EFFECT OF STRESS AND STRAIN ON MARTENSITIC TRANSFORMATION IN A Fe-Ni-Mo-C ALLOY WITH A HIGH Ms TEMPERATURE

The rare earth element Gd is added to Ni53Mn22Co6Ga19 high-temperature shape memory alloy to refine the grain size and adjust the distribution of γ phase, and their microstructure, martensitic transformation behaviors, mechanical and shape memory properties were investigated. The results show that the grain size is obviously decreased and the γ phase tends to segregate at grain boundaries with increasing Gd content. Small amounts of Gd-rich phase were formed with 0.1 at.% Gd addition. The martensitic transformation temperature abruptly increases with 0.1 at.% Gd addition, then almost keeps constant with further increasing Gd content. The addition of 0.1 at.% Gd is proved to be beneficial to both tensile stress and strain before fracture, but negative to the shape-memory effect.

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Prediction of Stress–Strain Curves of Metastable Austenitic Stainless Steel Considering Deformation-Induced Martensitic Transformation

Journal of Engineering Materials and Technology ◽

10.1115/1.4035623 ◽

2017 ◽

Vol 139 (3) ◽

Author(s):

T. Kumnorkaew ◽

V. Uthaisangsuk

Keyword(s):

Stainless Steel ◽

Flow Stress ◽

Martensitic Transformation ◽

Austenitic Stainless Steel ◽

Effective Stress ◽

Local Stress ◽

Uniaxial Tensile ◽

Stress And Strain ◽

Trip Effect ◽

Stress Strain

Transformation-induced plasticity (TRIP) effect is the outstanding mechanism of austenitic stainless steel. It plays an important role in increasing formability of the steel due to higher local strain hardening during deformation. In order to better understand forming behavior of this steel grade, the strain-induced martensitic transformation of the 304 stainless steel was investigated. Uniaxial tensile tests were performed at different temperatures for the steel up to varying strain levels. Stress–strain curves and work hardening rates with typical TRIP effect characteristics were obtained. Metallographic observations in combination with X-ray diffraction method were employed for determining microstructure evolution. Higher volume fraction of martensite was found by increasing deformation level and decreasing forming temperature. Subsequently, micromechanics models based on the Mecking–Kocks approach and Gladman-type mixture law were applied to predict amount of transformed martensite and overall flow stress curves. Hereby, individual constituents of the steel and their developments were taken into account. Additionally, finite element (FE) simulations of two representative volume element (RVE) models were conducted, in which effective stress–strain responses and local stress and strain distributions in the microstructures were described under consideration of the TRIP effect. It was found that flow stress curves calculated by the mixture law and RVE simulations fairly agreed with the experimental results. The RVE models with different morphologies of martensite provided similar effective stress–strain behavior, but unlike local stress and strain distributions, which could in turn affect the strain-induced martensitic transformation.

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403 Analysis of Stress and Strain Energy Yielded by Martensitic Transformation

The Proceedings of Ibaraki District Conference ◽

10.1299/jsmeibaraki.2000.95 ◽

2000 ◽

Vol 2000 (0) ◽

pp. 95-96

Author(s):

Hideaki NOZAKI ◽

Yo TOMOTA

Keyword(s):

Martensitic Transformation ◽

Strain Energy ◽

Stress And Strain

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Internal Stress and Strain Energy Yielded by γ→ε Martensitic Transformation in a Polycrystalline Ferrous Alloy

Materials Transactions JIM ◽

10.2320/matertrans1989.41.727 ◽

2000 ◽

Vol 41 (6) ◽

pp. 727-732 ◽

Cited By ~ 4

Author(s):

Hideaki Nozaki ◽

Yo Tomota

Keyword(s):

Martensitic Transformation ◽

Internal Stress ◽

Strain Energy ◽

Ferrous Alloy ◽

Stress And Strain

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In situ observation of the martensitic transformation in (Mg,Y)-PSZ

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100144036 ◽

1986 ◽

Vol 44 ◽

pp. 500-501

Author(s):

R-R. Lee

Keyword(s):

Martensitic Transformation ◽

High Strength ◽

Nucleation And Growth ◽

In Situ Observation ◽

Considerable Potential ◽

Transmission Electron ◽

Structural Applications ◽

Applied Stresses ◽

Kinetics Of

Partially-stabilized ZrO2 (PSZ) ceramics have considerable potential for advanced structural applications because of their high strength and toughness. These properties derive from small tetragonal ZrO2 (t-ZrO2) precipitates in a cubic (c) ZrO2 matrix, which transform martensitically to monoclinic (m) symmetry under applied stresses. The kinetics of the martensitic transformation is believed to be nucleation controlled and the nucleation is always stress induced. In situ observation of the martensitic transformation using transmission electron microscopy provides considerable information about the nucleation and growth aspects of the transformation.

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Evidence for ordered Fe3Ni

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100125981 ◽

1987 ◽

Vol 45 ◽

pp. 216-217

Author(s):

K.B. Reuter ◽

D.B. Williams ◽

J.I. Goldstein

Keyword(s):

Experimental Data ◽

Martensitic Transformation ◽

Electron Diffraction ◽

Room Temperature ◽

Direct Evidence ◽

Transformation Product ◽

Iron Meteorites ◽

X Ray ◽

Ni Content ◽

Temperature Transformation

In the Fe-Ni system, although ordered FeNi and ordered Ni3Fe are experimentally well established, direct evidence for ordered Fe3Ni is unconvincing. Little experimental data for Fe3Ni exists because diffusion is sluggish at temperatures below 400°C and because alloys containing less than 29 wt% Ni undergo a martensitic transformation at room temperature. Fe-Ni phases in iron meteorites were examined in this study because iron meteorites have cooled at slow rates of about 10°C/106 years, allowing phase transformations below 400°C to occur. One low temperature transformation product, called clear taenite 2 (CT2), was of particular interest because it contains less than 30 wtZ Ni and is not martensitic. Because CT2 is only a few microns in size, the structure and Ni content were determined through electron diffraction and x-ray microanalysis. A Philips EM400T operated at 120 kV, equipped with a Tracor Northern 2000 multichannel analyzer, was used.

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Structure of a new orthorhombic phase in NiTi: Mn shape memory alloys

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100178136 ◽

1990 ◽

Vol 48 (4) ◽

pp. 1000-1001

Author(s):

Jenö Beyer ◽

Lajos Tóth

Keyword(s):

Martensitic Transformation ◽

Structural Changes ◽

High Vacuum ◽

Intermetallic Phase ◽

Orthorhombic Phase ◽

Transformation Process ◽

Analytical Electron ◽

Analytical Electron Microscope ◽

Crystallographic Structures ◽

Ternary Additions

The structural changes during reversible martensitic transformation of near-equiatomic NiTi alloys can best be studied in TEM at around room temperature. Ternary additions like Mn offer this possibility by suppressing the Ms temperature below RT. Besides the stable intermetallic phases (Ti2Ni, TiNi, TiNi3) several metastable phases with various crystallographic structures (rhombohedral, hexagonal, monoclinic, cubic) have also been reported to precipitate due to suitable annealing procedures.TiNi:Mn samples with 0.9 and 1.3 at% Mn were arc melted in argon atmosphere and homogenized at 948 °C for 72 hours in high vacuum in an infrared furnace. After spark cutting slices of 0.2 mm, TEM specimens were prepared by electrochemical polishing with the twin-jet technique in methanol - perchloric acid electrolyte. The TEM study was carried out in a JEOL 200 CX analytical electron microscope.In this paper a new intermetallic phase is reported which has been observed in both samples by TEM during the martensitic transformation process.

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