Plasma Transferred Arc Process Research Articles

The hardfacing properties of the nickel-based coating deposited by the PTA process with the addition of wc nano-particles: Wear investigation

The impact of the addition of tungsten carbide (1 to 7 wt%) on the microstructure and wear characteristics of the nickel–tungsten carbide composite layer fabricated by the plasma transferred arc (PTA) process was studied. With the addition of nanoparticles, the degree of segregation becomes lower while heterogeneous nucleation increases and refining of the microstructure enhances. Wear rate and coefficient of friction for all samples with increasing the load from 1 to 5 N decrease and wear mechanism changes from abrasive to adhesive. The higher wear resistance for samples with 3%wt is due to a decrease in the porosity of the composite coatings, strong interfacial bonding, and promotion in the deposition efficiency at the same time.

Effect of ZrC on the Microstructure and Properties of CrMnFeCoNi High-Entropy Alloy Coatings Prepared by a Plasma Transferred Arc Process

The low strength caused by the single FCC structure of the CrMnFeCoNi high entropy alloy (HEA) limits its application in the field of coating. Here, we prepared high-entropy alloy coatings of CrMnFeCoNi with different ZrC contents on Q235 steel by a plasma transferred arc process. The effects of ZrC on the microstructure and properties of the CrMnFeCoNi HEA coating were investigated by optical microscopy, scanning electron microscope, and X-ray diffraction and by employing a potensiostat/galvanostat. The results showed that ZrC mainly existed in the coatings as a second phase, having little influence on the main crystal structure and micromorphology of the CrMnFeCoNi HEA coating. The hardness of the CrMnFeCoNi HEA coating increased with the ZrC content. ZrC can effectively improve the corrosion resistance of the CrMnFeCoNi HEA coating. In a 1 mol/L NaCl solution with 4 wt% ZrC, the annual corrosion rate was only 5.997% of that of the HEA coating. Nevertheless, the improvement in the wear resistance of CrMnFeCoNi high-entropy alloy coatings was not apparent with the addition of ZrC. Consequently, the addition of ZrC to the FeCoCrNiMn high-entropy alloy coating holds promise for applications in corrosion resistance, particularly in oceanic environments.

Comparative wear behaviour of Ni-Cr-B-Si hardface coatings made by cold metal transfer and plasma transfer Arc welding processes

Ni-Cr-B-Si hardface coating plays an important role in the mating components of nuclear power plants. Obtaining a crack-free coating with low dilution and optimum hardness is essential for reactor applications. In general, it is difficult to achieve this through conventional high heat input processes. In this work, Ni-Cr-B-Si hardface coating was successfully developed on 316LN stainless steel substrate by Cold Metal Transfer (CMT) welding process using metal-cored filler wire. Moreover, for comparative analysis, Ni-Cr-B-Si hardface coating was deposited using Plasma Transferred Arc (PTA) process. The obtained coatings were characterised for their microstructure, hardness, and wear behaviour. Results revealed higher hardness and lower specific wear rate of hardface coating made by the CMT process compared to the coating made by the PTA process. The superior behaviour of the CMT coating obtained may be due to its low dilution compared to the coating made using the PTA process. Confocal microscopy on the worn pins revealed abrasive and adhesive wear as a dominant mechanism in the CMT and PTA coatings, respectively. This study concluded that CMT could be used as an alternate potential process for depositing a crack-free hardface coating with superior wear behaviour.

Formation of different phases and their influences on the mechanical and tribological properties of surface alloyed FeCoCrNiAl particles using PTA technique

Titanium alloys (Ti–6Al–4V) are attractive in many industries due to their weight ratio, high thermal stability and corrosion resistance. However, their poor tribological properties limit their usage in many applications. In this work, Fe, Co, Cr, Ni and Al powders are mechanically mixed by ball milling and preplaced on the Ti–6Al–4V substrate. Plasma Transferred Arc (PTA) alloying process is performed to fuse the preplaced powder into the substrate surface. X-ray diffraction (XRD), microstructure and microhardness testing is performed to assess the presence of phases, formation of structure and hardness improvement, respectively. Then, the dry sliding pin-on-disc wear testing is conducted on the substrate and PTA alloyed samples. The various wear mechanism and their corresponding roughness were analysed and discussed. XRD result reveals that the ball milled powder and PTA samples possess BCC and FCC phases. However, BCC phases are formed higher than FCC phases due to rapid cooling and controlled heat input. Moreover, broadened BCC phases are observed in the PTA sample at 27°, 36°, 42°, 54° and 70° than that of the ball milled powder. Microstructure of the PTA sample contains both (Ni, Co) rich inter-dendrite and (Al, Fe, Cr) rich needle like dendrite. The microhardness of PTA region has improved with 2.39 times higher than substrate. The wear resistance of the PTA sample has improved by two times compared to substrate. Abrasive, adhesive and plastic deformation were observed on the worn out substrate while PTA sample showed with mild abrasive wear with reduced roughness. The overall results reveal that the various elements are properly alloyed on the Ti–6Al–4V surface through the PTA process and significantly improved the wear resistance. As a result, the PTA process can be used for alloying of other elements to improve the wear resistance of Ti–6Al–4V substrate.

