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1

Size‑dependent constitutive model incorporating grain refinement and martensitic transformation

Liu Shengqiang, Li Wei, Shen Jinxia, Yang Xiaoming, Wang Baoyu, Liu Jinping

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 1

art. no. e38, 2023

EN

The deformation behaviour of materials at the micro-scale level is different from that at the macro-scale level due to the effect of grain size (GS). The mechanism of the influence on martensitic transformation by GS is still unclear, and there are relatively few studies on the relationship between grain refinement and martensitic transformation, most of which focus on the relationship between the initial GS of the material and martensitic transformation. Therefore, in this study, the interaction between grain refinement and martensitic transformation was investigated using a dislocation density-based multiscale constitutive model that incorporated dislocation sliding, strain-induced martensitic transformation (SIMT) related to grain size, and grain refinement. The proposed model evaluated the GS-dependent deformation behaviour of 316L stainless steel (SS). Subsequently, a genetic algorithm was used to determine the parameters of the established model, and the calculated results were compared with that of the experimental data to verify the accuracy of the model. The developed multiscale constitutive model was implemented in Abaqus user subroutine to further investigate the deformation mechanism and validate its accuracy. The results demonstrated that the GS had a significant effect on the SIMT, with the volume fraction of martensite increasing with a rise in the initial austenite GS. In addition, grain refinement affected SIMT and the growth rate of martensite content decreased with the grain refinement caused by deformation. The formation of martensite led to grain refinement, with the refined grains producing negative feedback on the SIMT, thus inhibiting the occurrence of martensitic transformation. This study revealed the microscopic deformation mechanism of 316L SS and provided a constitutive model for micro-forming.

2

Internal Friction and Dynamic Modulus in Ultra-High Temperature Ru-Nb Functional Intermetallics

Nó M. L., Dirand L., Denquin A., San Juan J.

Archives of Metallurgy and Materials

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2015

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Vol. 60, iss. 4

3069--3072

EN

In the present work we have studied the high-temperature shape memory alloys based on the Ru-Nb system by using two mechanical spectrometers working in temperature ranges from 200 to 1450ºC and -150 to 900ºC. We have studied internal friction peaks linked to the martensitic transformations in the range from 300 to 1200ºC. In addition, we have evidenced another internal friction peak at lower temperature than the transformations peaks, which apparently exhibits the behaviour of a thermally activated relaxation peak, but in fact is a strongly time-dependent peak. We have carefully studied this peak and discussed its microscopic origin, concluding that it is related to the interaction of some structural defects with martensite interfaces. Finally, we perform a complete analysis of the whole internal friction spectrum, taking into account the possible relationship between the time-dependent peak and the martensitic transformation behaviour.

PL

W niniejszej pracy badano wysokotemperaturowe stopy z pamięcią kształtu z układu Ru-Nb, przy użyciu dwóch spektrometrów mechanicznych pracujących w zakresach temperatur od 200 do 1450ºC i -150 do 900ºC. Zbadano piki tarcia wewnętrznego związane z przemianami martenzytycznymi w zakresie od 300 do 1200ºC. Ponadto, wykazano występowanie innego piku tarcia wewnętrznego przy niższej temperaturze niż pików przemiany, który ma cechy aktywowanego termicznie piku relaksacji, ale w rzeczywistości jest to pik silnie zależny od czasu. Dokładnie zbadano ten pik i omówiono jego pochodzenie w mikro skali, stwierdzając, że jest to związane z oddziaływaniem niektórych wad strukturalnych z granicami martenzytu. Na koniec, wykonano kompletną analizę całego spektrum wewnętrznego tarcia, biorąc pod uwagę możliwość związku między pikiem zależnym od czasu i zachowaniem przemiany martenzytycznej.

3

Experimental measurements of shape memory alloys wires

Kłapyta G., Kciuk M.

