Plasma Transferred Arc Welding Process Research Articles

Effect of mating material on wear behaviour of Ni-based hardface coating

The selection of tribopairs, including mating materials, plays a crucial role in controlling material loss under rubbing conditions. In a fast breeder nuclear reactor, almost all moving components have been provided with a hardfaced coating at the mating surfaces for their longer life. Though, in most cases, the hardfaced surfaces come into contact with the components having the same coating; in some instances, they are allowed to rub against other materials. In the present investigations, an effort was made to study the wear behaviour of a Ni-based hardfaced coating made on 316LN stainless steel under similar and dissimilar mating conditions. Prior to wear tests, a defect-free hardface coating of Ni-based hardfacing alloy was made on 316LN stainless steel using plasma transferred arc welding process and subsequently characterized for its microstructure and hardness. Wear tests under dry sliding conditions were carried out at ambient temperature. The specific wear rate for dissimilar mating conditions was found to be one order of magnitude higher than the same rate obtained from similar mating conditions. Moreover, adhesive wear was the dominant wear mechanism in both mating conditions. It is clear from the study that similar material combinations should be given preference in the design of tribopairs instead of dissimilar material combinations to avoid significantly higher material losses for materials with lower hardness. The reported results will provide insight for carefully designing the tribopairs for critical applications.

Comparison between the spherical and angular type WC particles reinforced in Nickel-based matrix deposited using Plasma Transferred Arc Welding process

This research work aims to compare two different WC types (Spherical and angular) particles reinforced in a Nickel-based matrix to be produced by Plasma Transferred Arc Welding (PTAW) process on stainless steel (SS 304) substrate. The angular WC particles were recycled and crushed to obtain the desired size to have it reinforced in the Ni-Cr matrix. The weight percentages of reinforcement (WC) and matrix (Ni-Cr) have been kept at 30% and 70% respectively. The PTAW process parameters were optimized considering the flowability of angular particles and dilution. The produced coatings were characterised for microstructure (Scanning Electron Microscope), phase analysis (X-Ray Diffraction) and hardness (Vickers Hardness Tester). The spherical WC particles reinforced coatings have produced higher local hardness in the WC region and the angular type coatings exhibited higher matrix hardness due to higher dissolution.

Influence of tungsten carbide raw materials to microstructure and wear performance on PTA hard-facing materials with its micro-mechanism analysis

The wear performance of the plasma transferred arc (PTA) welding hard-facing materials manufactured reinforced by cast WC/W2C and coarse grain WC with different shapes are investigated. Coarse grain WC-Ni coating shows the best wear resistance in a high applied load condition, with spherical reinforced particles give higher wear performance than angular shape. WC, W2C, γ-Ni, M23C6, and M7C3 (M = Cr, Fe, W, and Ni) are detected in PTA coatings. The spherical cast and angular cast WC/W2C particles contain a higher volume of W2C, which is easier to be dissolved during the PTA welding process, resulting in lower retained reinforced particle volume and more precipitates concentration. In the PTA coating, the cast WC/W2C particles have a higher hardness, whereas the matrix has a relatively low hardness. The wear performance of PTA coating is more affected by the hardness rather than the coefficient of friction (COF). At a load of 5 N applied on the Si3N4 ball, the contact area between reinforced particles and counterparts, resulting in wear resistance is controlled by the hardness of the reinforced particles. When the load increases to 10 N, the hardness of the matrix controls wear performance. The precipitates formed between the carbides and matrix smooth the interface and strengthen the bonding, which prevents the cast WC/W2C from being pulled out from the matrix during the wear test.

On the performance of metallurgical behaviour of Stellite 6 cladding deposited on SS316L substrate with PTAW process

ABSTRACT Cobalt rich Stellite 6 cladding shows a superior result against wear, corrosion and galling. However, the metallurgical bonding at the cladding interface, if not achieved carefully, may result in failure during service. Hence, the proposed Stellite 6 weld overlay is deposited by plasma transferred arc welding (PTAW) process on SS316L substrate. Mechanical characterisation of this combination has been already attempted earlier with the help of a fine-tuned welding parameters. The same work has been reconsidered in the present research study for its detailed metallurgical investigation. In order to investigate the metallurgical variation at the interface, two samples with different weld parameters (sample A and B) have been considered. Cobalt rich phases have been obtained in both samples such as γ-Co (FCC), ϵ-Co (HCP), CrCo along with different carbides of chromium and tungsten such as Cr7C3, Cr23C6, W6C which are confirmed by EDS and XRD analysis. The formation of different phases shows the W6C, interdendritic eutectic phases Cr7C3, Cr23C6 and primary dendritic phases γ-Co, ϵ-Co and CrCo that are chiefly responsible for the higher hardness of sample B which has lower heat input.

