Influence Of Martensitic Transformation Research Articles

Influence of martensitic transformation on the surface integrity aspects during sustainable turning of NiTi-SMA

With the development of the equipment manufacturing industry towards the direction of intelligence, the demand for the use of intelligent materials is increasing, and high-performance shape memory alloy (SMA) products are getting more and more attention. However, the current machining quality of shape memory alloy products can not meet the existing quality requirements. The mechanism of surface integrity of NiTi SMA needs to be revealed. The influence of martensitic transformation on microstructure, roughness, hardness, and superelasticity was explored. The occurrence of martensitic transformation is determined by controlling the cutting speed (lower and higher cutting speeds) and machining conditions (dry and liquid nitrogen conditions). The superelasticity was expressed quantitatively by the remnant depth ratio. The occurrence of martensitic transformation promoted the formation of the affected layer and work hardening. Meanwhile, it is an important reason for the increase in roughness and the decrease in superelasticity.

Revealing the effects of martensitic transformation and dislocation slip in austenite on the micromechanical behaviors of a 9Ni steel using crystal plasticity finite element method

Austenite is an extremely important phase that significantly influence the mechanical properties of (austenite + martensite) duplex steels. Two different deformation mechanisms, i.e., dislocation slip and martensitic transformation, can be activated in the austenite upon plastic deformation. However, these two deformation mechanisms make different contributions to the work hardening and flow stress of the austenite which are hardly separated by experimental methods, making it difficult to clarify the effect of austenite on the micromechanical behavior of (austenite + martensite) duplex steels. In this work, the influence of martensitic transformation and dislocation slip in austenite on the micromechanical behaviors is investigated in a model 9Ni steel consisting of austenite and tempered martensite (TM) using the crystal plasticity finite element method (CPFEM). The austenite and fresh martensite (FM) formed within the austenite grain upon deformation process are regarded as a whole named as FM/A island in the CPFEM. To accurately model the rate of martensitic transformation, the martensitic transformation kinetics law used in the CPFEM is developed by relating the number of possible nucleation sites for fresh martensite to the mechanical driving force originating from the resolved shear stress on each transformation system. The material parameters for the TM were determined by micropillar compression tests. Besides, the method for separating and determining the material parameters accounting for dislocation slip in austenite and martensitic transformation by a combination of neutron diffraction and measurements of stress-strain curves and austenite volume fractions is developed and exemplified. The CPFEM simulation results show that the local concentration of equivalent plastic strain and stress triaxiality in the FM/A island can be enhanced by the dislocation slip in austenite but suppressed by the martensitic transformation. In addition, the martensitic transformation has a remarkable effect on strengthening the local concentration of maximum principal stress in the FM/A island.

Cooperative strengthening effect of transformation-induced plasticity and twinning-induced plasticity on strain hardening in a novel metallic glass matrix composite subjected to dynamic compression

A novel in-situ metallic glass matrix composite reinforced by transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects with a nominal composition of Ti40Ni39Ce1Cu20 (at. %) exhibits extensive strain hardening and high yield strength under quasi-static and dynamic compression. The TRIP and TWIP effects within the crystalline phase make a significantly positive contribution to the strain hardening capability. Strain-rate-mediated martensitic transformation (MT) is effective on hardness enhancement at dynamic strain rate, resulting in a higher hardness of the crystalline phase compared to quasi-static one. The MT temperature displays a negative sensitivity to Ni concentration and is insensitive to Ce content. Moreover, finite element analysis is employed to reveal the influence of MT on homogenizing the plastic flow under dynamic loading.