Archives of Electrical Engineering

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2012

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Vol. 61, nr 2

129-138

EN

Paper deals with examinations of properties of shape memory alloy actuators. Authors describe design of own laboratory stand for obtaining electro-thermo-mechanical characteristics of SMA wires (maximum length 900 mm). The stand allows for semi-automatic measurements of voltage and current (supplying the actuator), temperature of wire and its extension. Data acquisition and control signals are realized by PC computer. All elements of the measuring system are connected by GPIB network (IEEE 488.2 standard). Control program for static measurements was written in G language (LabVIEW environment). Temperature is measured using infrared camera Flir A325. Displacement measurement system contains optical sensor (converting piston movement into series of pulses), pulses counter, PWM signal generator (PWM signal fulfillment is proportional to number of pulses), lowpass filter and buffer conditioning external signal. For dynamic measurements data recording is performed using digital oscilloscope Tektronix MSO 2024 equipped with four separated channels and digital filter. Wide range of examinations of several SMA wires allowed for drawing its exploitative characteristic helpful for practical use. It shows length change of actuator as a function of mechanical load (Fig. 10). Finally some example static as well as dynamic characteristics are presented and short discussion is carried out.

4

Mechanical properties and corrosion resistance of burnished X5CrNi 18-9 stainless steel

Pałka K., Weroński A., Zaleski K.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 16, nr 1-2

57--62

EN

Purpose: In this paper there were presented the burnishing process and obtained mechanical properties and the structure of burnished stainless steel and its corrosion resistance. Design/methodology/approach: Burnishing was conducted in standard milling machine equipped with the 2-ball rotation head. The structural and mechanical researches were carried out by optical microscopy and the X-ray diffraction patterns. The corrosion research was performed using the potentiodynamic anodic polarization. The scope of this study was to achieve the correlations between mechanical and structural properties and corrosion resistance of burnished stainless steel. Findings: Results shown increasing of the open circuit potential (EOCP) and decreasing of breakdown (Eb) and repassivation potentials (Erp) with increasing of burnishing load. The breakdown potential and the repassivation potential changes were influenced by structural changes in surface layer and it indicated of slightly decreasing of corrosion resistance. It might be caused by martensitic transformation induced by the plastic deformation. The X-ray diffraction analysis showed increasing of Fe-α contain with the burnishing load. Research limitations/implications: There’s need to conduct future research on susceptibility to stress corrosion cracking and fatigue corrosion. The main difference between presented research and the future is necessity of double-sided burnishing of specimens. Practical implications: Burnishing increases the strength and the rigidity of elements, especially stream plates of heat exchangers which may have lower thickness to improve the heat transfer. Some of elements, such as homogenized valves achieving better erosion and wear resistance by higher surface hardness. Originality/value: Presented researches contain a lot of quantitative results which may be useful for design engineers in wide space of application.

5

Influence of point defects and grains size on the course of reversible martensite transformation in melt spun ribbons of the copper based alloys

Kostrubiec B., Wiśniewski R., Rasek J.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 16, nr 1-2

30--34

EN

Purpose: In the paper Cu-Al-Ni-(Mn, Ti) alloys exhibiting the shape memory effect were studied. For the investigated alloys the characteristic temperatures of the reversible martensitic transformation, the influence of grains size and vacancy concentration on the course of the transformation were examined. Design/methodology/approach: Using the resistometric method it was shown that the characteristic temperatures of the reversible martensite transformation strongly depend on the grains size. Findings: For Cu-Al-Ni alloy the activation energy of migration of monovacancies and the pre-exponential factor of the Arrhenius equation were determined as [wzór], respectively. Practical implications: The paper shows that the investigated alloys can be used as important functional or the so-called intelligent materials (actuators, sensors). Originality/value: The parameters of the electronic structure - i.e. the coefficient of conduction electron scattering at grain boundaries, the mean free path, the coefficient of reflection of conduction electrons at grain boundaries, and the electrical resistivity for Cu-Al-Ni in the martensite and parent phase were determined.