On the Phase Transformations in Cr–FeB and Fe–CrB Systems at High Temperature

The solid state interactions occurring at high temperature in the Cr–FeB and Fe–CrB systems were studied by transmission Mössbauer and X-ray diffraction techniques on samples prepared by powders carefully mixed, cold-compacted and then treated at 1000°C for times up to 16 h. In the Cr–FeB system, iron atoms liberated by the substitutional diffusion of Cr into FeB lattice preferentially destabilize the iron monoboride with formation of Cr-containing Fe₂B. In the Fe–CrB system, chromium atoms liberated by the substitutional diffusion of Fe into CrB lattice interacts with iron forming an Fe–Cr metal alloy. Moreover, zones of Cr-containing FeB and Fe₂B form at the contact between metal iron and chromium monoboride, and tend to disappear as iron is consumed by the alloying process.     

Mössbauer Studies of Electrodeposited and Ion Beam Mixed Alloy Coatings

CEMS, XMS, XRD and electron microprobe analysis were applied to study electrodeposited and ion beam mixed Fe–Cr–Ni as well as electrodeposited and ball-milled Sn–Cr alloys. In Fe–Cr–Ni alloys with composition 40% Cr and 20–30% Ni a metastable ferromagnetic phase has been found beside a metastable paramagnetic and an equilibrium phase in all deposits. The relative occurrence of the ferromagnetic phase exhibits an increase in the plating temperature range: 30–40°C. With plating temperature an increase of the short-range order in the ferromagnetic phase was observed. The highenergy heavy ion irradiation of Fe–Ni–Cr multilayer produces ferromagnetic and paramagnetic metastable phases. The electrodeposition of Sn–Cr alloys results in metastable Sn–Cr phases. In the case of ball-milling preparation the equilibrium Sn₃Cr₂ phase (=2.3 mm/s, =1.2 mm/s) appears in Sn–Cr alloys. The quantity of the Sn₃Cr₂ phase increases with the milling time.     

Microstructure and wear resistance of Al–SiC composites coatings on ZE41 magnesium alloy

Al and Al–SiC composites coatings were prepared by oxyacetylene flame spraying on ZE41 magnesium alloy substrates. Coatings with controlled reinforcement rate of up to 23 vol.% were obtained by spraying mixtures containing aluminium powder with up to 50 vol.% SiC particles. The coatings were sprayed on the magnesium alloy with minor degradation of its microstructure or mechanical properties. The coatings were compacted to improve their microstructure and protective behaviour. The wear behaviour of these coatings has been tested using the pin-on-disk technique and the reinforced coatings provided 85% more wear resistance than uncoated ZE41 and 400% more than pure Al coatings.     

The effect of cerium oxide argon-annealed coatings on the high temperature oxidation of a FeCrAl alloy

Ceria coatings were applied in order to improve the adherence of alumina scales developed on a model Fe–20Cr–5Al alloy during oxidation at high temperature. These coatings were performed by argon annealing of a ceria sol–gel coating at temperatures ranging between 600 and 1000 °C. The influence of these coatings on the alloy oxidation behaviour was studied at 1100 °C. In situ X-ray diffraction (XRD) was performed to characterize the coating crystallographic nature after annealing and during the oxidation process. The alumina scale morphologies were studied by means of scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The present work shows that the alumina scale morphology observed on cerium sol–gel coated alloy was very convoluted. On the cerium sol–gel coated alloy, argon annealing results in an increase of the oxidation rate in air, at 1100 °C. The 600 °C argon annealing temperature results in a good alumina scale adherence under thermal cycling conditions at 1100 °C.     

