Hardfacing Process Research Articles

Evaluation of Dry Sliding Wear Behaviour of Plasma Transferred Arc Hardfaced Stainless Steel

The effects of different experimental conditions on the dry sliding wear behavior of stainless steel surface produced by plasma transferred arc (PTA) hardfacing process were studied. The wear test was conducted in a pinon-roller wear testing machine, at constant sliding distance of 1 km. Mathematical models were developed to estimate wear rate incorporating with rotational speed, applied load and roller hardness using statistical tools such as design of experiments, regression analysis and analysis of variance. It is found that the wear resistance of the PTA hardfaced stainless steel surface is better than that of the carbon steel substrate.

Effect of abrasive slurry parameters on wear behaviour of cobalt-based (stellite) Plasma Transferred Arc hardfaced surface

In this paper, the effect of operating variables such as abrasive particle size, slurry concentration, speed of rotation and slurry bath temperature on Abrasive Slurry Wear (ASW) behaviour of cobalt-based alloy (stellite) surface produced by Plasma Transferred Arc (PTA) hardfacing process has been analysed. Of the four variables considered in this investigation, it is found that the slurry concentration has a predominant effect on wear rate of hardfaced surface compared with other variables. Both experimental and mathematical investigations show that wear resistance of hardfaced stellite surface is three times better than that of the substrate (carbon steel).

Optimisation of cobalt-based hardfacing in carbon steel using the fuzzy analysis for the robust design

In this paper, we present the application of the fuzzy logic analysis to a Taguchi orthogonal experiment for developing a robust model with high efficiency in multiple performance characteristics (MPCs) of the plasma transfer arc welding (PTAW) hardfacing process. It eliminates uncertain information and is a simple, effective, and efficient approach. A fuzzy logic system is used to simultaneously investigate relationships between various MPCs and to determine the efficiency of each trial of the Taguchi experiments. From the fuzzy inference process, we are able to determine the optimal setting of factor-levels for the MPCs. In addition, we also use the analysis of variance (ANOVA) to identify the significant factors, which coincide with findings from the fuzzy logic analysis and are found to account for about 79% of the total variance. Furthermore, a confirmation experiment of the optimal process is conducted, and it verifies that both individual performance characteristics and MPCs are successfully optimized and satisfy our desired levels of MPCs.

Analysis of Hard-Facing Appearance of Specific Powdered Superalloys for PTA-Coating Processes

Artificial neural network (ANN) modeling and multiple linear regression (MLR) analysis have been used to develop a powder hard-facing process using high-energy plasma-transferred (HEPT) heating. HEPT heating can produce coatings with minimal surface roughness. An optimal procedure was developed involving the least number of process parameters but producing the most desirable performance characteristic. The quality characteristic of interest is the surface roughness after HEPT processing, utilizing the “the-smaller-the-better” criterion. Process performance was evaluated with respect to the signal-to-noise ratios, which were obtainable through experiments. The experimental results conclude that ANN models demonstrate a greater accuracy of predicting the surface appearance than the MLR models in terms of prediction error and the coefficient of determination. The results also reveal the most significant process control parameters. The predicted value of powder hard-facing roughness, through the implementation of optimal settings, produces a satisfactory result. The confirmation experiment showed that the ANN method achieved the expected optimal design goals for the HEPT powder hard-facing, thereby justifying the reliability and feasibility of the approach.

Design and development of artificial neural networks for depositing powders in coating treatment

We propose the application of an artificial neural network to a Taguchi orthogonal experiment to develop a robust and efficient method of depositing alloys with a favorable surface morphology by a specific microwelding hardfacing process. An artificial neural network model performs self-learning by updating weightings and repeated learning epochs. The artificial neural network construct can be developed based on data obtained from experiments. The root of mean squares (RMS) error can be minimized by applying results obtained from training and testing samples, such that the predicted and experimental values exhibit a good linear relationship. An analysis of variance indicates that the significant factors explain approximately 70% of the total variance. Consequently, the Taguchi-based neural network model is experimentally confirmed to estimate accurately the hardfacing roughness performance. The experimental results reveal the hardfacing roughness performance of the product of PTA coating is greatly improved by optimizing the coating conditions and is accurately predicted by the artificial neural network model. The combination of the neural network model with Taguchi-based experiments is demonstrated as an effective and intelligent method for developing a robust, efficient, high-quality coating process.

