Major Alloying Elements Research Articles

Formation of nanosized grain structure in martensitic 100Cr6 bearing steels upon rolling contact loading studied by atom probe tomography

To understand the origin of white etching cracks (WECs), a systematic microstructural characterisation in the regions affected from the near-surface region down to the subsurface layers where WECs occur is necessary. As a starting point, we focus on the near-surface region of an axial thrust bearing, made of martensitic 100Cr6 steel, to study the influence of rolling contact loading on the microstructure and the resulting distributions of the major alloying elements C and Cr using atom probe tomography. We find that upon rolling contact loading the original plate-like martensitic structure evolves into a nanosized equiaxed grain structure with C segregation up to 5 at.-% at the grain boundaries. Cementite particles, located at grain boundaries and triple junctions, undergo spheroidisation. The originally homogeneously distributed Cr becomes enriched in spheroidised cementite particles. The microstructural changes give strong hints that rolling contact loading induces plastic deformation and an increased temperature on the near-surface region.This paper is part of a Themed Issue on Recent developments in bearing steels.

Corrosion behaviors of weathering steel 09CuPCrNi welded joints in simulated marine atmospheric environment

Purpose The purpose of this paper is to investigate the effect of welding procedure on the corrosion behaviors of weathering steel 09CuPCrNi in marine atmospheric environment. The corrosion processes of weathering steel 09CuPCrNi and its welded joints in marine atmospheric environment were simulated by a salt spray dry-wet test. Design/methodology/approach The corrosion behaviors of the base metal and the welded joints at corrosion times of 2, 4, 8, 12, 24 weeks were investigated by weight loss test, electrochemical techniques, scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA). The corrosion rates, as well as the morphologies and electrochemical characteristics of corrosion products, the distribution of major alloying elements in rust layer were obtained. The influence of welding on the atmospheric corrosion of 09CuPCrNi was studied. Findings The results indicate that the corrosion rate of the 09CuPCrNi welded joints decreases gradually with the corrosion time, and the major alloying elements are enriched in the inner rust layer, which are similar to that of the base metal. In the early stage during the corrosion process, the welded joints with inhomogeneous structure show the poorer corrosion resistance than that of the base metal. However, it looks the opposite way around in the late corrosion stage, when the uniform corrosion products with even thickness of the base metal tend to detach from the substrate easier and earlier and resulting in cracks, which increase the corrosion rate comparatively with that of the welded joints. Originality/value 09CuPCrNi low alloy steel is a kind of typical weathering steel developed in China which is similar to Corten A developed by USA. Nowadays, 09CuPCrNi low alloy steel is widely adopted in many fields which require welding processes. In the past years, the research of weathering steel welded joints was mainly concentrated on the strength, toughness and weldability. Less work has been done to investigate the difference of corrosion evolution and characteristics between the base metal and its welded joints. Thus, the main objective of the present work was to analyze the influence of welding on the atmospheric corrosion.

Predicting yield strengths of Al-Zn-Mg-Cu-(Zr) aluminium alloys based on alloy composition or hardness

A linear single variable model for describing precipitation heat treated Al-Zn-Mg-Cu aluminium alloy hardness and yield strength based on precipitate compositions was proposed. A concept composition model was developed based on the major alloying elements and the strengthening precipitate compositions, for the precipitation heat treatment condition. A Refined composition model was subsequently developed to account for the effect of minor alloying (Mn) and impurity elements (Fe, Si). Macro segregation of alloying elements had a significant effect on the results of the Refined composition model. Mechanical properties varied according to a simple linear relationship with the atomic fraction of the strengthening precipitate. The T6 and T73 hardness, and T6 yield strength were algebraically expressed, with linear relationships. The model describes existing yield strength data for Al-Zn-Mg-Cu aluminium alloys. The Refined composition model was also valid for predicting yield strengths of Al-Zn-Mg-Cu-Zr aluminium alloys in the T6 condition.

