Nickel-based Hardfacing Alloys 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.

Optimization of GTAW process parameters for deposition of nickel-based hardfacing alloy using Taguchi method

Optimization of GTAW process parameters for deposition of nickel-based hardfacing alloy using Taguchi method

Optimizing the Characteristics of the Laser Hardfacing Process Parameters to Maximize the Wear Resistance of Ni-Based Hard-Faced Deposits Using the RSM Technique

The nickel-based Colmonoy-5 hardfacing alloy is used to hard-face 316LN austenitic stainless steel components in fast reactors. The nominal composition (in wt%) was listed as follows: 0.01 C, 0.49 Si, 0.87 Mn, 17.09 Cr, 14.04 Ni, 2.56 Mo, 0.14 N, and balance Fe. Hardfacing is a technique of applying hard and wear-resistant materials to substrates that need abrasion resistance. The thickness of hardfacing deposit varies between 0.8 mm and 2 mm based on parameter combinations. In this study, laser hardfacing process parameters including laser power, powder feed rate, travel speed, and defocusing distance were optimized to reduce weight loss of laser hard-faced Ni-based deposit. The tribological characteristics of reactor-grade NiCr-B hard-faced deposits were investigated. The RSM technique was used to identify the most important control variables resulting in the least weight loss of the nickel-based alloy placed on AISI 316LN austenitic stainless steel. Statistical techniques like DoE and ANOVA are utilized. Changing the laser settings may efficiently track the weight loss of laser hard-faced nickel alloy surfaces. These are created using the response surface technique. The deposit produced with a laser power of 1314 W, powder feed rate of 9 g/min, travel speed of 366 mm/min, and defocusing distance of 32 mm had the lowest weight loss of 16.4 mg. Based on the F value, the powder feed rate is the major influencing factor to predict the hardness followed by power, travel speed, and defocusing distance.

High-Temperature Tribological Behavior of Nickel-Based Hardfacing Alloys

The friction and wear behavior of electrode rod nickel chromium (ER NiCr) nickel-based hardfacing alloys ER NiCr-A, ER NiCr-B, and ER NiCr-C deposited over austenitic stainless steel was studied against silicon carbide counter body by ball-on-disc tribotesting at 25 °C (1 bar pressure, 3 × 10−5 mbar vacuum) and at 550 °C (3 × 10−5 mbar vacuum) temperature. The wear tracks were examined using confocal microscope, profilometer and Raman Spectroscopy. The friction coefficient and wear rate of the deposits are correlated with the microstructure of the alloy. Wear rate of NiCr-B is found to be minimum both at ambient and elevated temperatures and can be considered as the best choice among the three alloys studied for hardfacing applications.

Analysis of Nickel Based Hardfacing Materials Manufactured by Laser Cladding for Sodium Fast Reactor

For improving the operational capacity, the maintenance and the decommissioning of the future French Sodium Fast Reactor ASTRID which is under study, it is asked to find or develop a cobalt free hardfacing alloy and the associated manufacturing process that will give satisfying wear performances. This article presents recent results obtained on some selected nickel-based hardfacing alloys manufactured by laser cladding, particularly on Tribaloy 700 alloy. A process parameter search is made and associated the microstructural analysis of the resulting clads. A particular attention is made on the solidification of the main precipitates (chromium carbides, boron carbides, Laves phases,…) that will mainly contribute to the wear properties of the material. Finally, the wear resistance of some samples is evaluated in simple wear conditions evidencing promising results on tribology behavior of Tribaloy 700.

Variation in Residual Stresses due to Thermal Cycling Induced on the Hardfaced Grid Plate in PFBR

In sodium cooled fast breeder reactors, the high operating temperature necessitates hard facing of grid plate to avoid galling and to reduce the wear loss of the base material . Nickel-base cobalt-free alloy called Colmonoy-5 has been chosen as the hard facing material for the Prototype Fast Breeder Reactor (PFBR) grid plate. The grid plate (GP) which is a critical component made of 316 LN SS that holds the core subassemblies are hard faced, to prevent galling and also to minimize wear caused by subassembly insertion/removal and erosion due to high sodium velocity at 670 K. Thermal cycling of hard faced circular grid plate made by Plasma Transferred Arc Welding (PTAW) generates residual stresses due to differential shrinkage of the molten deposit and difference in coefficients of thermal expansion between the deposit and substrate material. In this project the effect of thermal cycling of a nickel-base hardfacing alloy deposited on an austenitic stainless steel grid plate was studied. Finite element analysis of hard faced circular grid plate is performed for obtaining residual stress which includes elasto-plastic analysis. Coupled thermo-mechanical analysis is done for thermal cycling of hardfaced circular gridplate to quantitatively estimate the residual stress.

