To Transformation-induced Plasticity Research Articles

In-situ Laue micro-diffraction during compression tests on Ce-TZP single crystal micropillars

The widespread use of ceramics faces challenges due to their limited ductility, stemming from a lack of dislocation-induced plasticity. This study focuses on ceria-stabilized tetragonal zirconia a ceramic that benefits from its unique tetragonal-to-monoclinic phase transformation under stress, leading to transformation-induced plasticity (TRIP). Employing a micro-scale in-situ approach, the study aims to understand the mechanisms governing TRIP, particularly focusing on crystallographic features of the transformation. In-situ compression tests using synchrotron light source and Laue micro-diffraction were conducted on single crystal micropillars with various orientations. Results show that crystal orientation significantly affects the mechanical behaviour, with transformation being most likely when the resolved shear stress on {100} planes of the double-cell and along the <010> direction is highest. The martensite theory validates the correspondences obtained experimentally. This research provides insights into enhancing the mechanical properties of ceramics by leveraging the TRIP mechanisms.

Quenching and partitioning heat treatment: the third generation of advanced high-strength steel

This manuscript aims to present an overview of quenching and partitioning (Q&amp;P) heat treatment usually applied to transformation-induced plasticity (TRIP) and duplex steels (DP). TRIP and DP are the first generations of advanced high-strength steels (AHSS). AHSSs present multiphase microstructures that ensure an advantageous combination of strength and ductility. The Q&amp;P heat treatment process aims to obtain a mixed microstructure with martensite and retained austenite and improve the relation strength/ductility of common AHSS. The retained austenite of Q&amp;P steels is rich in carbon and stable at room temperature. The heat treatment process implicates quenching the steel between the martensite-start (Ms) and martensite-finish (Mf) temperatures, followed by partitioning. Partitioning is an isothermal heat treatment that occurs above the Ms temperature. A diffusion process enriches the remaining austenite with carbon that migrates from martensite. The stability of retained austenite at room temperature improves the mechanical performance of steel, once it increases the material’s toughness and elongation. The optimal control of microstructure originates the third generation of AHSS and enables to reduce of weight and improved mechanical response of automotive parts made of the TRIP and DP steels.

TRIP steels: the features of chemical composition and structure, prospects of application (overview)

This article provides a brief overview of steels prone to transformation induced plasticity (TRIP), which belong to the class of advanced high-strength steels (AHSS). The necessary set of properties in these steels is formed due to the partial preservation of supercooled austenite in the structure. The article considers the mechanism of TRIP transformation, which depends on the value of the temperature of the beginning of the martensitic transformation. It is shown that the amount and stability of supercooled austenite can be influenced by varying the temperature and time parameters of heat treatment. In addition to heat treatment, the qualitative and quantitative parameters of metastable austenite are significantly influenced by the alloying of TRIP steels, and the alloying elements themselves can be divided into several main groups (ferrite-stabilizing, increasing the stability of supercooled austenite and micro-alloying). In the final part of the article, the prospect of using TRIP steels in the aerospace industry is considered, where reducing the metal consumption of parts is a priority. It is also worth considering that the production of parts using additive technologies is widespread in the aerospace industry. Therefore, the use of TRIP steels as a material in additive manufacturing leads to the formation of a new concept for creating parts with a unique set of properties, primarily with high structural strength, light weight and the possibility of self-adaptation to extreme external exposures. The research was carried out under contract No.&nbsp;13.2251.21.0107 on the topic "Investigation on 3D-printing&nbsp;of Advanced High Strength Steels with TRIP effect for realization&nbsp;of self-adapting aerospace structural elements",&nbsp;funded by the Ministry of Science and Education of the&nbsp;Russian Federation within the joint program for science&nbsp;and technology cooperation and implementation of joint&nbsp;call for Russian-Italian projects for 2021-2023.