Icosahedral-Cluster-Reinforced Structures in Irradiated Metallic Materials

A nonequilibrium state has been discovered which is induced by ion irradiation in metallic materials (solid solutions of Fe–Ni, Fe–Cr–Ni, Ni–Cr, Cu–Ni, Fe–Cr, and V–Ti–Cr systems and in pure metals Zr and Ti) at high levels of radiation damage, and the features of this state are considered. In the region of existence of this state, both the ion and the electron subsystems of the metal show highly anomalous properties. Moreover, the occurrence of this state is accompanied by substantial diffraction effects – X-ray line splitting – and, as indicated by electron microscopy, by the formation of a cluster structure. Simulation by the methods of molecular dynamics suggests that the clusters observed are atomic groups of icosahedral (quintuple) symmetry formed in the neighborhood of radiation vacancies. These clusters reinforce the matrix, and this should result in substantial changes in strength and electronic properties of the material. The results of the computer simulation agree with the observed diffraction effects.     

Strength and wear resistance of nanocrystal structures on friction surfaces of steels with martensitic base

The formation of nanocrystal -martensite structures (NCS) in the surface layers of carbon and alloy steels under conditions of sliding friction and abrasion is investigated by electron microscopic, x-ray, and metallographic methods. The influence of the dynamic strain aging of martensite and strain dissolution of the carbide phase on the strength (microhardness and shear resistance) and tribological properties (wear resistance and friction coefficient) of nanocrystal surface layers of steels with martensitic base is demonstrated. The role of nanocrystal martensite in adhesive, abrasive, and fatigue wear resistance of steels is examined. The negative influence of the oxidizing air environment on the effective strength and wear resistance of friction NCS is demonstrated. The increased resistance of friction NCS of high-carbon steel to softening after tempering and friction heating is established.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 65–80, August, 2004.     

Electrochemical deposition and tribological behaviour of Ni and Ni-Co metal matrix composites with SiC nano-particles

Metal matrix composites reinforced with nano-sized particles have attracted scientific and technological interest due to the enhanced properties exhibited by these coatings. Ni-SiC composites have gained widespread application for the protection of friction parts in the automobile industry. The influence of variables like SiC content, current density and stirring speed on microhardness of nano-composite coatings has been studied. The improved microhardness was associated with the reduction in crystallite size determined by X-ray diffraction studies. The influence of incorporation of nano-SiC in hardened Ni-Co alloy matrix was also studied. It was observed that for 28 wt.% Co content in the matrix the microhardness was higher compared to 70 wt.% for a given nano-SiC content. This was associated to the crystal phase of Ni-28Co-SiC being fcc compared to hcp phase exhibited by Ni-70Co-SiC. The wear resistance of pure Ni, Co and nano-composite coatings was studied using pin-on-disc wear tester under dry sliding condition. The volumetric wear loss indicated that, the wear resistance of Ni-SiC nano-composite is better than that of pure nickel deposit. The wear resistance of Ni-Co composites was observed to be superior to Ni composite. The wear behaviour of Ni and Ni-28Co composite was in accordance with the Archard's law. However, the superior wear characteristic exhibited by Ni-70Co-SiC composite followed the reverse Archard's behaviour.     

Structural and mechanical properties of compositionally gradient CrNx coatings prepared by arc ion plating

Compositionally gradient CrN_x coatings were fabricated using arc ion plating by gradually increasing N₂ flow rate during the deposition process. The effect of substrate bias, ranging from 0 to −250 V, on film microstructure and mechanical properties were systematically investigated with XRD, SEM, HRTEM, nanoindentation, adhesion and wear tests. The results show that substrate bias has an important influence on film microstructure and mechanical properties of gradient CrN_x coatings. The coatings mainly crystallized in the mixture of hexagonal Cr₂N, bcc Cr and fcc rock-salt CrN phases. N₂ flow rate change during deposition results in phase changes in order of Cr, Cr + Cr₂N, Cr₂N, Cr₂N + CrN, and CrN, respectively, along thickness direction. Phase fraction and preferred orientation in CrN_x coatings vary with substrate bias, exerting an effective influence on film hardness. With the increasing of bias, film microstructure evolves from an apparent columnar structure to a highly dense one. The maximum hardness of 39.1 GPa was obtained for the coatings deposited at a bias of −50 V with a friction coefficient of 0.55. It was also found that adhesion property and wear resistance of gradient CrN_x coatings were better than that of homogeneous CrN coatings.     

