• Journal of the Korean Ceramic Society
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• v.42 no.11 s.282
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• pp.718-721
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• 2005

The high temperature tetragonal phase of zirconia containing $1.40{\~}1.60\;mol\%$ of yttria can be fully retained at room temperature by rapid cooling. The metastable tetragonal phase transforms into the monoclinic phase athermally upon subzero cooling. The transformation exhibited an athermal burst transformation. The effects of yttria content and grain size on the athermal martensitic transformation were studied in detail. The burst temperature linearly decreased with increasing yttria content or decreasing grain size. To consider the distribution of martensite nuclei, the Weibull modulus of the athermal martensitic transformation was evaluated from the distribution of the burst transformation temperature. From the Weibull analysis, the distribution of embryos appears to be more homogeneous than that of the defects responsible for the fracture of similar material.

• Corrosion Science and Technology
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• v.5 no.1
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• pp.1-4
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• 2006

Martensitic stainless steel is used when mechanical properties such as high tensile strength and hardness are required. Medium carbon-contained martensitic stainless steel which contains more than 0.2 wt% of carbon should be heat-treated and quenched at the temperature where undissolved carbides are totally dissolved into the matrix. In particular, the dissolution and reprecipitation behaviors of various forms of carbides are affected by such parameters as heating rate, heating temperature, duration time and cooling rate. This study is to investigate the effects of heat treatment parameters of 14Cr-3Mo martensitic stainless on corrosion resistance and phase transformation in relation to the dissolution and reprecipitation of carbides.

• Journal of Magnetics
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• v.9 no.2
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• pp.37-39
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• 2004

Polycrystalline Ni-Mn-Ga films have been deposited onto mica substrates held at 720 K by flash-evaporation method. At room temperature the films have a tetragonal structure with a = b = 0.598 and c = 0.576 nm typical for bulk $Ni_2MnGa$ below a martensitic transformation. Temperature measurements of ferromagnetic resonance reveal a martensitic phase transformation at 310 K. The transformation brings about a substantial decrease in the effective magnetization and a drastic increase in the ferromagnetic resonance linewidth due to a strong increase in the magnetic anisotropy in the martensitic phase.

• Journal of the Korean Society for Heat Treatment
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• v.8 no.1
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• pp.65-74
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• 1995

This research was performed to investigate the effect of ageing on grain refinement of 82wt%Cu-13.5wt%Al-4.5wt%Ni-0.1wt% misch metal alloy with ageing temperature and time. The results obtained in this study are as follows; The variation of transformation temperature with ageing temperature had very influence on ageing time at $300^{\circ}C$. But it had not influence on ageing time at $100^{\circ}C$. The variation of transformation temperature after second reversed transformation cycle was not occured in martensitic phase ageing, but $M_s$ point was appeared equally with third reversed transformation cycle in parent phase ageing. The variation of $M_s$ point was not nearly with ageing time at $100^{\circ}C$ ageing temperature. But it was decreasing with ageing time at $300^{\circ}C$ ageing temperature and $A_s$ point was increasing with ageing time. Structure of parent phase ageing was being M18R martensitic and N2H martensitic phase. It was found that ${\alpha}$ and ${\gamma}_2$ phase were created by ageing of long time at $300^{\circ}C$ ageing temperature.

• Applied Microscopy
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• v.45 no.2
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• pp.37-43
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• 2015

In present work, work-hardening behavior of TiCu-based bulk metallic glass composite with B2 particles has been studied by systemic structural and mechanical investigations. After yield, pronounced work-hardening of the alloy was clearly exhibited, which was mainly related to the martensitic transformation as well as the deformation twinning in B2 particles during deformation. At the early plastic deformation stage (work-hardening stage), the stress-induced martensitic transformation from B2 phase to B19' phase and deformation-induced twinning of B19' phase was preferentially occurred in the around interface areas between B2 phase and amorphous matrix by stress concentration. The higher hardness value was observed in vicinity of interface within the B2 particles which are probably connected with martensitic transformation and deformation twinning. This reveals that the work-hardening phenomenon of this bulk metallic glass composite is a result of the hardening of B2 particles embedded in amorphous matrix.