Microstructure and Mechanical Properties of the Weld Joint of Small Diameter Glass-Lined Metal Pipe with Inner Surface Layer

The width of 36mm of inner surface layer was formed by Ni625 welding wires in the ends of glass-lined 20# metal pipe, and the metal tubes were welded. The microstructure and the distribution of the main alloying elements of the weld joints were analyzed by optical microscope (OM) and electron probe microscope analysis (EPMA). The mechanical property and nondestructive inspection tests of the welded joints were carried out. The results show that the welded joints were divided into three layers including root layer, transition layer and cap layer. The microstructure in root layer was characterized by the cellular-dendrite structure. The transition layer contained martensite and retained austenite. The capping layer included acicular ferrite and pearlite. The defect free joint was produced and performed well. The concentration of nickel and chromium element in weld root were higher than inner surface layer which proves that welding wire of transition layer protects the major alloying elements in welding root.

The effect of laser remelting on the surface chemistry of Ti6al4V components fabricated by selective laser melting

Surface remelting/skin scanning of components is generally performed during the selective laser melting (SLM) process to improve the surface quality of a part. However, the chemical effects of surface remelting are not well understood. In this study, cuboidal parts fabricated with and without laser remelting were characterised using scanning electron microscopy (SEM), surface profilometry and X-ray photoelectron spectrophotometry (XPS). The SEM images showed a low-amplitude undulating pattern was observed on both surfaces. The surface chemistries of the surface remelted/skin scanned (SK) and non-surface remelted/non-skin scanned (NSK) samples were observed to significantly differ in their elemental composition. The thickness of the surface oxide layer of the SK surface was double that of the NSK surface. Also, the contribution of the major alloying elements, including titanium and aluminium, on the surface oxide layer varied for both NSK and SK surfaces. The surface chemistry of the NSK and SK surface was significantly different to a conventionally forged (CF) Ti6Al4V surface. The rate of decrease of oxide with depth was in the order of CF>NSK>SK. Although surface remelting is useful in rendering improved surface quality, its impact on surface chemistry should be carefully considered.

Modeling and Analysis of Mechanical Properties in Structural Steel-DOE Approach

Abstract The present work focuses on the modeling and analysis of mechanical properties of structural steel. The effect of major alloying elements namely carbon, manganese and silicon has been investigated on mechanical properties of structural steel. Design of experiments is used to develop linear models for the responses namely Yield strength, Ultimate tensile strength and Elongation. The experiments have been conducted as per the full factorial design where all process variables are set at two levels. The main effect plots showed that the alloying elements Manganese and Silicon have positive contribution on Ultimate tensile strength and Yield strength. However, Carbon and Manganese showed more contribution as compared to Silicon. All three alloying elements are found to have negative contribution towards the response- Elongation. The present work is found to be useful to control the mechanical properties of structural steel by varying the major alloying elements. Minitab software has been used for statistical analysis. The linear regression models have been tested for the statistical adequacy by utilizing ANOVA and statistical significance test. Further, the prediction capability of the developed models is tested with the help of test cases. It is found that all linear regression models are found to be statistically adequate with good prediction capability. The work is useful to foundrymen to choose alloying elements composition to get desirable mechanical properties.

The relationship between alloying elements and biologically produced ennoblement in natural waters

A range of stainless steels, nickel–chromium and nickel–chromium–molybdenum alloys were exposed to coastal seawater from Mandapam (Indian Ocean) and freshwater from a perennial pond. Biofilms from both test waters produced an ennoblement of the open circuit potential (OCP) on all alloys as expected, which was slower but substantially larger in freshwater. In both waters an interesting relationship was perceived between the plateau OCP (Emax) and the mass percentage of the major alloying elements. In particular, iron exhibited strong positive correlations with Emax (r2 ≥ 0.77; p < 0.0005), while the sum of chromium, nickel and molybdenum presented significant negative correlations (r2 ≤ –0.81; p = 0.0002). Consistent with the regression analyses, Euclidean distance clustering yielded patterns where Inconel-600 and the nickel–chromium–molybdenum alloys had the smallest similarities of OCP with other alloys. The results emphatically reinforce a key role for surface passive films in the ennoblement phenomenon in natural waters.

