Iron Dilution Research Articles

Effect of alloy 625 buffer layer on corrosion resistance of nickel base hardfacing

Nickel base hardfacing alloys serve to mitigate corrosion losses at elevated temperatures. Efficacy of Nickel base hardfacing alloys can be compromised when applied onto Fe base substrates due to iron dilution in hardfacing. The degree of Fe dilution can be reduced by using advanced deposition methods and optimized deposition parameters. Gas Tungsten Arc Welding (GTAW) method is commonly employed for its cost-effectiveness and versatility, but it tends to induce higher Fe dilution due to increased heat input. This study aims to reduce the degree of Fe dilution and enhance corrosion resistance by introducing a nickel base buffer layer (alloy 625) between the nickel base hardfacing alloy and AISI 316L stainless steel substrate. For comparative purposes, Ni base hardfacing alloy was deposited on the substrate without any buffer layer. Hardfacing depositions were prepared using manual GTAW process. Process parameters namely, deposition current, voltage, travelling speed, pre-heating temperature, and cooling method were kept constant. Samples underwent aging at 1123 K for 4 h, followed by microstructural examination via optical and scanning electron microscopes. Iron (Fe) dilution quantification was performed using energy dispersive spectroscopy (EDS). The EDS analysis showed that the use of buffer layer between the hardfaced deposit and the substrate decreased the degree of Fe dilution in the hardfaced deposit. X-Ray diffraction (XRD) analysis was performed to identify various phases formed in the hardfaced deposit. Potentiodynamic polarization test was performed to assess the corrosion resistance of hardfaced deposit in 3.5 wt% NaCl solution. Results show significant improvement in corrosion resistance of hardfacings deposited sample with buffer layer as compared to those without buffer layer. Aging treatment further enhanced corrosion resistance. The corrosion resistance data is correlated with the microstructure and phases formed in various samples.

Influence of iron dilution on plastic deformation mechanisms in cobalt-based alloys: Consequence of phase transformations on tribological behavior

The chemical composition and microstructure of metallic parts are parameters that affect plastic deformation accommodation mechanisms under friction stresses. The content of alloying elements impacts the stacking fault energy and the plastic deformation, and thus affects the tribological behavior. Depending on this content and the levels of mechanical stresses, plastic deformation of some alloys obtained under non-equilibrium conditions can occur. It is caused by different mechanisms, such as perfect slip and/or partial dislocation slip, as well as by phase transformation. The purpose of this study is to determine the influence of the plastic deformation accommodation mechanisms on tribological behavior by studying the effect of the iron content in cobalt-based alloys. For manufacturing purposes, cobalt-based coatings are produced on steel substrate using a additive manufacturing process (SLM). With this process, the microstructures of the cobalt-based coatings are essentially metastable FCC phase at room temperature with different contents of diluted iron. Tribological tests were carried out with a ball-to-disc contact. Iron contents were estimated by EDS-SEM. Analytical techniques such as XRD and EBSD were used to identify the microstructural changes observed in TTS due to tribological loading. The friction coefficient is linked to the evolution of the plastic deformation mechanisms activated to accommodate the contact. In particular, in addition to work-hardening phenomena, phase transformations are possible, namely a metastable FCC phase gives an HCP phase and a metastable FCC phase gives an α′-BCC phase under tribological loading. Both types of transformations can occur, individually or simultaneously, depending on the iron content in the coating.

Cavitation resistance of Stellite 21 coatings tungsten inert gas (TIG) deposited onto duplex stainless steel X2CrNiMoN22-5-3

AbstractCobalt-based alloys, called Stellite, have a microstructure consisting of complex carbides dispersed in a Co-based solid solution matrix. These alloys are resistant to corrosion, erosion through cavitation, abrasive, and sliding wear. To increase the erosion resistance through cavitation, hardfacing of the stainless steel duplex X2CrNiMoN22-5-3 with Stellite 21 alloy was performed using the pulsed tungsten inert gas (TIG) process. The positive effects of the hardfacing process are the low heat input, reduced distortions, controlled volume of the weld, and reduced susceptibility to hot cracking. The effect of dilution is essential for the quality of the deposited layers and, in this sense, the TIG pulsed current welding process was performed to reduce the excess linear energy and implicitly the substrate melting. Iron dilution levels were in the range between 5.9 and 6.1. The higher Fe content in the first layer does not significantly reduce its hardness or wear resistance through erosion cavitation. Compared with the substrate material, the cavity erosion resistance increases 7 to 11 times even in the first layer hardened by the TIG pulsed current welding process.

