Plasma Transferred Arc Hardfacing Research Articles

The effect of Si addition in NbTiZr coatings

Nb based alloys are considered the most appropriate to replace Ni alloys for new generation aircrafts, since Ni alloys can no longer meet the extreme environmental requirements. Processing Nb based alloys as coatings might bring a wider use of alloys depending on the available understanding of their processability. This investigation takes an important step to process Niobium alloys containing high hardness low toughness silicide compounds as multilayer coatings, taking advantage of in-situ synthesis of the alloy during the deposition of powder mixtures. Procedures started by preparing elemental powder mixtures adding Si to a NbTiZr solid solution composition with good processability. In-situ synthesis of silicides occurs during the deposition of (Nb24Ti18Si + 1Zr) (at.%) powder mixtures by Plasma Transferred arc hardfacing (PTA). Si accounts for the hardness increase of the deposited coatings and their reduced mass gain. The addition of Si into the powder mixtures induced the formation of primary Nb5Si3 that competes with the primary Nb(Ti,Si,Zr)ss. Three solidification paths are identified to be competing as the PTA torch moves and the melt pool solidifies. The thermal cycles of multilayer coating processing favour the epitaxial growth of Nb5Si3 at the remelted interface between layer and induce a coarsening of the silicides in the microstructure. Phase distribution in coatings, with the more ductile and toughness phases surrounding the silicides, contributes for the confinement of cracks within the larger silicides formed after the deposition of multilayer coatings.

A comprehensive review on recent developments in materials and technological parameters for plasma transferred arc hardfacing process

Critical equipments of process and heavy engineering industries are prone to significant wear due to intense service conditions. Uneven and uncontrolled wear causes significant changes in dimensional and geometrical accuracies of the part surfaces, which adversely affect the parts’ functionality and service life of these parts. Shorter service life of these equipments and subsequent replacement of the same is one of the serious economic concerns. Hardfacing or hardsurfacing is comparatively an advanced metal deposition technology to deposit a hard and complex metal substrate layer on simple and softer base material surface. This process is gaining popularity at commercial level due to its unique capabilities to develop superior wear, corrosion, and impact resistance properties on worn out parts and offer huge economic advantage as substitute to costly replacement. The primarily aim of this study is to present a comprehensive review of the work done on the probable candidates for deposition materials, and summarize the influence of various process parameters on hard-faced surface characteristics. The critical issues like dilution, debonding, and residual stresses have been discussed for multi-layered hardfacing for iron-, nickel-, and cobalt-based hardfacing materials. The secondary aim of this study is to address practical issues such as selection of proper combination of base-substrate material, to understand the response characteristics of ‘plasma transferred arc hardfacing (PTAHF)’ process to minimize the de-bonding, dilution, and residual stresses and finally to improve quality of hardfacing practice.

Optimization of material and process parameters for plasma transferred arc hard facing for high temperature applications

The authors in this research paper have investigated the process of hardfacing, which is a well-established manufacturing process for increasing the durability of industrial components, which are subjected to extreme wear, erosion, abrasion. The objective of this study is to establish a scientific methodology to select the most suitable combinations of materials as base-deposition materials for hardfacing, specifically focusing on Nickel-based and Cobalt-based materials. In order to make an informed decision, multi-criteria decision-making method known as “Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS)” is used. This technique permits to deal with wide range of important factors, such as the materials' high-temperature resistance, wear resistance, and corrosion resistance, among others. The paper discusses a step-by-step approach to selecting the best alternative material for hardfacing by considering eight different criteria and assigning preferences to each of the available materials. The results of this methodology suggested that Stellite-6 based cobalt-based alloy is best suitable for AISI 304 grade austenitic stainless steel materials used for high temperature applications.In addition, the paper also studies the effects of various welding parameters on the hardfacing process. This includes parameters such as welding current, welding speed, powder feed rate and the type of shielding gas used. The significance of each parameter is also studied, and the results of these investigations are discussed in detail. Overall, this research paper provides a comprehensive overview of the hardfacing process and the materials and techniques that are best suited for it, making it valuable resource for professionals and researchers in the field.