Simultaneous increase of ultimate tensile strength and uniform elongation of 30Si2MnCrMoVE ultra-high strength steel by hot deformation direct quenching and partitioning

In order to further improve the combination of strength and ductility for 30Si2MnCrMoVE ultra-high strength steel (UHSS), a thermomechanical treatment, named deformation direct quenching and partitioning (DQ&P), was carried out on it. The microstructure evolutions and mechanical properties of 30Si2MnCrMoVE UHSS treated by DQ&P were compared with those treated by conventional off-line quenching and tempering (Q&T) through various microscopic characterization methods and uniaxial tensile tests. Moreover, the effects of austempering temperature on the microstructure evolutions and mechanical properties of the studied steel after DQ&P process were also investigated. The results show that the DQ&P samples, although lower or slightly lower yield strength, possess significantly higher ultimate tensile strength due to higher work-hardening rate caused by high density dislocations and fine dispersed carbides. Moreover, DQ&P310 sample exhibit apparently higher uniform elongation than Q&T sample despite of comparable content of retained austenite due to more prone to transformation induced plasticity (TRIP) effect. The DQ&P process can increase the ultimate tensile strength by 267 MPã423 MPa and the uniform elongation by 78%∼85%, respectively, as compared to Q&T process, which indicates that DQ&P process may be a promising thermomechanical treatment method to improve the comprehensive mechanical properties of the studied steel. The strengths and elongations of DQ&P samples do not vary monotonously with the increase of austempering temperature, which are both closely related to the content of retained austenite.

Effect of austempering temperature on high cycle fatigue behaviour in nanostructured bainitic steels

The effect of three different austempering temperatures viz. 250°C (NB250), 300°C (NB300) and 350°C (NB350) on high cycle fatigue behaviour of carbide-free nanostructured bainite was investigated. There was an increase in yield strength with a decrease in austempering temperature due to finer bainitic ferrite (BF) and its higher volume fraction compared to retained austenite (RA). However, NB350 showed significant strain hardening compared to NB250 and NB300 due to transformation induced plasticity (TRIP). This also had implications in enhancing its fatigue life at almost all stress levels compared to NB250 and NB300 inspite of having a lower yield strength and tensile strength.

Influences of manganese content and heat treatment on mechanical properties of precipitation-strengthened steels

In order to reduce the cost and improve the ductility of maraging steels without sacrificing strength, the high content of costly Ni element is partially substituted by inexpensive Mn to achieve metastable austenite. Thermodynamic simulation, composition screening and critical experiments are integrated to design ultrastrong dual-phase steels with the compositions of Fe–10Ni–3Al–4Mo–xMn (x = 0–10, wt%) by tailoring austenite fraction and heat treatment. The results show that for ageing following solid solution and quenching (soft ageing for commercial maraging steels, SA), the phase fraction of fcc should be less than that of bcc to achieve B2 precipitation in the bcc matrix. For the 9Mn alloy with a volume fraction of fcc more than 50%, ageing following cold rolling (hard ageing, HA) recovers the B2 precipitation that is hindered by fcc reversion during SA, resulting in an ultrahigh ultimate strength (∼1600 MPa) with an improved tensile ductility (∼7%) compared with the SA alloys (∼1450 MPa and ∼5% at best). The improved strength-ductility synergy at ultrahigh strength is attributed to transformation-induced plasticity (TRIP) and ultrafine grain size, both of which turn the fracture mode from transgranular cleavages to ductile dimples. This work demonstrates a promising strategy by addition of austenite-stabilized element and ageing without solid solution for achieving low cost and high strength-ductility synergy, which paves the way for the development of precipitation-strengthened dual-phase steels.

Microstructure and Mechanical properties of Medium Manganese Steels

Medium manganese steel is a 3rd generation advanced high strength steel, which contains 3–12 wt% manganese. This steel is highly suitable material for the automobile industry due to good balance between the cost of material and the tensile properties. It has got the optimum amount of strength and elongation. Initially the microstructure of this steel after cold rolling is deformed martensite (ά). Intercritical annealing is done to get moderate amount of retained austenite (γr) having good stability, which leads to higher strength and better ductility due to transformation-induced plasticity (TRIP). The formation of stable retained austenite (γr) by intercritical annealing process is our prime interest. Medium Manganese steel usually exhibits austenitic-ferrite microstructure after the intercritical annealing process, which makes the steel suitable for 3rd generation advanced high strength steels as this microstructure gives good amount of elongation. From this study we get best combination of intercritical annealing and quenching to get the required microstructures and properties. Thermo-calc software is used to find the optimum temperature for intercritical annealing at which we get optimum amount of retained austenite (γr) containing maximum manganese. Tensile tests were carried out at different pre-strain level from the samples taken in both rolling and transverse directions. Samples were prepared for SEM and optical microscope characterization to see the changes from initial microstructure of the steel. X-ray diffraction was also done to find out the amount of retained austenite that we are getting from tensile sample after pre-strain it to different level. It was concluded that after intercritical annealing at 650 °C for 2 h the steel sample have approximately 22% retained austenite and ultimate tensile strength (UTS) of 843 MPa and total elongation of around 36%.