Study on Composition-Induced Microstructural Variation in the Interface Between Co-Based Hardfacing Alloys and IN738 Ni-Based Superalloy

Alloy mixtures with varying composition of two Co-based hardfacing alloys and IN738 Ni-based super alloy were examined using differential scanning calorimetry. The microstructure of the resulting specimens was then analyzed using optical and scanning electron microscopy and energy dispersive spectroscopy. The microstructural evolution between each hardfacing alloy and the IN738 substrate was documented and the formation of topologically close-packed and/or additional carbide phases was noted. Microstructures that are undesirable for high temperature and stress applications were produced in specimens with a higher degree of mixing (from 25 to 75 wt.% of hardfacing alloy in IN738). The two hardfacing alloys produced markedly different microstructures in the alloy mixtures due to differences in elemental composition. A hardfacing process that minimizes the degree of deposit-substrate mixing will be beneficial to the performance of the coating.

03/02194 Liberalizing and restructuring European natural gas — winners and losers: Noreng, Ø. The Journal of Energy and Development, 2002, 27, (1), 15–32

Abrasive slurry wear is generally defined as a mechanical interaction in which material is lost from a surface which is in contact with a moving particle-laden liquid. Slurry wear abrasion occurs in extruders, slurry pumps, and pipes carrying slurry of minerals and ores in mineral processing industries. The life of components used under slurry abrasion conditions is governed by the process parameters, properties of the abrasive particles in the slurry and the material properties. This paper analyzes in detail the effects of operating variables such as abrasive particle size, slurry concentration, speed of rotation and slurry bath temperature on the abrasive slurry wear behavior of a stainless steel surface produced by Plasma transferred arc (PTA) hardfacing process. Of the four variables considered in this investigation, it is found that the slurry concentration has a predominant effect on wear rate of hardfaced surfaces compared to other variables. Microstructural analyses of the worn surfaces were carried out using SEM. Both experimental and mathematical investigations show that the wear resistance of the PTA hardfaced stainless steel surface is four times better than that of the carbon steel substrate.

The impact characteristics of Ti–6Al–4V plates hardfacing by laser alloying NiAl+ZrO2 powder

This investigation considers the alloying of NiAl powders, with 0, 10, 20, 30, and 40wt.% of ZrO2 added, by the CO2 laser upon Ti–6Al–4V base metals. Trial experiments are performed to obtain the optimum thickness of the powder, 0.1mm, and the transverse speed, 1mm/s, upon which the hardfacing process was based. The microstructures of the alloying layers were analyzed by OM, X-ray spectroscopy and SEM/EDS. The mechanical properties of the alloying layers were analyzed by micro-hardness and impact tests. The results indicated that the microstructure of the hardfacing layer was finer and its micro-hardness was higher than those of the base material. During the hardfacing process, NiAl and ZrO2 powder were dissolved in a molten pool, reacted with other elements, and new phases were then formed. Impact tests revealed that the absorption of the vibration increased as the ZrO2 added.

Welding As a Hardfacing Process For Mining And Mineral Processing Industry

Welding As a Hardfacing Process For Mining And Mineral Processing Industry

Numerical simulation for the residual stresses of Stellite hard-facing on carbon steel

Hard-facing is an effective method for modifying the surface properties of metal parts, such as valves. The residual stresses in the hard-facing layer are important factors affecting the service properties and service life of the parts. This research has studied the decrease in the tensile residual stress in the hard-facing layer as well as the residual stress distributions and their affecting factors using a numerical simulation method with the aid of the commercial software abaqus. The computed results indicated that the residual stresses in the hard-facing layer are dependent on several factors, which include the heat-transfer coefficient, the thermal expansions of the materials, the thickness of the base metal and the pre-heating temperature, etc. In addition, local post-heating on the base metal surface can effectively reduce the tensile residual stress and this tensile stress can also be cut down if there is an austenitic stainless steel interlayer between the carbon base metal and the Stellite hard-facing layer. These results indicate that the numerical simulation method is a useful and convenient means by which to investigate the residual stresses of the hard-facing process.

