Composite Coating on Steel Surfaces by Adding TiC and h-BN Particulates under TIG Torch Melting

Abstract

Wear is a common problem for engineering components subjected to dynamic loading. Surface modification is mostly applied to reduce the wear. An exploratory research is conducted to form a composite coating on AISI 4340 steel surfaces by incorporating a mixture of TiC and hexagonal Boron Nitride (h-BN) particulates using powder placement and TIG torch melting techniques. Initial results show the evidence of TiC incorporation in all tracks but the presence of h-BN is limited in a few tracks. However, processing conditions are identified that can produce composite coatings incorporating both TiC and h-BN particulates. The melt microstructure consists of a small amount of un-melted TiC and h-BN, partially melted TiC particulates with eutectic structure containing precipitated TiC and TiB2 particles. Hardness of the coating is found to fluctuate along the melt depth. However, the maximum hardness of the coating is about 3 times the base hardness of 250 HV.

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

“…These types of TiC distribution and segregation have also been reported in laser processed MMC coatings on titanium surfaces 7 and TIG torch processed coatings on titanium and steel surfaces. 21,27,[32][33][34][35] TiC precipitates of globular, cubic and flower morphologies were seen in many overlapping tracks, but were not uniformly distributed in the melt microstructures. Similar morphologies of TiC precipitates were also reported in single track composite coatings.…”

Wear behaviour at 600°C of surface engineered low-alloy steel containing TiC particles

“…This result was the culmination of a series of trials using different amounts of preplaced powder with different energy inputs. The Gaussian energy distribution of the TIG torch that determines the heat intensity for narrow melt depths generates more melt in the centre and is gradually depleted towards the edges [6][7][8][9][10][11][12]. Therefore, when making use of this energy distribution for fabricating a surface area through multipass tracking, each single melt track was overlapped 50% by the next track.…”

“…An AISI 4340 low-alloy steel, composition: 0.4C-0.7Mn-0.20Si-0.04S-0.035P-0.8Cr-1.65Ni-0.20Mo, remainder Fe (all wt-%), was cleaned with ethyl alcohol, and TiC particulates, 45-100 μm in size, after mixing with a PVA binder, were preplaced at 1 mg mm −2 on the steel surface. The sample preparation before the TIG melting process to produce the single and multipass tracks is described in previous publications [6][7][8][9][10][11][12]. In single track melting, the TIG torch was scanned over the preplaced powder as shown in Figure 1, while for multipass track processing, which is necessary to cover an area, each track was overlapped by 50%.…”

“…If the material used is below the required specification, the consequences may be devastating, as the operating system can easily lose the permissible tolerance, leading to malfunction. Several materials such as titanium alloys, aluminium alloys and carbon steels are known for their proneness to severe wear, due to their reduction of hardness and strength from thermal softening effects, and require surface reinforcement, especially when operating at high temperatures [1][2][3][4][5][6][7]. To overcome these problems, the ubiquitous tungsten inert gas (TIG) technique that is cheap, flexible and low in operating and maintenance costs has been used to develop superior surfaces to the parent materials compared to the expensive and complex lasers or electron beam techniques [6][7][8][9][10][11][12][13].…”

“…Several materials such as titanium alloys, aluminium alloys and carbon steels are known for their proneness to severe wear, due to their reduction of hardness and strength from thermal softening effects, and require surface reinforcement, especially when operating at high temperatures [1][2][3][4][5][6][7]. To overcome these problems, the ubiquitous tungsten inert gas (TIG) technique that is cheap, flexible and low in operating and maintenance costs has been used to develop superior surfaces to the parent materials compared to the expensive and complex lasers or electron beam techniques [6][7][8][9][10][11][12][13]. Improving the wear resistance of alloys requires a significant knowledge of the material to be surface engineered and how the chosen process controls the microstructure of the modified surface.…”