Formation of wear-resistant graphitized layers on the surface of parts from iron and titanium alloys by the method of electric spark alloying

The process of formation of free graphite in the surface layer of specimens from alloys based on iron and titanium by the method of electric spark alloying is described. It is established that a high content of free graphite in the surface layer can be obtained only by feeding it in a powder form (together with the modifying materials) into the zone of electric spark treatment. The wear resistance of the thus graphitized surface layers of steel and titanium alloy specimens increases by a factor of 7–8. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov. No. 7, pp. 23–26, July, 2000.     

The role of alloying elements in commercial alloys for corrosion resistance in oxidizing‐chloridizing atmospheres. Part I: Literature evaluation and thermodynamic calculations on phase stabilities

In several high temperature processing environments the presence of chlorine may significantly reduce the life‐time of the components. Although metallic materials have been widely used under such conditions there is still a need for data on the role of the different alloying elements in commercial alloys. In the present work this role was investigated in detail at temperatures between 650 and 1000°C in synthetic air containing up to 2 vol.% Cl₂. Before starting the experimental investigation a detailed literature evaluation on chlorine high temperature corrosion was performed followed by a thermodynamic assessment of the stability and the partial pressures of the phases formed by the reaction between alloy and environment. The results of this “theoretical approach” are presented in the following first part of the publication while the experimental work will be reported in the second part appearing in a later issue of this journal. Already the results of the “theoretical approach” yield a clear picture of which alloying elements play a detrimental role and which elements are beneficial. These results can be used as a tool for a general assessment of metallic alloys with regard to their performance in oxidizing/chloridizing high temperature environments. In the second part of this work the results from this “theoretical approach” will be compared with the behavior of 14 commercial materials, where the content of the major alloying elements was varied in a systematic manner.     

Effect of severe plastic deformation on the structure,microhardness, and wear resistance of the surface layer of titanium subjected to gas nitriding

The effect of severe plastic deformation under dry sliding friction on the structure, microhardness, and wear rate of the VT1-0 titanium subjected to gas nitriding has been studied. It has been shown that this deformation leads to the formation of a nanocrystalline structure with an α-crystal size of 10–100 nm and a microhardness of ～3.1 GPa in a surface layer up to 10 μm thick. The presence of this structure intensifies the saturation of the surface of the titanium with nitrogen in the course of subsequent gas nitriding at temperatures of 650–750°C. The formation of the nitride nanocrystalline TiN phase in the deformed titanium occurs at a relatively low nitriding temperature (700°C) and a short-term holding (2 h). The volume fraction of the nitride phase, which is formed in the layer up to 10 μm thick, reaches a few tens of percent, which leads to an increase in the microhardness of the nitrided surface of the titanium deformed by friction. Preliminary severe plastic deformation has a negative effect on the fatigue wear resistance of the nitrided titanium due to an increased brittleness of the deformed and subsequently nitrided surface layer of this material.     

Scientific and technological fundamentals for the development of the controlled short-circuiting MIG/MAG welding process: a review of the literature. Part 2 of 3. Metal droplet formation,shield gases,penetration mechanisms,heat input and economical aspects

The second part of this series deals with the metal transfer modes of most interest to the MIG/MAG process, regarding the development of the controlled short-circuiting MIG/MAG welding process (CCC). The primary intention is to study pulsed arc and short-circuiting arc welding, both of which are the basis for the CCC. Also in relation to the metal transfer dynamics, the drop formation and the forces acting on it are reviewed. To provide a more complete understanding, aspects regarding shielding gases are described, including economic issues. Since they are important characteristics for any weld, information concerning short-circuiting MIG/MAG welding penetration and heat input are also provided.     

Eutectic modification in a low-chromium white cast iron by a mixture of titanium,rare earths,and bismuth: Part II. effect on the wear behavior

In this work, we studied the wear behavior of a low-Cr white cast iron (WCI) modified with ferrotitanium-rare earths-bismuth (Fe-Ti-RE-Bi) up to 2%. These additions modified the eutectic carbide structure of the alloy from continuous ledeburite into a blocky, less interconnected carbide network. The modified structure was wear tested under pure sliding conditions against a hardened M2 steel counter-face using a load of 250 N. It was observed that wear resistance increased as the modifier admixture increased. The modified structure had smaller more isolated carbides than the WCI with no Fe-Ti-RE-Bi additions. It was observed that large carbides fracture during sliding, which destabilizes the structure and causes degradation in the wear behavior. A transition from abrasive to oxidative wear after 20 km sliding occurred for all alloys. In addition, the modified alloys exhibited higher values of hardness and fracture toughness. These results are discussed in terms of the modified eutectic carbide microstructure.     

To the theory of the anomalously high diffusion rate in metals under shock action: II. Effect of shear stresses and structural and phase state of the diffusion zone on the rate of mass transfer

Phenomena of diffusion mass transfer in metals under shock mechanical actions have been investigated. The effect of shear stresses on the diffusion processes is considered. It is noted that the impact loads acting on alloys that possess polymorphic modifications lead to the development of structural phase transformations, which take place by the martensitic mechanism, and to the generation of numerous vacancies. In combination with the high temperatures and significant shear stresses in the diffusion zone, these phenomena substantially accelerate the processes of diffusional mass transfer. The basic result of an impact action is the changeover of the medium into a strongly nonequilibrium state which is characterized by anomalously high velocities of the displacement of diffusion fronts, which was observed experimentally.     

Nitrated petroleum product and some aspects of the mechanism of its action in an oil coating on steel—II. The investigation of surface layers on steel

Closer characterization of a nitrated petroleum product (US inhibitor) has been based upon infrared, chromatographic, group structure and potentiokinetic studies. It was established that the inhibitor is a complex mixture of hydrocarbons and their derivatives containing nitrogen, oxygen and sulfur. The mixture is a highly effective inhibitor only for certain ratios of its components. The polar molecules of the inhibitor which, in addition to nitro and carbonyl groups, also contain a hydrocarbon part with proper ratio of naphthenic and aromatic rings and aliphatic chains, have a fundamental effect on the region of stable passivation of steel. It would appear that the molecules interact with the anodic sites on the surface binding through oxygen of polar groups and π-electrons of the benzene ring. Non-polar molecules or those with small dipole moment enhance this interaction through physical adsorption. The protective film formed on steel as a result of interaction of components of US inhibitor is probably multilayered and has qualitatively diversified nature.     

The development of criteria for evaluating the effectiveness of the surface layer formation and its properties in the process of electrospark alloying (ESA). Part 2. The criteria of the effectiveness of the ESA process and electrospark coatings

The paper offers comprehensive and integrated specific criteria for the effective use of electrospark alloying (ESA) to determine the effectiveness of the conditions of applying electric-spark coatings with the required performance characteristics and parameters of the surface topography, taking into account the energy costs. A general criterion is also provided for the efficiency of the coating, allowing us to determine and compare the performance of different coating processes by ESA and other methods based on energy consumption, and economic and environmental factors.