13C NMR study of carbon distribution in Fe−C,Fe−Ni−C and Fe−Mn−C martensite

The distribution of carbon atoms in martensite have been studied by NMR. It was established that in virgin martensite metalloid was located only in octahedral intersticies. The analysis of hyperfine fields on¹³C nuclei for various types of martensite local arrangement was carried out. Comparison of analysis results with experimental data let to determine the possible models of carbon clustering in martensite at steel aging.     

CEMS of Sb+ implanted stainless steels

Martensitic transformations have been analysed in a series of antimony implanted austenitic stainless steels using CEMS. The implanted samples contain about 70 vols martensite, which is considerably more than can be formed conventionally by plastic deformation or cooling below the martensite start temperature. CEM spectra from implantation induced martensite and from martensite formed in conventional processes are virtually identical. In both cases the hyperfine field is ≈ 25T.     

Violation of the sequence of martensite crystals formation on cooling and their shrinking on heating during B2 ↔ B19′ martensitic transformation in Ti40.7Hf9.5Ni44.8Cu5 shape-memory alloy

An in situ transmission electron microscopy study of the B2 ? B19′ martensitic transformation in Ti_40.7Hf_9.5Ni_44.8Cu₅ shape memory alloy was carried out. It was observed that the sequence of the martensite crystals shrinking on heating differed from the sequence of the martensite crystal appearance on previous cooling. This was shown that strain nanodomain formation on cooling prior to the forward martensitic transformation resulted in accumulation of the elastic energy. This led to the dependences of the elastic energy stored on cooling or released on heating on the volume fraction of the martensite phase became different. In this case, at the same volume fraction of the martensite phase, the configuration of the martensite crystals on cooling and heating was different and it was a reason for a violation of the sequence of the martensite crystal formation on cooling and its shrinking on heating.     

Polytypic structures and morphology of martensite in alloy Ti50Ni40CU10

The methods of x-ray diffraction analysis and optical metallography were used to study the crystallography and morphology of martensite in alloy Ti₅₀Ni₄₀Cu₁₀. It was found that polytypic structures of monoclinic martensite B19 with 2H- and 4H-packings are formed in forward and reverse martensite-martensite transformations, while the morphology of martensite B19 is pyramidal. Martensite transformation into a B2-superstructure develops through the formation of new martensite B19 pyramids near previously formed pyramids, each of them being formed by the burst mechanism.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 73–78, June, 1989.     

Grain refinement and strengthening of austenitic stainless steels during large strain cold rolling

The microstructure/texture evolution and strengthening of 316?L-type and 304?L-type austenitic stainless steels during cold rolling were studied. The cold rolling was accompanied by the deformation twinning and micro-shear banding followed by the strain-induced martensitic transformation, leading to nanocrystalline microstructures consisting of flattened austenite and martensite grains. The fraction of ultrafine grains can be expressed by a modified Johnson-Mehl-Avrami-Kolmogorov equation, while inverse exponential function holds as a first approximation between the mean grain size (austenite or martensite) and the total strain. The deformation austenite was characterised by the texture components of Brass, {011}<211>, Goss, {011}<100>, and S, {123}<634>, whereas the deformation martensite exhibited a strong {223}<110> texture component along with remarkable γ-fibre, <111>∥ND, with a maximum at {111}<211>. The grain refinement during cold rolling led to substantial strengthening, which could be expressed by a summation of the austenite and martensite strengthening contributions.     

Aspects of thermal martensite in a FeNiMnCo alloy

Thermal martensite characteristics in Fe–29%Ni–2%Mn–2%Co alloy were investigated with scanning electron microscopy (SEM) and Mössbauer spectroscopy characterization techniques. SEM observations obviously revealed the lath martensite morphology in the prior austenite phase of examined alloy. As well, the martensitic transformation kinetics was found to be as athermal type. On the other hand, Mössbauer spectroscopy offered the paramagnetic austenite phase and ferromagnetic martensite phase with their volume fractions. Also, the internal magnetic field of the martensite was measured as 32.9 T from the Mössbauer spectrometer.     