Influence of interlayer time on the microstructural state of CoCrMo coatings applied by selective laser melting on an iron-based substrate for different numbers of layers

The Selective Laser Melting process was used to perform cobalt-based alloy coatings on a C35 steel substrate. The relationships between interlayer times, iron dilution, crystalline structures, and micro-hardness were studied for different numbers of layers with an initial lased powder layer of 50 µm thickness. Reducing the interlayer time increased the temperature reached in the melting bed and promoted matter transport from the substrate. The coating thickness consisted of a Co-Cr-Fe mixture, divided into two zones: a transition zone near the interface and a stabilized zone towards the substrate. The real coating thickness was found to be always greater when the interlayer time was reduced. For an interlayer time equal to 11 s (series 2), the iron dilution was always higher than for an interlayer time ranging between 42 s and 16 s (series 1), leading to a higher coating thickness. The microstructural state was also dependent on the interval time between successive layers. The coating microstructure was always cellular because of the high cooling rate. XRD analysis of the surface showed that this microstructure is essentially composed of two non-equilibrium phases: FCC and α’ BCC. The high hardness is due to the high content of iron which induces a martensite phase (series 2). Starting from 5 layers for series 1 and from 6 layers for series 2, the α’ BCC phase disappeared if the iron content on the coating surface was reduced by more than 45% content in weight. The mean coating hardness decreased with an increasing number of layers because of the decrease in the iron content. Finally, the micro-hardness of the FCC phase, for its part, was found to be dependent on the iron content in solution in the Co matrix.

Effect of a Cold Wire on the Metallurgical Characteristics of Nickel-Based Welds Deposited by GMAW-CW

This paper aims to study the solidification structure of Ni-based superalloy class AWS ER NiCrMo-4 metallic coatings deposited by GMAW and gas metal arc welding-cold wire (GMAW-CW) processes with two heat input levels (0.9 and 0.6 kJ mm−1) on carbon steel plates. The metallurgical characterization of the coating’s interface was performed by scanning electron microscopy, optical microscopy, and electronic dispersion spectroscopy. Mechanical evaluation was carried out by Vickers hardness test. The results revealed that the welding conditions did not influence the solidification structure (planar, columnar, and equiaxed); however, molybdenum microsegregation to interdendritic region was observed. Cold wire addition by GMAW-CW process decreased the iron dilution on weld metal, but increased the partially mixed zone thickness and hardness values. The increase in heat input produced the opposite behavior to the cold wire feeding.

The effects of substrate dilution on the microstructure and wear resistance of PTA Cu-Al-Fe aluminium bronze coatings

Cu-Al-Fe aluminium bronze alloys are good candidates for precious tools and forming dies due to their high wear resistance, good sliding properties and low tendency for adhesion to ferrous metals. Plasma transferred arc (PTA) is an effective process for deposition of such robust coatings by enhancing the bond between the bronze coating and steel substrate. However, the microstructure and wear characteristics of these coatings are strongly influenced by the diffusion of substrate elements (mostly iron) to the interface. In the present study, the effects of substrate dilution on the microstructure and wear behaviour of Cu-Al-Fe alloy deposited by PTA on medium carbon steel substrate were investigated. The results show that the deposition current controls the melting temperature and iron dilution which result in the formation of Cu3Al martensitic β1' phase in a low dilution and the ordered β1 phase in high dilution. The wear behaviour of the coating is dominated by failure of the matrix phase. Low dilution coating with martensitic phase exhibits the highest wear resistance. On high diluted Fe rich coating, pile up of dislocation on the intermetallic K phase leads to surface cracks and delamination of the coating resulting in a high wear rate.