A comparative study on hysteretic characteristics of austenitic stainless steel and carbon steel slit dampers under cyclic loading

Steel slit dampers were designed and fabricated for earthquake-resistant structures using austenitic stainless steel STS304 (ASTM type 304), and carbon steel SS275 (ASTM A36). Monotonic loading and cyclic loading tests were conducted for the materials and steel slit dampers. Monotonic material test results indicated that the tensile strength and elongation of STS304 material were superior to those of SS275. The repeated tests showed that the STS304 steel damper subjected to constant amplitude and incremental amplitude cyclic loading exhibited higher strength ratios and energy dissipation capacity than the SS275 damper until ultimate strength step and 30 mm displacement (story drift) on the skeleton curve of the stainless steel damper after yielding. However, the austenitic stainless steel (STS304) dampers exhibited brittle behavior under cyclic loading due to transformation induced plasticity (TRIP). The total number of cycles at the time of tensile fracture and compressive buckling occurrence was smaller than that of the carbon steel damper except for some specimens with short constant amplitude loading protocol, and thus the total energy dissipation capacity of austenitic stainless steel damper was also found to be on average 95% of that of the carbon steel damper. On the other hand, within the specified low cycle number of loading protocol and allowable story drift of retrofitted building, austenitic stainless steel STS304 slit damper possessed the excellent seismic performance. Finally, the predicted yield strength of the damper was compared with test yield strength and the effect of the cyclic plastic hardening on the yield strength of steel slit damper was also discussed.

Advanced mechanical properties obtained via accurately tailoring stacking fault energy in Co-rich and Ni-depleted CoxCr33Ni67-x medium-entropy alloys

This paper designs a new Co-rich and Ni-depleted CoxCr33Ni67-x medium-entropy alloy. Among them, the content of Cr is controlled, so that the alloys studied have the same short range-order (SRO), and make the changes of Co and Ni content directly and efficiently reflected in the reduction of stacking fault energy. With the increase of Co content and decrease of Ni, the stacking fault energy of Co38Cr33Ni29 alloy is reduced to ∼12 mJ/m2, and the deformation mode is changed from twinning induced plasticity (TWIP) to transformation induced plasticity (TRIP). At the same time, the tensile strength of 839 MPa and uniform elongation of 83% are obtained.

Adjustment of Mechanical Properties of Medium Manganese Steel Produced by Laser Powder Bed Fusion with a Subsequent Heat Treatment.

Medium manganese steels can exhibit both high strength and ductility due to transformation-induced plasticity (TRIP), caused by metastable retained austenite, which in turn can be adjusted by intercritical annealing. This study addresses the laser additive processability and mechanical properties of the third-generation advanced high strength steels (AHSS) on the basis of medium manganese steel using Laser Powder Bed Fusion (LPBF). For the investigations, an alloy with a manganese concentration of 5 wt.% was gas atomized and processed by LPBF. Intercritical annealing was subsequently performed at different temperatures (630 and 770 °C) and three annealing times (3, 10 and 60 min) to adjust the stability of the retained austenite. Higher annealing temperatures lead to lower yield strength but an increase in tensile strength due to a stronger work-hardening. The maximum elongation at fracture was approximately in the middle of the examined temperature field. The microstructure and properties of the alloy were further investigated by scanning electron microscopy (SEM), hardness measurements, X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and element mapping.

