Effect Of Interstitial Elements Research Articles

Mobility of dislocations in the iron-based C-, N-, H-solid solutions measured using internal friction: Effect of electron structure

Effect of interstitial elements on the Snoek-Köster relaxation and the amplitude-dependent internal friction is analyzed in terms of a change in the electron structure. The density of electron states in the bcc and fcc iron doped with carbon, nitrogen or hydrogen has been ab initio calculated paying due attention to that at the Fermi level. It is obtained that nitrogen and hydrogen increase density of states in the both iron phases, whereas the effect of carbon is opposite. In consistency, using electron spin resonance in the fcc iron alloys, the concentration of free electrons is found to be increased due to nitrogen and hydrogen and decreased by carbon. Based on the obtained results, a conclusion about corresponding change in the dislocation line tension controlling mobility of dislocations is derived. This correlation between electron structure and mobility of dislocations is confirmed for the Snoek-Köster relaxation in the bcc iron phase and for the internal friction background, ADIF, in the fcc phase.

Effect of Interstitial Elements on the Cryogenic Mechanical Behavior of FCC High Entropy Alloys

High entropy alloys (HEAs) with face-centered cubic (fcc) structure, namely equiatomic CoCrFeMnNi alloy, have attracted considerable attention because of impressive cryogenic mechanical properties – strength, ductility, and fracture toughness. Further increase of the properties can be achieved, for example, by proper alloying. A particularly attractive option is the addition of interstitial elements like carbon or nitrogen. In present work, a series of CoCrFeMnNi-based alloys with different amounts of C and N (0-2 at.%) was prepared by induction melting. The alloys doped with C had lower Cr content to increase the solubility of carbon in the fcc solid solution. It was revealed that the solid solution strengthening effect of both C and N is significantly increased when the testing temperature decreases from 293K to 77K. The effect of thermomechanical processing on the structure and mechanical properties of the alloys is analyzed.

Effect of Interstitial Elements on Pitting and Intercrystalline Corrosion of Austenitic Chromium-Nickel Steel

Abstract—The possibility of improving the resistance of austenitic chromium-nickel steel of 09Kh18N9 and 08Kh16N11М3 grades to pitting and intercrystalline corrosion under the conditions of standby mode of a fast neutron reactor facility has been investigated. Corrosion tests lasting up to 15 000 h have demonstrated that the corrosion rate decreases significantly upon the decrease in the carbon content and the increase in the nitrogen content.

CARBON, NITROGEN AND HYDROGEN IN STEELS: PLASTICITY AND BRITTLENESS

Interstitial elements in steel, carbon, nitrogen and hydrogen, are analyzed in terms of their effect on the electron structure, properties of dislocations, strengthening, plasticity and fracture. It is shown that similarities and differences in the mechanical properties of corresponding solid solutions are controlled by the effect of the above mentioned elements on the density of electron states at the iron Fermi level and, as a result, on the concentration of free electrons. The latter is decreased by the carbon and increased due to nitrogen and hydrogen in the iron, which changes the character of interatomic bonds: carbon enhances their covalent component, whereas nitrogen and hydrogen strengthen the metallic one. The velocity of dislocations in the course of plastic deformation is discussed using the approach of mobile and immobile interstitial atoms. In the fi rst case, they are obstacles for dislocation slip, and mobility of dislocations is determined by the enthalpy of binding between interstitial atoms and dislocations. If interstitial atoms are suffi ciently mobile to accompany dislocations, the character of interatomic bonds within the interstitial clouds around the dislocations is locally changed. As a result, the specifi c energy of dislocations (line tension) and the distance between them in the pile-ups are changed in accordance with the local change of the shear modulus around the dislocations. Based on the performed studies, the effect of interstitial elements on the mechanical properties of steels is discussed. Particularly, the essential similarity between the hydrogen-caused brittleness and the nitrogen-induced ductile-to-brittle transition in the austenitic steels is interpreted.

Effect of Interstitial Elements on Ductile-Brittle Transition Behavior of Austenitic Fe-18Cr-10Mn-2Ni Alloys

The effect of interstitial elements on the ductile-brittle transition behavior of austenitic Fe-18Cr-10Mn-2Ni alloys with different nitrogen and carbon contents was investigated in this study. All the alloys exhibited ductile-brittle transition behavior because of unusual low-temperature brittle fracture, even though they have a faced-centered cubic structure. With the same interstitial content, the combined addition of nitrogen and carbon, compared to the sole addition of nitrogen, improved the low-temperature toughness and thus decreased the ductile-brittle transition temperature (DBTT) because this combined addition effectively enhances the metallic component of the interatomic bonds and is accompanied by good plasticity and toughness due to the increased free electron concentration. The increase in carbon content or of the carbon-to-nitrogen ratio, however, could increase the DBTT since either of these causes the occurrence of intergranular fracture that lead to the deterioration of the toughness at low temperatures. The secondary ion mass spectroscopy analysis results for the observation of carbon and nitrogen distributions confirms that the carbon and nitrogen atoms were significantly segregated to the austenite grain boundaries and then caused grain boundary embrittlement. In order to successfully develop austenitic Fe-Cr-Mn alloys for low-temperature application, therefore, more systematic study is required to determine the optimum content and ratio of carbon and nitrogen in terms of free electron concentration and grain boundary embrittlement.