Effect of dilution on micro hardness of Ni–Cr–B–Si alloy hardfaced on austenitic stainless steel plate for sodium-cooled fast reactor applications

Abstract Many components in the assembly section of Sodium-cooled Fast Reactor are made of good corrosion-resistant 316 LN Stainless Steel material. To avoid self-welding of the components with the coolant sodium at elevated temperature, hardfacing is inevitable. Ni-based colmonoy-5 is used for hardfacing due to its lower dose rate by Plasma Transferred Arc process due to its low dilution. Since Ni–Cr–B–Si alloy becomes very fluidic while depositing, the major height of the weld overlay rests inside the groove. Hardfacing is also done over the plain surface where grooving is not possible. Therefore, grooved and un-grooved hardfaced specimens were prepared at different travel speeds. Fe content at every 100 μm of the weld overlay was studied by Energy Dispersive Spectroscopy and also the micro hardness was determined at those locations. A correlation between iron dilution from the base metal and the micro hardness was established. Therefore, if the Fe content of the weld overlay is known, the hardness at that location can be obtained using the correlation and vice-versa. A new correlation between micro hardness and dilution coefficient is obtained at different locations. A comparative study between those specimens is carried out to recommend the optimum travel speed for lower dilution.

Cladding of Tribaloy T400 on steel substrates using a high power Nd:YAG laser

Tribaloy T-400 is a cobalt based alloy with molybdenum additions, which has been developed for improved resistance to high temperature wear, galling and corrosion. Its hardness is provided by a hard intermetallic Laves phase, dispersed in a tough matrix of cobalt rich eutectic or solid solution. However, cracking limits its applications such as hard facing using laser surface cladding/coating. The primary aim of this work is accomplished by cladding crack free Tribaloy T-400 layer using a high power Nd:YAG laser. The optimal process conditions of cladding crack free Tribaloy T-400 coating on different steel substrates were obtained. The effects of iron dilution on the hardness of cladded Tribaloy T-400 coating are investigated. Dilution determined from clad geometry is verified from dilution calculated from an analysis of the composition of the clad. Microstructures of clad layers produced using optimal process parameters with and without preheating the substrate were analysed by Scanning Electron Microscopy (SEM). The chemical compositions of different phases present in the clad were analysed by Energy Dispersive X-ray Spectroscopy (EDS). Presence of phases with FCC and BCC structures and Laves phase (Co3.6Mo2Si0.4) in the clad were identified and analysed by X-ray Diffraction (XRD). The residual stresses in the clads were evaluated using hole drilling technique. The correlation between the process conditions and the resulting microstructures are discussed. Based on the results of this research, further scaling up to industrial application of laser cladding of Tribaloy T-400 is promising.

Improved high-temperature hardness and wear resistance of Inconel 625 coatings fabricated by laser cladding

In this study, Inconel 625 coatings were fabricated by laser cladding and shielded metal arc welding, and the microstructure, hardness and wear resistance at both room and elevated temperatures are investigated. The results indicate that laser cladded Inconel 625 coating has finer microstructure, alleviated segregation of Mo and Nb and lower dilution of iron compared with arc welded one as revealed by XRD, SEM and EDS results. The hardness profile at room temperature can be divided into four regions, namely coating zone, iron dilution zone, heat affected zone and substrate. Laser cladded Inconel 625 coating has slightly higher hardness in coating zone, whereas much higher hardness in iron dilution zone, indicating that iron distribution plays important role in the hardness. At elevated temperatures, the hardness of laser cladded Inconel 625 coating is higher due to finer microstructure and alleviated segregation. The wear test results show that abrasive wear is apparent at room temperature, whereas adhesive wear is dominant at elevated temperature. In comparison, laser cladded coating has lower wear rate because of lower dilution of iron and higher hardness. Therefore, laser cladded Inconel 625 coating is preferred due to its better mechanical performance at both room and elevated temperature.