Microstructurally flexible high entropy alloys: Linkages between alloy design and deformation behavior

Development of multicomponent alloys, popularly known as high entropy alloys (HEAs) provides abundant compositional space for designing a variety of HEAs, including equiatomic, dual phase and microstructurally flexible (MF-HEAs). Among them, the design of MF-HEAs further extends the HEA domain in terms of understanding adaptive phase evolution with respect to change in alloy chemistry and processing parameters. This responsive phase evolution enabled near single phase ε (h.c.p., 95%) or γ (f.c.c., 90%) dominant microstructures, depending on imposed processing strain, strain rate and temperature for a selected alloy chemistry. The γ-phase dominated HEAs showed slower yet sustained work hardening (WH) rates (~ 2000 MPa) owing to transformation induced plasticity (TRIP) effect whereas ε-phase dominated microstructure showed exceptionally high and sustained work hardening rates (2300–2700 MPa) due to formation of nano plates or twins in ε-phase upon deformation. Therefore, MF-HEA design leads to exceptional strength–ductility synergy (1100-1250 MPa, 30-43%) irrespective of the dominance of either γ- or ε-phase in the starting microstructure owing to selective operation of deformation mechanisms in the dominant phase.

Effect of tempering conditions on adiabatic shear banding during dynamic compression and ballistic impact tests of ultra-high-strength armor steel

In this study, roles of strain-hardening rate on susceptibility of adiabatic shear band (ASB) formation and subsequent cracking were investigated in two ultra-high-strength armor steel plates heat-treated differently. The quenched and tempered steel contained ~2% of retained austenite in the tempered martensitic matrix, while the quenched and austempered steel contained ~4% retained austenite in the bainitic matrix partly with the tempered martensite. The actual ballistic impact test results revealed the lower sensitivity of ASB formation in the austempered steel than in the tempered steel, which corresponded well to the higher critical strain for ASB formation in the dynamic compressive test using a laboratory-scale split Hopkinson pressure bar (SHPB). The austempered steel caused the higher internal stress among various constituents, and all the retained austenite transformed into martensite during the deformation, thereby leading to transformation-induced plasticity (TRIP) effect. The higher strain-hardening rate induced by these higher internal stress and TRIP effect increased resistance to ASB formation, which was confirmed by a calculation of ASB susceptibility. Thus, the austempered steel was much less susceptible to the ASB formation during the ultra-high-speed deformation. Consequently, the increased resistance to ASB formation retarded the initiation and propagation of ASBs and cracks.

Abnormal TRIP effect on the work hardening behavior of a quenching and partitioning steel at high strain rate

Quenching and partitioning (Q&P) steels possess high strength and good ductility because of the transformation of metastable austenite to martensite, which is referred to transformation-induced plasticity (TRIP) effect. In literature, TRIP effect generally results in an enhancement of work hardening rate during tensile test. Nevertheless, the present work observes an abnormal TRIP effect in a 1500 MPa Q&P steel. Although a considerable amount of retained austenite transformed to martensite during the tensile test at a strain rate of 1000 s − 1, no obvious enhancement of work hardening rate was observed. To explore the underlying mechanisms for such an abnormal TRIP effect, the evolution of dislocation density and martensitic transformation were characterized by synchrotron X-ray diffraction and electron microscopy. Comparing the quasi-static and high-strain-rate results, it is found that the dislocation density in the martensite matrix is suppressed at 1000 s − 1, resulting in a lower work hardening. Furthermore, the transformed martensite deforms plastically at 1000 s − 1. Without the composite-like deformation behavior (elastically in hard transformed martensite and plastically in soft martensite matrix), the corresponding work hardening is reduced.

Influence of carbon-partitioning treatment on the microstructure, mechanical properties and wear resistance of in situ VCp-reinforced Fe-matrix composite

The wear resistance of iron (Fe)-matrix materials could be improved through the in situ formation of vanadium carbide particles (VCp) with high hardness. However, brittleness and low impact toughness limit their application in several industries due to addition of higher carbon content. Carbon-partitioning treatment plays an important role in tuning the microstructure and mechanical properties of in situ VCp-reinforced Fe-matrix composite. In this study, the influences of carbon-partitioning temperatures and times on the microstructure, mechanical properties, and wear resistance of in situ VCp-reinforced Fe-matrix composite were investigated. The experimental results indicated that a certain amount of retained austenite could be stabilized at room temperature through the carbon-partitioning treatment. Microhardness of in situ VCp-reinforced Fematrix composite under carbon-partitioning treatment could be decreased, but impact toughness was improved accordingly when wear resistance was enhanced. In addition, the enhancement of wear resistance could be attributed to transformation-induced plasticity (TRIP) effect, and phase transformation was caused from γ-Fe (face-centered cubic structure, fcc) to α-Fe (body-centered cubic structure, bcc) under a certain load.

