Identifying the optimal HVOF spray parameters to attain minimum porosity and maximum hardness in iron based amorphous metallic coatings

Flow based Erosion e corrosion problems are very common in fluid handling equipments such as propellers, impellers, pumps in warships, submarine. Though there are many coating materials available to combat erosionecorrosion damage in the above components, iron based amorphous coatings are considered to be more effective to combat erosionecorrosion problems. High velocity oxy-fuel(HVOF)spray process is considered to be a better process to coat the iron based amorphous powders. In this investigation, iron based amorphous metallic coating was developed on 316 stainless steel substrate using HVOF spray technique. Empirical relationships were developed to predict the porosity and micro hardness of iron based amorphous coating incorporating HVOF spray parameters such as oxygen flow rate, fuel flow rate, powder feed rate, carrier gas flow rate, and spray distance. Response surface methodology(RSM) was used to identify the optimal HVOF spray parameters to attain coating with minimum porosity and maximum hardness.

Experimental and numerical investigation on under-water friction stir welding of armour grade AA2519-T87 aluminium alloy

Friction stir welding(FSW) is a promising welding process that can join age hardenable aluminium alloys with high joint efficiency. However,the thermal cycles experienced by the material to be joined during FSW resulted in the deterioration of mechanical properties due to the coarsening and dissolution of strengthening precipitates in the thermo-mechanical affected zone(TMAZ) and heat affected zone(HAZ). Under water friction stir welding(UWFSW) is a variant of FSW process which can maintain low heat input as well as constant heat input along the weld line. The heat conduction and dissipation during UWFSW controls the width of TMAZ and HAZ and also improves the joint properties. In this investigation, an attempt has been made to evaluate the mechanical properties and microstructural characteristics of AA2519-T87 aluminium alloy joints made by FSW and UWFSW processes. Finite element analysis has been used to estimate the temperature distribution and width of TMAZ region in both the joints and the results have been compared with experimental results and subsequently correlated with mechanical properties.? 2016 China Ordnance Society. Production and hosting by Elsevier B.V. All rights reserved.

Effect of pulsed current on temperature distribution,weld bead profiles and characteristics of gas tungsten arc welded aluminum alloy joints

Temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded aluminium alloy joints were compared. The effects of pulsed current welding on tensile properties, hardness profiles, microstructural features and residual stress distribution of aluminium alloy joints were reported. The use of pulsed current technique is found to improve the tensile properties of the weld compared with continuous current welding due to grain refinement occurring in the fusion zone.

Optimizing the micro-arc oxidation (MAO) parameters to attain coatings with minimum porosity and maximum hardness on the friction stir welded AA6061 aluminium alloy welds

Micro-arc oxidation(MAO) technique is capable of producing dense oxide films on the aluminium alloy surface. This oxide film protects the aluminium alloy from the corrosion attack for longer duration.Empirical relationships were derived to evaluate the MAO coating properties(porosity and hardness) by incorporating very important MAO parameters(current density, inter-electrode distance and oxidation time). MAO parameters were also optimized to achieve coatings with minimum porosity and maximum hardness. Further, the effect of MAO parameters on coating characteristics was analysed. From the results, it is found that the current density has greater influence on the responses than the other two parameters.

Establishing empirical relationships to predict porosity level and corrosion rate of atmospheric plasma-sprayed alumina coatings on AZ31B magnesium alloy

Plasma sprayed ceramic coatings are successfully used in many industrial applications,where high wear and corrosion resistance with thermal insulation are required.In this work,empirical relationships were developed to predict the porosity and corrosion rate of alumina coatings by incorporating independently controllable atmospheric plasma spray operational parameters(input power,stand-off distance and powder feed rate)using response surface methodology(RSM).A central composite rotatable design with three factors and five levels was chosen to minimize the number of experimental conditions.Within the scope of the design space,the input power and the stand-off distance appeared to be the most significant two parameters affecting the responses among the three investigated process parameters.A linear regression relationship was also established between porosity and corrosion rate of the alumina coatings.Further,sensitivity analysis was carried out and compared with the relative impact of three process parameters on porosity level and corrosion rate to verify the measurement errors on the values of the uncertainty in estimated parameters.

Influence of arc constriction current frequency on tensile properties and microstructural evolution of tungsten inert gas welded thin sheets of aerospace alloy

The main objective of this investigation is to study the influence of arc constriction current frequency(ACCF)on tensile properties and microstructural evolution of aerospace Alloy 718 sheets(2 mm in thickness)joined by constricted arc TIG(CA-TIG)welding process.One variable at a time approach of design of experiments(DOE)was used,in which ACCF was varied from 4 to 20 kHz at an interval of 5 levels while other parameters were kept constant.The joints welded using ACCF of 4 kHz exhibited superior tensile properties extending joint efficiency up to 99.20%.It is attributed to the grain refinement in fusion zone leading to the evolution of finer,discrete Laves phase in interdendritic areas.An increase of ACCF above 12 kHz caused severe grain growth and evolution of coarser Laves phase in fusion zone.Alloy 718 welds showed more obvious tendency for Nb segregation and Laves phase formation at higher levels of ACCF due to the slower cooling rate.The volume fraction of Laves phase was increased by 62.31%at ACCF of 20 kHz compared to that at 4 kHz,thereby reducing the tensile properties of joints.This is mainly due to the stacking of heat input in weld thermal cycles at increased levels of ACCF.

