30131 - Mechanical Metallurgy M

Learning outcomes

The aim of this course is to illustrate the mechanical behaviour of metallic materials, under different service conditions. Starting from the basic relationship between microstructure and mechanical properties, the main metallurgical aspects influencing the static and fatigue resistance, the low and high temperature behaviour, as well as the wear resistance, will be presented and discussed. The effects of the production technique, including solidification conditions, plastic deformation, heat treatment or surface engineering modifications, will be evidenced. The characteristics of the main engineering metallic materials will be presented, including: iron-based alloys, aluminium and titanium alloys, metal matrix composites. By the end of this course one should have the ability to select the material and the processing conditions more suitable for the design and construction of reliable mechanical components.

Course contents

Plastic deformation of metals. Plastic deformation by slip due to dislocation motion and by twinning. Effect of crystal structure on plasticity. Properties of dislocations. Strengthening mechanisms of metals.

Cold plastic deformation. Flow curve and strain hardening exponent. Effect of crystal structure on strain hardening.The role of stacking-fault energy. Applications of the strain hardening mechanism. Effect of cold working on microstructure and mechanical properties.

Warm and hot working: recovery and recrystallization processes. Variables affecting recrystallization. Examples of application of recrystallization: extrusion and Friction Stir Welding.

Short recalls to Fe-C phase diagram, main phase transformation in steels, designation of steels.

Extra-low carbon steels for cold forming: traditional and innovative steels (Interstitial Free e Bake Hardening).

Carbon-manganese steels for structural applications and high strength low alloy steels (HSLA): chemical composition, production processes, heat and thermomechanical treatments, microstructure and mechanical properties, applications.

Multi-phase advanced high strength steels: Dual-Phase (DP) e Transformation Induced Plasticity (TRIP) steels.

Special steels for high mechanically loaded components: quenched and tempered, carburised, nitrided, carbonitrided and nitrocarburised. Springs and bearings steels. Bainitic steels. Maraging steels.

Stainless steels: ferritic, martensitic, austenitic, duplex and precipitation hardening.

Failure analysis. Fractography: brittle and ductile failure. Metallography. The role of optical and scanning electron microscopes.

Impact and fracture toughness. The ductile to brittle transition: effect of crystal structure, chemical composition, hydrogen embrittlement, heat treatment and nuclear irradiation. A short introduction to linear elastic fracture mechanics: stress intensity factor and fracture toughness.

Fatigue – The role of crystal structure and dislocation on fatigue failure. Metallurgical and mechanical aspects of fatigue. The role of solidification defectes, heat treatment and surface modification techniques on fatigue strength. Case studies on fatigue failed components.

Tribology - The theory of friction and its control. Processes and mechanisms of wear of main mechanical components. Selection criteria of materials and treatments to control friction and wear. Case studies on mechanical components subjected to tribological problems.

High temperature deformation and failure: creep and superplasticity. Materials for high temperature applications: superalloys.

Cast and wrought Al alloys: designation, alloying elements, strengthening mechanisms, heat treatments, properties and applications. Case studies on Al based mechanical components.

Titanium alloys:designation, alloying elements, strengthening mechanisms, heat treatments, properties and applications. Case studies on Ti based mechanical components.

Metal matrix composites.

Readings/Bibliography

Course Material (slides and notes)

G.M. Paolucci, “Appunti dalle lezioni di Metallurgia per la laurea in Ingegneria Meccanica” Vol.1-2, Edizioni Libreria Progetto, Padova

W. Nicodemi “Metallurgia - Principi generali”, Zanichelli

W. Nicodemi “Acciai e leghe non ferrose”, Zanichelli

A. Cigada, T. Pastore "Struttura e proprietà dei materiali metallici", McGraw-Hill

G.E. Dieter "Mechanical Metallurgy", Mc Graw Hill

Teaching methods

Lectures according to the timetable. Pratice in laboratory

Assessment methods

Oral examination

Teaching tools

PC and projector, blackboard. Teaching lab (equipment for materialographic preparation;optical and stereo microscopy with image analyser; hardness testers; tensile tester) and research labs.

Office hours

See the website of Lorella Ceschini