Investigation of Single Layer and Bilayer of Plasma Transferred Arc (PTA) Coatings of Fe-Cr-V Powder

This paper presented an investigation result of single layer and bilayer of PTA coating of two different Fe-Cr-V powder commercially available and an improvement of the surface hardness by adding 35% of WC. In case of single layer, the microstructure was uniform across the thickness and also the hardness, while microstructure of the bilayer was obviously separated between interlayer and topcoat. The bilayer coating microstructure was changed, and approaching the topcoat, the microstructure was similar to single layer. The hardness of bilayer was decreased due to the dilution. After adding WC into the powder, the microstructure was changed and it could be seen that WC particles distributed across the coating. The hardness was increased due to dilution of some WC. Moreover, in all cases, PTA process offered coating with no crack and no re-precipitated with only small pores. However, adding WC could result in bigger pore size.

Wire based plasma arc and laser hybrid additive manufacture of Ti-6Al-4V

In this study, a novel wire based plasma transferred arc (PTA)-laser hybrid additive manufacture process was proposed for deposition of large-scale titanium parts with high deposition rate and near-net shape. The optimum processing conditions, including the heat source configuration, wire feeding position, and arc-to-laser separation distance, were investigated. The benefits of using the hybrid process over the single PTA and laser deposition processes on their own were studied. The results show that compared to the single PTA process, the hybrid process has extended energy distribution and melt pool size, giving more interaction time of the wire with the heat sources and therefore a higher deposition rate. Compared to the laser process, the hybrid process has a much higher wire melting efficiency and tolerance to wire positioning accuracy. Owing to more distributed energy across the two heat sources, the likelihood of keyhole formation in the hybrid process is lower than that in the single PTA process. The best configuration for the hybrid process is the PTA leading, combined with front feeding of the wire. In this configuration, the PTA is used to melt the feedstock and the laser is used to control the melt pool size, which allows independent control of deposition rate and bead shape. A set of multi-layer walls was built to demonstrate the feasibility of this process for the manufacture of engineering parts. The results show that the achieved flat beads are very desirable for low surface waviness and lead to near-net-shape deposition. The main limitation of the hybrid process is remelting into the underlying layer. To overcome this, a multi-energy source process with more evenly distributed energy has been proposed.

Corrosion Behavior of Ni-Based Coatings Reinforced with Chromium Carbide Particles Deposited by Plasma Transferred Arc in a Hydrochloric Acid Solution

The Ni-based coatings with different chromium carbide contents were deposited on H4140 steel by a plasma transferred arc process. The corrosion behavior of Ni-based chromium carbide coatings in a 0.5 mol/l HCl solution was studied by means of the potentiodynamic polarization curve, electrochemical impedance, and immersion corrosion test. The coatings were metallurgically bonded with the substrate. The addition of Cr3C2 particles resulted in more Cr-rich carbides in the coatings. In a 0.5 mol/l HCl solution, the four as-received coatings show active anodic dissolution due to the joint action of hydrogen and chlorine ions. With an increase in the Cr3C2 content, the corrosion potential of coatings shifts in the positive direction, the corrosion current density decreases, and the corrosive resistance of the coating is enhanced. The galvanic corrosion occurred between the Cr-rich carbides and the γ-Ni matrix phase, the coatings reinforced with chromium carbide particles showed preferential selective corrosion of the γ-Ni matrix phase. The cracks and pits are migration channels of the corrosion medium into the coating, causing a more serious corrosion damage.