Influence of magnetically constricted arc traverse speed (MCATS) on tensile properties and microstructural characteristics of welded Inconel 718 alloy sheets

The magnetically constricted arc technique was implemented to mitigate the heat input related metallurgical problems in Gas Tungsten Arc Welding(GTAW)of Inconel 718 alloy particularly Nb segregation and subsequent laves phase evolution in fusion zone.This paper reports the direct effect of magnetically constricted arc traverse speed(MCATS)on bead profile,tensile properties and microstructural evolution of Inconel 718 alloy sheets joined by Gas Tungsten Constricted Arc Welding(GTCAW)process.The mechanism amenable for the microstructural modification and corresponding influence on the tensile properties of joints is investigated both in qualitative and quantitative manner related to the mechanics of arc constriction and pulsing.It is correlated to the solidification conditions during welding.The relationship between MCATS and Arc Constriction Current(ACC)was derived.Its interaction effect on the magnetic arc constriction and joint performance was analysed.Results showed that the joints fabricated using CATS of 70 mm/min exhibited superior tensile properties(98.39% of base metal strength with 31.50% elongation).It is attributed to the grain refinement in fusion zone microstructure leading to the evolution of finer,discrete laves phase in interdendritic areas.

Surface Modification of AH36 Steel Using ENi-P-nano TiO2 Composite Coatings Through ANN-Based Modelling and Prediction

This study aims to analyse and forecast the significance of input process parameters to obtain a better ENi-P-TiO_(2) coated surface using artificial neural networks(ANN).By varying the four process parameters with the Taguchi L9 design,fortyfive numbers of AH36 steel specimens are coated with ENi-P-TiO_(2) composites,and their microhardness values are determined.The ANN model was formulated using the input and output data obtained from the 45 specimens.The optimal design was developed based on mean squared error(MSE)and R2 values.The experimentally measured values were compared with their predicted values to determine the ANN model’s predictability.The efficiency of the ANN model is evaluated with an R2 value of 0.959 and an MSE value of 34.5634.The authors have concluded that the developed model is suitable for designing and predicting ENi-P-TiO_(2) composite coatings to avoid extensive experimentation with economic production.Scanning Electron Microscope(SEM)and X-ray diffraction analysis(XRD)are also utilised to compare the base metal and optimal coated surface.

Electrochemical corrosion behaviour of stir zone of friction stir welded dissimilar joints of AA6061 aluminium-AZ31B magnesium alloys

Joining of dissimilar metals will offer many advantages in transportation sectors such as fuel consumption,weightreduction and emission reduction.However,joining of aluminium(Al)alloys with magnesium(Mg)alloys by fusion welding processis very complicated.Friction stir welding(FSW)is a feasible method to join these two dissimilar alloys.Mixing these two metalstogether in stir zone(SZ)leads to poor corrosion resistance.In this investigation,an attempt has been made to understand thecorrosion resistance of SZ of FSWed dissimilar joints of AA6061Al alloy and AZ31B Mg alloy.Potentiodynamic polarization testwas conducted by varying chloride ion concentration,pH value of the NaCl solution and exposure time.The corroded surfaces wereanalyzed using optical microscopy,scanning electron microscopy and XRD techniques.Of these three factors investigated,exposuretime is found to be the most significant factor to influence the corrosion behaviour of SZ of friction stir welded dissimilar joints ofAl/Mg alloys.

Influence of Multi-pass Friction Stir Processing on Microstructure and Mechanical Properties of Die Cast Al–7Si–3Cu Aluminum Alloy

The influence of overlap multi-pass friction stir processing on the microstructure and the mechanical properties, in particular, strength, ductility and hardness of die cast A1-7Si-3Cu aluminum alloy was investigated. It was observed that increase in the number of overlap passes friction stir processing resulted in significant refinement and redistribution of aluminum silicon eutectic phase and elimination of casting porosities. The microstructural refinement by the friction stir processing not only increases the ultimate tensile strength from 121 to 273 MPa, but also increases the ductility as observed by the increase in fracture strain from 1.8% to 10%. Analysis of the fractured surface reveals that the microstructural refinement obtained by friction stir processing plays a vital role in transforming the fracture mode from completely mixed mode to the ductile mode of the fracture with increasing number of passes. The change in the size, shape, morphology and distribution of eutectic silicon particles and elimination of the porosities are the main reasons for the increases in tensile strength and ductility due to friction stir processing.

Effect of Welding Processes on Tensile and Impact Properties,Hardness and Microstructure of AISI 409M Ferritic Stainless Joints Fabricated by Duplex Stainless Steel Filler Metal

The effect of welding processes such as shielded metal arc welding, gas metal arc welding and gas tungsten arc welding on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade is studied. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the welded joints have been evaluated and the results are compared. From this investigatio.n, it is found that gas tungsten arc welded joints of ferritic stainless steel have superior tensile and impact properties compared with shielded metal arc and gas metal arc welded joints and this is mainly due to the presence of finer grains in fusion zone and heat affected zone.

Application of Response Surface Methodolody to Prediction of Dilution in Plasma Transferred Arc Hardfacing of Stainless Steel on Carbon Steel

The application of response surface methodology was highlighted to predict and optimize the percentage of dilution of iron-based hardfaced surface produced by the PTA （plasma tratisferred arc welding） process. The experiments were conducted based on five-factor five-level central composite rotatable design with full replication technique and a mathematical model was developed using response surface methodology. Furthermore, the response surface methodology was also used to optimize the process parameters that yielded the lowest percentage of dilution.

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 kin. 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.