Influence of Mg and Si Content in Aluminium Alloys on Severe Plastic Deformation Behaviour during Solid-State Coating Deposition using Friction Surfacing

Support code: HA 7834/1-1

Duration: Mai 5th, 2017 – April 30th, 2020

Abstract:
Dynamic recrystallization has a major influence on process characteristics and material flow in friction-based solid state joining techniques. In addition to general material properties, a.o. heat capacity and high temperature strength, dynamic microstructural processes, e.g. dislocation movement, grain boundary migration, formation of substructures or precipitation of phases, have a strong effect on the acting flow stresses. Small changes in the content of alloying elements, e.g. in Aluminium alloys, require significant adaptations of the process parameters, which are to date established by empirical or statistical approaches.

In the scope of this project 6 custom-made Aluminium alloys are processed by Friction Surfacing (FS), in cooperation with the Helmholtz-Zentrum Geesthacht. Each of these alloys only differs in its content of Mg or Si, allowing a direct comparison and therewith the investigation of the effects of those alloying elements on the material behaviour. The Si content will be raised up to 17.5 wt%, providing undissolvable hard phases during processing, which will further influence the deformation and recrystallization mechanisms. Besides examining process forces and coating geometry, XRD, EBSD and TEM investigations of the microstructural mechanisms of plastic deformation will be carried out, and correlated with the material behaviour during FS.

Research area: Materials Science, Severe Plastic Deformation

Contact: Dr.-Ing. Stefanie Hanke

Metallurgical mechanisms of cyclic plastic deformation by High Pressure Torsional Fatigue (HPTF)

Program for the Advancement of Excellent Young Researchers (by University Duisburg-Essen)

Duration: August 1st, 2017 – December 31st, 2018

Abstract:
Plastic deformation of metals and alloys has been used for centuries to modify their properties and increase their strength. In recent times the generation of nanocrystalline microstructures by severe plastic deformation (SPD) has become a topic of high scientific interest. The very high strains achieved by SPD techniques are realized through the superposition of hydrostatic pressure, and lead to recrystallization at low temperatures. Thereby the grain size can be decreased into the nm-scale. Classical SPD techniques are based on monotonic deformation. In the scope of this project it will be investigated, wether the cyclic accumulation of plastic strains can lead to comparable effects. By torsional loading various strains and strain rates will be introduced into the material across the radius of cylindrical samples. Which microstructural mechanisms take place under this kind of loading will be clarified through electron microscopy.

Research area: Materials Science, Severe Plastic Deformation

Contact: Dr.-Ing. Stefanie Hanke

Monitoring and Quantification of Cavitation Corrosion Erosion through Electrochemical Noise Method

DFG – Grants to Support the Initiation of International Collaboration

Project number: 407436768

Duration: June 1st, 2018 – August 31st, 2018

Abstract:
Cavitation corrosion erosion results from the interaction of mechanical and chemical phenomena, which contributes to material removal from mechanically eroding surfaces exposed in corrosive environments. The synergism between cavitation erosion (mechanical factor) and corrosion (electrochemical factor) during cavitation corrosion erosion can cause an overall material loss greater than the sum of the material loss as it would be produced by each mechanism acting separately. This is the result of effect of corrosion on cavitation erosion as well as the effect of cavitation erosion on corrosion.

In a first step, the possibility of monitoring and quantification of cavitation corrosion erosion using a non-destructive method, i.e., the electrochemical noise technique (ECN) is investigated. A possible application to marine components is of strong interest for future research, aiming at monitoring the material deterioration and developing methods to predict the remaining service life.

In this project, a collaboration between Dr.-Ing. Stefanie Hanke (Materials Science and Engineering, Uni DUE), Dr. Morteza Abedini (Department of Metallurgy and Materials Engineering, University of Kashan, Iran) and Dr. rer.nat. Fabian Reuter (Institute of Ship Technology, Ocean Engineering and Transport Systems, Uni DUE) is initiated.