Wear, erosion and corrosion behavior of laser cladded high entropy alloy coatings – A review

High entropy alloy is the new development in material compositions. It is a mixture of various metallic and non-metallic elements with different percentages of compositions. It has several superior properties compared to a traditional alloying system like good refractoriness, better resistance to a corrosive environment, excellent wear resistance due to high hardness, stability in various temperature range, resistance to irradiation, and high toughness. The high entropy alloy can be synthesized by many cladding techniques such as plasma transfer arc, magnetron sputtering, electrochemical cladding, and laser-assisted cladding process. Among the mentioned methods, laser cladding is most beneficial due to many advantages such as high melting solidification rate, narrow heat-affected zone, better metallurgical bonding, optimum dilution, and accurate control over operating parameters of cladding process. In this article, recent advancement in high entropy alloy coatings achieved through the laser-assisted cladding process and its wear, erosion, and corrosion behavior were reviewed.

Corrosion Behavior of Cobalt Alloy Coating in NaCl Solution

Two kinds of Co-based coatings were obtained through the laser cladding (LC) and plasma transfer arc (PTA) process. The phase composition and microstructure of the coatings were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The corrosion behaviour of the different Co-based alloy coatings in 3.5wt% NaCl solution were compared by means of open-circuit potential (OCP), polarization curve and electrochemical impedance spectroscopy (EIS). XRD and SEM measurements demonstrated that the microstructures of the two different Co-based coatings were composed of primary solid solution γ-Co and eutectic structure Cr23C6, whereas, fish-bone typed (CoCrW)6C was also detected in the coating produced by PTA. The polarization curves and EIS results showed that in 3.5wt% NaCl solution, the passivation zones of the two coatings occurred obviously, the self-corrosion potential of the two coatings shifted to the right, and the self-corrosion current density was much smaller than that of the substrate. In addition, the Co-based coating made by LC showed lower corrosion current density and larger diameter of a capacitive arc than that of Co-based coating produced by PTA, indicating the LC coating had the best corrosion resistance in the three samples.

Microstructure and Wear Behavior of MMC Coatings Deposited by Plasma Transferred Arc Welding and Thermal Flame Spraying Processes

In this study, two erosion protection MMC coatings with WC particles were deposited by the plasma transferred arc (PTA) welding. One of the coatings with tungsten carbide WC in the NiBSi matrix (WC/NiBSi), and the second coating WC in NiCrBSi matrix (WC/NiCrBSi) was deposited by the flame spray process on the same substrate material S235JR steel. Experiments were performed using a gas blast sand erosion test facility with high-velocity erodent particles impact (approximately 100 m/s) at different particle impact angles (20°–45°), with an objective to study erosion wear characteristics and mass loss of two MMC coatings. Microstructural characterization of MMC coatings was done by scanning electron microscope equipped with energy-dispersive X-ray spectroscopy, whereas X-ray diffraction analysis was used for identification of present phases. The hardness of coatings was determined by Vickers hardness measurements. WC/NiBSi obtained by the PTA process shows superior hardness and erosion properties.

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.

A study on the intergranular corrosion and pitting resistance of Inconel 625 coating by PTA-P

ABSTRACTThis study aims to evaluate the influence of heat input and dilution on the corrosion behaviour of a weld overlay coating of Inconel 625 deposited using a plasma transferred arc process. Cyclic potentiodynamic polarisation, double-loop electrochemical potentiometric reactivation and critical pitting temperature (CPT) experiments were performed to determine sensitisation and pitting corrosion resistance of the coating, besides microstructural characterisation and microhardness testing. The overlay showed to be resistant to sensitisation in all cases. Within the scope of this study, only the CPT test was able to cause pitting in the alloy, which showed that increments of the specimen's chemical dilution and heat input induced a lower CPT. This is mainly due to different chemical compositions among the distinct phases present in the coating.

Microstructure and oxidation resistance of a multiphase Mo-Si-B ceramic coating on Mo substrates deposited by a plasma transferred arc process

To improve the oxidation resistance of a Mo substrate, a multiphase Mo-Si-B ceramic coating was deposited using a plasma transferred arc (PTA) process. The phase constituents, microstructure, and oxidation resistance of the coating were investigated. The results show that the microstructure of the Mo-Si-B coating is characterised by rod-like Mo5SiB2 dendrites, a lamellar structure of Mo3Si/Mo5SiB2 binary eutectics, and cellular Mo5Si3 dendrites. Compared with the Mo substrate, the Mo-Si-B coating exhibits a significant improvement in the oxidation resistance at 1300 °C in an air atmosphere. This is mainly owing to a dense and continuous borosilicate layer formed on the surface of the Mo-Si-B coating, which acts as an oxygen diffusion barrier. Moreover, it is observed that the Mo5SiB2 dendrites exhibit a higher oxidation resistance compared to Mo3Si/Mo5SiB2 eutectics during high-temperature oxidation exposure. The oxidation behaviour is discussed based on the oxidation kinetics and a cross-sectional microstructure analysis of the oxidised Mo-Si-B specimen.

