A systematic research into the cladding of stellite 6 on stainless steel by pulsed Nd:YAG laser has been carried out. The effects of pulse energy, pulse frequency, powder mass flow rate and spot overlap on the clad layer height, dilution and heat-affected zone (HAZ) have been examined. It was found that both the clad height and penetration into the substrate increase with the pulse energy, spot overlap and pulse frequency, but the effects of these parameters on dilution are complex. The dilution reaches the lowest value (4%) at the incident energy of 18 and 25 J/ pulse, spot overlap of 89% and pulse frequency of 40 Hz. The powder mass flow rate of 22 g/min (for energy of 25 J/pulse and spot overlap of 83%) produces thick clad layer with low dilution but results in the formation of defects. The hardness of the clad layer decreases linearly with increasing dilution. No cracks have been found in single-track clad layers at a spot overlap of 89%, however, cracks occurred at lower spot overlap. These cracks were eliminated by the multi-track cladding when the track increment is less than 1/3 of the width of track, which is believed to be due to the remelting or heat treatment of the previous clad track by the subsequent track. The track bands in multi-track clad show coarser structure, higher element segregation and lower hardness.

Pulsed Nd:YAG laser cladding of stellite 6 on stainless steel

Microstructure and mechanical properties of TiC-Ni coating on AISI304 steel produced by TIG cladding process

Surface Engineering Of Light Alloys Aluminium Magnesium And Titanium Alloys

An overlapping composite track coating was produced on a steel surface by preplacing a 0·5 mm thick layer of TiC powder and then melting using a tungsten inert gas torch of constant energy input. The influence of the overlapping operation on preheating of the substrate, the dissolution of TiC particulates and the subsequent depth and hardness of the composite layer was analysed. The melt microstructure consisted of both undissolved and partially dissolved TiC particulates, together with a variety of morphologies and sizes of TiC particles precipitated during solidification. Preheating, resulting from the overlapping operation, occurred, producing additional melting of the TiC particulates and deeper melt depths but with a reduced volume fraction of TiC precipitates in the subsequent tracks. A maximum hardness of over 800 HV was developed in the composite layer. The high hardness was unevenly distributed in tracks melted at the initial and final stages, while it varied across the melt depths in oth...

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Overlapping tracks processed by TIG melting TiC preplaced powder on low alloy steel surfaces

Overlapping tracks were processed by melting preplaced titanium carbide (TiC) powder on steel surfaces using a tungsten inert gas torch. The tracks produced ∼1·0 mm melt depth free from cracks, but occasional pores were observed. The microstructure consisted of unmelted and partially melted TiC particulates together with reprecipitated TiC particles, which were prominent in tracks processed in the initial stage. A greater number of reprecipitated globular and cubic TiC particles were observed in tracks processed in the later stages, indicating more dissolution of TiC particulates from the overlapping operation. Those multitracks processed in the initial stage developed a maximum hardness of 850–1000 HV, which was lower in most other tracks, although comparable hardness values were recorded in the last track.

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Melting of multipass surface tracks in steel incorporating titanium carbide powders

The use of a tungsten inert gas (TIG) welding torch has resulted in the development of an economical route for surface engineering of alloys, giving similar results to the more expensive high power laser. Owing to the preheating generated by both techniques, the extent of the temperature rise is sufficient to produce significant changes to the melt dimensions, microstructure and properties between the first and last tracks melted during the coating of a complete surface. The present study examines if similar changes can occur between the start and finish locations of a single track of 50 mm length. The results show that for a TIG melted surface of a microalloy steel substrate, with or without incorporating preplaced SiC particles, in either argon or argon–helium environments, a maximum temperature of 375°C developed in the second third of the track. Even over this short distance, a hardness decrease of >300 HV was recorded in the resolidified SiC coated substrate melt zone, microstructure of a cas...

Influence of shielding gases on preheat produced in surface coatings incorporating SiC particulates into microalloy steel using TIG technique

A surface engineering technique based on a tungsten inert gas (TIG) torch was used to melt single tracks on the surface of a microalloyed steel with a hardness of 150 HV. The influence of three shielding gases, argon, helium and nitrogen, on the microstructure and hardness of the re-solidified surfaces was analysed. In all melting techniques, the heat generated by the source is normally conducted to the substrate ahead of the torch and has been described as ‘preheat’. This leads to a gradually higher substrate temperature, from the start to the finish of a melted surface track. The aim of this research was to analyse any inhomogeneities in the microstructure, due to ‘preheat’, which is rarely considered in the published literature. Three thermocouples were located along the melted track in order to record the temperature at three different points. An energy input of ~840 J/mm was used in each experiment, and the results show that the maximum temperature recorded by the last thermocouple, No three ...

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Effect of shielding gas on the properties and microstructure of melted steel surface using a TIG torch

A comparison of a coating of Fe–Cr–B alloy powder processed on a plain carbon steel by surface melting using either laser or gas tungsten arc welding (GTAW) torch was made. The alloy powder was injected in laser melted surface, while the preplaced powder was melted using the GTAW technique. The topography of the GTAW tracks showed a relatively smooth surface, but the laser track surface was very rough. Because of high energy input, the GTAW method produced very wide and deep tracks with a high dilution compared to those of the laser tracks. Pores and fine cracks were seen in laser tracks; the cracks were elongated across the track width, and some of them propagated down to the melt depth. The GTAW track produced at a low energy was free from any cracking, but a centreline crack was present when processed at a high energy input.

neville Baker

Papers

Influence of shielding gases on preheat produced in surface coatings incorporating SiC particulates into microalloy steel using TIG technique

Effect of shielding gas on the properties and microstructure of melted steel surface using a TIG torch

Laser and GTAW torch processing of Fe-Cr-B coatings on steel : Part I - melt features

Oxidation protection behaviour of titanium aluminide coatings develped by TIG technique