CHARACTERIZATION OF A NEW HIGH ABRASION AND EROSION RESISTANCE IRON-BASED ALLOY FOR PTA HARDFACING

The article presents the results of research on an innovative iron-based alloy for industrial arc surfacing using the Plasma Transferred Arc (PTA) hardfacing process. The use of high cooling rates makes it possible to obtain a structure partially similar to metallic glass. Thus, it was possible to avoid the conventional dendritic solidification, resulting in the grain refinement through a eutectoid growth of laths of bainitic ferrite. The surface layer consisted of the fine structure of a Feα, Feγ and a high-volume fraction of borocarbide phases. An even distribution of borocarbide phases in a ductile iron matrix appears to be particularly desirable for achieving high hardness and resistance to metal-mineral abrasive wear (ASTM G-65). The surface layer showed a hardness of up to 69 HRC and resistance to abrasive wear that was more than 14 times higher than of steel type AR 400. In addition, the surfacing layer is characterized by high erosion resistance (ASTM G 76-95) and resistance to impact loads up to 200 J. The developed PTA hardfacing alloy is expected to be useful in applications requiring high abrasion and erosion resistance combined with high impact strength.

Influence of Fe Dilution and W Dissolution on Abrasive Wear Resistance of NiCrBSi–WC Composite Hardfacing Deposited by Plasma Transferred arc Hardfacing

The control of Fe dilution and carbide dissolution plays a vital role on the performance of metal matrix composite hardfacings. In this paper, the NiCrBSi–WC composite hardfacing is deposited on 304 austenitic stainless steel by plasma transferred arc hardfacing at 120[Formula: see text]A (specimen 1) and 140[Formula: see text]A (specimen 2) transferred arc current values to obtain different levels of Fe dilution and W dissolution for comparative investigations. The Fe dilution examined by scanning electron microscopy for specimen 1 was 24.54% and for specimen 2 was 33.09%. The microstructural investigations revealed higher W dissolution for specimen 2 due to higher heat input which led to significant reduction in the amount of WC and W2C hard phases. The slurry abrasive wear test performed as per ASTM G105 showed two times reduction in abrasive wear resistance of specimen 2 as compared to specimen 1. The significant reduction in the performance of specimen 2 is mainly due to higher Fe dilution and higher W dissolution caused due to higher heat input. Hence, selection of appropriate process parameters is vital to control Fe dilution and carbide dissolution in order to achieve superior performance of composite hardfacings.

Microstructural and mechanical characterization of Stellite-hardfaced coatings with two types of buffer layers

In recent years, a major challenge facing the power generation industry is delamination of Stellite-hardfaced coatings from high-temperature valves. In order to meet this challenge, IN82 buffer layer was evaluated to replace the problematic S21 buffer layer. S6 and either S21 or IN82 hardfacing alloys were deposited onto F91 steel substrates using plasma-transferred arc hardfacing. Aging was conducted at temperatures between 550 and 650 °C for three exposure durations within a one-year period. A comparative study was carried out on the microstructure and mechanical properties of IN82 and S21 hardfaced specimens. The F91/S21 interface is unstable during aging because a hard and brittle interfacial layer grows, which significantly reduces the impact energy of S21 hardfaced specimens. In contrast, the F91/IN82 interface is microstructurally much more stable than the F91/S21 interface; an interfacial band, part of the F91 steel, and some discrete M23C6 carbides along this band grow during aging at 650 °C for 8760 h. The impact energy loss of the IN82 specimens is much less significant than that of the S21 specimens. Moreover, the toughness degradation is not related to the F91/IN82 interface, but rather to coarsening and precipitation of the intergranular/interdendritic carbides in the IN82 bulk material during aging. To conclude, the IN82 buffer layer is a good alternative to replace the problematic S21 buffer layer, enhancing the durability of the S6 coating components. However, the hardness of the S6 top layer is compromised due to dilution of Fe and Ni. To maintain its hardness, more S6 layers can be deposited and process optimization can be undertaken to reduce dilution in the applications where wear resistance is critical.

Characterization of Stainless Steel 410 L weld bead for Plasma Transferred Arc Hardfaced Valve Seat Rings

Wear brings about drastic fallout in metallic components during their application. It is established that hardfacing process has substantially matured over the recent times. To start with, Stainless steel 410 L is hardfaced over the face of low carbon steel IS-2062 valve seat rings by plasma transferred arc hardfaced process. The main and interaction effects of Plasma Transferred Arc hardfaced variables for stainless steel were obtained. These investigations were based on a design matrix of five factors, five level factorial method. The Regression analysis was tested for scrutinizing the adequacy. The percentage dilution was optimized. The conformity test was conducted and the optimized results were verified, with the percentage of error being calculated. The impact factors on the dry sliding wear resistance of Stainless Steel 410 L alloy was investigated under conditions leading to an obdurate metallic wear condition of the hard facing alloy. Mathematical model was developed relating the wear and the main factors, such as, normal load, Disc Speed, track radius. The Optimized wear model was obtained for minimizing the wear rate. Mathematical models relating wear testing parameters to wear and coefficient of friction were developed. The developed mathematical model can be used to assess the wear and the wear was found to increase.