Development and characterization of low-silicon cast aluminum alloys for thermal dissipation

Two low-silicon quaternary aluminum alloys, Al–(0.5–1.5)Mg–1Fe–0.5Si and Al–(1.0–1.5)Si–1Fe–1Zn, are investigated for their potential to combine a high thermal conductivity with good castability and anodizability. By comparing to the physical and casting properties of the commercial ADC12 alloy, the developed alloys show 170–190% of thermal conductivities (160–180W/mK), a similar medium-thick-wall fluidity, 60–85% of thin-wall fluidity, 100–130% of hot tearing susceptibility (HTS), and a comparable ultimate tensile strength. As Mg and Si, the major alloying elements, increase, the thermal conductivity decreases and the strength increases. The thin-wall fluidity and the HTS are both inversely proportional to the Mg content and directly proportional to the Si content. These opposite trends within the two alloy systems arise mainly from differences in the Al dendrite coherency and first intermetallic crystallization points, and in the crystallization behavior of β-AlFeSi phase. The lower viscosity and lower surface energy of the Al–(0.5–1.5)Mg–1Fe–0.5Si and Al–(1.0–1.5)Si–1Fe–1Zn alloys, respectively enhance their fluidity in thicker and thinner sections. A large fluidity sensitivity to the channel diameter of the aluminum alloys developed here is attributed to their higher melting points, lower latent heats, and higher formation tendency of oxide films and inclusions.

Solidification behaviour of a high chromium nickel base alloy weld deposited metal

The solidification behaviour including microsegregation and secondary phase formation of a high chromium nickel base alloy weld deposited metal was examined with optical microscopy, scanning electron microscopy and transmission electron microscopy. Microsegregation potential of major alloying elements in the weld deposited metal was investigated. The microconstituents formed during solidification were identified to be TiC and γ/Laves eutectic constituent. Most γ/Laves eutectic constituents were located at the dendrite interstices due to the microsegregation of Nb, Mo and Si. The volume percent of γ/Laves constituent was predicted by using Scheil equation, and there was a reasonable agreement between the predicted and measured value. Last, two possible solidification paths added to the γ-Nb-C pseudoternary solidification diagram were proposed to analyse the solidification sequence of the new high chromium nickel base alloy.

Effect of Boron Addition on Oxide Scale Formation of Ni-Base Superalloys

Ni-base superalloys are commonly used as construction materials for high temperature components e.g. in the hottest sections of aero engines and industrial gas turbines due to a combination of excellent creep and high-temperature oxidation resistance at elevated temperature. Apart from major alloying elements such as Cr, Co, Al, Mo, W, Ti, modern Ni-based superalloys contain minor (between 0.01 and 1 at.%) additions of elements such as Hf, Zr or B for obtaining improved mechanical properties, in particular grain boundary strengthening. However, these minor elements also form thermodynamically very stable oxides and can therefore participate in the oxidation process. Whereas several investigations are available on the effect of Hf and Zr additions on the oxidation behaviour of high temperature alloys, hardly any publications deal with studies related to the effect of B additions on oxide formation mechanisms. In the present investigation the air oxidation behaviour of two commercially available B containing Ni base alloys (Rene80, CM247) was studied at temperatures in the range 850°C to 1050°C. After various exposure times up to 100h the oxidized samples were investigated with a number of analysis methods, including glow discharge optical emission spectroscopy (GD-OES), optical and scanning electron microscopy (SEM combined with EDX/WDX and EBSD) as well as X-Ray diffraction. B was found to become incorporated into the oxide scale whereby the participation in the oxidation process strongly depended on alloy composition. The oxidation of B resulted in its depletion from the bulk alloy and was found to be dependent on the exposure conditions, being stronger at higher exposure temperatures and longer exposure times. A modelling approach is presented to correlate B incorporation in the surface oxidation process with its depletion in the bulk alloy.