Research area: Tribology, Corrosion, Cavitation

Contact: Dr.-Ing. Stefanie Hanke

Bionische Werkzeugkonzepte für die schädigungsfreie Bearbeitung von modernen faserverstärkten Hochleistungspolymeren

Support Code: Pr-2012-0002

Duration: Januar 1st, 2013 - Dezember 31st, 2014

Abstract:
Für die in einem breiten gesellschaftlichen Konsens als notwendig erachtete Reduzierung der CO2‐Emissionen
spielt der Leichtbau, vor allem in der Fahrzeug‐ und Luftfahrttechnik, eine zentrale Rolle. Besonders die Verwendung
kohlenstofffaserverstärkter Kunststoffe (CFK), die ein geringes Gewicht bei gleichzeitig hoher Festigkeit
zeigen, gilt hierfür als geeignetes Mittel. Diesem Vorteil stehen allerdings Nachteile in Bezug auf die Fertigung
entgegen. Vor allem die spanende Bearbeitung ist schwierig, weil die Kohlenstofffasern einen starken
Verschleiß an den Werkzeugschneiden bewirken, die somit schnell stumpf werden, was zu Schädigungen der
CFK bei der Bearbeitung führt. Die Natur zeigt für Probleme dieser Art einen Lösungsansatz: Nagetierzähne
schärfen sich selbst nach. Durch geschickte Kombination harter und weicher Bestandteile wird der Schneidenverschleiß
nicht vermieden, sondern so gesteuert, dass der Materialverlust nicht zum Abstumpfen, sondern
zum Schärfen der Schneide führt. Dieses Konzept lässt sich auf technische Anwendungen übertragen und wurde
für Schneidanwendungen erfolgreich umgesetzt. Im hier beantragten Projekt soll das Konzept auf einen
Zerspanprozess übertragen werden. Dazu werden unterschiedliche Schichtkonzepte und Schnittparameter
untersucht. Sowohl das Werkzeug als auch das zerspante Material werden werkstoffkundlich eingehend analysiert,
um die Werkzeugverschleiß‐ und Werkstoffschädigungsmechanismen zu verstehen und auf dieser Basis
den Selbstschärfungseffekt zu optimieren und die Grundlagen für die industrielle Anwendung zu erarbeiten.

Contact: Dipl.-Ing. Priska Stemmer

Research area: Material Science

Erhöhung von Leistungsdichte und Lebensdauer hochbelasteter Funktionsflächen durch spanende Oberflächenkonditionierung

Support Code: Pr-2011-0002

Duration: Januar 1st, 2012 - Dezember 31st, 2013

Abstract:
Die heutigen Wettbewerbsbedingungen und politischen Vorgaben fordern ein ständig höheres technisches Niveau von Produkten bei stetig steigenden Beanspruchungen und erhöhter Verfügbarkeit. Dieses führt dazu, dass tribotechnische Systeme, die früher unter hydrodynamischen oder elastohydrodynamischen Bedingungen betrieben wurden, zunehmend unter reibungs- und verschleißintensiveren Misch- und Grenzreibungsbedingungen eingesetzt werden. Dies gilt u.A. für Motorkomponenten im Ventiltrieb, Windkraftgetriebe und Hartgewebeimplantate bei Verschleißraten unterhalb von 3 nm/h im Bereich des sog. (ultra-mild wear). Die niedrige Verschleißrate hängt dabei im Wesentlichen von der Ausbildung einer stabilen oberflächigen Grenzschicht - dem sog. Tribomaterial - ab, das strukturell und chemisch gegenüber dem Grundwerkstoff verändert ist. Tribomaterial wird in der Einlaufphase erzeugt. Dabei treten Verschleißraten auf, die drei bis sechs Größenordnungen größer sind als in der daran anschließenden stationären Phase, in der sich das Tribomaterial aufgrund seiner nanoskaligen Struktur ständig regeneriert. In diesem Projekt geht es darum, den Einlauf zu verkürzen oder ganz zu unterdrücken und eine durch eine gezielte spanende Endbearbeitung entsprechend bzgl. Topographie und Tribomaterial optimierte Oberfläche vorliegen zu
haben. Das stabile Tribomaterial ergäbe sich damit nicht mehr zufällig im Einsatz sondern würde gezielt werkstoff- und belastungsabhängig in der Endfertigung erzeugt. Die genauen Wechselwirkungen aller beteiligten Elemente sind bis heute nicht geklärt. Deshalb soll wissenschaftlich untersucht werden, welche Parameter für die Induktion (hier: spanende Endfertigung) und welche Mechanismen für die Regeneration (hier: Gleitverschleiß unter „ultra-mild wear“ Bedingungen) der Grenzschichten an drei ausgewählten metallischen Werkstoffen (Perlit, Martensit, Austenit) aus den Bereichen Automobil-, Energie- und Medizintechnik maßgeblich sind. 