Parameter optimization for tungsten carbide/Ni-based composite coating deposited by plasma transferred arc hardfacing

Abstract Ni-based composite coatings with a high content of tungsten carbides (Stelcar 65 composite coatings) were synthesized by plasma transferred arc (PTA) hardfacing. The welding parameters of Stelcar 65 composite coatings were optimized by orthogonal tests. The PTA welding parameters including welding current, powder feed rate and welding speed have significant influence on the tungsten carbide degradation. The values for the optimum welding current, powder feed rate and welding speed were determined to be 100 A, 25 g/min and 40 mm/min, respectively. The produced WC/Ni-based composite coatings were crack- and degradation-free. The microstructure of deposited layers, as well as the microstructure and microhardness of the optimal coating were further analyzed.

Cobalt-based PTA coatings, effects of addition of TiC nanoparticles

The novel filler metals of cobalt-based alloys reinforced with titanium carbide nanoparticles (TiC-NPs) were used for the fabrication of plasma transferred arc hardfacing coatings. The effect of tribological behavior for TiC-NPs addition on two Co-based filler metals (Stellite 6 and Stellite 12), as well as the dilutions, was studied. Mixtures of Co-based filler metals without and with 0.5% and 2% TiC-NPs were deposited onto D2 steel plates. Stellite 12 had an increase in the dilutions (70%) and enthalpies due to a major surface energy and endothermic reactions. The results of DSC (Differential Scanning Calorimeter) in the filler metals with TiC-NPs showed a shell of nanowhiskers on the sintered surface, which were observed and chemically analyzed via SEM (Scanning Electron Microscope) and EDS (Energy Dispersive Spectroscopy). Stellite 6 with 2% TiC-NPs was the most effective in increasing the wear resistance. These outcomes might be of interest for mining industries, where machinery and equipment are exposed to extreme wear conditions.

Influence of laser surface melting on the characteristics of Stellite 12 plasma transferred arc hardfacing deposit

Stellite 12 hardfacing alloy deposited by plasma transferred arc (PTA) process on the 4140 steel substrate was subjected to laser surface melting (LSM) process. The effect of LSM on the PTA deposit was studied in terms of changes in microstructure and resultant variations in sliding wear properties. In the PTA state the microstructure, which consisted of Cr-rich (Cr7C3 and/or Cr23C6) and complex ((CoCrW)6C) carbides in Co matrix, was altered upon the application of LSM process. In short, LSM process led to the formation of a duplex layer, on the surface, consisting of carbide deficient and rich zones whose thickness tended to decrease with increase in the laser scan speed. As the result of formation of carbide rich zone at the outermost surface, LSM process provided an enhancement in surface hardness. On the other hand, the positive effect of LSM process on wear resistance became more apparent at high wear testing load causing carbide cracking and removal on the contact surface of Stellite 12 PTA hardfacing deposit.

Friction Stir Welding of Copper Alloys by PTA Hardfaced Chromium Carbide Tools

In the present work an attempt was made to develop high temperature wear resistant hardfaced tools for friction stir welding (FSW) of commercial grade copper alloys. Hardfacing was applied on mild steel rod using chromium carbide forming powder by plasma transferred arc (PTA) hardfacing process. Commercially available tool materials like high carbon steel (HCS), high speed steel (HSS) and super high speed steel (SHSS) were also used to friction stir weld copper alloy for comparison purpose. From this investigation, it is found that the PTA hardfaced tool yielded defect free joints without tool wear compared to other tools. The optimum level of heat generation, formation of finer grains and higher hardness of stir zone are main reasons for the superior tensile properties of the joints fabricated by PTA hardfaced tungsten carbide tools.

Evaluating the Performance of Conventional Tools and Plasma Transferred Arc Hardfaced Tungsten Carbide Tools for Friction Stir Welding of Copper Alloy

Evaluating the Performance of Conventional Tools and Plasma Transferred Arc Hardfaced Tungsten Carbide Tools for Friction Stir Welding of Copper Alloy

Liquid phase separation microstructure and properties of mixed Cu-Sn and Co-base alloys without or with molybdenum addition processed by plasma transferred arc hardfacing

