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.     

Martensite and hydride transformations in the V-N-H and V-O-H systems

Optical metallography has been applied to vanadium containing traces of oxygen and nitrogen on electrolytic saturation with hydrogen; a martensite phase is formed near room temperature and above (formation controlled by the H/V concentration), and hydrides segregate, which suppress further martensite growth.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 39–42, March, 1990.     

TEM characterization of a nitrogen implanted austenitic stainless steel

Pure austenitic stainless-steel samples (18% Cr, 10% Ni) were implanted at room temperature with nitrogen ions at an energy of 40 keV with fluences from 10¹⁷ to 6X10¹⁷ ions cm^-2. Microstructures obtained after implantation were studied by transmission electron microscopy and selected-area diffraction. The observations show the formation of ε martensite (hexagonal), of α' martensite (tetragonal) and the appearance of nitrides (Fe, Cr, Ni)₂N_1-x hexagonal or orthorhombic.     

Determining orientation relationships for the <Emphasis Type="Italic">B</Emphasis>2 → <Emphasis Type="Italic">B</Emphasis>19′ transformation in single crystal titanium nickelide according to the texture of <Emphasis Type="Italic">B</Emphasis>19′ martensite

A precision method for determining orientation relationships upon the B2 → B19′ transformation in titanium nickelide has been developed. The method is based on analyzing the martensite texture formed in the initial high-temperature B2 phase of a single crystal having a high degree of perfection. The orientation relationships between the B19′ lattice and the initial B2 lattice of the TiNi single crystal were established from the B19′ martensite texture formed in single crystals of titanium nickelide upon the B2 → B19′ transformation and from measurements of the lattice parameters. Crystal mechanism of B19′ martensite was proposed which included the shear in the (21-1) B2 plane in the direction [−11-1] B2 by 10°. Such a shear system is typical of the bcc crystals at deformation by twinning. Absolute shear values are in a ratio of 1:4 for B2 → B19′ transformation and for twinning, respectively. Martensite deformation at an invariant lattice is accompanied by small rotations of martensite crystals (±1.6°), that increases the quantity of martensite orientations from 12 to 24.     

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.     

Bulk and Surface Quenching of Structural Steel: Morphological Analysis of the Structure

Structures formed in medium-carbon low-alloy steels during bulk quenching from furnace heating and surface quenching initiated by a low-power high-current electron beam are investigated by the methods of diffraction electron microscopy. The influence of the carbon concentration, initial austenite grain size, and cooling rate on the morphology of martensitic crystals and self-tempered carbide particles, long-range stress fields inside a packet and plates, and their dislocation substructure is analyzed. The temperature intervals for the formation of high-temperature plate martensitic crystals and packet (lath) martensite are estimated. It is demonstrated that the structure formed at ultrahigh heating and cooling rates is determined mostly by the morphology of martensite in the initial steel samples.     

Formation of cementite in tempered Fe–Co–C alloys

In Fe–Co–C alloys, undesirable grain coarsening results from the specific austenite orientation variants that form after the γ→→γ transformations. Tempering of martensite before reheating prevents austenite returning to its original orientation and also limits grain coarsening. However, the reasons for this are unclear. It may be assumed that some differences between cementite formed in tempered and rapidly heated alloys may cause the variation in the final austenite structure. In the present work the orientation relationships between cementite and martensite in two tempered Fe–Co–C alloys have been studied using microbeam electron diffraction in a transmission electron microscope. In both alloys after short-term (rapid heating at 100°C s⁻¹ followed by quench) and long-term (1 and 3 h) tempering treatments the orientation relationships were shown to obey the Isaichev orientation relationships:

However, after rapid tempering, only one carbide variant was found in each crystal, while after long-term tempering, up to three variants were present. This might account for the observed crystallographic reversibility in rapidly heated alloys, contrary to the multiplication of γ variants formed from the long-term tempered martensite.     

