Scaling Up The Tribological Assessment of Laser Clad Rail to Build The Case For Field Implementation

The wheel/rail contact in railways is one of the most examined parts and from the beginning of railway travel new solutions were needed to optimise its performance. Wear and rolling contact fatigue (RCF) are the two biggest problems. Those problems directly affect the rail and wheel life in the railway industry. When rails have high deformation (taking the rail profile outside of acceptable geometrical thresholds defined by standards) or damage, they need to be taken out and replaced and that causes many delays and problems. This would be longer in lighter traffic lines, but in heavy and mostly used traffic lines the rail life is 2-3 years. Surface treatment methods increase the lifetime of rails and coating over rail surface have given good solution for those problems.
Laser cladding is an additive manufacturing coating method. It allows the same or a different type of material to be coated over a rail or wheel substrate. Laser cladding process parameters and material selections are important factors for achieving this purpose.
In this thesis work showed that laser clad coated rail specimens tested under different test scales: small-scale tests, full-scale tests in laboratory conditions and field tests with actual environmental conditions. Material selection of laser clad specimens was based on previous tests for improved wear and RCF resistance. They were compared with standard grade rails and premium rails. The clad materials were martensitic stainless steel (MSS), Stellite 6, R260, and T400. The substrate rail material used was R260 grade rail. Also, some premium rail tests were conducted for comparison: Manganese (Mn), Chromium (Cr) and R400 HT.
Small-scale twin disc tests were conducted to find the full lifespan of MSS clad and some repair solutions with MSS clad, Stellite 6 clad and R260 clad over R260 rail specimen “damage”. The premium rail specimens were analysed and compared with R260 rail specimen and MSS clad specimens. Also, laser cladding process parameters were changed with MSS clad over R260 rail and tested to find how clad “quality” affects the performance of clad specimens and how defects change or cause problems when optimal clad parameters changed. Full-scale tests were conducted to see how clad specimens and repair specimens perform under actual loading conditions. MSS clad, Stellite 6 clad and R260 un-clad pocket specimens were analysed and compared with small scale tests. A T400 rail specimen was tested for repair analysis. The results of small-scale tests were reflected in the full-scale test outcomes. In all tests the clad layers performed well in terms of wear and RCF resistance which gave the confidence needed to initiate field tests. MSS clad twin-disc experiments showed that the clad disc did not fail over 400,000 cycles. However, experiments with R260 standard grade rail discs observed failures occurring around 15,000 cycles in the literature. It is evident that the MSS clad disc exhibited at least 20-25 times higher wear and rolling contact fatigue (RCF) resistance than the standard grade rail disc. These were started, and data collection undertaken for R260 rails, HP 335 premium rails, MSS clad rails with different clad thickness, Stellite 6 clad rails, and insulated block joint (IBJ) components.