Transformation-induced Stress Research Articles

Microstructure and mechanical properties of the laminated heterostructured material with 316L stainless steel/18Ni300 maraging steel fabricated by WAAM

Heterostructured materials (HMs) have attracted extensive interest due to their excellent properties, and additive manufacturing presents great potential in fabricating HMs. A laminated HM (LHM) was prepared by wire and arc additive manufacturing with alternating deposition of 316L stainless steel (SS) and 18Ni300 maraging steel (MS). The microstructure, chemical composition, texture and mechanical properties of the LHM thin walls were investigated and compared with those of the corresponding single-material thin walls. Remelting and mixing of the previously deposited layer caused deviations in the chemical composition in both regions. The 18Ni300 MS region microstructure was composed of austenite and martensite phases with the K-S orientation relationship, and the 316L SS region microstructure consisted of the austenite phase. All samples exhibited obvious austenite phase epitaxial growth, causing grains with the same orientation to pass through multiple deposited layers. The cubic texture in the as-fabricated 316L SS sample disappeared in the 316L SS region of the LHM samples. The Goss texture intensity in the 18Ni300 MS region decreased compared with that in the 18Ni300 MS thin walls, from 20.6 to 6.36. The 18Ni300 MS region microhardness of the LHM samples of 263 HV was lower than that of the 18Ni300 MS sample due to the lower-hardness austenite phase. The ultimate tensile strength of the LHM samples was 635.25 ± 31.1 MPa, which was between those of 316L SS and 18Ni300 MS. The uniform and total elongations of the LHM samples were 19.85 ± 3.6% and 29.2 ± 2.3%, which were higher than the mixing law-calculated values. The plasticity improvement was attributed to transformation-induced plasticity and stress state variation. In the initial plastic deformation stage, the 18Ni300 MS region underwent more plastic strain with a high dislocation density, causing the strain-induced martensitic transformation. The 316L SS region was strengthened with high strain, and its necking caused stress state conversion from uniaxial to multiaxial stress.

Emergence of microbial resistance against nanoparticles: Mechanisms and strategies.

Antimicrobial nanoparticles have gained the status of a new generation of drugs that can kill bacterial pathogens by multiple means; however, nanoparticle resistance acquired by some bacterial pathogens has evoked a cause of concern. Several reports suggested that bacteria can develop nanoparticles, specifically metal nanoparticle resistance, by mechanisms: nanoparticle transformation-induced oxidative stress, membrane alterations, reversible adaptive resistance, irreversible modifications to cell division, and a change in bacterial motility and resistance. Surface properties, concentration and aggregation of nanoparticles, biofilm forming and metal exclusion capacity, and R plasmid and flagellin synthesis by bacteria are crucial factors in the development of nanoparticle resistance in bacteria. Studies reported the resistance reversal by modifying the surface corona of nanoparticles or inhibiting flagellin production by bacterial pathogens. Furthermore, strict regulation regarding the use and disposal of nano-waste across the globe, the firm knowledge of microbe-nanoparticle interaction, and the regulated disposal of nanoparticles in soil and water is required to prevent microbes from developing nanoparticle resistance.

Anisotropic cleavage fracture caused by transformation-induced internal stress in an as-quenched martensite

The effect of microscopic internal stresses (Type-II) generated via martensitic transformation from austenite (A) to martensite (M) on {001} M cleavage fracture was investigated in an as-quenched 0.1C–5.0Mn steel (mass%). Crystallographic orientation analysis using the electron backscatter diffraction technique revealed that cryogenic {001} M cleavage fracture was promoted predominantly in mode I fracture by Charpy impact testing, and that the Bain group, where martensite variants belong to the same Bain variants, acted as an effective unit to prevent fracture. It was also discovered that the cleavage crack preferentially propagates on (001) M rather than on (100) M in the Bain group, where (001) M was nearly parallel to (001) A in the Bain lattice correspondence ([−110] A // [100] M , [110] A // [010] M , (001) A // (001) M ). In addition, by using a combination of a micro-scale focused ion beam and high-precision digital image correlation techniques, it was found that microscopic internal stresses were anisotropically developed in each Bain group. The principal axes of the internal stresses corresponded to the <001> M coordinate axes in the Bain lattice correspondence, and the principal stress parallel to [001] M is much higher than that of the other two. After the measurement of the internal stresses, it was proved that the cleavage fracture behavior obeyed the effective normal stress in the normal direction of {001} M consisting of the resolved bending stress in the impact test and the anisotropic internal stress generated via martensitic transformation. This suggests that the transformation-induced internal stress originating from the Bain strain leads to the anisotropy of the cleavage fracture in lath martensite. • The effect of microscopic Type-II internal stress on the macroscopic cleavage fracture was investigated in lath martensite. • FIB-DIC technique revealed that martensitic transformation induces the anisotropic elastic strain in each Bain group while maintaining <001> as the principal axes. • EBSD analysis proved that mode-I cleavage crack preferentially propagates on (001) rather than on (100) in a Bain group regardless of carbon contents. • Transformation-induced internal stress originating from Bain strain leads to the anisotropy of the cleavage fracture in lath martensite.