Hard-yet-tough high-vanadium hierarchical composite coating: Microstructure and mechanical properties

In this work, we report a high-vanadium hierarchical coating prepared on the surface of nodular cast iron substrate by a low-cost plasma transferred arc (PTA) surface alloying process. The coating consists of a graded layer with an alloyed zone (AZ) rich in submicron sized granular (V-Ti-Nb-Cr-Mo) composite carbides on top of intermediate melted zone characterized by refined ledeburite and martensite. The dense spherical particles in the AZ are FCC structured MC-type (M = V, Ti and Nb) carbides which tend to aggregate while M7C3 and M2C carbides nucleate on MC. The super-lattice V8C7 maintains its cube-on-cube orientation relationship with TiC. The hardness of the AZ is 9.6 ± 1.0 GPa, ~ 4 times that of the substrate. Nano- and micro-indentations point at a superior strength-toughness in the AZ, where cracks are deflected and bridged by the spherical MC carbides in a compressive residue stress state. The fracture mode appears to be rather ductile in the AZ whereas brittle failure appears in both the melted zone and substrate. TEM and EDS results confirm that such a microarchitecture design, assisted by the rapid solidification rate of the PTA process, concurrently activates various strengthening micromechanisms including the precipitation hardening and grain refinement.

Corrosion resistance of metalized layers on steel parts in ventilation mill

Corrosion behavior of metalized layers, obtained by Plasma Transferred Arc (PTA) process and by High-Velocity Oxygen Fuel (HVOF) process with the purpose to improve the wear resistance of vital parts of ventilation mill in a thermal power plant, has been tested. The test is performed using three electrochemical techniques, in a solution containing chloride and sulfate ions. It is shown that the steel surface (base metal) dissolves uniformly, without pitting or other forms of local dissolution. Morphology of metalized layers surface indicates that dissolution is non-uniform, but it still can be considered as general corrosion. The corrosion rate of base metal and metalized layer obtained by PTA process is rather low, while the corrosion rate of the metalized layer obtained by HVOF process is much higher. Also, the difference in corrosion potentials between the base metal and the HVOF layer is pretty high but slightly less than maximum allowed difference (prescribed by the standard), to avoid excessive galvanic corrosion. The values of corrosion rate obtained by different electrochemical techniques are in excellent agreement.

Microstructure and wear resistance of Mo coating deposited by plasma transferred arc process

To improve the wear resistance of a C45E4 steel substrate, a Mo coating was deposited by plasma transferred arc (PTA) process. The phase and microstructure of the coating were characterized by X-ray diffraction (XRD), optical microscope (OM), scanning electron microscopy equipped with an energy dispersive spectrometer (SEM-EDS) and transmission electron microscopy (TEM), respectively. The hardness and wear resistance were investigated by Vickers hardness and pin-on-disk wear testers. It was found that the metastable Fe63Mo37, Fe solid solution, Fe7Mo6, and a certain amount of amorphous phases co-existed in the as-deposited Mo coating. The peritectic coupled growth in Fe-Mo alloys was observed. Based on the undercooling and eutectic growth theory, the possibility of the Fe63Mo37/α-Fess peritectic coupled growth has been discussed. The microhardness was much higher than that of the C45E4 steel substrate. The results showed that the coating exhibited higher wear resistance ascribed to the high hardness phases and low-friction MoO3 film on the worn surface of the coating under dry sliding wear test against ZrO2 disc at room temperature.