Effect of Interstitial Elements on the Toughness of Ferritic Stainless Steel Weld

In this study, the toughness of 11Cr ferritic stainless steel weld was evaluated by DBTT (Ductile-Brittle-Transition-Temperature) with the interstitial elements level. DBTT of the weld increased with increasing interstitial level due to the formation of martensite phase and solidsolution strengthening. Interstitial elements level should be limited by the adoption of back shielding gas during welding process because increased C+N level detrimentally affects the toughness of ferritic stainless weld. Adoption of Ar as back shielding gas lowered N content in the weld.

Effect of Interstitial Elements on Hall–Petch Coefficient of Ferritic Iron

Yield strength was investigated in iron with different grain size and different contents of carbon and nitrogen. The Hall-Petch coefficient; k y is originally very small in high purity iron (about 100 MPa · μm 1/2) but it increases with increasing the amount of solute carbon content. The value of k y is enlarged to around 550 MPa · μm 1/2 by 60ppm of solute carbon and levels off at around 600 MPa·μm 1/2 in the region above 60ppm solute carbon. On the other hand, nitrogen hardly influences the k y value. The mechanism of the change in Hall-Petch coefficient was then discussed in terms of the grain boundary segregation of carbon and nitrogen atoms.

On the Effects of Interstitial Elements on Microstructure and Properties of Ternary and Quaternary TiAl based alloys

ABSTRACTTi-Al-Cr ternary and Ti-Al-Cr-Nb quaternary alloys have been studied as a function of initial purity and added interstitial content. Using strict clean processing together with either ultra high purity or commercial purity alloys, the effects of interstitial elements (essentially O, but also C and N) on microstructure and hardness, yield stress and fracture strain have been studied for both fully lamellar microstructures and duplex microstructures. The results are clear and similar trends are observed : as long as they do not precipitate, these stabilise the lamellar microstructure and affect the kinetics of the α-γ phase tranformation, leading to a higher than equilibrium value for the α2phase for continuous cooling. Both the lamellar spacing and the α2phase fraction correlate with increased hardness and yield stress, and also with decreasing fracture strain. The effects are significant.

On the Influence of Microstructure on the Fracture Behavior of Gamma-Based Titanium Aluminides. III. Effects of Interstitials and Microalloying with W

ABSTRACT The results of a recent study of the effects of interstitial elements and microalloying with 0.2 at.% W on the tensile and fracture properties of Ti-48Al (compositions quoted in atomic % unless stated otherwise) base gamma alloys are presented in this paper. Lower interstitial oxygen levels are shown to promote higher levels of tensile ductility at the expense of yield/ultimate tensile strength and fracture toughness. Microalloying with W is also shown to result in microstructural instability and a concomitant degradation in tensile and fracture properties. Ductility and yield/ultimate tensile strengths in binary gamma alloys at room - and elevated-temperature are shown to exhibit a simple Hall-Petch dependence on the average grain/lamellar packet size. The observed Hall-Petch behavior is found to be independent of lamellar volume fraction and fracture mechanism at room- and elevated-temperature. The implications of the results are discussed for future alloy/process development.

The effects of interstitial elements on the phase stability and mechanical behavior of selected intermetallics

The possibility of stabilizing by interstitial element alloying a crystal structure more favorable for mechanical behavior was explored in a number of high temperature intermetallics. The base intermetallics A 3B were mainly of the Cr 3Si (A15) structure type and alloying with interstitials A 3BX x , where X ≡ C, O or N, in many cases resulted in the ordered f.c.c. Cu 3Au (Ll 2) or perovskite (L′l 2) structures. At least 16 alloy systems exhibit this effect, as determined from our research and from the literature. The V 3AuX (X ≡ O, C,) and V 3PtO systems were selected for quantitative study of the mechanical behavior. The fracture toughness K IC, as estimated by both microhardness indentation cracking methods and fractal geometry measurements of fractured surfaces, indicated that the interstitial-stabilized L′l 2 phase had K IC values two to three times greater than those of the base A15 compound, although the absolute values were still low.

Effects of interstitial elements in iron-rare earth alloys

Iron-rare earth metal alloys are the most promising hard magnet compounds. These alloys belong to either the Nd 2Fe 14B, the ThMn 12 or the Th 2Zn 17 structure type. They accomodate light elements such as H, C and N, inducing dramatic effects on the magnetic properties. This insertion is an interesting route for a better understanding of the fundamental properties.

純チタンの耐食性に及ぼす侵入型元素およびFe添加の影響について

Effect of interstitial elements and iron on corrosion resistance of commercially pure titanium in hydrochloric and sulfuric acids