Study of restoration by welding of pearlitic ductile cast iron

The objective of this investigation is to study the restoration and/or hardfacing by welding of worn-out parts manufactured from pearlitic ductile cast iron. The work may be divided into two sections. The first deals with studying the weldability of pearlitic ductile cast iron by means of five different types of filler material, namely, pure Ni, Fe–Ni alloy, Ni–Cu alloy, stainless steel and ferritic steel. Particular attention was directed towards the parameters affecting welding by ferritic steel filler metal. This material is attractive because of its low cost. In addition, weldments produced are characterized by excellent colour match, satisfactory hardness and the variety of austenitic transformation products which occur on cooling. Process variables such as preheating, heat input, post weld heat treatment (PWHT), multipass and multilayer techniques, and hardfacing process were studied in detail. Microstructural analysis, microhardness distribution of the melt region (MR) and heat affected zone (HAZ), and nondestructive evaluation were all applied to assess the weldment quality.

Laser cladding

Laser cladding is a hardfacing process that uses a high-powered laser beam to melt the coating material and a thin layer of the substrate to form a pore- and crack-free coating 50 μm–2 mm thick with low dilution that is perfectly bonded to the substrate. The process may be used for large area coverage by overlapping individual tracks, but it is the ability to protect smaller, localized areas that makes it unique. The wide range of materials that can be deposited and its suitability for treating small areas make laser cladding particularly appropriate to tailor surface properties to local service requirements and it opens up a new perspective for surface engineered materials. Laser cladding processes differ in the way the coating material is supplied. In two-step processes a thin layer of material is deposited on the substrate, for example, as a slurry or a thermally sprayed coating, and subsequently melted with the laser beam. In single-step processes the material is fed continuously into the laser generated melt pool, usually in the form of a powder. Laser cladding by powder injection is superior to alternative processes and is the only one that has found practical use, because it is more energy efficient and it allows for better process control and reproducibility. Laser cladding has found relatively widespread use for the protection of materials against wear, corrosion and oxidation, for the deposition of self-lubricating coatings and thermal barriers, and for the refurbishing of high cost industrial components. Other applications with considerable potential are nonequilibrium synthesis of advanced materials, alloy development and free-form near-net shape manufacturing. Some examples of applications are discussed.

Amorphous diamond-like carbon coatings with graded metal interfaces

In laser cladding, high cooling rates create outcomes with superior mechanical and metallurgical properties. However, this characteristic along with the additive nature of the process significantly contributes to the formation of thermal stresses which are the main cause of any potential delamination and crack formation across the deposited layers. This drawback is more prominent for additive materials such as Stellite 1 which are by nature crack-sensitive during the hardfacing process. In this work, parallel to the experimental investigation, a numerical model is used to study the temperature distributions and thermal stresses throughout the deposition of Stellite 1 for hardfacing application. To manage the thermal stresses, the effect of preheating the substrate in a localized dynamic fashion is investigated. The numerical and experimental analyses are conducted by the deposition of Stellite 1 powder on the substrate of AISI-SAE 4340 alloy steel using a 1.1 kW fiber laser. Experimental results confirm that by preheating the substrate a crack-free coating layer of Stellite 1 well-bonded to the substrate with a uniform dendritic structure, well-distributed throughout the deposited layer, can be obtained contrary to non-uniform structures formed in the coating of the non-preheated substrate with several cracks.

Low Pressure Plasma Spraying Process-An Economical Substitute for Laborious, Costly Plasma Weld Surfacing Process for Hardfacing Critical Components

At present critical components like steam turbine spindles and power plant valve components etc. are being handfaced (stellited) using Plasma weld surfacing process involving laborious post weld heat treatment and weld distortion etc. Again, plasma weld surfacing is quite expensive due to deposition of higher build up layer of about 3 to 5 mm of costly consumable (stellite powder). Low pressure Plasma spraying (LPPS) is an economical and productive substitute to conventional weld surfacing process and IS being attempted for various critical applications in developed countries. Since LPPS is a new process and the LPPS system (imported equipment cost approx. Rs. 2 Crores) is not available indigenously, WRI Is developing this facility to establish the LPPS technology for hard facing applications. This paper describes the new hard facing process, its capabilities, advantages, limitations and industrial applications with respect to conventional plasma weld surfacing and spraying process. The new LPPS facility being developed at WRI has also been discussed.

