Martensite Aging Research Articles

Effect of repeated-tempering induced martensite on the microstructural evolution in 17–7 PH stainless steel

Single long-time tempering and triple tempering processes have been applied to 17–7 PH stainless steel (chemical composition: Fe-0.09C-16.4Cr-7.7Ni-0.9Al, wt%) to investigate the effects of the stability of austenite on subsequent martensitic transformation and aging hardening. The as-received steel was composed of 0.55 austenite and 0.45 martensite (volume fraction). Scanning electron microscopy images showed that the volume fraction of martensite (up to 0.98) in triple-tempered specimens ((0.5 h @ 760 °C) × 3) was about 0.15 higher than that (0.83) in single-tempered ones ((1.5 h @ 760 °C) × 1). The results clearly indicate the effectiveness of the triple-tempering process in progressively improving martensitic transformation. Direct observation of the austenite/martensite interface has provided evidence that the preceding martensitic transformation induces accommodation strain into the adjacent austenite, which brings about the mechanical stabilization of austenite but will facilitate the succeeding martensitic transformation after three consecutive tempering operations. The relevant microstructural evolution has been explored and discussed. Furthermore, subsequent aging at 565 °C led to precipitation hardening associated with the formation of NiAl nanoparticles. The triple-tempered specimen yielded the higher peak hardness value (424 HV) in 20 min, significantly faster than the single-tempered specimen, which took 90 min to reach the lower one (357 HV). The corresponding number density of NiAl nano-precipitates and dislocation densities of martensite at various aging times have been examined by transmission electron microscopy to elucidate the benefits of the triple tempering process for precipitation strengthening.

Phase Transformations and Martensite Stabilization in Ni<sub>2.36</sub>Mn<sub>0</sub><sub>.64</sub>Ga High-Temperature Shape Memory Alloy

We report on experimental investigations of a Ni2.36Mn0.64Ga Heusler alloy, which transforms to tetragonal martensite at cooling below Ms ≈ 271°С. The evolution of lattice constants was tracked by in situ neutron diffraction measurements. It was found that the martensite tetragonality c/a gradually decreases during heating from room temperature to austenite transition start temperature As ≈ 272°С. The phenomenon of martensite stabilization was investigated by differential scanning calorimetry utilizing three different protocols of the martensite aging. It was found that the martensite aging at a constant temperature T = 255°С merely shifts the reverse transformation to higher temperatures, while the reverse transformation temperature interval (Af – As) remains the same (≈ 30°C) independently of aging time. On the other hand, a multistep aging at different temperatures starting from T = 255°С not only shifts the reverse transformation temperature, but makes the transformation temperature interval narrower down to As – Af ≈ 10°C.

Cyclic Stability of Two-Way Shape Memory Effect in Aged Ni50.3Ti32.2Hf17.5 Polycrystals after Various Thermomechanical Treatments.

In the present paper, the cyclic stability of the high-temperature two-way shape memory effect was studied in high-strength Ni50.3Ti32.2Hf17.5 polycrystals after various thermomechanical treatments-training (thermocycling under stress) and stress-induced martensite aging. The effect of training and stress-induced martensite aging on the microstructure, the two-way shape memory effect, and its cyclic stability was determined. It was found out that both thermomechanical treatments induce the high-temperature two-way shape memory effect at T > 373 K, with a strain of 1.5% in tension. The influence of cyclic tests (up to 100 stress-free cycles of cooling/heating) on the two-way shape memory effect strain, the transformation temperatures, and the microstructure was established. Different degradation mechanisms of the two-way shape memory effect were established after thermocycling and stress-induced martensite aging.