In this study, two types of blended alloys were processed by plasma transferred arc (PTA) hardfacing to form coatings. In the first case, a pre-alloyed Cu-Sn alloy and a pre-alloyed Co-base alloy were blended at a weight ratio of 85:15 (Cu-Sn/Co-base). In the second case, the pre-alloyed Cu-Sn and Co-base alloys were mixed with the molybdenum (Mo) element at a weight ratio of 81:15:4 (Cu-Sn/Co-base/Mo). Metastable liquid phase separation formed in the Cu-Sn/Co-base and Cu-Sn/Co-base/Mo coatings. The Co-rich spheroids as the minor precipitating alloy particles distributed on the Cu-rich matrix. The Co-rich spheroids consisted of α(Co) and M7C3 phases, and the Cu-rich matrix included α(Cu, Sn) and Cu10Sn3 phases. The relative content of α(Co)+M7C3 phases in the Cu-Sn/Co-base/Mo coating was higher than that in the Cu-Sn/Co-base coating. The numbers of the Co-rich spheroids in the cross section of the Cu-Sn/Co-base coating increased with increasing the distance from the substrate, and an obvious macroscopic segregation could be found in the coating close to its substrate. When Mo as additive was further added, the numbers of the Co-rich spheroids in the cross section of the coating increased and the macroscopic segregation could not be seen when compared to that in the Cu-Sn/Co-base coating. The wear rate of the Cu-Sn/Co-base and Cu-Sn/Co-base/Mo coatings was lower than that of the Cu-Sn coating, and a distinct improvement of the wear rate could be obtained in the Cu-Su/Co-base/Mo coating, attributing to mainly the increasing hardness of the coatings by sequence of the Cu-Sn coating, Cu-Sn/Co-base coating, and Cu-Sn/Co-base/Mo coating. The friction coefficient of the coatings has an increasing trend by sequence of the Cu-Sn coating, Cu-Sn/Co-base coating, and Cu-Sn/Co-base/Mo coating, but an obvious difference could not be seen in the coatings.

Feasibility of surface-coated friction stir welding tools to join AISI 304 grade austenitic stainless steel

Abstract An attempt is made to develop the tools that are capable enough to withstand the shear, impact and thermal forces that occur during friction stir welding of stainless steels. The atmospheric plasma spray and plasma transferred arc hardfacing processes are employed to deposit refractory ceramic based composite coatings on the Inconel 738 alloy. Five different combinations of self-fluxing alloy powder and 60% ceramic reinforcement particulate mixtures are used for coating. The best friction stir welding tool selected based on tool wear analysis is used to fabricate the austenitic stainless steel joints.

Deign of Experiment and Optimization of Plasma Transferred Arc Hardfacing on Structural Steel with Titanium Carbide

The aim of the Plasma Transferred Arc (PTA) hardfacing process is improving a technical surface locally with a dedicated material; Hardfacing became an issue of intense development related to wear resistant application. The hardfacing procedures can be differentiated by the intensity of mixture with the base body, which is usually increasing along with an increasing fusion efficiency rate. Nearly all kinds of weldable materials can be hardfaced and mostly all types of known wear resistant metals in combination can be used as hardfacing materials. The PTA hardfacing process has been widely employed due to several advantages such as higher volume of metal deposition rates and achieving very low dilution level. Heat input which influences dilution can be controlled by proper selection of PTA process parameters. In this study, an attempt has been made to analyze PTA hardfacing of IS: 2062 structural steel with Titanium Carbide (TiC). Experiments were conducted based on a fully replicable five-factor, five-level central composite rotatable design. Mathematical models were developed using response surface methodology to study the effects of PTA hardfacing process parameters such as welding current, welding speed ,powder feed rate, oscillation width and pre heat temperature on bead geometry parameters like penetration, reinforcement, bead width and dilution. Direct and interaction effects of PTA process parameters on bead geometry were analyzed. From mathematical model, the process parameters were optimized.

A Study on Microhardness, Microstructure and Wear Properties of Plasma Transferred Arc Hardfaced Structural Steel with Titanium Carbide

The Plasma Transferred Arc (PTA) hardfacing allows for homogeneous refined microstructure, low distortion and dilution resulting on enhanced surface properties when compared to hardfacing by conventional welding processes. This paper deals with PTA surfacing of a structural steel with a consumable containing TiC. TiC is a very hard refractory material finding increasing usage for wear resistance application. The composition and amount of heat input evidently affect the microstructure and properties of the hardfacing. The microstructure and microhardness of PTA hardfaced structural steel with TiC were investigated at different heat input conditions across the various zones. The influence of hardfacing parameters on the resulting microstructure, microhardness and wear resistance performance was evaluated. Wear resistance of the hardfaced surface was increased significantly.