Contact: Dipl.-Ing. Priska Stemmer (Mikroskopy); Dipl.-Ing. Daniel Stickel (Wear experiments)

Research area: Material Science

Strukturbildung und Selbstregenerationsmechanismen der triboinduzierten Randschicht von Metallen

Duration: July 1st, 2011 - June 30th, 2013

Abstract:
Metallische Werkstoffe bilden unter günstiger Reibbelastung eine charakteristische oberflächennahe Zone aus. Jüngste Ergebnisse zeigen, dass durch die Bildung dieser Zone Reibung und Verschleiß deutlich sinken. Das wesentliche Ziel des Vorhabens besteht darin, das tribologische Verhalten (Reibung und Verschleiß) metallischer Werkstoffe bei Gleitverschleiß und Grenz‐ und Mischreibung über den Reibvorgang zu optimieren. Dies kann erreicht werden, wenn es gelingt, während der Reibbelastung die Eigenschaften des tribologischen dritten Körpers einzustellen. Um dieses Ziel zu erreichen ist ein grundlegendes, mechanismen‐basiertes Verständnis der Bildung oberflächennaher Veränderungen für verschiedene Werkstoffe nötig, was in diesem Projekt erstmalig durch Laborversuche und Computersimulation mit identischen Tribosystemen ermöglicht werden soll.

Contact: Dipl.-Ing. Priska Stemmer

Research area: Material Science

Einladungen von ost- und mitteleuropäischen Wissenschaftlern nach Deutschland

Support Code: DFG 436 POL 17/10/04, DFG 436 POL 17/02/03, DFG 436 POL 17/06/02, DFG 436 POL 17/01/01, DFG 436 POL 17/12/00, DFG 436 POL 17/02/06

Abstract:
In Zusammenarbeit mit dem Institute of Materials Science and Applied Mechanics der Technischen Universität Wroclaw in Polen (Prof. Dr. Wlodzimierz Dudzinski werden mehrere Projekte aus dem Bereich der Transmissions-Elektronenmikroskopie bearbeitet. Prof. Dudzinski ist in jedem Jahr für mehrere Wochen in Duisburg zu Gast und steht den Wissenschaftlern und Studierenden mit seinem Fachwissen zur Verfügung. In diesem Zusammenhang werden zurzeit Untersuchungen zu Verformungsstrukturen in hochstickstoffhaltigen Stählen, an verschlissenen Oberflächen von explantierten Hüftgelenk - Prothesen und an magnetischen Werkstoffen nach Verschleißbeanspruchung durchgeführt. Darüber hinaus findet ein Austausch von Studierenden beider Universitäten statt.

Research area: Material Science

Contact: Priv.-Doz. Dr.Ing.habil. Sabine Weiß

Wissenschaftliche Zusammenarbeit mit Ägypten

Projekt: öffentlich gefördertes Forschungsprojekt

Support Code: 445 AGY 112/9/06

Abstract:
Im Rahmen einer Kooperation zwischen der Universität Duisburg-Essen, Werkstofftechnik und dem Central Metallurgical Research and Development Institute (CMRDI) Cairo, Egypt werden mehrere Projekte aus dem Bereich der Mikrostrukturentwicklung bearbeitet:

• Untersuchungen auf dem Gebiet des Hochtemperatur­kriechens von ausscheidungsgehärteten Stählen und Nickelbasis-Superlegierungen.

• Projekt zur Schwellbeanspruchung von Eisen- und Kobaltbasislegierungen mit unterschiedlichen Stapelfehler­energien: Grundlagenforschung zur Ermittlung des Einflusses der Mikrostruktur auf das Verformungsverhalten bei schwellender zyklischer Belastung.

Research Area: Material Science

Contact: Priv.-Doz. Dr.Ing.habil. Sabine Weiß

Friction Stir Welding Equipment for Joining Large Steel Structures - FSW Steel, Joint Project supported by the Ministry of Economy and Technology (BMWi)

Subproject: "Development of Efficient Tools for Friction Stir Welding of Steel"

Support Code: VP2095003PK9

Duration: Dec. 1^st, 2009 - Oct. 31^st, 2011

Associate partners: SLV Berlin-Brandenburg, Ingenieurtechnik und Maschinenbau GmbH, Lippold Hydraulik und   Wälzlager GmbH, Helmholtz-Zentrum Geesthacht, Materion GmbH, H.Loitz - Robotik GbR

Abstract:
The objective of this project is the development of efficient tools and production equipment for friction stir welding of large, thin steel sheets, aiming at an economic application of this innovative joining technology.