The effect of heat input on the microstructure and mechanical properties of 18Ni 300 maraging steel fabricated by arc directed energy deposition

The effect of heat input on the microstructure and mechanical properties of 18Ni 300 maraging steel fabricated by arc directed energy deposition is investigated, and a thermodynamic simulation model is designed for the investigation. Cold metal transition welding (CMT), pulse-gas metal arc welding (P-MIG), and the combination of CMT and P-MIG (CMT + P-MIG) technologies are designed to control the heat input. The additive mode is changed every two layers for the CMT + P-MIG mode. The results show that the CMT sample has the lowest fraction of ferrite in the middle region; meanwhile, the P-MIG sample has the highest fraction of ferrite. The CMT + P-MIG sample shows alternate variations in microstructure morphology along the building direction, especially in the middle region, leading to soft and hard variations in the microhardness. The EBSD results show that the low heat input is beneficial for obtaining {110} < 001 > Goss texture. As the heat input increases, the {110} < 001 > Goss texture gradually disappears and the {100} < 001 > Cube texture gradually forms. The low heat input is beneficial for obtaining better mechanical properties, the CMT sample has the best UTS and EL in the horizontal direction (1271 ± 28 MPa and 19.7 ± 0.6%, respectively). The results of the study reveal the successful application of WAAM technology in manufacturing 18Ni 300 martensite aging steel components, and verify the feasibility of controlling the heat input to achieve hierarchical changes in the microstructure.

Atomistic simulation of the collective carbon motion in body-centered tetragonal iron: A new insight into the martensite ageing

Atomistic simulation of the collective carbon motion in body-centered tetragonal iron: A new insight into the martensite ageing

Effect of martensite ageing on the orientation dependence of the B2-phase yield stress and the shape memory effect in Ti-40Ni-10Cu alloy single crystals

For the [001]- and [123]-oriented single crystals of the Ti-40Ni-10Cu alloy, it was shown for the first time that martensite ageing at 250 MPa leads to a strong orientation dependence of the B2-phase yield stress under tension, which is weakly manifested in the initial crystals. The maximum increase in the B2-phase yield stress by 350 MPa compared with the initial state was found in the [001]-oriented crystals. At external tensile stresses of 100 MPa, the shape memory effect in [001]-oriented crystals was 4.0± 0.2% in the initial state and increased to 5.0± 0.2% after martensite ageing, while in [123] orientation, on the contrary, it decreased from 8.7± 0.2% to 5.4± 0.2%. Keywords: Single crystals, Martensite ageing, B2-phase, Shape memory effect, Tension.

Влияние старения в мартенсите на ориентационную зависимость предела текучести B2-фазы и эффект памяти формы в монокристаллах сплава Ti-40Ni-10Cu

For the [001]-and [-123] -oriented single crystals of the Ti–40Ni–10Cu alloy, it was shown for the first time that martensite ageing at 250 MPa leads to a strong orientation dependence of the B2-phase yield stress under tension, which is weakly manifested in the initial crystals. The maximum increase in the B2-phase yield stress by 350 MPa compared with the initial state was found in the [001]-oriented crystals. At external tensile stresses of 100 MPa, the shape memory effect in [001]-oriented crystals was 4±0.2% in the initial state and increased to 5±0.2% after martensite ageing, while in [-123] orientation, on the contrary, it decreased from 8.7±0.2% to 5.4±0.2%.

Superelasticity and elastocaloric cooling capacity in stress-induced martensite aged [001]А-oriented Ni54Fe19Ga27 single crystals