Influence of molybdenum on the microstructure and properties of a FeCrBSi alloy coating deposited by plasma transferred arc hardfacing

FeCrBSi alloy powders without and with 2–6wt.% Mo (Mo-free and Mo-added, respectively) were deposited on a plain steel using plasma transferred arc (PTA) hardfacing. The effects of Mo addition on the microstructure and properties of the FeCrBSi alloy coating were investigated by X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) attachment, transmission electron microscopy (TEM), Vickers hardness tester, hydraulic universal testing machine, dry sand abrasion test (DSAT) and water quenching method. The results show that the Mo-free coating consists of γ (Fe, Ni), M7(C, B)3, and (Fe, Cr)2B phases. Adding Mo leads to the formation of M23(C, B)6, Mo2(B, C) and Fe3Mo3(C, B) phases, except for those phases existed in the Mo-free coating. The twinning with 101¯ twinning plane is observed in the orthorhombic M7(C, B)3 (M=Fe, Cr, Mo) phase. A hypoeutectic microstructure can be seen in the Mo-free and 2wt.% Mo-added coatings. Increasing Mo addition to 4wt.% and 6wt.%, a hypereutectic microstructure can be obtained. The microstructure of the Mo-free coating can be refined after adding 2–6wt.% Mo. The finest microstructure can be obtained in the 4wt.% Mo-added coating. Adding Mo in the FeCrBSi alloy coating can increase its abrasive wear resistance that has no direct relation with H/E or H3/E2 because brittle fracture occurred occasionally in the abrasive wear test. The thermal shock resistance of the Mo-free coating can be improved after adding 2–6wt.% Mo. The best abrasive wear resistance and thermal shock resistance can be received in the 4wt.% Mo-added coating.

Characterisation of TiC–NiMo reinforced Ni-based hardfacing

In the present study, TiC–NiMo composites were remilled to particle size of 250–315μm and used as reinforcements for NiCrBSi alloy by plasma transferred arc hardfacing process. The manufactured hardfacing alloy was characterised in terms of microstructure, mechanical properties and abrasive wear resistance. Deposition results indicate good quality thick coating with uniform distribution of hard cermet (TiC–NiMo) particles in the matrix, minimum level of hard particle dissolution and low porosity of the hardfacing. Cermet particles remain in initial form and consist of agglomerates (TiC and (Ti,Mo)C grains) embedded into Ni-based matrix. The mechanical properties of the TiC and (Ti,Mo)C phases measured by nanoindentation are very similar exhibiting a narrow distribution. The nano-scratching test reveals excellent bonding between the matrix and cermets in the hardfacing. No crack propagation was found in the interface matrix/hard phase region.The abrasive wear results ensure the promising features of TiC–NiMo reinforcements for Ni-based alloys. Produced coatings showed excellent performance under high-stress abrasion with wear values lower than for industrially used WC/W2C reinforced coatings.

Wear Behaviour of Recycled Hard Particle Reinforced NiCrBSi Hardfacings Deposited by Plasma Transferred Arc (PTA) Process

The main goal of present work was to study room temperature wear behaviour of advanced cermet particle reinforced hardfacings. For this purpose three different recycled powders: WC-Co, TiC-NiMo and Cr3C2-Ni were used as reinforcements for the commercially used NiCrBSi matrix alloy. Plasma transferred arc hardfacing process was used for deposition of the hardfacings. Manufactured hardfacings show only average wear resistance compared to WC/W2C reinforced NiCrBSi hardfacing with two times higher wear values. However, in combined impact/abrasive and erosive contacts, manufactured hard particle reinforced hardfacings have shown very promising results with high wear resistance. It was shown, that double structuring along with right material constituent and coating procedure selection may provide high wear resistance.

Effect of PTA Hardfaced Interlayer Thickness on Ballistic Performance of Shielded Metal Arc Welded Armor Steel Welds

Ballistic performance of armor steel welds is very poor due to the usage of low strength and low hardness austenitic stainless steel fillers, which are traditionally used to avoid hydrogen induced cracking. In the present investigation, an attempt has been made to study the effect of plasma transferred arc hardfaced interlayer thickness on ballistic performance of shielded metal arc welded armor steel weldments. The usefulness of austenitic stainless steel buttering layer on the armor grade quenched and tempered steel base metal was also considered in this study. Joints were fabricated using three different thickness (4, 5.5, and 7 mm) hardfaced middle layer by plasma transferred arc hardfacing process between the top and bottom layers of austenitic stainless steel using shielded metal arc welding process. Sandwiched joint, in addition with the buttering layer served the dual purpose of weld integrity and ballistic immunity due to the high hardness of hardfacing alloy and the energy absorbing capacity of soft backing weld deposits. This paper will provide some insight into the usefulness of austenitic stainless steel buttering layer on the weld integrity and plasma transferred arc hardfacing layer on ballistic performance enhancement of armor steel welds.