling. The results indicate that the P {110}〈122〉 component of retained austenite preferentially undergoes DIM transformation during uniaxial tensile deformation at room temperature. It is also found that the P component of retained austenite possesses the lowest Schmid factor value compared with other possible texture components. The lowest Schmid factor value of the P component results in the highest resolved shear stress value for its slipping. As a result, during plastic deformation when most of the initial components of the retained austenite reorient themselves to other relatively stable orientations, the P component remains almost unaffected. Accumulation of stress concentration thus increases along this component, which eventually leads to its deformation-induced transformation to martensite. © 2020, The Minerals, Metals & Materials Society and ASM International.

Metallurgical and Materials Transactions A

Orientation Dependence of Deformation-Induced Martensite Transformation During Uniaxial Tensile Deformation of Carbide-Free Bainitic Steel

This paper investigates the effect of microstructure modification by heat treatment on stress corrosion cracking (SCC) behavior of Mg–4Zn alloy in simulated body fluid (SBF). Mg–4Zn alloy in as cast, solution heat treated and peak aged conditions was susceptible to SCC in SBF when strained at 3.6 × 10−6 s−1. SCC index based on fracture energy is least for solutionized alloy (0.84), while 0.88 for as cast and peak aged alloys. Fractographic analysis indicates predominantly intergranular SCC for solution treated alloy initiated by anodic dissolution near grain boundaries. As cast and peak aged alloy shows mainly transgranular failure due to hydrogen embrittlement adjacent to secondary phase particles. © 2019 Elsevier B.V.

Materials Science and Engineering C

Elucidating the role of microstructural modification on stress corrosion cracking of biodegradable Mg–4Zn alloy in simulated body fluid

A metastable transformative Fe39Mn20Co20Cr15Si5Al1 high entropy alloy (Al-HEA) was friction stir butt welded with Al-7050 alloy. Extensive mechanical mixing was evident in the weld nugget wherein sheared HEA particles were dispersed in Al-alloy matrix. Detail investigation of the weld interface showed suppression of intermetallic formation thereby approaching a clean interface. Tensile testing of the weld nugget showed a strength of 400 MPa with ~ 10% ductility whereas corrosion testing showed no sign of extensive pitting at the Al-HEA/Al-7050 weld interface. Therefore, use of high entropy alloy is an effective pathway for obtaining strong dissimilar joints with high strength Al alloys for lightweight applications. © 2020

Materialia

Friction stir butt welding of a high strength Al-7050 alloy with a metastable transformative high entropy alloy

Controlling the elastic modulus of simple synthetic hydrogels like polyacrylamide is essential to their use in many areas of biotechnology, including tissue engineering, medical device development, and drug delivery applications. Indentation-based methods for measuring hydrogel elastic moduli are preferred over measurements in shear rheometers or tensile testing instruments when the freedom to choose sample volume and shape are restricted; contact lenses represent such an example. It is often believed that the local application of indentation loads will volumetrically compress hydrogels, increasing the sample's polymer concentration even when the applied pressure is less than the hydrogel's osmotic pressure. Here, we test this idea by volumetrically compressing polyacrylamide hydrogels of different compositions while measuring the degree of compression with increasing applied pressure. Our results reveal that at applied pressures below the hydrogel osmotic pressure, the gels exhibit only marginal compression, while above the osmotic pressure the gels compress as predicted by classical polymer physics theory. Combining measurements of osmotic pressure and polymer mesh size, we determine the scaling relationships between hydrogel composition, mesh size, and osmotic pressure. By demonstrating agreement between experiment and theory, we use our measurements to determine the Kuhn length of the individual polymer chains constituting the hydrogels. © 2020

Biotribology

Hydrogel compression and polymer osmotic pressure

The present study correlates the effect of enhanced metastability on both the well-understood γ-f.c.c. stacking fault energy (SFE) and deformation mechanisms in the ε-h.c.p. phase of a metastable high entropy alloy (HEA). The SFE of a Fe40Mn20Cr15Co20Si5 alloy (CS-HEA) was experimentally determined to be ∼6.31 mJ m−2 using in-situ neutron diffraction. The relatively low-measured SFE of the CS-HEA results in a high fraction of the ε-h.c.p. phase (58 %) triggering significant stress partitioning to ε-h.c.p. and a marginal fraction of γ-f.c.c. → ε-h.c.p. transformation (∼25 %). The ε-h.c.p. phase accommodated a significant amount of strain marked by the large stress-induced decrease of c/a ratio (from ∼1.619 to 1.588), which was accompanied by activation of non-basal deformation modes, such as deformation twinning and pyramidal slip. Using in-situ neutron diffraction, we show by decreasing SFE and stabilization of large fractions of ε-h.c.p., activation of non-basal deformation modes are responsible for high work hardenability in absence of significant γ-f.c.c. → ε-h.c.p. transformation. © 2019 Elsevier Ltd

Materials Today Communications

Investigating the deformation mechanisms of a highly metastable high entropy alloy using in-situ neutron diffraction

The ability to produce atomically precise, artificial oxide heterostructures allows for the possibility of producing exotic phases and enhanced susceptibilities not found in parent materials. Typical ferroelectric materials either exhibit large saturation polarization away from a phase boundary or large dielectric susceptibility near a phase boundary. Both large ferroelectric polarization and dielectric permittivity are attained wherein fully epitaxial (PbZr0.8Ti0.2O3)n/(PbZr0.4Ti0.6O3)2 n (n = 2, 4, 6, 8, 16 unit cells) superlattices are produced such that the overall film chemistry is at the morphotropic phase boundary, but constitutive layers are not. Long- (n ≥ 6) and short-period (n = 2) superlattices reveal large ferroelectric saturation polarization (Ps = 64 µC cm−2) and small dielectric permittivity (εr ≈ 400 at 10 kHz). Intermediate-period (n = 4) superlattices, however, exhibit both large ferroelectric saturation polarization (Ps = 64 µC cm−2) and dielectric permittivity (εr = 776 at 10 kHz). First-order reversal curve analysis reveals the presence of switching distributions for each parent layer and a third, interfacial layer wherein superlattice periodicity modulates the volume fraction of each switching distribution and thus the overall material response. This reveals that deterministic creation of artificial superlattices is an effective pathway for designing materials with enhanced responses to applied bias. © 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Fulltext

Advanced Electronic Materials

Large Polarization and Susceptibilities in Artificial Morphotropic Phase Boundary PbZr1− xTixO3 Superlattices

After long-term service, boat samples of 1Cr-1/2Mo steel seemed to have aged, evidenced by the spheroidisation of carbides in the pearlite region, and a dispersion of fine M23C6 precipitation in the ferrite matrix. The yield strength of the cracked boat samples was two to three times the reported values of new A387 Grade 12 Class 2 material. The ductility is less than 0.5 times the reported values of the new grade. The intergranular fracture mode was likely due to the fine carbide precipitation inside the ferrite grains that strengthened the metal matrix, and the coarse intergranular CrMo-rich carbides that weaken the precipitate/grain boundary interfaces. Cavities similar to creep were observed along the grain boundaries in some of the boat samples, suggesting a possible creep-oxidation damage mechanism for coke drum steels. © 2020 Institute of Materials, Minerals and Mining.