Modeling diffusive phase transformation and fracture in viscoplastic materials

In recent years, the phase-field method has attracted a lot of attention and has emerged as one of the most efficient tools for modeling fracture and phase transformation. The phase-field method is based on the regularization of discontinuities which allows the resolution of complex problems using classical numerical methods. A multiphase-field model which is essential for describing crack propagation in non-static heterogeneous materials is still missing. In this work, we fill this gap by combining the fracture phase-field approach based on Griffith’s theory with the phase-field approach for diffusive phase transformation in viscoplastic materials. Several benchmark examples of increasing complexity demonstrate, the effect of viscoplasticity and diffusive phase transformation on fracture behavior based on the critical loading, energy density until failure and crack topology. We show that viscoplastic activity at the crack tip mitigates the effect of pre-existing defects on mechanical strength. In a heterogeneous case, it is shown that viscoplastic activity introduces an intermediate fracture response between the reference behavior, which does not take into consideration the phase transformation-induced residual stresses, and the elastic behavior, which integrates these residual stresses by taking into account only the elasticity. The interaction between the heterogeneities and the crack topology is also highlighted.

Retained Austenite Transformation-Induced Residual Stress Change in Carburized 16MnCr5 Steel

Abstract Carburization, a heat treatment commonly used in industries to improve fatigue performance of components, usually results in untransformed austenite in a transformed matrix of martensite or other phases. The subsequent transformation of the retained austenite due to service loading is complex and can result in the alteration of beneficial residual stresses. The amount of retained austenite decomposed under a few axial loading cases was determined by measuring the retained austenite content before and after loading of through-carburized- and carburized case only (composite)–hardened 16MnCr5 steel samples. Separate case and core stress−strain curves and the retained austenite transformation in the case layer of the composite model were used to predict the stress−strain and the residual stress behavior of the composite samples with a simple compatibility model and a finite element model.

Solid-state phase transformation-induced residual stress in selective laser melting of martensitic stainless steel

Solid-state phase transformation-induced residual stress in selective laser melting of martensitic stainless steel

The evolution of local stress during deformation twinning in a Mg-Gd-Y-Zn alloy

In this study, we perform in-situ tensile testing and high-resolution electron backscatter diffraction (HR-EBSD) to monitor the twin local stresses at different stages: (i) before twinning, (ii) twins that have propagated into the parent crystal, and (iii) thickening of the twin lamella. The resolved shear stress (RSS) at the twin interface is calculated during deformation twinning, which indicates that the RSS evolution is a dynamic process. Negative shear stress is observed during the propagation stage, which provides evidence for the twinning shear transformation-induced stress reversal. Furthermore, a local Schmid factor (LSF) is used to evaluate the extent to which the local stress is dominated by the RSS on the identified twin plane. The experimental results indicate that the LSFs evolve with strain and are at their maximum level before twinning. The initiated twins are correlated with the highest LSFs compared with the unactivated variants. In addition, the product of the Luster Morris m′ value times the LSF of the twin variant may reveal a threshold for the slip-induced twinning process.

The evolution of the martensitic transformation at the high-driving-force regime: A microsecond-scale time-resolved X-ray diffraction study

The reverse martensitic transformation proceeds through several sub-processes at various length and time scales. We study the transformation kinetics at the high thermodynamic driving force regime, by inducing a rapid heating-pulse in a shape memory alloy wire. We track the evolution of the transformation at the microsecond scale by multi-frame time-resolved X-ray diffraction at synchrotron radiation with simultaneous high-bandwidth force measurements. The x-ray probed a narrow region at the periphery of the wire, while the force was a measure for the transformation-induced stress in the bulk of the wire. We reveal three stages occurring at different times and length-scales in the material. During the first 5 μs the transformation is undetectable. Then, a rapid transformation occurs near the surface and saturates after 9 μs. The evolution of the transformation in the bulk becomes discernible only after the transformation near the surface completes and lasts for approximately 40 μs.