The research paper presents a study of the effect of stress-induced martensite aging along the [001]A-deformation axis of the sample on both elastocaloric cooling capacity and superelasticity in Ni54Fe19Ga27 single crystals in compression. It has been experimentally shown that L10-martensite stabilization after the stress-induced martensite aging enhances the superelasticity parameters for the elastocaloric performance in the studied single crystals. In the stress-induced martensite aged Ni54Fe19Ga27 single crystals, the stress level of martensite formation σMs and stress hysteresis Δσ decrease by 130 MPa and by 16–17 MPa, respectively, compared with the as-grown crystals. Therefore, the stress-induced martensite aging increases the material efficiency for solid-state cooling systems: specific adiabatic temperature change per unit stress ΔTad/σMs increases by 4.4 times (ΔTad/σMs = 291.9 K/GPa (at Т = 348 K)) and coefficient of performance reaches COP = 24.5 in stress-induced martensite aged crystals as compared with the as-grown crystals (ΔTad/σMs = 62.4 K/GPa (at Т = 348 K), COP = 21.7). Smaller stress hysteresis corresponds to less energy dissipation in an operating cycle, which is also certainly useful for optimizing elastocaloric properties of a material. Moreover, both as-grown and stress-induced martensite aged crystals demonstrate high cyclic stability during loading/unloading cycles and weak temperature dependence of the elastocaloric cooling capacity ΔТad = 10.3–11.0 K in a wide operating temperature range up to 145–197 K. Thus, stress-induced martensite aged Ni54Fe19Ga27 single crystals oriented along the [001]А-direction are expected to be promising materials for elastocaloric application.

Effect of the Stress-Induced Martensite Aging Time on the Functional Properties of Heterophase Ni49Fe18Ga27Co6 Single Crystals

Effect of the Stress-Induced Martensite Aging Time on the Functional Properties of Heterophase Ni49Fe18Ga27Co6 Single Crystals

Neutron diffraction analysis of martensite ageing in high-carbon FeCMnSi steel

Abstract A high-carbon metastable austenite phase was quenched in liquid nitrogen to obtain fresh athermal martensite. Different ageing treatments were performed in order to study the transformation of the martensite phase and the formation of carbides. Neutron diffraction experiments give detailed information on the transformations during the annealing treatment itself. The tetragonal athermal martensite transformed immediately, i. e. during the heating to the ageing temperature, to cubic martensite. Ageing at 400 °C resulted in the decomposition of the austenite in ferrite and carbides and the formation of bainite. Those carbides could be determined as η-carbides transforming in χ-carbides after extended annealing times. As was expected, ageing at 170 °C resulted in the formation of a small amount of η carbides while the austenite phase remained stable.

The Effect of Subsequent Stress-Induced Martensite Aging on the Viscoelastic Properties of Aged NiTiHf Polycrystals

This study investigated the effect of stress-induced martensite aging under tensile and compressive stresses on the functional and viscoelastic properties in Ni50.3Ti32.2Hf17.5 polycrystals containing dispersed H-phase particles up to 70 nm in size obtained by preliminary austenite aging at 873 K for 3 h. It was found that stress-induced martensite aging at 428 K for 12 h results in the appearance of a two-way shape memory effect of −0.5% in compression and +1.8% in tension. Moreover, a significant change in viscoelastic properties can be observed: an increase in internal friction (by 25%) and a change in elastic modulus in tensile samples. The increase in internal friction during martensitic transformation after stress-induced martensite aging is associated with the oriented growth of thermal-induced martensite. After stress-induced martensite aging, the elastic modulus of martensite (EM) increased by 8 GPa, and the elastic modulus of austenite (EA) decreased by 8 GPa. It was shown that stress-induced martensite aging strongly affects the functional and viscoelastic properties of material and can be used to control them.

Cutting forces when grinding parts from martensite aging steels with highporous abrasive, borazon and diamond wheels