Study on microstructure and wear properties of different nickel base hardfacing alloys deposited on austenitic stainless steel

Results of studies carried out on the microstructure, hardness, and wear properties of three nickel base Ni–Cr–B–Si hardfacing alloys deposited on austenitic stainless steel by gas tungsten arc welding are presented here. Sliding wear resistance of the deposits is evaluated by ball-on-disc tribo-test followed by electron microscopy and Raman spectroscopy of the worn out surfaces. It is found that dilution in the deposit by the substrate alters microstructure and hardness and brings down wear resistance. The effect of dilution on wear resistance is more for the alloy with the highest alloy content due to change in the volume fraction of precipitate caused by dilution. Oxides formed on the wear track are different for these alloys and friction coefficients of the deposits are influenced by these oxide layers.

Mapping the micro-abrasion resistance of a Ni-based coating deposited by PTA on gray cast iron

Micro-scale abrasion was used to characterize abrasion resistance of a nickel-based hardfacing alloy deposited by Plasma Transferred Arc on gray cast iron using silica as abrasive agent. In order to investigate the occurrence of different abrasion mechanisms, several test conditions were used, namely: different silica abrasive contents and a range of normal loads and test durations. A scanning electron microscope (SEM) was used to study the morphologies of the spherical cup-shaped depressions induced by different test conditions. The results are discussed in terms of the effect of the dominant wear mechanisms on the abrasion resistance and the influence of the test conditions on the mechanism transition. The wear results lead to the conclusion that the specific wear rate essentially depends on the wear mechanisms (rolling or grooving) involved and not on the tests conditions employed, since these do not produce changes in the wear mechanism.

A Study on Influence of Aging Treatment on Sliding Wear Resistance of a Nickel Based Hardfacing Alloy

In the present study, Ni-based Colmonoy 5 was deposited on Type 316L (N) stainless steel. The deposit was aged at 580 and 650°C for 5,000 h to study the influence of aging on sliding wear resistance. The aged deposits show more wear loss due to reduced hardness. However, the reduced hardness after aging was not reflected on wear test at 550°C irrespective of sliding distance. This is due to stability of microstructure as well as the generation of oxide layer during high temperature tests. Subsequently, an empirical relation was developed based on outcome experimental data using full factorial design of experiments in terms of hardness (H), test temperature (T) and sliding distance (D). Based on the empirical relation, it was found that the test temperatures (T) play a predominant role on wear loss than hardness (H) and sliding distance (D). Further, the developed relationships were validated using analysis of variance (ANOVA).

Influence of aging treatment on microstructure, wear and corrosion behavior of a nickel base hardfaced coating

► In this study, we coated nickel based hardfacing alloy powder on 316 L (N) stainless steel. ► Aging at 923 K for 5000 h resulted in decrease of hardness due to coarsening of microstructure. ► This coarsening resulting in decrease in wear resistance only at RT tests. ► However at higher test temperatures, as-deposited and aged deposit showed similar wear behavior. ► The overall wear and corrosion resistance of the aged coatings found to be inferior. In this work nickel based hardfacing alloy (Colmonoy 5) was deposited on 316 L (N) stainless steel substrate to study the effects of aging treatment on coating microstructure, wear and corrosion properties. Coatings, deposited through plasma transferred arc (PTA) welding process, were aged at 923 K for 5000 h. Microstructural characterization studies carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the coarsening of dendrites and precipitation of Cr 23 C 6 particles in the aged coating. The wear behavior of the as deposited and aged coatings was compared in room temperature (RT) and high temperature (823 K) under dry sliding wear condition (pin-on-disc configuration). At RT, aged coating experienced more wear loss when compared to as-deposited. At high temperature, the wear loss was almost same with similar operating wear mechanisms (tribo-oxidation) for both as-deposited and aged coating. From pitting corrosion studies, it was found that aged coatings are more prone to pitting when compared to the as-deposited coatings.

Effect of arc current on microstructure and wear characteristics of a Ni-based coating deposited by PTA on gray cast iron

