30 credits – High temperature corrosion in exhaust application for heavy-duty trucks i Sodertalje

Scania genomgår nu en transformation från att vara en leverantör av lastbilar, bussar och motorer till en leverantör av kompletta och hållbara transportlösningar.

Ingress:
The Materials Technology department in Sodertalje evaluates materials for the present and future needs of Scania. As Scania moves towards vehicles powered by biofuel, the material issues are of great importance.

Background:
Scania aims at lowering the carbon dioxide emissions from trucks. The use of different biofuels is one option, and Scania has in recent years introduced vehicles fuelled by ethanol, gas and biodiesel. Both ethanol and gas vehicles use the spark ignited Otto engine instead of the Diesel engine. This implies higher exhaust gas temperatures and increased material challenges compared to diesel engines. High temperature corrosion is one of the identified issues that is important to characterise in order to choose the most suitable material.

High temperature corrosion is the reaction of a gas with a material at temperatures above the dew point of the gas, typically above 250°C. For iron-based materials used in an engine, the high temperature corrosion is manifested as formation of oxides. Despite the name – high temperature corrosion – the formation of oxides on the surface can protect the underlying metal from further oxidation if the right alloying is chosen. Up to approximately 500°C, iron oxides can be protective, but at higher temperatures, aluminium, silicon and/or chromium are needed to form protective oxides. The formed oxides may spall at thermal variations and new oxide will form. The spallation will with time deplete the underlying material of oxide forming elements and the protection is lost.

Target:
Four candidate materials will be exposed in thermal cycling and isothermal experiments. The target is to evaluate the materials regarding high temperature corrosion and characterise the obtained oxide layers after different high temperature exposures.

Assignment:
The thesis will be divided in four parts

1. Literature study of cast materials in exhaust environment and their high temperature corrosion properties. For future comparison of the results, also wrought materials will be included.
2. Experimental work: Exposures of the candidate materials in exhaust environment and air. The exposures in exhaust environment will be performed in a thermal cyclic furnace to simulate the large scale thermal variation of the truck during the day.
3. Analysis and simulation: Characterisation of the formed oxide layers and possibly nitrides by scanning electron microscopy including element analysis (SEM/EDS). Also earlier exposed samples will be included. The results could be compared with results from wrought materials, to elucidate the differences and similarities in high temperature corrosion behaviour. Simulation using ThermoCalc is included to explain differences among the materials and expected behaviour.
4. Report

Education:
MSc/Civilingenjör in Materials technology, Chemical Engineering or similar. Merit: Earlier experience of ThermoCalc
Number of students: 1
Start date: January 2019
Estimated time needed: 20 weeks

Contact persons and supervisors:
Thesis supervisor: Ragna Elger, , 08/553 854 12
Group Manager: Jan Linder, , 08/553 814 65