Crystallographic specific features of the martensitic structure of Ni<Subscript>47</Subscript>Mn<Subscript>42</Subscript>In<Subscript>11</Subscript> alloy

The structure of Ni₄₇Mn₄₂In₁₁ alloy after annealing has been investigated. It is shown that the martensitic transformation in Ni₄₇Mn₄₂In₁₁ alloy upon cooling is accompanied by the formation of 14M modulated martensite. Crystallographic analysis of the martensite structure has been performed. The orientation relationships between the high-temperature austenitic phase and martensite and habit planes of the martensite plates have been determined.     

Stability and stabilization of 2H martensite in Cu–Zn–Al single crystals

The stabilization of the 2H martensitic phase in Cu–Zn–Al single crystals with an electron concentration e/a?=?1.53 was investigated. This orthorhombic 2H martensite was first induced from the cubic β phase by the direct β?→?2H or the indirect β?→?18R?→?2H transformations. On loading the 2H martensite, a transition without hysteresis is observed at a stress which was denoted σ_T1. It was found that this stress is associated with a change in the behaviour of the 2H martensite. A high stabilization of the 2H martensite, around 300?K, is only obtained if an ageing is performed at a stress above σ_T1. Additionally, the stresses of the transformation to another martensitic phase, called 18R₂, were found to be constant when the value of σ_T1 is below the retransformation stress. The 2H martensite and its behaviour on ageing were studied by dilatometry, calorimetry, mechanical testing, optical microscopy and transmission electron microscopy (TEM). Models accounting for the stabilization of the 2H martensite on ageing are proposed.     

Characterization of martensite in Fe-25%Ni-15%Co-5%Mo alloy

Kinetic, morphological, crystallographical, magnetic and thermal characteristics of thermally induced martensite in Fe-25%Ni-15%Co-5%Mo alloy have been investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), Mössbauer spectrometer, and differential scanning calorimeter (DSC). Kinetics of the transformation was found to be athermal. Also only lenticular martensite morphology was observed during microscope observations. In addition, martensite start temperature (M_s) was determined as −63 °C from differential scanning calorimeter. On the other hand, Mössbauer spectra revealed a paramagnetic character for the austenite phase and a ferromagnetic character for thermally induced martensite phase.     

Effect of cooling rate on microstructural formation and hardness of 30CrNi3Mo steel

The variation of microstructural formation and the hardness of the 30CrNi3Mo steel were systematically explored as a function of applied cooling rates in the range of 1–500°C/min. According to the measured Rockwell hardness results, four characteristic stages could be separated as different ranges of cooling rates, which corresponds well with the microstructural evolution observed. With the applied cooling rate increasing, the transformed structure evolves from granular bainite, lower bainite, self-tempered martensite, to finally martensite without self-tempering. Among them, the self-tempered martensite, obtained in the transformed specimens cooled with rates of 25–80°C/min, exhibits the highest hardness values due to the precipitation of fine carbides within it.     

Orientation relationship and the mechanism of martensite transformation in medium-carbon steel with batch martensite

Exact orientation relationship for martensite transformation in medium-carbon 37KhN3A steel with lath martensite are determined. The mechanism of deformation during the transformation of martensite in steel is described.     

Surface influence on the behavior of stabilized zirconia nanoparticles under pressure

The surface state of partially stabilized zirconia with nanoparticles of sizes 10–30 nm after temperature and pressure treatments was investigated by Fourier transform infrared spectroscopy, X-ray diffraction and small-angle X-ray scattering. It is shown that the synthesized nanoparticles are surface fractals and the fractal dimensions non-monotonically change with nanoparticles size change. The martensite tetragonal-to-monoclinic transition of the partially stabilized zirconia nanoparticles under hydrostatic pressure (100–1000 MPa) was investigated. It was shown that the character of the martensite transition in nanoparticles’ system depends on the pressure values. Three ranges of pressures were revealed. It was shown that the stability of martensite tetragonal–monoclinic transition decreases with the increase in size of the nanoparticles only for the pressures range of 300–500 MPa. Below 200 MPa, the character of the martensite transition is extreme and has a maximum for the particle size of 17 nm. In pressure range of 600–1000 MPa, the degree of martensite transition is dependent on the fractal dimension of the surface.     

