Unveiling the pitting corrosion degradation response and the structural propagation of composite break block failure in different medium

Abstract

Failure in manufacturing, aerospace, marine, construction, and locomotive industries often stems from issues like fracture, corrosion, wear, distortion, and erosion. This research investigates the failure of railway composite brake block materials in different environments. Tests were conducted on used composite brake blocks in three media: 1.75% and 3.5% wt NaCl, 0.5 M and 1 M HCl and H₂SO₄. Corrosion analysis utilized linear polarization and open circuit techniques with a potentiostat/galvanostat. Microstructure, crystallography, and hardness were characterized using SEM/EDS, X-ray diffraction, and a digital superficial Brinell hardness tester. Results showed a hardness of 238.3 kgf/mm² for the controlled sample, 236.8 kgf/mm² for NaCl, and lower values of 233.4 kgf/mm² and 233.6 kgf/mm² for HCl and H₂SO₄, respectively. Corrosion rates were highest in acidic media, with 5.2390 mm/year for H₂SO₄ and 5.1342 mm/year for HCl, compared to 2.51662 mm/year in NaCl. SEM/EDS analysis revealed pronounced pitting in acidic media and uniform pits in chloride media. Phase formation indicated the presence of chloride halides and sulfide compounds like Fe(OCl) and C₂(Fe, Na)CuCl. The primary components of the brake block were iron, silicon, aluminum, and carbon. Acidic environments accelerate failure due to weak bonding in the composite, while chloride systems demonstrate higher stability in rail applications.