Pump operators know that impellers face relentless stress. Cavitation, abrasive sediment, and corrosive fluids steadily erode surfaces, raising energy use and driving up maintenance costs. Surface coatings are one way to improve performance, and recent research has explored how the Twin Wire Arc Spray (TWAS) process performs when applied to stainless steel pump impellers.
The study, published in Scientific Reports, was led by Dr Deni Fajar Fitriyana of the Department of Mechanical Engineering, Universitas Negeri Semarang. Working alongside Dr Windy Desti Puspitasari, the team investigated an iron (Fe)-based alloy coating primarily composed of chromium (Cr), boron (B), manganese (Mn), and silicon (Si), chemically known as FeCrBMnSi, applied over a intermetallic nickel and aluminium (NiAl) alloy bond coat on 304 stainless steel substrates. They examined two levels of surface roughness (35 µm and 40 µm) and three preheat temperatures (50 °C, 100 °C, and 150 °C). Testing included hardness, adhesion, porosity, and corrosion resistance, using light microscopy and scanning electron microscopy.
Findings showed that greater surface roughness combined with higher preheat temperatures produced denser coatings with lower porosity and fewer unmelted particles. This directly improved hardness and adhesion. The best result came from a 40 µm substrate preheated to 150 °C, which achieved a hardness of 1114.6 HV and bonding strength of 20.29 MPa. By comparison, uncoated stainless steel measured 206.8 HV, confirming a 360–439 per cent improvement in hardness.
Coating thickness decreased with higher roughness and temperature, creating thinner yet tougher layers. Corrosion resistance, however, was still below that of uncoated 304 stainless steel, which benefits from a naturally protective chromium oxide layer. The coated samples showed higher corrosion rates, highlighting a need for further development to balance mechanical strength with corrosion performance.
For pump engineers, the study reinforces how surface preparation and temperature control during TWAS directly affect coating outcomes. Optimised settings can deliver the hardness and adhesion levels required for impellers, even if corrosion remains a challenge for future refinement.