Microstructural Features of Multicomponent FeCoCrNiSixAlloys

Recently, one of the new types of multicomponent alloys, high entropy alloy with major alloying elements in equiatomic or near-equiatomic ratios, receives a great attention as a new potential alloys due to their unique microstructural features and outstanding properties (Ranganathan, 2003; Cantor et al., 2004; Hsu et al., 2004; Huang et al., 2004; Yeh et al., 2004). The most eminent property enhancement including wear resistance, corrosion resistance, oxidation resistance and hardness has been reported previously (Chen et al., 2004; Huang et al., 2004; Chen et al., 2005; Wu et al., 2006). These findings have brought new insight in design of alloys when compared with the alloys which are currently being developed, and has provided a new concept in designing of modern alloys. As a result, a series of new multicomponent systems has been investigated (Wang & Zhang, 2008). Among the alloying elements available for new alloy design, Fe, Co, Ni, Ti, Cu, and Al have been used most frequently to synthesize the high entropy alloys. Among the alloying elements which have been mostly used, Fe, Co, Ni, Ti, Cu are transition metal elements. It has been shown that the addition of small amount of alloying element can occasionally induce a dramatic property enhancement in traditional alloys (Itabashi & Kawata, 2000; Lin & Chang, 2003; Kondo & Takahashi, 2006). While there are quite few reports on the effect of alloying element such as Si with small atomic radius on the microstructure development and property enhancement in high entropy alloys. Therefore, the aim of the present study is to investigate the effect of addition of alloying elements Al, Si on the microstructural development in FeCoCrNi high entropy alloys. The addition of Al in FeCoCrNi high entropy alloy has been reported to cause the change of the crystal structure of solid solution from fcc to bcc (Wang et al., 2012). In the present study, effect of Al addition has been investigated to confirm the previous result. Then, the effects of Si addition on the microstructural development in FeCoCrNi high entropy alloy has been investigated systematically. The result shows that the addition of Si element changes the alloy structure evidently, which further provides the potential for improvement of properties. pISSN 2287-5123·eISSN 2287-4445 http://dx.doi.org/10.9729/AM.2015.45.1.32

Corrosion of Modified 9Cr–1Mo Steel in Pb–17Li in a Rotating Disc Experiment at 773 K

A rotating disc type corrosion test facility has been developed to study the compatibility of structural steels in lead–lithium eutectic at selected temperatures and flow velocities. The compatibility of a modified 9Cr–1Mo steel (P91) disc in Pb–17Li was studied at 773 K and 700 revolutions per minute during an exposure of 2,000 h. Results indicated that weight loss occurred at a rate of 4.2 µg/cm2 h for a total duration of 2,000 h. The corrosion mechanism was governed by dissolution of iron and chromium from the sample surface into molten Pb–17Li. The depth of dissolution of major alloying elements and selective removal of the Fe and Cr depleted surface layers depended upon the variation of linear flow velocities along the radial direction.

Microstructure and Mechanical Tests of AlNiMnZnCu High Entropy Alloys

High entropy alloys (HEAs) are a newly developed family of multi-component alloys composed of several major alloying elements, such as copper, nickel, aluminum, cobalt, chromium, iron, silicon, titanium, etc. The fact that HEA alloys is formed participation molar is approximately equal with at least five elements, entropy configuration is double that of binary systems, entitles us to call them "high entropy alloys'. Recent studies suggested that the refractory HEAs exhibited great promise for high temperature structural materials. This alloy can be processed and analyzed as an ordinary material AlNiMnZnCu high-entropy alloys are prepared by an induction furnace. The microstructure and properties of alloy samples were examined by SEM and testing machine for obtained materials. Mechanical tests were made with a INSTRON 3382 machine.