A residual stresses numerical simulation and the relevant thermal-mechanical mapping relationship of Fe-based coatings

Abstract Residual stresses model comprehensively considers the three main sources of residual stress during the coating deposition process: quenching stress, thermal stress and phase transformation-induced stress. With the deposited layer temperature, coating thickness, number of deposited layers and relevant workpiece dimensions as the input, the model can easily calculate the final residual stress distribution in the coating. Moreover, the thermal–mechanical behavior during the coating deposition process was revealed through experimental and theoretical analysis of coatings. The results showed that the coating fabricated within the range of 65.2–122.5 °C have relatively low residual stresses, ensuring relatively high service reliability.

Engineering Heterogeneous Multiphase Microstructure by Austenite Reverted Transformation Coupled with Ferrite Transformation

A heterogeneous multiphase medium Mn steel (Fe-10Mn-0.47C-2Al-0.7V, wt.%) consisting of prior austenite, martensite, reverted austenite, and ferrite is, for the first time, realized by both austenite reverted transformation and ferrite transformation. The phase fraction, kinetics, mechanisms, and microstructure evolution during the transformation sequence are systematically investigated. The heterogeneous multiphase medium Mn steel has great potential for high strain hardening by a continuous transformation-induced plasticity effect, grain-size gradient, and stress–strain partitioning. The present work provides a new pathway to design a heterogeneous multiphase microstructure in medium Mn steel.

Multicomponent Metallic Ni–Mn-Based Alloys with Thermally, Mechanically, and Magnetically Controlled Shape Memory Effects

This paper presents the results of a systematic study of structural and magnetic phase transformations and properties of Ni–Mn-based alloys of the main four quasi-binary NiMn–NiTi, NiMn–NiAl, NiMn–NiGa and Ni2MnGa–Ni3Ga systems. Generalized phase diagrams of existing structural and magnetic phase transformations have been constructed. This study found that alloying with a third component (Ti, Al, Ga, and Mn) decreases the critical temperatures of thermoelastic martensitic transformations with respect to the critical temperatures of parent intermetallics. The morphology of martensite was shown in the hierarchy of packets of thin coherent nano- and submicron-sized crystals with inrterphase boundaries close to {011}B2; the martensite crystals are twinned along one of the 24 {001}〈01 $$\bar {1}$$ 〉 “soft” twinning shear systems in the austenite. This mechanism provides the coherent accommodation of thermoelastic martensitic transformation-induced elastic stresses.

Transformation-induced stress at telomeres is counteracted through changes in the telomeric proteome including SAMHD1.

Telomeres play crucial roles during tumorigenesis, inducing cellular senescence upon telomere shortening and extensive chromosome instability during telomere crisis. However, it has not been investigated if and how cellular transformation and oncogenic stress alter telomeric chromatin composition and function. Here, we transform human fibroblasts by consecutive transduction with vectors expressing hTERT, the SV40 early region, and activated H-RasV12. Pairwise comparisons of the telomeric proteome during different stages of transformation reveal up-regulation of proteins involved in chromatin remodeling, DNA repair, and replication at chromosome ends. Depletion of several of these proteins induces telomere fragility, indicating their roles in replication of telomeric DNA. Depletion of SAMHD1, which has reported roles in DNA resection and homology-directed repair, leads to telomere breakage events in cells deprived of the shelterin component TRF1. Thus, our analysis identifies factors, which accumulate at telomeres during cellular transformation to promote telomere replication and repair, resisting oncogene-borne telomere replication stress.

Mechanical properties and advanced subjects in shape memory alloys and polymers

Advanced subjects in mechanical properties of shape memory alloys and polymers are di- scussed. In the subloop loading under a stress-controlled condition of the shape memory alloy, the transformation-induced stress relaxation appears due to variation in temperature. The enhancement of corrosion and corrosion fatigue life of the shape memory alloy is discus- sed. The development of a functionally-graded shape memory alloy and polymer is expected to obtain better performance. Three-way motion appears in the shape memory composite with the shape memory alloy and polymer.

A non-local implicit gradient-enhanced model for thermomechanical behavior of shape memory alloys

A three-dimensional, implicit gradient-enhanced, fully coupled thermomechanical constitutive model is developed within the framework of thermodynamic principles for NiTi shape memory alloys. This work focuses on unstable behaviors of NiTi samples under different thermomechanical loading conditions. Temperature variation and its coupling effect on non-local behavior of a shape memory alloy during a loading–unloading cycle at different strain rates are considered. The proposed constitutive equations are implemented into the finite element software ABAQUS, and the numerical investigations indicate that the used procedure is an effective computational tool for simulation of several behaviors of NiTi samples including phase front nucleation and propagation, stress–strain–temperature responses, and transformation-induced stress relaxation. The obtained results are shown to be in a good agreement with available experimental and numerical findings in the literature. The effectiveness of the model in removing mesh sensitivity is evaluated by investigating the mesh-dependence issue for the low strain rate problems through numerical examples.