Crystallographic patterns of the shape memory effect in non-ordered solid solutions

A method is proposed to estimate the possibility of achieving shape memory effects in martensite alloys with disordered lattices. The analysis of orientational relationships between the lattices of austenite and martensite allows one to detect those which are able to form self-accommodation complexes, an important part of the memory effect mechanism. This method has been applied to the Ti₄₈Zr₄₈Nb₄ alloy in which two martensite phases are formed: hexagonal α′ and orthorhombic α″ martensites.     

Magnetic and structural transition of Ni50+xMn25−x/2Ga25−x/2 (x=2–5) alloys

Magnetic and structural transitions of non-stoichiometric Ni_50+xMn_25−x/2Ga_25−x/2 (x=2–5) alloys are systematically investigated. Differential scanning calorimetry and modified thermogravimetry (TG) are used to measure magnetic and structural transitions simultaneously. The structural transition temperatures increase monotonically with increasing Ni substitution for Mn and Ga. Different magnetic transition sequences on heating were observed from ferromagnetic martensite to ferromagnetic autensite, then to paramagnetic autensite, from ferromagnetic martensite to paramagnetic austensite or from ferromagnetic martensite to paramagnetic martensite, respectively. Three kinds of NiMnGa alloys were obtained according to the sequence of the structural and magnetic transition, whose structural transition temperatures are lower, equal to or higher than the magnetic transition temperatures.     

Comparative Mössbauer study of the aging of Fe-C and Fe-N martensites

The clustering-ordering synergy which forms Fe₆C precipitates by aging Fe-C martensite is compared to the long-range ordering which forms Fe₁₆N₂ by aging Fe-N martensite.     

Effect of Martensite Volume Fraction on Strain Partitioning Behavior of Dual Phase Steel

Monotonic deformation behavior of ferrite-martensite dual phase steels with martensite volume of 13-43% have been analyzed in the current investigation using micromechanics based finite element simulation on representative volume elements. The effects of martensite volume fraction on the strain partitioning behavior between soft ferrite matrix and hard martensite islands in dual phase steels during tensile deformation have been investigated. As a consequence of strain incompatibility between hard martensite and soft ferrite phases, inhomogeneous deformation and finally deformation localization occur during tensile deformation. Restricted local deformation in ferrite phase caused by the adjacent martensite islands triggers the local stress triaxiality development. As the martensite volume fraction increases, the local deformation restrictions in ferrite phase also increases and which results in higher stress triaxiality development. Similarly the strain partitioning behavior between ferrite matrix and martensite island is also influenced by the volume fraction of martensite. The strain partitioning coefficient increases with increasing martensite volume fraction.     

Surface martensite on plastically deformed austenite

The influence of the plastic deformation of austenite before grinding on the formation of surface martensite is studied. Plastic deformation was excited by compression. It was found that surface martensite, produced on plastically deformed austenite, is conformable with surface martensite on undeformed austenite. As compression increases, the particles of surface martensite are merely oriented at an angle of 45 to the axis of compression. The orientation is connected in the paper with the formation of fibrous texture in the samples during strong compression and the orientation of the austenite lattices connected with it, especially of the (100) planes with respect to the surface.     

Localised surface segregation and martensite nucleation in noble metal based ternary alloys

A recent model connecting martensite nucleation with localised surface segregation phenomena is extended to dilute ternary alloys based on -CuZn and -AuCd. Experimental data about composition induced variations of the critical temperature for the onset of martensitic transformation are organised in a coherent fashion by the atomistic Valence Electron Localisation Degree variation model. An analysis of the surface segregation properties of the original and effective alloys involved in micro nucleation events of martensite is performed by a model relying upon charge transfer effects. It is concluded that martensite nucleation may be interpreted in terms of preferential, localised surface segregation events.Preliminary results of the research were presented at the Discussion Meeting on CuZnAl Martensite Shape Memory Alloys, 19–21 June 1984, Leuven, Belgium