Impact-sliding behavior of Ni-based coating prepared on tunnel boring machine disc cutter material produced using a plasma transferred arc welding process

The working condition of the disc cutter of the tunnel boring machine (TBM) is extremely harsh and is severely worn during the rock-cutting and tunneling process. Reducing the wear rate of the cutter and extending the service life of the cutter are essential to improving the economic costs and safety of the TBM. This article explores the feasibility and effectiveness of using surface coatings to improve the wear resistance of the cutter ring. NiCrBSi/WC coatings with different current intensities were prepared on the disc surface using plasma surfacing technology. The wear performance of the coating was evaluated using a bespoke impact-sliding device that fits the actual working conditions, and the wear mechanism was studied in detail. According to the “tadpole-like” wear scar characteristics of the coating after the impact-sliding wear experiment, the wear scar zone can be divided into two regions: the impact region and the sliding region, which are consistent with the actual wear characteristics of the cutter ring. In addition, the wear behavior of the coating noticeably changed under each experiment parameter, and the evolution process of the impact-sliding wear of the gage cutter at each position can be well reproduced. When the impact angle was 45°, the wear depth and wear volume of the coating were significantly smaller than those of the uncoated samples. This is mainly due to the metallurgical bond between the Ni-based alloy zone (binder phase) and the spherical WC particles (hard phase) on the surface of each specimen. When impacted by the tribo-ball, the WC particles can undergo plastic deformation and relaxation through the Ni-based alloy zone under the applied force, thereby obtaining excellent impact and sliding resistance. When the impact angle was 60°, the impact dominates, causing the impact force to increase. Furthermore, compared with the uncoated specimens, the wear depth and wear volume of the coated specimens significantly increased, indicating that the anti-impact ability was seriously degraded in such situation. In summary, the powder composition and preparation process parameters should be reasonably selected according to the impact angle, and the impact-sliding wear experiment can effectively evaluate the impact and sliding wear performance of different coatings. This approach has an important directive function in the promotion and application of cutter ring coatings.

Nickel-based overlay materials: recent developments, characteristic effects and applicability with plasma transferred arc welding

Plasma transferred arc welding (PTAW) is being used extensively to improve surface characteristics of materials. Apart from PTAW process parameters, the selection of appropriate overlay material is vital to obtain desired properties. Nickel-based overlay materials are gaining attraction of researchers and industrialists due to their excellent performance in numerous aggressive service conditions. However, there are wide variants of nickel-based overlay materials which need a thorough study to understand several investigation aspects. This article presents a comprehensive survey on nickel-based overlay materials used in depositing functional coatings by PTAW. Recent developments on surface characteristics such as wear resistance, corrosion resistance, metallurgical bonding characteristics, oxidation resistance, microstructural characterisations, etc. are critically reviewed and summarised. This dedicated review on nickel-based overlay materials used for PTAW at one place would be ready information for subsequent authors to understand the associated problems and future aspects which may help them to decide their further research direction.

Effective role of short time furnace heat treatment and laser treatment on the residual stress and mechanical properties of NiCrBSi–WC weldments produced using plasma transferred arc welding process

The present study reports the effect of WC particle (20%, 30%, and 40%) and secondary processes (Heat Treatment and Laser Treatment) on the mechanical properties of NiCrBSi and NiCrBSi–WC deposits. A detailed comparative analysis of As Welded (AW), Heat Treated (HT) and Laser Treated (LT) deposits was made in terms of morphology, interface thickness, hardness, residual stress, tensile and flexural strength. Higher surface hardness was obtained for Laser treated NiCrBSi–WC(40%) deposits as compared to the heat-treated and as-welded deposits. The higher weight percentage of WC particles modified the solidification pattern and stress distribution in the NiCrBSi matrix, which eventually decreased the mechanical strength of NiCrBSi–WC (40%) deposits. In addition, fractographic examinations were used to delineate the various toughening mechanisms present in the post-treated NiCrBSi and NiCrBSi–WC deposits.