Transformation-Induced Stress Relaxation of TiNi Shape Memory Alloy in Several Ambient Conditions during Subloop Loading

Transformation-Induced Stress Relaxation of TiNi Shape Memory Alloy in Several Ambient Conditions during Subloop Loading

Transformation-Induced Stress Relaxation of TiNi Shape Memory Alloy in Loading

Transformation-Induced Stress Relaxation of TiNi Shape Memory Alloy in Loading

Anomalous expansion of Nb nanowires in a NiTi matrix under high pressure

Under high pressure, materials usually shrink during compression as described by an equation of state. Here, we present the anomalous volume expansion behavior of a one-dimensional Nb nano-wire embedded in a NiTi transforming matrix, while the matrix undergoes a pressure-induced martensitic transformation. The Nb volume expansion depends on the NiTi transition pressure range from the matrix, which is controlled by the shear strain induced by different pressure transmitting media. The transformation-induced interfacial stresses between Nb and NiTi may play a major role in this anomaly. Our discovery sheds new light on the nano-interfacial effect on mechanical anomalies in heterogeneous systems during a pressure-induced phase transition.

Thermomechanical modeling and experimental investigation of transformation-induced creep and stress relaxation in shape memory alloy wires

Creep and relaxation phenomena are being observed in shape memory alloys, not only at high temperatures but also at room temperature, due to their martensitic transformation. Transformation-induced creep and stress relaxation in shape memory alloys occur due to temperature variations during loading and unloading cycles. In this work, a one-dimensional fully coupled thermomechanical model was employed to develop a continuum framework for studying these behaviors in shape memory alloy wires. A decrease or increase in stress was observed during forward or reverse transformation at a constant amount of strain, showing the stress relaxation and stress recovery, respectively. Similarly, the model predicts that strain increases or decreases when stress is held fixed in the course of forward or reverse transformation, meaning the phenomena of creep and creep recovery, respectively. This model provides the ability of investigating the effects of different ambient temperatures, strain rates, applied stresses and strains, and wire radii on the creep and relaxation responses of shape memory alloys. Relaxation and creep experiments at different ambient temperatures and loading or unloading rates were also done on NiTi wires, and the theoretical predictions were shown to be in a good agreement with the empirical observations.

The effect of porosity on the hot corrosion failure of thermal barrier coatings

It has been found that the use of low-grade fuels in land-based turbines results in the hot corrosion (Type-I) degradation of turbine blades in Saudi Arabia. Due to the diffusion of a molten salt, V2O5, into the top coat of thermal barrier coatings, volumetric expansion of the coating occurs as a result of the tetragonal-to-monoclinic transformation of zirconia. The top coat material is usually made porous due to the need for higher thermal resistance in the coatings. In the present study, a phase field model that estimates the kinetics of microstructure evolution during the corrosion process is estimated at 900 °C. The transformation-induced stresses are predicted by coupling the phase transformation with elasticity. The governing equations are implemented numerically using the finite element method. The effect of pore size, shape, orientation, and dispersion is also investigated. The result shows that very high compressive stresses are developed within the coating cross-section, which eventually causes the spallation failure of the coating.

Prediction of Residual Stresses During Gas Nitriding of H13 Steels Using Phase Field Approach

Gas nitriding is a common surface treatment practice to improve the wear resistance of AISI H13 hot extrusion die cavities. However, due to the presence of complex and sharp features of die cavities, it has been observed that nonuniform nitride layer develops in these regions. Moreover, the formation of compound layer in the surface vicinity of nitrided surfaces leads to the development of transformation-induced stresses. The present work presents the application of the phase field method in predicting the evolution of the nitride layers and associated residual stresses during the gas nitriding of AISI H13 tool steels. Nitriding process is modeled and simulated in line with experimental setup, which uses automated two-stage controlled nitriding process. Some representative samples having commonly used geometric features are manufactured and nitrided for validation purpose. Both experimental and numerical results are found in close agreement in terms of nitrogen concentration and corresponding microhardness profiles. The results show that high stresses are induced at the surface due to formation of the nitride layers, and these stresses are found to be higher at the sharp corners. In view of the current results, some process and design strategies are suggested for improved and more effective nitriding treatment of hot extrusion dies used in the industry.