Cold metal transfer (CMT) technology - An overview

The study of dissimilar metals’ welding is an important issue due to their increasing applications in many industrial fields. Welding of dissimilar metals is challenging because of the formation of large residual stress and brittle intermetallic compounds (IMCs). In order to solve this problem, intermediate interlayers were used to eliminate or inhibit the formation of brittle intermetallic reaction layers in many welding techniques, such as diffusion bonding, laser welding, electron beam welding, and other welding techniques. The aim of this paper is to review the recent progress of dissimilar metals’ welding methods and mechanisms with interlayer to offer a basis for the following research. The work discussed several criteria for the selection of interlayer, such as physical properties, metallurgical compatibility, mode, and thickness of the interlayer. Then, formation enthalpy, Gibbs energy of formation (ΔG), and brittleness of the IMCs, as well as welding parameters, were also discussed. Simultaneously, the present work had proposed a design guideline for the selection of interlayer in dissimilar metals’ welding to acquire a welded joint with good quality.

A review on dissimilar metals’ welding methods and mechanisms with interlayer

Investigations on the parametric effects of cold metal transfer process on the microstructural aspects in AA6061

A study of microstructure and volumetric dilution of Cold Metal Transfer (CMT) clad of Nickel based super alloy, Inconel 617M on type 316L stainless steel (SS) substrate was carried out. Overlay coatings were deposited at three different current inputs (80, 90 and 100 A) to synergetic CMT welding set while the wire feed rate and pulse frequency were pre-programmed. The ability of CMT to produce very low dilution and low heat input with the minimal heat affected zone (HAZ), when compared to conventional Tungsten Inert Gas welding (TIG) process was successfully demonstrated. Detailed microstructural evaluation of the cross sections revealed porosity and crack free Inconel 617M overlay with complete fusion, making a metallurgical bonding at the interface. Transverse micro Vickers hardness evaluation from clad to substrate showed the absence of significant HAZ for overlay produced by CMT. Calculation of percentage volumetric dilution, based on elemental Energy Dispersive Spectroscopy (EDS) of Fe-K counts, revealed that the cladding deposited at 100 A current exhibited low dilution value of 6.3% at 100 μm away from the interface while clad produced by TIG show significantly higher dilution value of ~50% at 100 μm from interface. Electron Backscattered Diffraction (EBSD) studies revealed morphology similar to epitaxial growth, with same crystallographic orientation of grains across the interface for CMT overlaid coatings.

Weld overlay coating of Inconel 617 M on type 316 L stainless steel by cold metal transfer process

Microstructure and mechanical properties of Co-based alloy coatings fabricated by laser cladding and plasma arc spray welding

Cold metal transfer (CMT) welding is a new gas metal arc welding process having several advantages such as low heat input and spatter free welding. This makes it of great advantage in weld cladding applications. In this study, hardfacing of AISI H13 die steel with Stellite 21 alloy has been carried using CMT process. Coatings were deposited on H13 substrate in annealed as well as quenched & tempered (Q&T) condition at room temperature as well as with a preheat of 400 °C. The Q&T substrate with and without preheat and the annealed substrate without preheat were found to be susceptible to underbead cracking upon Stellite deposition. The cracking in the heat affected zone (HAZ) was due to formation of brittle martensite upon rapid cooling which is associated with formation of high tensile residual stresses at the bead toe. The annealed substrate with preheat of 400 °C showed the least cracking tendency. The cracking tendency was investigated by studying the variation of the microstructure and microhardness along the depth of HAZ. The dilution levels based on Fe content was found to be 3–4%, which was considerably lower than that of conventional arc welding deposits. The Stellite coated H13 plate (annealed with preheat) could be successfully subjected to quenching & tempering heat treatment to restore the properties of the substrate without introducing any defects.

Hardfacing of AISI H13 tool steel with Stellite 21 alloy using cold metal transfer welding process

The cold metal transfer (CMT) process was explored as a weld overlay technique for synthesizing Al-Si-Mn alloy coating on a commercially pure Al plate. The effect of welding speed on the bead geometry, deposition rate, and the dilution were studied and the best parameter was used to synthesize the coatings. The CMT process can be used to produce thick coatings (>2.5 mm) without porosity and with low dilution levels. The Vickers hardness number of the Al substrate increased from 28 in the bulk to 57 in the coating. It is suggested that the CMT process can be an effective and energy-efficient technique for depositing thick coatings and is useful in weld repair of aluminum alloy components.

Al-Si-Mn Alloy Coating on Aluminum Substrate Using Cold Metal Transfer (CMT) Welding Technique

A comparative study of the Stellite 21 hardfacing on H13 steel produced by cold metal transfer (CMT) process and conventional plasma transferred arc welding (PTAW) process was carried out The lower heat input of the CMT process resulted in finer microstructure and lesser dilution in the Stellite 21 coating than the PTAW process The volumetric dilution values showed much scatter across the thickness of the PTAW coating than CMT The effect of lower dilution and finer structure of the CMT coating resulted in a marginal increase in the microhardness The room temperature (RT) and high temperature (600 °C) wear performance of the coatings were studied using a ball-on-disc tribometer using alumina ball The wear tracks were analyzed using an optical profilometer and the volume loss was calculated The CMT deposited coating showed better wear performance than PTAW coating X-ray diffraction (studies of the room temperature wear tracks showed the transformation of γ-fcc phase in the as-deposited coating to e-hcp phase after the wear The volume percentage of the e-hcp was observed higher for CMT deposited coating than the PTAW coatings, which can be attributed to lower dilution and finer microstructure of the former

Comparison of microstructure, dilution and wear behavior of Stellite 21 hardfacing on H13 steel using cold metal transfer and plasma transferred arc welding processes

The 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 Transf...

G. P. Rajeev

Papers

Hardfacing of AISI H13 tool steel with Stellite 21 alloy using cold metal transfer welding process

Al-Si-Mn Alloy Coating on Aluminum Substrate Using Cold Metal Transfer (CMT) Welding Technique

Comparison of microstructure, dilution and wear behavior of Stellite 21 hardfacing on H13 steel using cold metal transfer and plasma transferred arc welding processes

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

Microstructure and high temperature mechanical properties of wire arc additively deposited Stellite 6 alloy