In-Situ Characterization by High-Energy X-ray Diffraction of the Phase Transformations Leading to Transformation-Induced Plasticity-Aided Bainitic Steel

The phase transformations occurring during the heat treatments leading to transformation-induced plasticity (TRIP)-aided bainitic steel have been investigated in-situ by high-energy X-ray diffraction (HEXRD) conducted with synchrotron light at 90 keV. Direct microstructure characterization has been performed by electron microscopy using electron backscatter diffraction and orientation and phase mapping in a transmission electron microscope. HEXRD data allow the quantification of the evolution of the austenite phase fraction with the heat treatments, as well as its carbon content and the fraction of carbides, from the lattice parameter evolution. It is shown that different combinations of austenite fraction and carbon content can be reached by adjusting the heat treatment temperature.

Phase transformation induces plasticity with negligible damage in ceria-stabilized zirconia-based ceramics

Ceramics and their composites are in general brittle materials because they are predominantly made up of ionic and covalent bonds that avoid dislocation motion at room temperature. However, a remarkable ductile behavior has been observed on newly developed 11 mol.% ceria-stabilized zirconia (11Ce-TZP) composite containing fine alumina (8 vol.% Al2O3) and elongated strontium hexa-aluminate (8 vol.% SrAl12O19) grains. The as-synthesized composite also has shown full resistance to Low Temperature Degradation (LTD), relatively high strength and exceptionally high Weibull modulus, allowing its use in a broader range of biomedical applications. In this study, to deepen the understanding of plastic deformation in Ce-TZP based composites that could soon be used for manufacturing dental implants, different mechanical tests were applied on the material, followed by complete microstructural characterization. Distinct from pure Ce-TZP material or other zirconia-based ceramics developed in the past, the material here studied can be permanently strained without affecting the Young modulus, indicating that the ductile response of tested samples cannot be associated to damage occurrence. This ductility is related to the stress-induced tetragonal to monoclinic (t-m) zirconia phase transformation, analogue to Transformation-Induced Plasticity (TRIP) steels, where retained austenite is transformed to martensite. The aim of this study is to corroborate if the observed plasticity can be associated exclusively to the zirconia t-m phase transformation, or also to microcraking induced by the transformation. The t-m transformed-zones produced after bending and biaxial tests were examined by X-ray refraction and SEM/TEM coupled with Raman. The results revealed that the observed elastic-plastic behavior occurs without extensive microcracking, confirming a purely elastic-plastic behavior driven by the phase transformation (absence of damage).

Electrochemistry Behavior and Surface Film Characterization of Fe50Mn30Co10Cr10 medium Entropy Alloy in Sulfuric Acid Solution

The Fe50Mn30Co10Cr10 medium entropy alloy (MEA) has been found to yield superior mechanical properties to CoCrFeMnNi Cantor high entropy alloys (HEA) due to transformation induced plasticity (TRIP) effect. However, the corrosion resistance between these two alloys has not been compared. In this study, the corrosion behavior of MEA and HEA was investigated in 0.1M H2SO4 solution at ambient condition. The preliminary results showed that both alloys exhibited the passive behavior with similar passive current density in 0.1M H2SO4 solution; nevertheless, some differences in anodic features and critical anodic current densities were found by comparing their anodic branch of the polarization curve. The SEM surface observation revealed both alloys tended to suffer uniform corrosion and intergranular corrosion in 0.1M H2SO4 solution. The microstructure and composition of passive films formed in 2 h on MEA and HEA at 440 mVSCE in 0.1M H2SO4 solution were also investigated in this study. The high resolution transmission electron microscope (HRTEM) pictures showed that the passive film formed on the MEA was approximately 2-5nm thick with amorphous structure.