Starting by determining process parameters for joining thin steel structures on experimental welding machines, the necessary parameters for future equipment and welding tools are identified. Concurrent to the development of new tools (materials, design, surface treatment), the concept for a production facility for joining large steel structures of a thickness of 3 to 4 mm is created. Solutions for the main components for clamping, process control and tool fixture are developed, prototypes are produced, integrated into the equipment and tested on lab scale.

The outcome of this project will be efficient friction stir welding tools as well as a functioning example for a production facility. Those will be the basis for the following design, construction and commercialisation of production facilities for friction stir welding of thin steel sheets.

Research area: Tooling

Contact: M. Sc. Stefanie Hanke

Website: www.innowelding.de

Fatigue behaviour of Cu-based single and stranded wires

Associate partner: Deutsches Kupferinstitut Berufsverband e.V. & International Copper Association

Abstract:
Dimensioning of technical components in order to reach endurance strength makes the use of mechanical values necessary. For many technical materials this values can be found in standards or guidelines as minimum or standard values. The determination of mechanical values for Cu-base materials in thin single wire or stranded wire shape under cycling loading is the aim of this project. The test and investigation methods for this material shape may differ compared to usually known since the microstructure is oligocrystalline due to the grain size/wire diameter ratio in this small profiles. Here the use of adequate or adapted investigation methods is necessary. Beside the wire surface and stranded wire structure the anisotropic properties need to be considered. In a first approach the mechanical behaviour of single wire samples is investigated and statistically secured under bending load.

Research area: Material Science

Contact: Dipl.-Ing. Michael Schymura

Metal Friction Surface Welding

Project: Ford- University Research Program

Abstract:
The demands on production tools of one car line with approximately 600.000 cars per year over the running period of app. 6 years or more are extremely high. Stamping tools areas with high tool wear are e.g. die radii or draw beads. The use of low cost tool materials with enhanced wear resistance will support both cost reduction and quality improvement. For mild steels, low cost tools like globular grey iron castings (GGG70L or GG25) are used as tool material for stamping tools. Today, coatings are used to reduce wear, which make fast and flexible tool and die changes in production impossible.

Friction Surfacing opens up new possibilities for the repair of worn and damaged components. This process is also potentially useful as an alternative surfacing process as it allows for a compromise between the bulk substrate, which can be dictated by strength or economic constraint, and that of the surface, which can be altered by the application of selective materials to form a protective barrier against wear and corrosion.

The possibility of forming a high quality and regular layer onto a substrate by Friction Surfacing process depends of the selection of appropriate welding parameters. The reproducibility of the weld however, depends of the controllability of the machines used for this purpose.

The Friction Surfacing Process can be divided in two Phases: Pre-heating Phase and Welding Phase. During the Pre-heating stage the rotating stud is pressed onto the substrate, the heat is developed due to the energy generated by friction between the substrate and the rotating stud. The temperature rises just below the melting point of the material, where the yielding strength of the material decreases and the shear stress produced in the stud is high enough to enable plastic deformation in the material.

The welding phase of the process is responsible for the production of the coating layer onto the plate by start of the transversal motion of the rotating rod. In this phase a quasi-steady thermal condition is reached influencing the properties of the HAZ formed. At this point the dimensional properties and the quality of the layer formed are significantly influenced by the transversal speed, rotational speed and the load applied.

When the weld length required is reached, the transversal and rotation motion is stopped and the axial load is maintained, assuring the high bonding quality of the end of the layer.

The projected benefits from this project are cost reduction due to reduced maintenance time and enabling low cost tool material. Further, an improved quality due to reduced tool wear and scratches is expected. The implementation of this advanced technology, which can be used on machines which are already available (milling) with low investment costs is regarded as new solution for well known challenges.

Research area: Tooling

Contact: M.Sc. Stefanie Hanke

Nanocrystalline Composite Coatings with nano textured surface for Cylinder Running Surfaces of highly stressed Gasoline and Diesel Engines - NaCoLab

Support Code: BMBF 03X0003K

Duration: Jun. 1^st, 2005 - Mai 31^th, 2008

Abstract:
The aim of this research project is to replace grey cast iron liners in aluminium crank cases by a new coating material. By thermal spraying of a newly invented iron based filler wire feedstock alloyed with chromium, carbon and boron a hard, wear resistant and low friction coating is generated. The microstructure of these coating is an amorphous matrix with nanocrystalline precipitates. Increasing pressures during ignition (200 bar and higher) demand coatings which for all that ensure a good reliability and low wear rate.