The Effect of Martensitic Transformation on the Evolution of Residual Stresses and Identification of the Critical Linear Mass Density in Direct Laser Metal Deposition–Based Repair

Abstract Direct laser metal deposition (DLMD) is a promising additive manufacturing technique which has a huge potential in remanufacturing and restoration of high-value dies/molds and aerospace components. The residual stresses developed in the material deposited via DLMD affect the structural integrity of the restored components. The service life of the restored component will be compromised if tensile residual stresses are present in the deposited layer. The residual stresses originate due to differential thermal expansion/contraction and martensitic transformation-driven volumetric dilation and transformation-induced plasticity. The influence of martensitic transformation and processing conditions on the residual stresses of DLMD-processed components needs to be understood and modeled for sustainable repair. Hence, a finite element model has been developed to capture the coupled effect of thermomechanics and martensitic transformation on the evolution of residual stresses in DLMD. In this study, the individual and coupled effects of strains due to volume dilation and transformation-induced plasticity on residual stress evolution have been analyzed for the deposition of crucible particle metallurgy (CPM) 9 V on H-13 tool steel. The finite element model has been experimentally validated using X-ray and neutron diffractions. The inclusion of both transformation strains in the residual stress decreases the prediction errors of peak tensile residual stress from ∼48% to ∼15%. The fully coupled thermomechanical and metallurgical model has been used to obtain a critical linear mass density (m˙/v) corresponding to the onset of a fully compressive longitudinal residual stress state in the deposited layer to ensure sustainable repair.

A modified stress-strain relation for austenitic stainless steels at cryogenic temperatures

Low-temperature stress-strain relation of austenitic stainless steels (ASS) is essential for understanding the performance of pressure vessel at cryogenic temperatures. This paper experimentally investigated the stress-strain relation of ASS S30408 in a wide range of 77–293 K by quasi-static tensile tests. A significant strain-induced martensitic transformation is observed during the plastic deformation, which results into a change in the shape of stress-strain curve from a parabola to an inverted ‘S’. However, the Ludwigson stress-strain relation, which is widely used for ASS at 300–1023 K, cannot be used to characterize the low-temperature deformation of S30408 with martensitic transformation, because it does not rationally consider the influence of martensitic transformation on deformation. To precisely describe the stress-strain relation at cryogenic temperatures, a modified Ludwigson relation is proposed based on the assumption that the mechanical work difference between experimental curve and fitted Ludwigson curve is linearly proportional to martensite content. It is found that the proposed relation shows a good fitness with low-temperature experimental results. Furthermore, when no martensitic transformation occurs, the proposed relation transfers to the original Ludwigson relation, which means that the proposed relation has a wide applicability from cryogenic temperatures to high temperatures. Additionally, the proposed relation can also be used for different types of ASS and shows a significant potential application in design and safety assessment of ASS structures.

Influence of martensitic transformation on welding residual stress in plates and pipes

ABSTRACTMartensitic filler metals with low transformation temperatures can efficiently mitigate harmful tensile welding residual stress. It is vital to clarify the difference in the influence of martensitic transformation for different shapes of welded joints. This article outlines the influence of martensitic transformation in a butt-welded plate and a butt-welded pipe which were designed to have the same dimensions of the cross-section perpendicular to weld line. A clear difference in the influence of martensitic transformation was found in these two joints. Longitudinal tensile stress in weld zone is efficiently reduced in both joints, whereas longitudinal tensile stress is formed in base metal near the weld zone in the pipe. A notably greater influence on transverse stress is found in the pipe than in the plate.

Effect of deformation-induced phase transformation on AISI 316 stainless steel corrosion resistance

Abstract Austenitic stainless steels are the mostly used stainless steels in sheet metal forming and are subject of a large variety of applications including plate heat exchangers. During cold plastic deformation of heat exchanger plates, the martensitic transformation can take place. Martensite formation can be considered as a function of temperature, stress or strain. This paper is focused on the influence of martensite transformation on the corrosion resistance of AISI 316 austenitic stainless steel. Corrosion analysis showed that martensitic transformation which occurs due to cold forming process and under cyclic loading conditions had a substantially influence on the corrosion resistance of plate heat exchangers made by AISI 316 austenitic stainless steel. The role of molybdenum in the passive film formation has been considered and it was attributed to the ability of Mo to form insoluble chloride complexes at the base of pits. However, the protective film formed as a result of passivation or repassivation process was continuously broken due to continuously martensitic transformation as a result of cyclic working conditions of plate heat exchanger. The martensite volume expansion continuously broke the passive film and consequently new unprotected surfaces were exposed to chlorine-treated water, which was used as thermal agent for the plate heat exchanger. During working period, the heat exchanger plates are subjected to fluctuating stresses and strains that may result in cracks or fracture after a sufficient number of fluctuations. Fatigue fractures are caused by simultaneous action of cyclic stress, tensile stress and plastic strain. The martensite transformation as a result of applied cold plastic deformation process, changes not only the steel structure, but also its physical and chemical properties. The magnetic properties of stainless steel are very dependent on the elements added into the alloy. Having different corrosion potentials, it is easy for them to become the anode and the cathode, respectively, of a corrosion battery.