Structure of tetragonal martensite in the In<Subscript>95.42</Subscript>Cd<Subscript>4.58</Subscript> cast alloy

The structure of martensite in the In_95.42Cd_4.58 alloy has been studied by metallography, X-ray diffraction, dilatometry, and transmission electron microscopy. It has been shown that a massive structure built of colonies of tetragonal lamellar plates divided by a twin boundary {101}FCT is formed in the alloy under cooling below the martensite FCC → FCT transition temperature. The alloy recrystallizes after a cycle of FCT → FCC → FCT transitions with a decrease in the grain size by several times compared with the initial structure such fashion that the size of massifs and individual martensite lamella in the massif correlates with the change in the size of the alloy grain. Using thermal cycling, it has been revealed that the alloy tends to stabilize the high-temperature phase.     

周期性多层膜合金化制取的TiNi形状记忆薄膜的室温微结构特征

用掠入射X射线衍射及X射线反射对磁控溅射制取的等原子比Ni／Ti周期性多层膜晶化热处理 后的TiNi形状记忆薄膜室温微结构进行了研究.TiNi形状记忆薄膜在深度方向的相分布和元 素分布是不均匀的，都是一种多层结构.室温下其微结构特征为最外层是Ti氧化膜，再下层 是Ti₃Ni₄,B19’马氏体相和少量的B2奥氏体相的三相混合物，靠近 基体为主要相成分马氏体，最后是Ni和Si界面反应层.X射线反射率的拟和结果显示薄膜微结 构的分析是合理的.薄膜中相深度分布的不均匀性主要是动力学因素决定的. 关键词： 相深度分布 形状记忆 TiNi 多层膜     

Preparation and microstructure characteristics of low-temperature bainite in surface layer of low carbon gear steel

A kind of technology was proposed for the development of low-temperature bainitic microstructure in the surface layer of low-carbon gear steel 20CrMnMo, which is based on carburization and succedent low-temperature austempering. The carbon content in the surface carburization layer increases to 0.81 wt.%, making the martensite starting point depressed. Low-temperature bainite formed in the carburization layer and lath martensite with low carbon content in the center by austempering at a low temperature slightly higher than the martensite starting point of the surface layer. Aluminum is added as alloying elements with the purpose of enhancing the driving force of bainitic transformation and retarding the precipitation of cementite during austempering. With the excellent toughness of low-temperature bainite, this low-temperature austempering technology could be a potential substitute of the traditional quenching and tempering heat treatment in the manufacture of gear.     

Laves Phases in Ferrite-Martensite EC-181 Steel

The microstructure and phase composition of EC-181 ferrite-martensite steel were studied in dependence on their heat treatment (temperature and aging time after quenching from 1080°C). It was established that Laves phases are formed only at the boundaries of ferrite grains, whereas Me ₂₃C₆ and V₂C carbides are formed in the ferrite and martensite components of the structure.     

Crystallographic features of the structure of a martensite packet of the NiMn intermetallic compound

Optical microscopy, scanning electron microscopy, and X-ray diffraction are used to show that a pseudosingle crystal forms upon cooling of an alloy Ni₄₉Mn₅₁ single crystal below the temperature of the β→θ (bcc → fct) transformation. At room temperature, this pseudosingle crystal has the structure of tetragonal L1₀ martensite with parameters a = 0.3732 nm and c = 0.3537 nm and a tetragonality c/a = 0.94775. The temperatures of the forward and reverse B2 → L1₀ transformations are determined. The crystallographic features of martensite packet formation are analyzed. As shown by EBSD, neighboring martensite packets always have three kinds of tetragonal martensite plates, which are in a twin position and have different tetragonality axis directions. Repeated heating and quenching of the pseudosingle crystal result in recrystallization with the formation of coarse grains. The packet structure of the tetragonal martensite is retained in this case, and the sizes of the packets formed within a grain decrease by a factor of 2–3 as compared to the initial pseudosingle crystal.     

Metallic clusters in the AlN ceramic

Characterization of the local environment of metallic ions (Cu, Fe, Ti, Ni and Er) implanted in the ceramic matrix AlN have led us to conclude that the heat of formation (\Delta H) of the implanted ion nitride (I-N) is the parameter which has to be considered in order to predict the final system. When ΔH_I-N is negative, bonds between the implanted ion and nitrogen atoms are formed, when ΔH_I-N is positive, clusters of the implanted ion are formed. Moreover, we give some physical characteristics of the Cu and Ni clusters in the AlN matrix and show the differences between imbedded and deposited clusters of the same size. This revised version was published online in August 2006 with corrections to the Cover Date.     