Dependence of austenite stability and deformation behavior on tempering time in an ultrahigh strength medium Mn TRIP steel

In the present study, the microstructure, tensile property and deformation behavior were investigated in Fe-8Mn-8Al-0.8C steel after quenching and tempering treatment (Q&T). The steel exhibited a ferrite-austenite-martensite mixed microstructure, and a good combination of ultrahigh ultimate tensile strength (UTS) of ~1500 MPa and total elongation (TE) of ~30%. The tensile property was improved after tempering at 200 °C, which is mainly due to an improvement of austenite stability. Tempering process promoted the uniform distribution of carbon element in austenite, resulting in an elimination of the serrated behavior in the strain hardening rate curve. The element partitioning from the supersaturated martensite and δ-ferrite to austenite during tempering, as well as its contributing effects to austenite stability, was also discussed. Two methods were used to quantitatively monitor austenite stability as a function of tempering time with regard to transformation-induced plasticity (TRIP) effect. After an optimal tempering treatment at 200 °C for 60 min, the continuous strain-induced martensite transformation resulting from an optimized austenite stability led to an ultrahigh tensile strength and a product of strength and elongation (PSE) of 41 GPa·%. A fracture transition from brittle cleavage to ductile fracture was observed, which is due to variation of the local stress distribution between coarse δ-ferrite and adjacent austenite.

Keyhole refilled friction stir spot welding of aluminum alloy to advanced high strength steel

A keyhole refilled Friction Stir Spot Welding (FSSW) process is developed, which consists of two steps. Regular FSSW is performed in the first step. After that, the tool travels along a circular path to refill the original keyhole. The process is applied for joining aluminum alloy 6061 to Transformation Induced Plasticity (TRIP) steel. It increases the joint strength by 56.33% compared with that of conventional FSSW joints. A ductile failure mode is observed. The process can be implemented in any universal CNC machine and needs only one simple FSSW tool. An additional pure circular path welding process shows the enhanced performance of the keyhole refilled FSSW joints relies on three bonding mechanisms: the refilled original keyhole, the increased bonding area between steel and aluminum as well as the hook structure generated from the regular FSSW process. Three distinct layers of grain structures can be observed on the hook, which reveal the material flow pattern during the process.

Influence of grain structure on the deformation mechanism in martensitic shear reversion-induced Fe-16Cr-10Ni model austenitic alloy with low interstitial content: Coarse-grained versus nano-grained/ultrafine-grained structure

Nanograined/ultrafine-grained (NG/UFG) materials characterized by high strength-high ductility combination are excellent vehicles to obtain an unambiguous understanding of deformation mechanisms vis-à-vis their coarse-grained counterparts. In this context, the innovative concept of phase reversion-induced NG/UFG structure enabled achieving high strength besides comparable ductility, for instance, in metastable austenitic stainless steels. In the phase reversion process, severe deformation of austenite at room temperature (typically ~60–80%) transforms face-centered cubic austenite (γ) to body centered cubic martensite (α′). Upon annealing, martensite reverts to austenite leading to extensive grain refinement. The objective of the present study to fundamentally understand the deformation mechanisms in NG/UFG structure in relation to that of the coarse-grained (CG) structure was accomplished by combining depth-sensing nanoscale experiments on an Fe-16Cr-10Ni model austenitic alloy conducted at different strain rates, followed by the study of structural evolution in the deformed zone using transmission electron microscopy (TEM). In the high strength NG/UFG steel (YS~585MPa), stacking faults and nanotwins contributed to the enhanced ductility (El~35%), while in the case of low strength (YS~260MPa) coarse-grained (CG) counterpart, ductility was also high (El~40%), but chiefly due to strain-induced martensite, which points to a clear case of grain size effect (and the corresponding level of strength). The distinct change in the deformation mechanism from stacking faults and twinning-induced plasticity (TWIP) in the NG structure to transformation-induced plasticity (TRIP) in the CG structure is elucidated in terms of austenite stability-strain energy relationship. The insights on the relationship between grain structure (and strength) and deformation mechanisms are envisaged to be important in providing a new direction for the futuristic design of high strength-high ductility NG/UFG materials such as austenitic stainless steel and twinning induced plasticity steels.