Extending sleeve life in a borehole pipe by thermocyclic treatment

The wear resistance of cylindrical bushes in borehole pumps may be improved by thermocyclic treatment of the cast Kh12 steel blanks, including 3–4 cycles over the range 25–950°C, with 30-min holding at the elevated temperature. In that case, a relatively hard martensite layer (HRC 65) is formed at the bush’s working surface. The martensite layer is also characterized by elevated impact strength. The wear resistance of the bush may also be increased by the formation of considerable compressive stress (500 MPa) in a (5–6)-mm layer at the bush’s working surface under the influence of martensitic transformation at the end of heat treatment.

Influence of Martensitic Transformation on the Fatigue of Low Temperature Metastable Stainless Steel

The influence of martensitic transformation on the fatigue of AISI 316 type stainless steel, which presents a low temperature metastable behavior, was investigated at-196 and 25°C. Fatigue tests were conducted on both annealed and cold worked conditions. The results from stress versus number of cycles curves showed that the fatigue resistance is not affected by the “dynamically” induced martensite in annealed specimens at both temperatures. On the contrary, the previously induced “static” martensite in work hardened specimens contributes to decrease the fatigue resistance limit. The contribution of the martensite stability is discussed.

The Role of Martensitic Transformation in Thermomechanical Development of Microstructure and Plasticity of Two-Phase Ti-6Al-4V Titanium Alloy

Phase constituent morphology in microstructure of two-phase α+β titanium alloys is determined by conditions of thermomechanical processing consisting of sequential heat treatment and plastic deformation operations. Results of previous research indicate that particularly solution treatment preceding plastic deformation significantly changes α-phase morphology and determines hot plasticity of titanium alloys. In the paper thermomechanical processing composed of β solution treatment and following hot forging of Ti-6Al-4V titanium alloy was analysed. Development of martensite plates during heating up and hot deformation was evaluated. Microscopic examinations revealed that elongated and deformed α-phase grains were fragmented and transformed into globular ones. Significant influence of martensitic transformation on elongation coefficient of α-phase grains after plastic deformation was confirmed. Based on results of elevated temperature tensile tests it was established that α-phase morphology in examined two-phase α+β titanium alloy, developed in the thermomechanical processing, can enhance their hot plasticity – especially in the range of low strain rates.

ChemInform Abstract: Ni—Mn—X Heusler Materials

AbstractReview: X: Al, Ga, In; 45 refs.

The influence of martensitic transformation on mechanical properties of cast high alloyed CrMnNi-steel under various strain rates and temperatures

Metastable austenitic steels show excellent mechanical properties, such as high strength combined with excellent ductility and toughness due to martensitic transformation under mechanical loading (transformation induced plasticity effect). A good energy consumption, and, in the case of high-alloyed metastable austenitic steels, a high corrosion resistance, increase the potential of these materials for diverse applications, also in regard of safety requirements. Up to now, numerous wrought alloys were investigated concerning mechanical behaviour, TRIP-effect, martensitic transformation behaviour and modelling of transformation kinetics or stress-strain behaviour. New high alloyed cast CrMnNi-steels, developed at Technical University Bergakademie Freiberg, provide the chance to reduce processing steps, production time and costs. In order to understand the influence of temperature on the martensitic phase transformation behaviour and therefore on mechanical properties and failure, the mechanical response under tensile loading in a temperature range between -70°C and 200°C was investigated. The mechanical behaviour under compressive loading was also examined in a wide range of strain rates between 10−4 s−1 and 103 s−1 to obtain information about the strain rate effect on stress-strain behaviour and microstructural changes.