Microstructure and friction and wear behavior of laser boronizing composite coatings on titanium substrate

Three kinds of laser boronizing composite coatings were in situ synthesized on Ti substrate by using powders of B, BN and B₄C as starting materials. Microstructures of the laser boronizing composite coatings were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM); and their worn surface morphologies were also observed by using SEM. Moreover, the friction and wear behavior of the boronizing composite coatings under dry sliding condition were evaluated using a UMT-2MT friction and wear tester. It was found that all the three types of laser boronizing composite coatings had higher microhardness and better wear resistance than pure Ti substrate; and their microstructure and wear resistance varied with varying pre-placed powders of B, BN, and B₄C. Under the same dry sliding test conditions, the wear resistance of the three kinds of laser boronizing composite coatings, i.e., sample 1 prepared from pre-placed B, sample 2 obtained from pre-placed BN, and sample 3 fabricated from pre-placed B₄C, is ranked in an order of sample 1 > sample 2 > sample 3, which, surprisingly, well conforms to their order of hardness and friction coefficients.     

An Investigation of Phase Diagrams of Decomposing Magnetic Alloys

The interaction of phase decomposition and magnetic ordering processes in an A–B alloy of an arbitrary structure is studied theoretically. The decomposition and magnetization temperatures are calculated. The phase diagrams are constructed and compared with experiment on Fe–Cr, Fe–Co, and Pt–Co alloys.     

Ti6Al4V合金表面激光沉积复合涂层的组织和性能

为了增强Ti6Al4V钛合金的耐磨性,采用激光沉积制造方法在其表面上制备了以原位生成的TiC颗粒和直接添加的WC颗粒为增强相的耐磨涂层,观察了各涂层的微观组织,并测量了涂层的显微硬度和涂层在室温大气条件下的摩擦磨损性能。结果表明各涂层和基体呈现冶金结合,原位自生的TiC和部分熔化的WC颗粒均能够均匀弥散分布于基体上,由于增强相颗粒的弥散强化及激光沉积组织的细晶强化作用,基材的硬度和耐磨性均得到了提高。原位自生的TiC涂层比WC涂层硬度梯度分布平缓,但耐磨性稍差。     

Novel powder metallurgy technique for development of Fe–P-based soft magnetic materials

Novel powder metallurgy technique (hot forging technique) is used for the development of high-density Fe–P-based soft magnetic alloys such as Fe–P binary, Fe–P–Cr ternary and Fe–P–Cr–Si quaternary alloys. In this process, mild steel encapsulated powders were hot forged into slabs, hot rolled and annealed to relieve the residual stresses. These alloys were subjected to in-house characterization, e.g. density and theoretically calculated porosity content at various stages. Microstructural study has been carried out to compare observed porosity with the theoretically calculated porosity. X-ray diffraction studies of these alloys revealed presence of only ferrite as product phase. Various soft magnetic properties such as resistivity, coercivity, maximum flux density (at 350 G magnetic field), retentivity and total magnetic losses were also evaluated and reported. These alloys were made by hot forging using two different kinds of dies, e.g. flat die and channel die. It was observed that the flat-die forged alloys had more porosity than the channel-die forged alloys. Addition of alloying elements such as P, Cr and Si increased the resistivity of Fe. The higher the alloying addition, the higher is the alloy's resistivity. Fe–0.7P–0.7Cr–1Si alloy showed a resistivity as high as 44.1 μΩ cm. Coercivity values of the alloys ranged from 1.0 to 2.2 Oe. Addition of Si and P helped in reducing the coercivity values of the alloys. The higher the Si, P content, the lower were the coercivity values observed. Combined addition of P and Si helped in reducing the coercivity values significantly, for example Fe–0.7P–0.7Cr–1Si alloy showed coercivity value approximately 1.0 Oe. It was observed in this investigation that maximum flux densities of the alloys were linearly related with their porosity levels. Total magnetic losses of these alloys varied from 6.0 to 7.8 W/kg. The total magnetic loss of Fe–0.7P–0.7Cr–1Si alloy was the lowest (6.0 W/kg) owing to its highest resistivity combined with its lowest coercivity amongst the alloys developed in the present investigation. Alloys developed in this investigation were capable of hot/cold working to very thin gage of sheet (0.5 mm thickness). These alloys could find their possible application in manufacturing of transformer core.     