Process Parameter Effects over Bead Properties during Material Deposition of PTAW Process

The quality and geometry of deposited bead depend on their input process parameters and their interaction effects in fusion welding process. Minimum dilution and maximum bead size are the most desirable property in material processing applications. The effects of process parameters on dilution and bead geometry have been analysed during material deposition by Plasma Transferred Arc Welding (PTAW) process using the response surface method. The experimental data are used for modelling using three level factorial techniques. The mathematical models have been developed for bead height, width and dilution. The accuracy of the models has been checked using the analysis of variance. The effects of process parameters on bead geometry and dilution have been investigated.

Comparison of microstructure, dilution and wear behavior of Stellite 21 hardfacing on H13 steel using cold metal transfer and plasma transferred arc welding processes

A comparative study of the Stellite 21 hardfacing on H13 steel produced by cold metal transfer (CMT) process and conventional plasma transferred arc welding (PTAW) process was carried out. The lower heat input of the CMT process resulted in finer microstructure and lesser dilution in the Stellite 21 coating than the PTAW process. The volumetric dilution values showed much scatter across the thickness of the PTAW coating than CMT. The effect of lower dilution and finer structure of the CMT coating resulted in a marginal increase in the microhardness. The room temperature (RT) and high temperature (600 °C) wear performance of the coatings were studied using a ball-on-disc tribometer using alumina ball. The wear tracks were analyzed using an optical profilometer and the volume loss was calculated. The CMT deposited coating showed better wear performance than PTAW coating. X-ray diffraction (studies of the room temperature wear tracks showed the transformation of γ-fcc phase in the as-deposited coating to ε-hcp phase after the wear. The volume percentage of the ε-hcp was observed higher for CMT deposited coating than the PTAW coatings, which can be attributed to lower dilution and finer microstructure of the former.

Characterization of spontaneous magnetic signals for residual stress in plasma transferred arc welding process

The residual stress produced in plasma transferred arc welding (PTAW) has strong effects on the service performance of remanufacturing components. In this study, a novel non-destructive testing method based on spontaneous magnetic signals is used to characterize the residual stress in PTAW. Experimental results show that both magnetic signal tangential components Hp(x) and normal components Hp(y) can locate the high residual stress zones from the welded specimen. A new characteristic value Hp is proposed to reflect the residual stress distribution, and its average value Hpa is further calculated to quantify the residual stress level. The characteristic value Hpa increases exponentially with an increase in average residual stress σa paralleled to the cladding coating, whereas it decreases linearly perpendicular to the cladding coating. Except for the temperature gradients, the various phases with different material mechanical properties may lead to different volume shrinkage during cooling process, which is the possible reason underlying the high residual stress and large magnetic field at heat affected zone (HAZ).

Development and Deployment of Welding Technologies for the Indian Sodium-Cooled Fast Reactor and Advanced Ultra Super Critical Thermal Power Programmes

Robust manufacturing technology for Sodium-cooled Fast Reactor (SFR) components necessitates development of various research-backed innovative welding technologies. Prior to the start of construction of the 500 MWe Prototype Fast Breeder Reactor, extensive technology development was planned and implemented for development of welding consumables, procedures and technologies for fabrication of components with stringent specifications. With close interaction amongst design, materials and non-destructive evaluation engineers, materials and welding consumable manufactures, and the fabrication industries, it has been possible to overcome the challenges and establish robust manufacturing technologies for fabrication of all the structural components. Extensive welding is involved in the fabrication of reactor vessels, steam generators, fuel sub-assemblies etc. Further, Activated Tungsten Inert Gas (A-TIG) welding process, along with activated flux developed in-house, has been successfully implemented on various SFR-related components. Also, a computational-intelligence based welding system for online monitoring and control during welding has been developed for obtaining near defect-free welded components. Plasma Transferred Arc Welding process has been deployed for deposition of the chosen nickel-base alloy for hardfacing of SFR components, which require improvement in resistance to high temperature wear, especially galling, of mating surfaces in liquid sodium. To reduce carbon footprint substantially, India has initiated a national mission programme of design, development and establishment of 800 MWe Advanced Ultra Supercritical (AUSC) power plant having steam parameters of 710°C / 720°C / 310 bar. Materials and fabrication technologies play decisive roles in the success of such mission project. For this purpose, two important India-specific high-temperature tube materials, 304HCu austenitic stainless steel (304HCu SS) and modified Alloy 617M, as also large cylindrical forgings of Alloy 617M of up to 800 mm diameter for turbine rotors have been indigenously developed. Development of welding consumables and welding procedure has also been established for TIG welding of the tubes, including the 304HCu SS/Alloy 617M dissimilar joint. Based on the tensile and creep tests properties, welding consumables for the tubes and their dissimilar joint have been finalized. Technology for dissimilar metal welding between Alloy 617M and 10Cr-steel forgings for turbine rotors has also been developed. Using narrow-gap TIG welding process, the dissimilar metal weld between 200 mm Alloy 617M and 10Cr-steel have been produced by directly welding the two forgings using Alloy 617 filler wire. The weld exhibited no lack-of-penetration defects and passed dye-penetrant, radiographic and ultrasonic examinations. Similarly procedure for NG welding of superheater headers has also been demonstrated. The details of the Indian efforts towards development and deployment of welding technologies for application to the fabrication to components for the Indian programmes for SFR-based nuclear power and AUSC thermal power plant are presented and discussed.