Single-crystals as an indicator of fatigue damage: Zasimchuk, E. E., Radchenco, A. I. and Karuskevich, M. V. Fatigue Fract. Eng. Mater. Struct. (Dec. 1992) 15 (12) 1281–1283

Prototype Fast Breeder Reactor (PFBR) is first of its kind 500MWe pool type, sodium cooled nuclear reactor which is presently in advanced stage of construction at Kalpakkam, India. Intermediate Heat Exchanger (IHX) is a shell and tube type, counter current, sodium to sodium heat exchanger. IHX is a very important, massive, over dimensional (∼42 tones in weight, ∼2 meters in diameter and ∼18 meters in length) and critical component of reactor, as it transfers heat from the radioactive primary circuit sodium to non-radioactive secondary circuit sodium forming the boundary between these two circuits. The principal material of construction of IHX is austenitic stainless steel grade 316LN. Each IHX has 3600 nos. of straight seamless tubes which are rolled and then welded to the either ends of top and bottom tubesheets by autogenous pulsed Gas Tungsten Arc Welding (GTAW) process. The shell welding around the tube bundle is extremely difficult and challenging task due to small gap between the tube bundle and shell inside diameter. Special arrangements were made to avoid arc strike or fusion on the tube during shell welding around the tube bundle.A mechanical hardfaced seal arrangement at the interface of the IHX outer shell and the inner vessel stand pipe is the chosen design concept to ensure leak tightness in the IHX penetrations. Based on radiation dose rate & shielding considerations during maintenance, handling and decommissioning, nickel based ENiCr-B hard facing alloy (Colmonoy-5) was chosen to replace the traditionally used cobalt based stellite alloys to improve the resistance to high temperature wear, especially galling of mating surfaces in sodium environment. The more versatile Plasma Transferred Arc Welding (PTAW) and Gas Tungsten Arc Welding (GTAW) were used for deposition of Colmonoy-5. The hardfacing on the seal ring is really challenging task, as the diameter is too large and thickness & width is too small and which has hardfacing on all mating surfaces. Extensive varieties of trials were conducted on the mockup to optimize the hardfacing process along with heat treatment cycle to obtain minimum distortion deploying special tools and fixtures.Intermediate Heat Exchanger involves 10 mm and 28 mm thick borated stainless steel components around the tube bundle and bottom portion confirming to ASTM 887, Type 304 B4, Grade B classification to reduce the radiation level in secondary sodium system while flowing through the IHX. Various types of welding trials were conducted on the test coupons for welding procedure qualification of borated stainless steel components using versatile grades of welding consumables. More than hundred nos. of trial coupons welded using 10 varieties of welding consumables have shown fissures and cracks in weld, as these welding consumables found not having good compatibility with SS 304 B4, Grade B borated steel. Special development work was taken-up for the first time in the country by developing a special grade ∼1% borated welding consumable (GRINOX-308BRN electrode) specifically for welding of borated steel components of IHX. This paper highlights on welding aspects and challenges during fabrication of Intermediate Heat Exchangers for 500MWe Prototype Fast Breeder Reactor.

On the structure of Ni–Cr–B–Si hardfacing alloys and their bonding reactions

Silicon is dissolved in the nickel-rich mixed crystal of Ni–Cr–B–Si alloys which are used for hardfacing. Boron forms several different borides due to the small solubility in the mixed crystals. There is a wide liquidus range during solidification of these alloys caused by the metastable solidification of the Ni–Ni2B eutectic instead of the stable solidification of the Ni–Ni3B eutectic. This wide liquidus range facilitates the hardfacing process which can be conveniently done by fusing the alloyed powders in a furnace. The hot hardness of nickel-based hard alloys is higher, up to 900 °C. The boron diffusion into the base metal is of the volume diffusion type; no grain boundary diffusion was observed with type 316 stainless steel.