铁基合金激光熔覆层的高温磨损性能

 为提高40Cr钢表面耐磨性,采用预置激光熔覆法在40Cr基体表面制备Fe基涂层,利用HT-500摩擦磨损实验机测定干摩擦条件下,基体和熔覆层的摩擦因数随温度变化的规律。利用表面粗糙度轮廓仪测量磨痕的深度和宽度,SEM观察熔覆层以及磨痕的显微组织形貌,使用HV-1000型显微硬度仪检测基体和熔覆层结合部分的硬度。研究结果表明:熔覆层平均显微硬度值达到373.8HV(0.2);显著高于基体硬度198.4HV(0.2)。在干摩擦条件下,随着温度升高,磨损过程逐渐变平缓,平均摩擦因数降低,磨损率增加,耐磨性下降;在350~400 ℃之间,熔覆层磨损性能优于基体。     

Characterization and magnetic properties of Fe–Co ultrafine particles

Characterization and magnetic properties of Fe–Co ultrafine particles were investigated systematically by means of X-ray diffraction, Mössbauer spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, energy disperse spectroscopy analysis, chemical analysis, oxygen determination and magnetization measurement. In comparison with bulk iron–cobalt alloys, the corresponding Fe–Co ultrafine particles have significant difference in the phase structure and magnetic properties, depending on the condition of evaporating and subsequent quenching. The mechanism for the formation of the ultrafine particles as well as the origin of ferromagnetism and paramagnetism (or superparamagnetism) were discussed.     

Multi-functional properties of iron-based ferromagnetic shape memory ribbons

This paper presents measured multi-functional properties of Fe–Mn–Cr–Si–Tb–B ribbons developed by means of the melt-spinning technique in air. The alloys are multi-functional materials, which have both ferromagnetic and shape memory properties. If we can simultaneously improve the material properties, the applications of the shape memory alloys will be widened dramatically in the field of the electromagnetic sensors and actuators. The base shape memory material, Fe–Mn–Si alloy, is nonmagnetic due to its high manganese content (28–34 Mn, 4–6.5Si wt%). In order to improve ferromagnetic function of the Fe–Mn–Si alloy, we have investigated the addition of rare earth elements. Addition of about 0.7–1.0 wt% Tb was effective in increasing the saturation magnetization. However, ductility of the samples was not good and it was difficult to evaluate the shape memory properties with shape recovery strain measurements. The detailed magnetic and shape memory properties of the Fe–Mn–Cr–Si–Tb–B alloys are discussed in this paper.     

Friction and wear properties of the co-deposited Ni-SiC nanocomposite coating

Ni-SiC nanocomposite coatings were produced by electrodeposition from a nickel sulfate bath containing SiC nanoparticles with an average particle size of 30 nm. The characteristics of the coatings were assessed by scanning electron microscopy and microhardness test. The friction and wear performance of Ni-SiC nanocomposite coatings and Ni film were comparatively investigated sliding against Si₃N₄ ceramic balls under non-lubricated conditions. The results indicated that compared to Ni film, Ni-SiC nanocomposite coating exhibited enhanced microhardness and wear resistance. The effect of SiC nanoparticles on the friction and wear resistance is discussed in detail.     