Plastic strain of cobalt-based hardfacings under friction loading

Aeronautic forging dies are subjected to very high loads and temperatures for a long contact time between the pre-heated parts and dies. Cobalt-based hardfacings are commonly deposited on dies and their main wear mechanism is large plastic deformation of the die radii.This paper deals with the wear damage mechanisms of three different cobalt-based hardfacings: Stellite 21 deposited by a MIG process, Stellite 21 and Stellite 6 deposited by a LASER process. The tribological tests are carried out on a high load Ring on Disc tribometer at room temperature. The post-mortem investigations are undertaken by SEM observations, micro-hardness measurements as well as by X-ray diffraction analyses.Results show that the increase of the hardness, in order to improve the wear behaviour, can be achieved by a higher carbon content and by a lesser iron dilution that depends on the deposition process. A very important work-hardening, up to 90%, is also observed under sliding conditions and a relationship is established between the increase of the micro-hardness and the plastic strain level. Two different plastic strain mechanisms are observed. For high (MIG) or low (LASER) iron dilution levels, the plastic strain causes respectively a reorientation of grains or a FCC to HCP phase transformation; the latter being associated with a lower friction coefficient.

Microstructural Evolution of Inconel 625 and Inconel 686CPT Weld Metal for Clad Carbon Steel Linepipe Joints: A Comparator Study

Microstructural evolution of Inconel 625 and Inconel 686CPT filler metals, used for the fusion welding of clad carbon steel linepipe, has been investigated and compared. The effects of iron dilution from the linepipe parent material on the elemental segregation potential of the filler metal chemistry have been considered. The results obtained provide significant evidence to support the view that, in Inconel 686CPT weld metal, the segregation of tungsten is a function of the level of iron dilution from the parent material. The data presented indicate that the incoherent phase precipitated in the Inconel 686CPT weld metal has a morphology that is dependent on tungsten enrichment and, therefore, iron dilution. Furthermore, in the same weld metal, a continuous network of finer precipitates was observed. The Charpy impact toughness of each filler metal was evaluated, and the results highlighted the superior impact toughness of the Inconel 625 weld metal over that of Inconel 686CPT.

The role of iron(ii) dilution in the magnetic and photomagnetic properties of the series [FexZn1−x(bpp)2](NCSe)2

The effects of metal dilution on the spin-crossover behavior of iron(II) in the mixed crystal series [Fe(x)Zn(1-x)(bpp)2](NCSe)2 (bpp = 2,6-bis(pyrazol-3-yl)pyridine) have been studied using magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. For each mixed-crystal system, the thermal spin transition temperature, T(1/2), and the relaxation temperature of the photo-induced high-spin state, T(LIESST), have been systematically determined. It appears that T(1/2) decreases with the metal dilution while T(LIESST) remains unchanged. Dilution also tends to decrease the hysteresis width and smooth the transition curves. These effects were discussed first qualitatively and then quantitatively on the basis of a kinetic study governing the photo-induced back conversion taking into account the relative sizes of Zn(II) and Fe(II) ions. Interestingly, single crystals were obtained for [Fe(0.6)Zn(0.4)(bpp)2](NCSe)2 allowing the X-ray diffraction crystal-structure determination.

Fibre laser cladding of turbine blade leading edges: the effect of specific energy on clad dilution