The plasma transferred arc (PTA) technique is currently used to coat the edges of moulds for the glass industry with nickel-based hardfacing alloys. However the hardness and wear performance of these coatings are significantly affected by the procedure adopted during the deposition of coatings. The aim of the present investigation is to study the effect of arc current on the microstructure, hardness and wear performance of a nickel-based hardfacing alloy deposited on gray cast iron, currently used in molds for the glass industry. Microstructure, hardness and wear assessments were used to characterize the coatings. Electron probe micro analysis (EPMA) mapping, scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDAX) and X-ray diffraction (XRD) were used to characterize the microstructure of the deposits. The effect of post weld heat treatment (PWHT) on the microstructure and hardness was also studied. The typical microstructure of the coatings consists of dendrites of Ni–Fe, in the FCC solid solution phase, with interdendritic phases rich in Cr–B, Ni–Si and Fe–Mo–C. Increasing the arc current reduces the proportion of porosity and hardness of the coatings and modifies their composition due to the increasing dilution of the cast iron. The partial melted zone (PMZ) had a typical white cast iron plus martensite microstructure, while the heat affected zone (HAZ) had only a martensite structure. The wear tests showed decreasing wear resistance with decreasing hardness of the coatings. PWHT reduces the hardness of the PMZ and HAZ but does not significantly alter the hardness of the bulk coating.

Effect of Aging Treatment on Microstructure and Wear Behaviour of a Nickel Based Hardfaced Coating

The nickel based Colmonoy 5 alloy powder was deposited on 316 L (N) austenitic stainless steel substrate. In order to examine the effects of aging treatment on the wear behavior of a nickel based hardfacing alloy, the as-deposited coating was aged at 580°C for 5000h in ambient atmosphere. Coating microstructures were characterised by scanning and transmission electron microscopy. Sliding tests were conducted under self mated condition at room temperature and 550°C using a pin-on disc type apparatus. The wear loss of the aged coating was found to be higher than that of the as deposited coating. The coarse grained structure with carbide (Cr23C6) precipitation in the aged coating would account for the higher sliding wear loss. However, the aged coating, with reduced hardness exhibits similar wear behavior of as deposited coating during sliding at 550°C.

Hardfacing of austenitic stainless steel with nickel-base NiCr alloy

Fast breeder reactors components encounter adhesive/abrasive wear nature and erosion. Hardfacing by weld deposition improves resistance to high temperature wear, especially galling, of mating surfaces in sodium. Based on induced radioactivity rate and shielding considerations, nickel-base E NiCr-B hardfacing alloy was chosen to replace cobalt-base Stellite alloys. Studies on this hardface deposit on austenitic stainless steel substrate demonstrated that deposits after exposure at service temperatures up to 823 K would retain adequate hardness (> RC 40) at end design service-life of 40 years. Also, the plasma transferred arc welding process was chosen for hardfacing to ensure that width of dilution zone could be controlled by optimising deposition parameters. The selection of nickel-base hardfacing alloy and deposition process used for development of hardfacing technology for various components of the Indian prototype fast breeder reactor is discussed.

Scanning Electron Microscopy of Some Slowly Cooled Nickel-Based Hardfacing Alloys Containing Iron Additions

The service lifespan of components used at higher temperatures in corrosive and abrasive environments can be prolonged by high-temperature corrosion-resistant coatings. This study is concerned with the microstructural characterization of some slowly cooled Nickel–based hardfacing alloys investigated by differential thermal analysis (DTA), energy dispersive X – ray analysis (EDXA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The alloys were prepared in high frequency induction furnace under controlled atmosphere. Three major primary hard phases (Ni (α), M7C3, and the π phase) were identified during slow cooling in DTA depending on the nominal compositions of the alloys. Large undercoolings as well as intense solid state precipitations were observed in alloys with iron additions. The precipitations formed the basis of the high hardness values and strength of the alloys. It was also reported that the hardness values of the alloys increased as the iron contents increased.

Effect of Solidification Process Parameters on the Microstructure of Some Meltspun Nickel-Based Hardfacing Alloys

The influence of solidification parameters on the morphology of a number of meltspun Nickelbased hard alloys has been investigated by means of scanning electron microscopy (SEM), conventional transmission electron microscopy and energy dispersive X-ray analysis (EDXA). It was established that the wheel velocity played a prominent role in the types of microstructure observed. Very high wheel velocity could lead to the formation of amorphous structure as observed in some of the alloys investigated. No appreciable effect of the ribbon thickness was observed on the microhardness of the alloys. It was also reported that the thermal transfer mode between the ideal and newtonian coolings was observed in all the alloys investigated.

