Deposition Of Stellite Research Articles

Multi-track laser metal deposition of Stellite6 on martensitic stainless steel: Geometry optimization and defects suppression

Direct Laser Deposition has been considered as a method to repair and rebuild the industrial parts. Considering the possibility of the formation of structural defects due to the process parameters, assessing the selection of the optimum laser cladding parameters to minimize these defects is a crucial subject. Therefore, a model to predict the single-track geometric characteristics based on the three main process parameters namely, laser power, scanning speed and powder feed rate was presented to prevent the formation of defects in the deposition of Stellite 6 on martensitic stainless steel. Application of the linear regression method coupled with genetic optimization algorithm resulted in the optimum combined parameters (PαVβFγ), which were the basis for the generation of the process map. Eventually, based on track geometric attributes, an optimum region was introduced on the process map and to validate the capability of the prediction model, three single tracks were selected for multi-track laser deposition with a 30%, overlapping ratio concluded from derived equations. Investigation of these three multi-tracks indicated that the one with the least dilution (2.14 %) and the most wetting angle (52°), contained various defects, namely lack of fusion, delamination, and unmelted powder defect. Furthermore, the multi-track with high dilution resulted in the penetration of alloying elements from the substrate to the deposited clad and vice versa. Finally, the multi-track which was selected from the optimum region, presented the best deposited layer with no visible defects, which validated the proposed model.

Effect of correction parameters on deposition characteristics in cold metal transfer welding

ABSTRACTThe present work investigates the effect of dynamic correction (DC) and the arc length correction (ALC) parameters on the deposition of Stellite 6 filler wire on AISI H13 steel by Cold Metal Transfer (CMT) welding. The changes in the current and voltage waveforms were studied along with high-speed camera imaging of the process during single bead deposition. The effect of the arc correction parameters on the area and volumetric dilution, bead geometry, microstructure, and hardness are presented. The DC parameter influences the current waveform whereas the ALC parameter affects the voltage waveform and duration of the CMT cycle. It is shown that the ALC parameter has a strong effect on the dilution as compared to DC parameter. A wide scatter in the dilution values with similar heat input for different arc correction parameters was observed. Lower heat-input results in lower dilution and finer microstructure resulting in high hardness of the bead.

Optimization of the process of deposition of wear-resisting Stellite coatings on steel by laser radiation

Methods for the optimization of parameters of laser powder deposition of Stellite 6 on the surface of AISI 4340 steel are investigated. The methods are used in particular for depositing coatings on shafts of power engineering systems produced from this steel. Optimization was carried out using two methods: experimental–selective; processing of the experimental results by statistical models. It is shown that the experimental–selective method can be used to select several optimum conditions ensuring the highest wear resistance. Processing the experimental results using the statistical models determines the dependence of the geometrical parameters of the bead on the surfacing conditions.

Deposition of Stellite 6 on Nickel Superalloy and Mild Steel substrates with Laser Cladding

A B S T R A C T Stellite 6 was deposited by laser cladding of two different steel substrates (nickel superalloy and mild steel). The chemical compositions and microstructures of these coatings were characterized by atomic absorption spectroscopy, optical microscopy and scanning electron microscopy. The microhardness of the coatings was measured and the wear mechanism of the coatings was examined using a pin-on-plate (reciprocating) wear testing machine. The results showed less cracking and pore development for Stellite 6 coatings applied to the mild steel (MS) substrate. Further, the Stellite coating on mild steel was significantly harder than that deposited on the superalloy. The wear test results showed that the weight loss for the coating on mild steel was significantly lower than for the nickel superalloy substrate. It is concluded that the lower hardness of the coating on the nickel superalloy, together with the softer underlying substrate structure, markedly reduced the wear resistance of the Stellite 6 coating

Stellite 21 coatings on AISI 410 martensitic stainless steel by gas tungsten arc welding

Degradation of AISI 410 martensitic stainless steel, a typical alloy for many applications such as steam turbine blade, could impair its efficiency and lifetime. To overcome this problem, critical surfaces could be modified by weld cladding via gas tungsten arc welding technique. In the present research, a comparative study of Stellite 21 weld overlays deposited in three different thicknesses, i.e. dilutions, at various preheat and post-weld heat treatment temperatures on the surface of AISI 410 martensitic stainless steel, has been made. The surface of coatings has been examined to reveal their microstructures, phase characterisation and mechanical properties using XRD, microhardness tester and metallographic techniques. The results showed that the deposition of Stellite 21 coating on AISI 410 martensitic stainless steel improved its corrosion resistance. Moreover, the volumetric dilution had a considerable effect on the hardness, microstructure and electrochemical corrosion behaviour of Stellite 21 weld overlays.

The effect of localized dynamic surface preheating in laser cladding of Stellite 1

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.

Prediction and Optimisation of Weld Bead Geometry of Plasma Transferred Arc Hardfaced Valve Seat Rings

Automatic weld hardfacing is being employed increasingly in process and power industries. Plasma transferred arc welding (PTAW) has become a natural choice for automatic hardfacing due to its reliability, better process control, ease of use, low dilution and high volume production. Increasing the use of PTAW in its automatic mode, will increase dependence on the use of equations to predict the dimensions of the weld bead. The development of such mathematical equations using a five factor, five level factorial technique to predict the geometry of the weld in the deposition of Stellite 6 (Co-Cr-A) alloy onto carbon steel valve seat rings (ASTM A105) is presented. The developed models have been checked for their adequacy and significance by the F test and t test respectively. Main and interaction effects of the control factors on dilution and bead geometry are presented in a graphical form that aids rapid selection of the process parameters to achieve the desired quality of overlay. The results obtained from the mathematical models have been optimised and also tested using conformity test runs. Optimising the process parameters reduced the amount of metal deposited and enhanced the mechanical and metallurgical properties of the hardfaced layers.

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.