PurposeThe present work aims at developing the laser cladding technology by means of an active fiber laser source applicable for hardfacing of martensitic steel turbine blades. It also aims to investigate two process parameter conditions to reproduce two different heat inputs, in order to highlight the effect of the thermal input on the thermal alteration and dilution of the substrate material and clad layer.Design/methodology/approachThe experimentation was performed initially at a sample level, reproducing the material and thickness of the blade leading edge, then on an industrial real component. Cladding process parameters were experimentally selected and two different process parameter conditions, at different specific energy, were determined. The microstructural and geometrical features of the clad samples were analyzed both by optical microscopy and scanning electron microscopy, in this latter case combining the information supplied by different probes, among which the EDX microanalysis to obtain chemical profiles. Hardness distribution was also evaluated by means of Vickers hardness tester.FindingsAll the two investigated conditions were suitable for laser cladding of the blade leading edge, since a crack and pore free clad layer with a strong metallurgical bond to the substrate was obtained. The experimented two different heat inputs affected the extension of the HAZ as well the chemical and geometrical dilution. The clad integrity was preserved in both cases. The condition at higher specific energy was chosen to clad the turbine blade. The high specific energy condition was preferred because the iron dilution in the clad layer was inferior.Research limitations/implicationsFurther research is needed to correlate the chemical dilution and the thermal alteration introduced by the laser cladding process on such a kind of substrate at different process parameter conditions to the wear and corrosion resistance of the turbine blade.Practical implicationsLaser cladding process with an innovative active fiber laser source of the leading edge of a steam turbine blade was developed. Progress achieved in laser cladding technology development is of practical value for manufacture of turbine blades, made of martensitic steels.Social implicationsThe paper investigates the effect of different energy input on the laser cladding of steam turbine blades, mainly used in coal, gas and nuclear plants to produce electricity by heating water to create steam. The laser cladding process is an effective technology to increase the steam blades toughness and resistance to creep, stress and corrosion. This increase in the turbine blade properties contributes to extend the life of such a critical components, decreasing cost and time of substitution and ensuring better service conditions.Originality/valueThe most original aspect of the paper is related to the focus on the difference between the chemical and the geometrical dilution, being the first one mainly related to the corrosion and wear resistance of the clad layer, while the later mainly regards the clad layer adhesion to the substrate. More in general the paper presents one of the first experiments accomplished while making use of the active fiber laser source.

Constraints on core formation from molybdenum solubility in silicate melts at high pressure

We report results from 43 new molybdenum solubility experiments performed in order to test molybdenum’s compatibility with the magma ocean hypothesis for core formation. A Walker-type multi-anvil press was used for all experiments and we investigated the pressure range of 2.5–12GPa and temperature range of 1585–2200°C. Eight different silicate compositions were also employed. Our data show that increasing temperature causes solubility to increase, whereas pressure has a negligible effect over the range investigated here. In general, increasing silicate melt polymerization causes solubility to decrease; however, the effect of silicate composition is best addressed by looking at the effects of individual oxides versus a universal melt parameter such as NBO/T (ratio of non-bridging oxygens to tetrahedrally coordinated oxygens). From our solubility data, we calculated metal–silicate partition coefficients at infinite iron dilution. Parameterization of our data plus data from the literature shows that there is no discrepancy between partition coefficients determined directly from experiments and those calculated from solubility data, so long as all variables are taken into account, i.e. changes in metal phase composition. Additionally, most of the experiments in the literature were conducted at pressures below 2GPa, therefore the addition of our high pressure data set makes extrapolations to deep magma ocean conditions more accurate. We determined that the observed mantle abundance of Mo can be explained by both single-stage and multi-stage magma ocean models. Previous siderophile element studies have suggested a wide range of possible single-stage core formation conditions, from 10 to 60GPa along the peridotite liquidus. Our results narrowed this range by constraining the P–T conditions to 40–54GPa and 3050–3400K. Our results also further constrained the multi-stage core formation models by limiting the depth of metal–silicate equilibration during the final impacts of accretion to 31–42% of the core–mantle boundary depth.

Microstructure and bonding behavior on the interface of an induction-melted Ni-based alloy coating and AISI 4140 steel substrate

An induction-melted Ni-based alloy (NiCrBSi) coating on AISI 4140 steel was prepared using induction melting under different melting conditions. To determine the microstructure and bonding behavior of their interfaces, the techniques of micro-diffraction, X-ray mapping and wavelength dispersive spectrometry (WDS) were employed. The experimental results showed that a white zone appears on the Ni-based alloy side of the final interface, becoming wider and wider with increasing temperature and time, which was identified as a solid solution of γ-Ni at 1000 °C and 1180 °C. A higher heating temperature and time caused a more severe iron dilution in the Ni-based alloy and decreased the microhardness.

