Date of Award


Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Materials Science and Engineering (MS)

Administrative Home Department

Department of Materials Science and Engineering

Advisor 1

Paul Sanders

Committee Member 1

Douglas Swenson

Committee Member 2

Stephen Kampe


Brake rotor composition and microstructure must be optimized for thermal and mechanical performance to avoid thermal-mechanical cracking, excessive wear, and to reduce noise. Niobium is an element that increases the strength and wear resistance of gray iron; however, the interaction of niobium with other common alloying elements (chromium and molybdenum) is not well understood. Thirteen gray cast iron alloys were produced with varying levels of carbon equivalent (CE), Cr, Mo, and Nb. Bars with four different diameters (8, 14, 22, and 30 mm) were cast from each alloy and microstructural and physical properties such as graphite flake morphology, pearlite spacing, electrical resistivity, and thermal diffusivity were measured. Mechanical measurements included tensile testing from ambient up to 680°C and room temperature pearlite microhardness, macro Brinell hardness, and ASTM G65 sand abrasion wear testing. Fluidity was measured using a purpose-built finger mold. It was found that niobium refined the graphite morphology, reduced pearlite spacing, and precipitated eutectic NbC. High CE rotors are attractive for their higher thermal and damping properties, but they have lower mechanical and wear properties than low CE iron. It was found that alloying high CE gray iron with small amounts of chromium and niobium can provide good mechanical and thermal properties while simultaneously increasing wear resistance.