Plasma transferred arc surface modification of atmospheric plasma sprayed ceramic coatings

In this study, a 90MnCrV8 steel surface was coated with aluminum oxide and chromium oxide powders through the Atmospheric plasma spray (APS) and Plasma transferred arc (PTA) methods. The effects of PTA surface melting on the microstructure, hardness, and wear behavior were investigated. The microstructures of plasma-sprayed and modified layers were characterized by Optical microscopy (OM), Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDS). The dry-sliding wear properties of the samples were determined through the ball-on-disk wear test method. Voids, cracks, and nonhomogeneous regions were observed in the microstructure of the APS ceramic-coated surface. These microstructure defects were eliminated by the PTA welding process. The microhardness of the samples was increased. Significant reductions in wear rate were observed after the PTA surface modification. The wear resistance of ceramic coatings increased 7 to 12 times compared to that of the substrate material.

Analysis of Discontinuous Bead Formation by PTAW Process

This research investigates the effects of input parameters on discontinuities in bead formation during material deposition by the plasma transferred arc welding (PTAW) process. Experiments based on L27 orthogonal array have been carried out by deposition of stainless steel powder (SS304 L) on stainless steel plate (SS316). Three types of depositions have been observed, namely continuous, partially continuous and discontinuous deposition. A process map has been developed, based upon powder and energy deposition per length, where the above-mentioned three types of depositions are distributed. The discontinuities in the deposition can be overcome by increasing the energy deposition per length or by reducing the powder deposition per length.

Plasma Transferred Arc Welding of Stellite 6 Alloy on Stainless Steel for Wear Resistance

Austenitic stainless steel was deposited on 9Cr-1Mo steel (ASME Grade 91) by flux cored arc welding process and above that Stellite 6 (Co-Cr alloy) was coated by plasma transferred arc welding process to improve wear resistance for high temperature valves applications. Microstructural characterization was carried out on Stellite 6 coatings and hardness and chemical composition were measured by vicker's hardness tester and optical emission spectrometer respectively. The impact of alloying elements in Stellite 6 deposits and fusion line of Stellite 6 and stainless steel were analyzed by electron dispersive spectroscopy line scan. It was observed that dilution of Iron in PTA welding deposit in Stellite 6 is below 2% and hardness of more than 600 HV0.3 was obtained. Microstructure of Stellite 6 consisted of Co - solid solution matrix with dendritic structure and interdendritic eutectic carbides which provides the hardness. Pin-on-disc tests were carried out at 400°C and characterized using scanning electron microscope of worn out surfaces. The wear mechanism was identified as delamination and abrasive wear in the worn-out surfaces as observed. Abrasive form of wear was reported due to the presence of alloying elements such as Co, Cr & W.

Microstructure and Mechanical Properties of Cr-SiC Particles-Reinforced Fe-Based Alloy Coating

In this study, SiC particles were first coated with Cr to form a layer that can protect the SiC particles from dissolution in the molten pool. Then, the Cr-SiC powder was injected into the tail of molten pool during plasma-transferred arc welding process (PTAW), where the temperature was relatively low, to prepare Cr-SiC particles reinforced Fe-based alloy coating. The microstructure and phase composition of the powder and surface coatings were analyzed, and the element distribution and hardness at the interfacial region were also evaluated. The protective layer consists of Cr3Si, Cr7C3, and Cr23C6, which play an important role in the microstructure and mechanical properties. The protective layer is dissolved in the molten pool forming a flocculent region and a transition region between the SiC particles and the matrix. The tribological performance of the coating was also assessed using a ring-block sliding wear tester with GGr15 grinding ring under 490 and 980 N load. Cr-SiC particles-reinforced coating has a lower wear rate than the unreinforced coating.