Influence of fusing temperature on microstructure, wear and corrosion resistance of induction melted bimetal of Co-based alloy and AISI 4140 steel

Two bimetals composed of a Co-based alloy and AISI 4140 steel were fabricated by induction fusing at 1200 °C and 1250 °C, respectively. Their microstructures were examined and their wear and corrosion resistances were investigated using a ball-on-disc system and immersion tests. The results show that the phases of the Co-based alloy of the bimetal, fused at 1200 °C, are inherited from its original powder and consist of a Co-rich phase, a Cr-rich phase and W 3CoB 3; however, the effect of iron dilution causes the formation of σ-CrFe and Co 0.72Fe 0.28. When fusing at 1250 °C, W 3CoB 3 decomposes to form Co 3B and increases the W content in the Co-rich phase thereby reducing the corrosion rate of the Co-rich phase and resulting in improved corrosion resistance of the bimetal. However, a higher fusing temperature causes a significant drop in hardness due to severe alloy dilution by iron diffusing from AISI 4140 steel and results in declined wear resistance. The associated wear behavior also changes from abrasion wear to oxidation wear.

Activity of commercial zeolites with iron impurities in direct N2O decomposition

Various commercially available zeolite frameworks (MFI, FER, BEA, MOR, FAU) with iron impurities ranging from 85 to 780ppm and nominal Si/Al ratios of 10–15 have been tested in direct N2O decomposition after calcination and steam treatment. Our results show a significant impact of the framework type on the catalytic activity at these high degrees of iron dilution (Fe/Al<0.01). H-beta was the most effective material in the reaction, followed by the other pentasyl-type H-ferrierite and H-ZSM-5 zeolites.

Caracterización de hierros sinterizados fabricados con virutas procedentes de la mecanización de piezas sinterizadas

The objective of the present work is the iron swarfs reusing as raw material to manufacture sintered parts. Particle size reduction using Horizontal attrition milling within iron dilution is the way used to get the raw materials. Two powder mixtures were obtained: Commercial Iron+50 % milled swarfs, and the milling mixture of iron+50 %swarfs. After powder characterization, the powder mixtures were die pressing and sintering at 1150 -C during 30min under N 2 -5 %H 2 atmosphere. Density and dimensional change were determined on sintered materials. Also mechanical properties were obtained. Influence on properties from Microstructure and powder sinter ability were analyzed.

Co-ordination and oxidation changes undergone by iron species in Fe-silicalite upon template removal, activation and interaction with N 2O: an in situ X-ray absorption study

We report on the characterization of a Fe-silicalite sample having a sufficient iron dilution (Si/Fe=90) to be considered a ‘true’ catalysts in partial oxidation reactions (e.g. benzene→phenol). Fe 3+ species are incorporated during zeolite synthesis in framework Si sites, where they exhibit a tetrahedral symmetry being co-ordinated to four oxygen atoms of the lattice. Template burning in air and sample activation in vacuo causes a progressive migration of ordered iron from framework sites into disordered extra-framework positions. This phenomenon is associated to a reduction from Fe 3+ to Fe 2+. The fraction of iron species involved in this phenomenon depends upon the activation temperature, and can reach the value of one when severe treatments are adopted. The structural disorder of extra-framework Fe species is monitored by the striking decrease of the EXAFS signal, while the changes of the oxidation state has been indicated in the XANES part of the X-ray absorption spectra. So obtained extra-framework Fe 2+ species are characterized by very high co-ordinative unsaturation, being able to form Fe 2+(NO) 3 complexes upon interaction with NO at RT (as evidenced by IR spectra). Interaction with N 2O at 523 K causes the overall re-oxidation of iron species resulting in a catalyst containing extra-framework species characterized by a less pronounced co-ordinative unsaturation. Infrared (IR) spectroscopy shows the dissociation of N 2O, while EXAFS spectroscopy shows the increase of the co-ordination sphere of iron. This fact has been interpreted in terms of an additional oxygen atom (coming from the decomposition of N 2O) co-ordinated to Fe 3+ species. The described Fe 3+→Fe 2+→Fe 3+ redox cycle has also been qualitatively followed by EPR spectroscopy.

Effect of iron dilution on corrosion resistance of Ni-Cr-Mo alloy cladding

Effect of iron dilution on corrosion resistance of Ni-Cr-Mo alloy cladding