Formation of TiN Dispersed Composite Layer on Steel Surfaces by Titanium Powder Preplacement and TIG Surface Melting Processes

Abstract

The possibility of forming a TiN dispersed composite layer on steel was studied by preplacement of titanium powder on steel surface and melting under TIG (Tungsten inert gas) torch in a reactive environment. The surface melting of preplaced 1.8 mg/mm2 Ti powder was performed under TIG torch with energy inputs of 324,378 and 432 J/mm in a pure nitrogen environment. With these melting conditions, the powder layer along with a thin layer of the substrate melted and produced a melt pool of around 1mm thickness. The resolidified melt layer consisted of dispersion of TiN dendrites in ferrite matrix and thus a composite of TiN in ferrite is created on the steel surface. The concentration of dendrite population was found to be higher nearer the melt surface compared to the deeper depth. A maximum surface hardness of about 2000 Hv was developed at the surface when glazed with an energy input of 432 J/mm and the hardness decreased gradually away from the surface. The hardness development is directly related to the concentration of TiN dendrites.

Melting of multipass surface tracks in steel incorporating titanium carbide powders

“…Their formation is associated with the rapid solidification of the melt, entrapping gases which may arise from the shielding gas and also through burning off the binder used for adhering the TiC powder on to the substrate surface. 4,11,19 Pores have been reported when other melting techniques were used for surface modification work.…”

“…[1][2][3][4][5][6][7][8] However, application of these techniques is limited in practice because of the high costs of the equipment. Previous surface engineering work using the tungsten inert gas (TIG) welding torch melting technique, [9][10][11][12][13][14][15][16][17][18][19] produced either a small hemispherical volume of a modified surface, or a single melt track with a width of a few millimetres running the length of the specimen. However, in many service applications there is frequently a requirement to modify a much greater surface area.…”

Comparison of empirical and predicted substrate temperature during surface melting of microalloyed steel using TIG technique and considering three shielding gases

“…Following [11][12][13][14][15][16][17], the boundary condition on the TIG affected boundary is proposed to be ( , 10, ) = 0 + (P/kd) −( ( − ) 2 ) + (Pβ/kd)(1/(x-vt)) 2 (Eq.4)…”

“…Techniques such as high powered lasers for transformation hardening [1] surface melting [2][3][4] and development of surface metal matrix composites [4][5][6][7][8] are well established. More recently the tungsten inert gas (TIG) technique has been explored as a heat source for the surface modification of steels as a much cheaper option than lasers [9][10][11][12]. Both techniques require a gaseous shielding atmosphere, usually 2, Ar, He, CO2 or mixture of these gases.…”

Effect of shielding gas and energy input rate on the surface geometry and microstructure of a microalloyed steel surface melted with a TIG torch

“…For structural engineering applications where the surfaces will be in moving contact, it is recommended that the surface microstructure is modified to a depth ≥ 1mm. This can be achieved by a melting process provided by a high energy source, such as a laser [2][3][4][5][6] or a TIG torch [7][8][9][10]. Molten surfaces must be protected from the atmosphere by shielding gases.…”