Effects of molybdenum on the microstructure and wear resistance of nickel-based hardfacing alloys investigated using Rietveld method

The nickel-based hardfacing alloys with different Mo contents have been deposited on Q235-carbon steel using a plasma transferred arc (PTA) welding machine. The effects of Mo on the microstructure and wear resistance properties of the nickel-based hardfacing alloys were investigated using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). More detailed information about the crystallographic structure and phase compositions of the deposited coatings was obtained with the application of Rietveld refinement method to analyze XRD spectra. It was found that the addition of Mo did not lead to a change in phase compositions. Furthermore, it can also be seen that the relative contents of the total Cr-rich compounds increased from 36 wt.% to 45 wt.%, though the M 23C 6 type carbide increased but the relative contents of the M 7C 3 type carbide decreased with the increasing of Mo contents from 0 wt.% to 6 wt.%. The component segregation, which existed in the Mo-free coating, decreased gradually then disappeared finally with the increasing of Mo contents. The morphology of Cr-rich compounds observed in the interdendritic region changed from plate-like to net-like, as well as the refinement of Ni-rich dendrites because of the addition of Mo. The wear resistance increased but the microhardness decreased with the increasing of Mo contents from 0 wt.% to 6 wt.%. The microstructural change and phase contents variation were responsible for the improvement of the mechanical properties such as wear resistance of the Mo-modified nickel-based hardfacing alloy.

Microstructural aspects of plasma transferred arc surfaced Ni-based hardfacing alloy

In the current investigation, nickel-base hardfacing alloy AWS NiCr-B was deposited on austenitic stainless steel substrate 316 LN using the plasma transferred arc-welding process. The deposit was characterized by hardness measurements, microstructural examination and sliding wear assessment. Identification of precipitates was carried out using X-ray diffraction, scanning electron microscope/energy dispersive X-ray analysis (SEM/EDAX), electron probe micro analyzer (EPMA) mappings and line-scan profiles. The microstructure of the hardfacing deposit predominantly consists of the γ-Ni phase and the interdendritic eutectic mixture comprised of γ-nickel and nickel-rich borides. These studies also revealed the presence of chromium-rich carbides and borides in a γ-nickel matrix. The sliding wear behaviour of the hardfacing alloy was investigated in air at three different temperatures viz., room temperature, 300 and 500 °C. The study revealed significant weight loss at room temperature and abrupt decrease at high temperatures. This behaviour at high temperatures has been attributed to the formation of a wear protective oxide layer at the surface during sliding. To evaluate the microstructural stability of the deposit, ageing studies were carried out at 650 °C for 250 h. Microstructural examination and hardness testing revealed that there is no deterioration in the microstructure and that the hardness remains intact. Sliding wear tests at room temperature and at high temperatures also demonstrated that there is no significant change in the weight loss or the wear behaviour after the thermal exposure.

Microstructure and wear characteristics of nickel based hardfacing alloys deposited by plasma transferred arc welding

In the present investigation, a nickel based hardfacing alloy (AWS NiCr–B) was deposited on an austenitic stainless steel substrate 316LN using the plasma transferred arc welding process. The deposit was characterised by hardness measurements, microstructural examination and sliding wear assessment. Identification of precipitates was carried out using X-ray diffraction and SEM/EDAX. These studies revealed the presence of chromium rich carbides and borides in a γ-Ni matrix. Down to a distance of 1 mm from the interface, the hardness of the deposit was found to be 52 HRC. The sliding wear behaviour of the hardfacing alloy was investigated in air in the room temperature to 550°C range, with a pin on disk configuration using a cylindrical pin with tip radius of 3 mm under loads of 30, 40 and 50 N. Wear experiments were conducted up to a sliding distance of 180 m at a sliding speed of 0·1 m s−1. The elastic modulus and Poisson's ratio of the hardfaced deposits were evaluated by the ultrasonic method and these values were used for calculating initial Hertzian contact stress. The study showed that, while significant wear loss occurred at room temperature, there was practically no measurable weight loss at temperatures of 300 and 550°C. This could be attributed to the formation of an oxide layer at the surface during wear testing.

Thermal sensitivity of the π - phase in Nickel-based industrial hardfacing alloy

Thermal sensitivity of the π - phase in Nickel-based industrial hardfacing alloy

Cladding of Ni–Cr–B–Si coatings with a high power diode laser

Laser surface cladding is a well recognised technique to obtain wear and corrosion resistance coatings, or for repairing damaged parts. Recently, the use of high power diode laser (HPDL) has undergone rapid growth for materials processing. The present work describes the process for obtaining two boride-containing nickel-based hardfacing alloy coatings, primarily composed of Ni–Cr–B–Si on carbon steel using a HPDL. After laser treatment the microstructure is composed of a matrix of γ-Ni with different intermetallics depending on the initial composition of the powder. For the alloy with lower concentration of alloying elements, X-ray diffraction indicates the presence of nickel (Ni 3Fe, Ni 3Si,), boron (B 4C, CrB) and chromium (Cr 3Si) intermetallics. On the other hand, for the alloy with higher amount of C, B and Cr, the analysis revealed the presence of Ni 3B together with lesser proportions of Ni 3Fe and Ni 3Si and the presence of chromium carbides Cr 23C 6 and (Fe·Ni) 23C 6.