Object of research. The article investigates the cutting forces when grinding martensitic-aging steels with highly porous grinding wheels.&#x0D; The problem to be solved is the regularities of the change in the magnitude of the cutting forces when grinding maraging steels with highly porous CBN wheels.&#x0D; Main scientific results. The studies were performed on martensiticaging steel H8K18M14. As a result of the experiments, it was found that when grinding wheels made of materials such as electrocorundum, CBN (borazon) and diamond, a significant role is played by the values of the cutting force, which increase during processing.&#x0D; During the experiment it was found out: the cutting forces Py and Pz in the width of the allowable modes, which are most often used in circular and flat grinding, can reach the following values: with the structure of the wheel 26 come to values from 2.714N to 30.721 and with the structure of the wheel 40 come to values from 2.49N to 28.185N.&#x0D; Reducing the grain size of the wheel, let’s obtain the effect of increasing the energy costs of the grinding process, by increasing the magnitude of the cutting forces.&#x0D; If to compare the cutting forces that occur when grinding different wheels, it is possible to note the following: in comparison with electrocorundum wheels when using wheels with KNB cutting forces are reduced by 20-25 %, and when grinding with diamond wheels, the effect of cutting forces is reduced by 25 - 30 %. When grinding with highly porous wheels, the cutting force is 15-20 % higher than when grinding with wheels of normal porosity.&#x0D; The area of practical use of research results-grinding technology for maraging steels.&#x0D; Innovative technological product – relationship between processing modes and the magnitude of cutting forces when grinding maraging steels.&#x0D; Scope of application of an innovative technological product-mechanical engineering technology

Effect of stress-induced martensite ageing on the one-way and two-way shape memory effect of [0 1 1]-oriented TiNiCu crystals under tension

In this paper, for the first time, we found that at tension value of the one-way shape memory effect (SME) was 9.9% at external stresses of 250 MPa of the [011]-oriented Ti50Ni40Cu10 alloy (at%) crystals, which exceeds the theoretical value 7.14% for the B2-B19-B19′ martensitic transformation (MT) under tension. It was shown that stress-induced martensite ageing (SIM-ageing) creates conditions for the realization of a tensile two-way SME (TWSME) of 2.5% and does not decrease the value of the one-way SME.

Impact of Ni alloying on Fe-C martensite ageing: an atomistic investigation

We propose a computational investigation of Ni-alloying impact on Fe-C martensite ageing, at the atomic scale. Using the Climbing Image Nudged Elastic Band technique, we showed the repulsive nature of Ni-C pairwise interactions in α-iron, and demonstrated that Ni alloying lowers the migration energies and force dipole tensor components associated to an interstitial carbon in α-iron. Computed values of pairwise interactions, migration energies and dipole components were used to implement a Kinetic Monte-Carlo approach. We found that Ni alloying: (i) has negligible impact on martensite thermodynamical stability, (ii) accelerates ageing kinetics, by increasing carbon diffusivity.

The cyclic stability of rubber-like behaviour in stress-induced martensite aged Ni49Fe18Ga27Co6 (at.%) single crystals

In present work, the cyclic stability of the rubber-like behaviour (RLB) was investigated in Ni49Fe18Ga27Co6 (at.%) single crystals. Crystals were aged in the martensite phase at 423 K for 1 h under a compressive stress of 450 MPa, applied along the [110]B2||[100]L10-direction. The RLB was induced by a preliminary chemical stabilization of the oriented L10-martensite during stress-induced martensite aging (SIM-aging) and following the reversible reorientation of martensitic variants under a compressive stress applied along the [001]B2||[001]L10-direction. The high cyclic stability of the RLB was obtained in 200 loading/unloading cycles, due to the low reorientation stresses of the L10-martensite variants (no higher than 140 MPa) and the high strength properties of the L10-martensite (~1.6 GPa). The irreversible strain after 200 cycles did not exceed 0.6%. An increase in the number of cycles did not lead to the effect of destabilization of the L10-martensite.

Temperature Dependence of Martensite Variant Reorientation in Stress-Induced Martensite Aged Ni49fe18ga27co6 Single Crystals

In the present study, the temperature dependence of martensite variant reorientation in stress-induced martensite aged at 423 K along the [110]B2||[100]L10-direction Ni49Fe18Ga27Co6 single crystals was investigated in compression. This martensite aging induces a rubber-like behavior with a reversible strain of up to –16.0% along the [001]B2-direction in the temperature range from 248 K to 344 K, which is caused by L10-martensite variant reorientation. At higher temperatures between the forward and reverse transformation from 344 K to 382 K, the stress-induced martensite aged crystals demonstrate a two-stage stress-strain response with a reversible strain of up to –13.5%. The first stage is characterized by low critical stresses of σcr1 ≈ 1 – 15 MPa and an inverse elastocaloric effect (heat absorption) under loading. Super-elasticity is observed in the second stage with σcr2 ≥ 100 MPa. In this temperature range, the martensite variant reorientation occurs through reverse and then forward martensitic transformation.