Steels with High Temperature Carbides - New Possibilities for Semi-Solid State Processing

Semi-solid processing of steels is typically studied using high-alloy steels with higher carbon levels, as those offer a long freezing range which is favourable for conducting the process. The drawback to their application is their microstructure which typically consists of austenite grains embedded in ledeburitic network. This type of microstructure typically fails in brittle manner by fracturing along the interface of the hard network and ductile austenite grains. This is why a way was sought to altering or even inverting the configuration of the microstructure. Eventually, suitable steel chemistries were found which allow the inverted microstructure to be obtained. With regard to the high content of alloy additions, these steels have to be made by powder metallurgy methods. Five different steels of this kind were selected for the experimental programme. All contained high amounts of alloying elements and a large fraction of carbides. Their carbon content was taken into account as well, ranging from 0.55 to 3.4 %. Differences between the steels consisted in the levels of major alloying elements, namely chromium, vanadium, molybdenum, tungsten and cobalt. After suitable process parameters were found, semi-solid processing was used to prepare demonstration products. The transition through semi-solid state transformed the ferritic matrix to austenitic-martensitic one, in which the high-stability carbides were retained. The resulting microstructures were of unconventional nature where carbide particles were embedded in tough metal matrix. Their configuration was thus inverted in contrast to the ones typically obtained by semi-solid processing of tool steels.

A high thermal gradient directional solidification method for growing superalloy single crystals

The experiments here were conducted at withdrawal rates of 3mm/min and 1mm/min using a CMSX-6 and a CMSX-4 superalloy, respectively. The process was assessed in terms of the thermal gradient (GL), structural refinement, microsegregation and porosity distribution, and compared to those using a Bridgman process. The GL of the process was 200–236K/cm, which was 10–12 times higher than that in the Bridgman process. A more refined microstructure was produced having average primary and secondary dendrite arm spacing values as low as 243μm and 72μm, as well as 272μm and 76μm in the CMSX-6 and the CMSX-4 castings, respectively. The diameter of γ′ phase in the dendrite core of CMSX-6 and CMSX-4 castings was reduced from 0.8μm to 0.3μm and from 1.2μm to 0.6μm, respectively. The average areas of (γ′+γ) eutectic pools became smaller and more homogeneously distributed. The mean pore sizes in the castings were reduced by 57% and 43% for the CMSX-6 and CMSX-4 superalloys, respectively, and the area fractions of the pores in the CMSX-6 and CMSX-4 samples were 16% and 12% of those produced in the Bridgman samples. The segregation coefficients of the major alloying elements were closer to unity than those in the Bridgman process, which indicates that the composition distribution is more uniform.

Virtues of Giambologna from Grimaldi Chapel Archaeometrical Characterization

This scientific investigation on metal artwork is meant to expand knowledge regarding the technical skills developed by artists in sculpture manufacturing. Moreover all the gathered data support the speculation about the motivations behind the choices of certain material or a specific manufacturing method (e.g., economic or technical reasons, or both). The subject of this study is the Virtues sculptural group made at the end of the XVI century by Giambologna to decorate the Grimaldi Chapel in the church of San Francesco di Castelletto (Genoa, Italy). Six life-size statues depicting Charity, Justice, Hope, Fortitude, Faith, and Temperance (i.e., the artwork discussed in this article); seven bas-reliefs; and six winged representations of putti are what remains of the original monumental project. X-ray fluorescence, a nondestructive investigation method, was applied to determine the chemical nature of the metallic substrate and of the “artistic” and natural patinas. The achieved results allowed for distinguishing variations in the content of the major alloying elements that might correspond to a motivated will of the artist connected to technical and aesthetic aims: the production of defect-free and golden bronze artifacts.

