Material characterization-based wear mechanism investigation for biomass hammer mills

Biomass, as harvested, is composed of inorganic compounds both intrinsically and extrinsically and can be quite abrasive. The present study investigates the wear modes and mechanisms of two types of blades of hammer mills used in biomass size reduction (impacting particle size and distribution) and densification (impacting size, shape, and density). The dominant wear modes for the stage 1 steel blades are determined to be erosive and polishing wear. For the stage 2 blades with a carbide weld overlay, the main wear mechanisms are erosion and fracture. Partial replacement of Co by Fe in the outer layer of carbide grits, likely induced by diffusion during the high-temperature welding, has been correlated to the microcracking observed. The microcracking is believed to weaken the grit strength and fracture toughness and make the overlay prone to fracture and erosion due to repetitive contact with the inorganic contents in chopping biomass.