• Transactions of Materials Processing
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• v.32 no.4
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• pp.191-198
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• 2023

We examined the martensitic transformation kinetics for metastable stainless steel during electrochemical polishing (EP) using different types of electrolytes. Martensite fraction measured with EBSD showed that the electrolyte with high relative permittivity exhibited comparably higher levels of martensitic transformation. The amount of charge build-up on the specimen surface during EP with different types of electrolytes was calculated using COMSOL multiphysics simulations to understand these phase transformation characteristics. The effect of charge build-up-induced stress was analyzed using previously published first-principles calculations. We discovered that the electrolyte with high relative permittivity accumulated a greater amount of charge build-up, resulting in a stronger driving force for stress-induced martensitic transformation.

• Corrosion Science and Technology
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• v.6 no.2
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• pp.56-61
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• 2007

Carbide dissolution during heating processes can change chemical composition of martensitic stainless steel in its austenitic phase. Although the austenitizing treatments were carried out at a homogeneous austenite region, the amount of carbon atom in the matrix differs. Increase in the amount of carbon contents in the matrix resulted in decreasing MS temperature, which consequently causes the volume fraction of the retained austenite to increase. This study reveals the effects of the austenitizing treatment on the properties of Fe - 0.3C - 14Cr - 3Mo martensitic stainless steel change with different austenitizing temperatures.

• Korean Journal of Materials Research
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• v.30 no.5
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• pp.231-238
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• 2020

The composition of martensite transformation in NiAl alloy is determined using pure nickel and aluminum powder by vacuum hot press powder metallurgy, which is a composition of martensitic transformation, and the characteristics of martensitic transformation and microstructure of sintered NiAl alloys are investigated. The produced sintered alloys are presintered and hot pressed in vacuum; after homogenizing heat treatment at 1,273 K for 86.4 ks, they are water-cooled to produce NiAl sintered alloys having relative density of 99 % or more. As a result of observations of the microstructure of the sintered NiAl alloy specimens quenched in ice water after homogenization treatment at 1,273 K, it is found that specimens of all compositions consisted of two phases and voids. In addition, it is found that martensite transformation did not occur because surface fluctuation shapes did not appear inside the crystal grains with quenching at 1,273 K. As a result of examining the relationship between the density and composition after martensitic transformation of the sintered alloys, the density after transformation is found to have increased by about 1 % compared to before the transformation. As a result of examining the relationship between the hardness (Hv) at room temperature and the composition of the matrix phase and the martensite phase, the hardness of the martensite phase is found to be smaller than that of the matrix phase. As a result of examining the relationship between the temperature at which the shape recovery is completed by heating and the composition, the shape recovery temperature is found to decrease almost linearly as the Al concentration increases, and the gradient is about -160 K/at% Al. After quenching the sintered NiAl alloys of the 37 at%Al into martensite, specimens fractured by three-point bending at room temperature are observed by SEM and, as a result, some grain boundary fractures are observed on the fracture surface, and mainly intergranular cleavage fractures.

• Journal of Powder Materials
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• v.8 no.1
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• pp.42-49
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• 2001

Ti-50Ni(at%) and Ti-40Ni-10Cu(at%) alloy powders have been fabricated by ball milling method, and their microstructure and phase transformation behavior were investigated by means of scanning electron microscopy/energy dispersive spectrometry, differential scanning calorimetry (DSC), X-ray diffractions and transmission electron microscopy. In order to investigate the effect of ball milling conditions on transformation behavior, ball milling speed and time were varied. Ti-50Ni alloy powders fabricated with the milling speed more than 250 rpm were amorphous, while those done with the milling speed of 100rpm were crystalline. In contrast to Ti-50Ni alloy powders, Ti-40Ni-10Cu alloy powders were crystalline, irrespective of ball milling conditions. DSC peaks corresponding to martensitic transformation were almost discernable in alloy powders fabricated with the milling speed more than 250 rpm, while those were seen clearly in alloy powders fabricated with the milling speed of 100 rpm. This was attributed to the fact that a strain energy introduced during ball milling suppressed martensitic transformation.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.26-28
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• 2005

The purpose of this study is to evaluate the behavior of the welding distortion of the 9% Ni steel weldment involving the martensitic phase transformation. In order to do it, an uncoupled thermal-mechanical finite element (FE) model was developed to evaluate the effect of the phase transformation on the distortion for the weldment. High speed quenching dilatometer tests were employed to define the variations of the coefficient of thermal expansion (CTE) with the fraction of the martensitic phase transformation, which strongly depends on the cooling speed after welding. Comprehensive experiments for the welding distortion of the weldment with reference to welding heat input were employed to verify the FE model.