Effects of rod carbide size, content, loading and sliding distance on the friction and wear behaviors of (Cr,Fe)7C3-reinforced α-Fe based composite coating produced via PTA welding process

In this paper, three distinct sizes of rod carbide (Cr,Fe)7C3 (20.9, 35.2 and 66.3μm) were in-situ synthesized in the composite coatings using three mass ratios of Cr3C2/Fe–CrNiBSi (1:5, 3:5 and 5:5) powder blends via plasma transferred arc (PTA) welding. The present investigations evaluate the effects of rod carbide sizes, contents, loading and sliding distance on the friction and wear behaviors of (Cr,Fe)7C3-reinforced α-Fe composite coating as sliding against hard alloy AISI W1-1.0C on a block-on-wheel dry sliding wear tester. The focuses are given on the friction coefficient (FC) and wear rate (WR) as function of parameters such as sliding distances (210–1260m) and normal loads (100–300N). It was found that the size and content of rod carbide (Cr,Fe)7C3 increase with the mass ratio of Cr3C2, by which the hardness and wear resistance of the coatings were improved. The stability of FC increases with the content of rod carbide (Cr,Fe)7C3 as the load increased from 100 to 300N. The coatings' worn surfaces were examined and analyzed by using SEM and EDS. It was found that the main wear mechanisms of the coatings vary with the applied normal loads. Cracks nucleated and propagated on the worn surfaces of (Cr,Fe)7C3 rods as the loads increased from 100 to 300N. The micro-mechanisms of crack formation were analyzed.

Analysis of Weld Bead Parameters of Overlay Deposited on D2 Steel Components by Plasma Transferred Arc (PTA) Process

Plasma Transferred Arc (PTA) process is increasingly used in applications where enhancement of wear, corrosion and heat resistance of metals surface is required. The shape of weld bead geometry affected by the PTA welding process parameters is an indication of the quality of the weld. PTA is a versatile method of depositing high-quality metallurgically fused deposits on relatively low cost surfaces. The overlay deposited is an alloy that is hard and more corrosion resistant than counterparts laid down by Gas Tungsten Arc Welding (GTAW) or Oxy Fuel Welding (OFW) processes. Weld deposits are characterized by very low levels of inclusions, oxides, and discontinuities. This process produces smooth deposits that significantly reduce the amount of post weld machining required. Metal-Mechanic industry continuously requires recovering tool steel components subjected to severe wear. The steel known as D2 is considered to be a high carbon, high chromium cold work tool steel. In this research, weld beads were deposited on D2 steel by using PTA process with different parameters as welding current and travel speed using base nickel filler metal. In order to evaluate the metallurgical features on the weld beads/substrate interface a microstructural characterization was performed by using Scanning Electron Microscopy (SEM) and to evaluate the mechanical properties was conducted the wear test.

High temperature corrosion studies of cermet particle reinforced NiCrBSi hardfacings

Metal matrix composite hardfacings provide various types of heat and wear resistant products. They are widely used in high temperature aggressive environments due to their excellent high temperature corrosion and wear resistance. In this study, Cr3C2–Ni and TiC–NiMo particles were used to reinforce a NiCrBSi matrix in plasma transferred arc welding process. These cermet particle reinforced hardfacings were examined on their oxidation behaviour and high temperature corrosion in different solid salts to optimise the field of application under high temperature conditions. Corrosion behaviour in solid salts is strongly dependent on the corroding anion. Cr3C2–Ni reinforced hardfacings behave better in oxidative and sulphate/phosphate environment, while TiC–NiMo hardfacings show better resistance against chlorine and carbonate ions up to 700°C. Additionally, oxidation is no critical exposure for these types of hardfacings.

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.

Selection of welding process for hardfacing on carbon steels based on quantitative and qualitative factors

Weld hardfacing techniques are employed mainly to extend or improve the service life of engineering components either by rebuilding or by fabricating in such a way as to produce a composite wall section to combat wear, erosion, corrosion, etc. In this paper, an attempt has been made to determine the best welding process to hardface boiler grade steels based on quantitative factors (by measuring percentage of dilution) and qualitative factors (using the analytic hierarchy process [AHP]). Five different welding processes including shielded metal arc welding (SMAW), gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), submerged arc welding (SAW), and plasma transferred arc welding (PTAW) have been compared. Based on the quantitative and qualitative factors, the PTAW process is found to be the best method to hardface boiler grade steels.