Anisotropic radiation-induced segregation in 316L austenitic stainless steel with grain boundary character

Radiation-induced segregation (RIS) and subsequent depletion of chromium along grain boundaries has been shown to be an important factor in irradiation-assisted stress corrosion cracking in austenitic face-centered cubic (fcc)-based alloys used for nuclear energy systems. A full understanding of RIS requires examination of the effect of the grain boundary character on the segregation process. Understanding how specific grain boundary structures respond under irradiation would assist in developing or designing alloys that are more efficient at removing point defects, or reducing the overall rate of deleterious Cr segregation. This study shows that solute segregation is dependent not only on grain boundary misorientation, but also on the grain boundary plane, as highlighted by markedly different segregation behavior for the Σ3 incoherent and coherent grain boundaries. The link between RIS and atomistic modeling is also explored through molecular dynamic simulations of the interaction of vacancies at different grain boundary structures through defect energetics in a simple model system. A key insight from the coupled experimental RIS measurements and corresponding defect–grain boundary modeling is that grain boundary–vacancy formation energy may have a critical threshold value related to the major alloying elements’ solute segregation.

On the mobility of vacancy clusters in reduced activation steels: an atomistic study in the Fe–Cr–W model alloy

Reduced activation steels are considered as structural materials for future fusion reactors. Besides iron and the main alloying element chromium, these steels contain other minor alloying elements, typically tungsten, vanadium and tantalum. In this work we study the impact of chromium and tungsten, being major alloying elements of ferritic Fe–Cr–W-based steels, on the stability and mobility of vacancy defects, typically formed under irradiation in collision cascades. For this purpose, we perform ab initio calculations, develop a many-body interatomic potential (EAM formalism) for large-scale calculations, validate the potential and apply it using an atomistic kinetic Monte Carlo method to characterize the lifetime and diffusivity of vacancy clusters. To distinguish the role of Cr and W we perform atomistic kinetic Monte Carlo simulations in Fe–Cr, Fe–W and Fe–Cr–W alloys. Within the limitation of transferability of the potentials it is found that both Cr and W enhance the diffusivity of vacancy clusters, while only W strongly reduces their lifetime. The cluster lifetime reduction increases with W concentration and saturates at about 1–2 at.%. The obtained results imply that W acts as an efficient ‘breaker’ of small migrating vacancy clusters and therefore the short-term annealing process of cascade debris is modified by the presence of W, even in small concentrations.

Castable Aluminium Alloys for High Temperature Applications

Most traditional aluminium casting alloys are based on the aluminium-silicon eutectic system because of its excellent casting characteristics. However, the solidus in this system does not exceed 577 °C and the major alloying elements used with silicon in these alloys have high diffusivity in aluminium. Therefore, while these elements enhance the room temperature strength of the alloy, they are not useful at elevated temperatures. Considering nickel-base superalloys, whose mechanical properties are retained up to temperatures that approach 75% of their melting point, it is conceivable that castable aluminium alloys can be developed on the same basis so that they are useful at temperatures approaching 300 °C. In this publication, we present the thought process behind developing a new castable aluminum alloy that is designed specifically for such high temperature applications and we present the alloy’s measured castability characteristics and its elevated temperature tensile properties.

On the Dissolution of the γ′ Phase at the Dendritic Scale in a Rhenium-Containing Nickel-Based Single Crystal Superalloy After High Temperature Exposure

MCNG is a nickel base single crystal superalloy containing both rhenium and ruthenium. The γ′ phase dissolution evolutions have been studied after very high temperature exposures for various times up to the thermodynamic equilibrium. Very different γ′ phase dissolution behaviors have been observed across the dendritic structure. In the temperature range investigated, the dissolution of the γ′ phase is more pronounced within the dendrites compared to its dissolution observed within the interdendrites. The physical parameters likely to promote the different dissolution behavior at the dendritic scale such as the diffusion coefficients of the major alloying elements, the γ′ solvus temperature, and the γ′ precipitates morphologies are discussed. Special attention is paid to the very first steps of the dissolution process.