Thermodynamics and surface properties of liquid Cu–B alloys

The study of the thermodynamic and the surface properties of liquid Cu–B alloys can help better understanding of a complex interfacial chemistry related to liquid Cu–brazes in contact with boride substrates. Despite a simplicity of the Cu–B phase diagram, only a few thermodynamic data are available in the literature, while in the case of the surface properties a complete lack of data is evident. The quasi-chemical approximation (QCA) for the regular solution has been applied to describe the mixing behaviour of liquid Cu–B alloys in terms of their thermodynamic and surface properties as well as the microscopic functions. In view of joining processes related to liquid Cu–brazes/solid boride systems a particular attention is paid to the surface properties of the Cu-rich part of the system and the calculated values are substantiated by the new surface tension experimental data of liquid Cu and Cu–10 at.% B alloy. The tests have been performed by the sessile-drop method under the same experimental conditions. Considering the experimental uncertainties, the effect of oxygen on the surface tension of liquid Cu and Cu–10 at.% B alloy has been analysed by simple model that combines the physical property data included in Butler’s equation with the oxygen solubility data and it gives the same results as Belton’s adsorption equation.     

Morphological study of ternary Ni–Cu–P alloys by atomic force microscopy

Ternary electroless Ni–Cu–P alloy films were deposited by using nickel sulphate (B1)- and nickel chloride (B2)-based alkaline baths. Alloy films were characterized for their structure, morphology, chemical composition and microhardness. A single broad peak was obtained in XRD for both B1 and B2 films and the calculated grain sizes are 1.6 and 1.9 nm, respectively. Optical microscopic examination of the deposited coatings revealed a less nodular structure for B2-based coatings. SEM micrographs showed that films were smooth and nodular. Compositional analysis made on these deposits using EDX and the chemical state identification by XPS showed that the coatings are almost identical. AFM studies showed that the deposits from B2 bath are comparatively smoother with less nodular structure. Microhardness measurements and potentiodynamic polarization studies in 3.5% NaCl solution showed that both deposits have similar properties.     

Evolution of phase,texture, microstructure and magnetic properties of Fe–Cr–Co–Mo–Ti permanent magnets

Magnetic phase evolution, crystallographic texture, microstructure and magnetic properties of Fe–28Cr–15Co–3.5Mo–1.8Ti alloy have been investigated by X-ray diffractometry, scanning transmission electron microscopy and magnetometry techniques as a function of processing conditions. Heat treatment conditions for obtaining optimum textural, microstructural and magnetic properties have been established by the experimentations. The Goss {110}〈001〉 and cube type {001}〈010〉 textures have been developed in an optimal treated Fe–28Cr–15Co–3.5Mo–1.8Ti magnets. The coercive force in Fe–28Cr–15Co–3.5Mo–1.8Ti magnets depends critically on the shape anisotropy of rod-like Fe Co Ti-rich α₁ particles and remanence on the alignment and elongation of α₁ particles parallel to applied magnetic field 〈100〉 directions. The optimum magnetic properties obtained in Fe–28Cr–15Co–3.5Mo–1.8Ti alloy are intrinsic coercive force, _iH_c, of 78.8 kA/m (990 Oe), remanence, B_r of 1.12 T (11.2 kG) and energy product, (BH)_max of 52.5 kJ/m³ (6.5 MGOe). The development of Fe–28Cr–15Co–3.5Mo–1.8Ti magnets as well as characterization of texture, microstructural and magnetic properties in the current study would be helpful in designing the new Fe–Cr–Co–Mo based magnets suitable for scientific and technological applications.     

Microstructure and wear properties of TiCN/Ti coatings on titanium alloy by laser cladding

Titanium carbide nitride (TiCN) reinforced Ti coating was fabricated on the surface of Ti–6Al–4V alloy by laser cladding method. Microstructure and wear properties at the surface of the coating in atmosphere were investigated. Three zones can be distinguished of the coating: the clad zone (CZ), the heat affected zone (HAZ) and the substrate. The clad zone is composed of TiCN dendrites, TiO₂ and Ti. A metallurgical bonding between the coating and the substrate was obtained. The microhardness and wear resistance of the TiCN/Ti coating are significantly improved. The average hardness of the coating is about 3 to 6 times of that of the substrate. The friction coefficients of the substrate and the coating are 0.48 and 0.34 respectively. The friction coefficient of the Ti–6Al–4V substrate was insensitive to the normal load, while that of the cladded TiCN/Ti coating was very sensitive to the normal load. The wear mass losses of the cladded samples are much lower than that of the substrate whatever the normal load is.