Characterization and Optimization of Ni-WC Composite Weld Matrix Deposited by Plasma-Transferred Arc Process

This work is dedicated to optimization of carbide particle system in a weld bead deposited by PTAW technique over D2 tool steel with high chromium content. The paper reports partial melting of the original carbide grains of the Ni-based filling powder, and growing of the secondary carbide phase (Cr, Ni) $$_3$$ W $$_3$$ C in the form of dendrites with wide branches that enhanced mechanical properties of the weld. The optimization of bead parameters was made with design of experiment methodology complemented by a complex sample characterization including SEM, EDXS, XRD, and nanoindentation measurements. It was shown that the preheat of the substrate to a moderate temperature 523 K (250 $$^\circ $$ C) establishes linear pattern of metal flow in the weld pool, resulting in the most homogeneous distribution of the primary carbides in the microstructure of weld bead.

Surface alloying of high-vanadium high-speed steel on ductile iron using plasma transferred arc technique: Microstructure and wear properties

A high-vanadium high speed steel (HVHSS) alloying layer was synthesized from pre-placed powders (V-Cr-Ti-Mo) on ductile iron (DI) substrate using plasma transferred arc (PTA) technique. The PTA-alloyed layer, characterized by microhardness, optical microscopy, XRD, EDS enabled SEM, TEM and pin-on-disk tribometry, consists of three main regions: top alloyed zone (TAZ), intermediate remelted zone (IRZ), and heat affected zone (HAZ) of the DI substrate. A large number of globular carbides particles with size smaller than 5μm form in the TAZ through in-situ reactions between the alloying elements and graphite in the molten pool. Further microstructural characterizations indicate that the carbides are primarily vanadium carbide (VC), confirming the formation of the HVHSS layer. The maximum microhardness of the PTA-alloyed sample occurring at the subsurface is 950HV0.2 which is 5 times that of the substrate. The HVHSS layer exhibits superior tribological performance in comparison to PTA-remelted DI, Mn13 steel and DI substrate. The enhanced performance is attributed to the formation of mixed hard-phases such as MC, M7C3, M23C6, martensite and grain refining through rapid solidification accompanying the PTA process.

Carbide reinforced Ni–Cr–B–Si–C composite coating on 4Cr5MoSiV1 steel by comprehensive plasma melt injection method

The present work deals with fabricating a carbide reinforced nickel matrix composite coating on 4Cr5MoSiV1 steel. Electroless nickel coated silicon carbide particles (Ni/SiCp) were injected into plasma generated nickel alloy melt pool using plasma melt injection (PMI) method and plasma transfer arc (PTA) process simultaneously. The appropriate injection angle (θ) in this comprehensive PMI method (PTA+PMI) was calculated to satisfy the specific requirement of injection position for reducing the gasification of SiC particles (SiCp). The effects of the PTA+PMI method and electroless nickel coating (ENC) on SiCp were identified in a comprehensive manner by comparing the microstructural aspects of the coatings. The results show that the appropriate value of θ ranges from 57° to 64° in the present study. The deposition of ENC on SiCp is found to be very effective in retarding the gasification of SiCp during the PTA+PMI process. Meanwhile, the improved wettability of SiCp by the ENC decreased the necessary minimal vertical velocity of SiCp, which consequently promoted the impregnation of SiCp in the PTA+PMI process. The nickel matrix composite coating reinforced by Ni/SiCp (S5) using the PTA+PMI method mainly consists of large amount of in situ chromium-rich carbides (M7C3) together with nickel silicide (Ni3Si) in a nickel iron solid solution (γ-Ni(Fe)). Microhardness and tribological tests reveal considerable improvement in surface microhardness and wear resistance properties of 4Cr5MoSiV1 steel.

Microstructure and Wear Properties of FeCrC, FeW and Feti Modified Iron Based Alloy Coating Deposited by PTA Process on AISI 430 Steel

Abstract The plasma transferred arc (PTA) process was used for developing wear resistance of AISI 430 steel substrate. Appropriate quantities of FeCrC, FeW and FeTi powders were combined to create conditions that synthesized M7C3 particles into reinforced Fe-based composite surface coating. The phase transformations on new created coated surfaces were comprehensively examined by using a combination of scanning electron microscopy (SEM), microanalysis by energy dispersive spectrometry (EDS), X-Ray diffraction (XRD), microhardness and abrasive wear tests. The microstructure studies of the superficial layers of the coating revealed presence of a mixture of the dendritic phase structure of austenite (γ) and fine eutectic M7C3 carbides. The results show that; the concentrations of the elements (Cr, W, Ti) added as ferroalloys, the size of dendrites formed in the coated surface, the change of hardness of the coated surfaces, the carbide volume rate and thickness of the coating changed by the variation of the processing parameters (ratio of reinforcement particulates and heat input).