Debonding initiation in a NiTi shape memory wire–epoxy matrix composite. Influence of martensitic transformation

The effect of martensitic transformation on the debonding initiation in single shape memory NiTi wire–epoxy matrix composite was studied. Three different heat treatment cycles were performed in order to obtain wires with different transformation characteristics. The composite samples were prepared using NiTi wires and steel wire for comparison. The single-wire specimens were subjected to the pull-out test. The in situ observations of the interfacial debonding and sliding behaviour during the test were carried out. In the pull-out tests, the embedded length is usually small and the interfacial shear strength (IFSS) can be estimated by dividing the maximum force to the lateral surface. But for evaluating the phase transformation effect, a long embedded length is required. In this case, a new method must be developed to estimate the IFSS. In the present study, a new method has been developed for the long embedded wire length samples using an analytical model. The IFSS was determined by implementing the experimental results into the model. It has been observed that the debonding stress for NiTi wire is significantly less than that for steel wire. It can be associated with the difference between the elastic modulus of the wires. The interfacial shear strength was then determined for these systems. It has been experimentally found that, when there is no phase transformation the IFSS is about 9 MPa while it is about 14 MPa when the martensitic transformation/reorientation occurs in the reinforced wire.

Influence of martensitic transformation on the low-cycle fatigue behaviour of 316LN stainless steel at 77 K

Tensile and low-cycle fatigue tests were performed on a 316LN austenitic stainless steel at 300 and 77 K. The tensile and low-cycle fatigue properties were obtained and analysed in terms of influence of temperature on the plastic deformation process, and particularly on the strain-induced martensite formation. The martensite content was measured by a magnetic-at-saturation method. No martensite was detected at 300 K. On the contrary, strain-induced martensite transformation is responsible for the higher tensile elongation at 77 K and for the secondary hardening observed on softening-hardening curves in low-cycle fatigue at 77 K. The induced martensite content in tensile tests is a function of the strain according to Angel's model, and in low-cycle fatigue it is a function of the strain level and of the accumulated plastic strain.

Influence of Martensitic Transformation on Carrier Concentration and Mobility in the Superconductor La3S4

Influence of Martensitic Transformation on Carrier Concentration and Mobility in the Superconductor La3S4

2相ステンレス鋼の疲労強度について

The present work was carried out so as to investigate the change in fatigue strength by pre-working, welding of stainless steel which has two phases, austenite and ferrite. The fatigue test was done by pulsating tension and the structural changes associated with the fatigue were also examined by means of X-ray, electron-microscopy and EPMA.The results obtained are summarized as follows:(1) The fatigue strength of austenitic-ferritic stainless steel was considerably stronger than that of austenitic stainless steel and that a difinite fatigue limit was obtained similary with carbon steel by means of age-hardening of ferrite during the fatigue test. The influence of martensitic transformation by pre-working on the fatigue strength was negligibly small.(2) In the γ-phase Cr was lower than Ni, while in the α-phase Ni was rather lower. The variation of composition by welding was considerably violent in the heat affected zone.(3) This alloy was not sensitive to a mechanical or welding notch. The decrease of fatigue strength was due largely to the change of composition and structure by welding heat.(4) The change of fatigue strength of this alloy was little by welding. Moreover the solution-treatment temperature of about 1100°C after welding was deemed adequate.(5) As stainless steel with two phases was relatively unstable in structure, a complicated striation pattern was obseved in the fatigue fractured surface.

Fe-Cr-Ni系ステンレス鋼の機械的性質に対するマルテンサイト変態と化学組成の影響

Fe-Cr-Ni系ステンレス鋼の機械的性質に対するマルテンサイト変態と化学組成の影響