The effect of stress-induced martensite aging in tension and compression on B2–B19′ martensitic transformation in Ni50.3Ti32.2Hf17.5 high-temperature shape memory alloy

The present study investigates the high-temperature shape memory effect (SME) in heterophase Ni50.3Ti32.2Hf17.5 polycrystals with nanosized H-phase particles after stress-induced martensite (SIM) aging in tension and compression. SIM aging created the conditions for fully reversible two-way SME with a strain of up to 50% of the one-way shape memory strain. SIM aging altered the viscoelastic properties of material, in particular, the elastic moduli of austenite and martensite increased, as did internal friction. Increased interface mobility is suggested as the reason for internal friction growth.

Temperature dependence of martensite variant reorientation in stress-induced martensite aged Ni49Fe18Ga27Co6 single crystals

In the present study, the temperature dependence of martensite variant reorientation in stress-induced martensite aged at 423 K along the [110]B2||[100]L10-direction Ni49Fe18Ga27Co6 single crystals was investigated in compression. This martensite aging induces a rubber-like behavior with a reversible strain of up to –16.0% along the [001]B2-direction in the temperature range from 248 K to 344 K, which is caused by L10-martensite variant reorientation. At higher temperatures between the forward and reverse transformation from 344 K to 382 K, the stress-induced martensite aged crystals demonstrate a two-stage stress-strain response with a reversible strain of up to –13.5%. The first stage is characterized by low critical stresses of σcr1 ≈ 1 – 15 MPa and an inverse elastocaloric effect (heat absorption) under loading. Superelasticity is observed in the second stage with σcr2 ≥ 100 MPa. In this temperature range, the martensite variant reorientation occurs through reverse and then forward martensitic transformation.

The effect of thermoplastic processing on the structure and mechanical properties of metastable austenitic steel

The patterns of structural transformations and the change in the mechanical properties of a metastable austenitic steel subjected to cold plastic deformation by drawing with high total degrees of compression and subsequent aging were studied in this work. The studies showed that after quenching, the use of intense plastic deformation by drawing revealed the high technological capabilities of the studied austenitic steel. Austenite in the steel is deformation-unstable and turns into deformation martensite during cold plastic deformation by drawing. Aging of deformed steel causes an additional increase in mechanical properties, due to the separation of the intermetallic phase NiAl from the bcc solid solution (strain martensite). It was revealed that almost carbon-free corrosion-resistant austenitic steel, as a result of correctly selected alloying, combines the advantages of three steels: metastable austenitic steels, Transformation-Induced Plasticity (TRIP)-steels and martensitic aging steels. As a result of using all possible hardening mechanisms, a high-strength state was achieved.

Superelasticity and two-way shape memory effect in [0 0 1]-oriented TiNiCu single crystals under compression

The paper reports the effect of stress-induced martensite ageing (SIM-ageing), and subsequent training in the superelasticity temperature range (SE-training) upon compression, on the shape memory and superelastic response of [001]-oriented crystals of the Ti50Ni40Cu10 (at.%) alloy. It was shown that after SIM-ageing and SE-training, stabilized B19-martensite was observed. Stabilized B19-martensite does not suppress superelastic behavior, leads to development of martensitic transformation under loading with high hardening and creates the conditions for a compressive two-way shape memory effect of 0.9%. The magnitude of the normal shape memory effect was 3.2% at an external stress of 100 MPa and superelasticity up to 2–2.5%.