Differential dislocations in martensite-type interphase boundaries

The tensor describing the density of differential dislocations, formed on interphase surfaces with a martensite transformation and on boundaries of mechanical twins, is calculated. Differential dislocations arise due to the transformation of Burgers vectors and dislocation lines in the process of their succession from the parent crystal. The dependence of the density of differential dislocations on the starting dislocation structure, transformation geometry, and the transformation matrix of the lattice with the transformation is demonstrated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 76–79, June, 1981.     

Formation of long-period nanostructural phases in Ni<Subscript>2</Subscript>MnGa-based <Emphasis Type="Italic">L</Emphasis>2<Subscript>1</Subscript> alloys with thermoelastic martensitic transitions

The crystalline structures of martensite phases in Ni₂MnGa-based ternary alloys have been studied in a wide range of temperatures and compositions transmission and scanning electron microscopy, X-ray diffraction, and electron diffraction. It is found that long-period nanostructural phases with thin-plate morphology are formed as a result of martensitic transformation in Ni₂MnGa-based alloys.     

钢中马氏体在回火转变中所引起的内耗峰

用扭摆测量淬硬碳钢的内耗,当测量温度由室温渐渐升高时,在130℃附近有一个内耗峰出现。当温度达到170℃后再降温测量,这个内耗峰完全消逝不见。上述的现象在含碳0.29％到1.4％的几种淬硬碳钢和淬硬滚珠钢中都曾经看到。由内耗峰的出现可以认为马氏体在第一个回火阶段中的转变产物(ε-碳化铁)与母体具有共格性,由于共格界面的应力感生运动而引起内耗。曾用具有马氏体组织的0.25％碳钢试样作实验,没有观测到上述的内耗峰。但是当回火温度达到280-300℃以后,在降温或升温测量中都观测到一个内耗峰(在150℃附近)。这表示低碳马氏体在第三个回火阶段中的转变产物与母体具有共格性。但是由于这个内耗峰的表现与上述高碳试样的内耗峰不同,所以我们认为这转变产物并不是ε-碳化铁。     

Phase analysis of Fe-N powders prepared by spark synthesis

The phase composition of Fe-N powders prepared by spark synthesis in as-prepared and annealed states was investigated. Contrary to the conventional quenching methods, where the α″-Fe₁₆N₂ appears during the annealing of martensite at a temperature below 200°C, in our case it is formed during the spark synthesis of powder.     

Low-temperature tempering kinetics of hardened steel 38KhN3MFA

Diffraction electron microscopy was used in a study of the decay kinetics of the α-iron solid solution and the growth kinetics of cementite particles in steel 38KhN3MFA after tempering at 200–550°C. Growth equations are written for cementite particles formed in lamellar high-temperature martensite crystals. Tomsk Structural Engineering Institute, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 39–44, February, 1993.     

Electron-beam modification of a surface layer deposited on low-carbon steel by means of arc spraying

State-of-the-art means of physical materials science are used to study the structure, phase composition, defect substructure, and tribological properties of a coating formed on low-carbon Hardox 450 martensite steel via the electrocontact deposition of an Fe–C–Ni–B wire and modified through subsequent irradiation with high-intensity pulsed electron beams. It is shown that electron-beam treatment results in the formation of a modified 50-μm thick surface layer, the main phases of which are the α-phase, iron boride FeB, and boron carbide B₄C. In the layer modified by electron-beam treatment, the transverse size of batch martensite crystals is reduced by a factor of 3, relative to the initial Hardox 450 steel, and ranges from 50 to 70 nm. It is established that the wear resistance of the deposited layer after electron-beam treatment grows by more than 20 times with respect to the wear resistance of Hardox 450 steel, and the friction coefficient is reduced by a factor of 3.5. The microhardness of a deposited layer ~7 mm thick is more than double that of the base metal.