Within this project a complete, innovative manufacturing chain for coating aluminium crank cases with this nanocrystalline material is developed. It includes the mechanical roughening of the substrate, thermal spraying of the filler wire feedstock and finally the surface finish by honing.

The institute of product engineering, materials science and engineering, advances the furthering of knowledge and understanding of the tribosystem piston ring - cylinder running surface by investigating the acting wear mechanisms. Running-in and wear influence the formation of the lubrication oil film in the contact zone. This results in differing friction losses, emissions and oil consumption which are significantly related to the durability of the motor. Advancing simulation tools to predict running-in and wear within the highly stressed positions top and bottom dead center is an additional objective within this project.

Research area: Automotive

Contact: Dipl.-Ing. Mareike Hahn

Solving Steel Welding Problems by the use of Friction Stir (SOLVSTIR)

Project: EU-Projekt

Support Code: RFS-PR-03077

Abstract:
Conventional fusion welding processes are reaching their applicability limits as far as the weldability of thin gauge, modern high alloy steels (i.e. UHSS, TRIP, CP, MS, DP and IF steels) is concerned. Weldability issues are also a matter of concern in Cr-containing steels employed in the energy sector (i.e. 9Cr1MoNbVN, 12Cr1MoV, etc) due to microstructural control, embitterment and particularly environmental concerns. The Friction Stir Welding (FSW) process, a low heat input, solid state joining method, offers a number of advantages likely overcome weldability problems in difficult-to-weld steel grades. Moreover, FSW has also shown to be able to produce multi-material joints between steel and non-ferrous alloys. Starting from the present state of art in FSW of steels this project intends to focus on two lines of development: process technology and application to relevant steel grades and multi-material joints. The process technology focus will aim at alternative tool materials and geometry, their respective process parameter fields as well as pre- and post-weld heat treatment methods viewing increased tool life and the cost effectiveness of the process. The suitability of the process to different steel grades will be investigated on modern high alloy and Cr-alloyed materials with emphasis on the microstructure development and joint perfromance. This development work will be supported by modelling (temperature and deformation) and by an economic evaluation and concluded with the manufacturing of demonstration structures from the automotive, shipbuilding and energy sectors. In summary, the main objective of this project is to define the merits of FSW when applied to steels based on the achievable joint performance, applicability to structures and economics.

Research area: Tooling

Contact: Dr.-Ing. Christian Zietsch

Reducing the Emission of Wear Debris in Metal on Metal Hip Joints by Means of Microstructured Surfaces.

Project: Industrial project

Duration: Jan. 1^st, 2007 - Dec. 31^th, 2008

Associate partner: Zimmer GmbH

Abstract:
For years surface texturing is known to be an effective method to improve the properties of certain tribological systems. One approach is to create lubricant reservoirs by non-corresponding dimples in the surface of one of the articulating surfaces. In MEMS devices, surface texturing is used to reduce the contact area in order to overcome adhesion and friction. Another interesting beneficial effect of a textured micro-topography is its function as a wear particle trap. By eliminating particles from the tribological system, third-body-wear is prevented. The metal-on-metal (MOM) artificial hip joint is a system which does not suffer third body wear by means of abrasion. Nevertheless, wear particles are suspected to be responsible for implant failure due to osteolysis, a bone degrading disease that causes implant loosening. A major improvement would be the elimination of wear particles, in particular, during the run-in of the artificial joint. In order to apply a micro-topography different techniques can be performed like machining, ion beam texturing, laser texturing, and etching. For this study an electrochemical etching process is used. The advantage of this process is the homogeneity of the material. Furthermore, this process is a less expensive application than, for example, laser texturing. In order to observe whether an electrochemically textured surface is beneficial for wear performance in a first step, a reciprocating sliding wear test rig has been established. The characterization of the textured surfaces will be performed by means of confocal white light microscopy.

Research area: Biomedical Engineering

Contact: Dipl.-Ing. Robin Pourzal

Microstructure and Deformation Behavior of Coronary Stents under Fatigue

Project: Publicly funded research project

Support Code: DFG FI495/9-1, DFG FI495/9-2, DFG WE2671/1-3

Abstract:
Stents are metal vessel scaffolds which are inserted to prevent vessel walls from collapsing. During implantation these stents have to tolerate a distinctly inhomogeneous plastic deformation due to crimping and dilation. Subsequently the implant has to sustain up to 700 million cycles induced by the cyclic diameter change of coronary arteries. During this time biofunctionality as well as biocompatibility have to be guaranteed. Because of the oligocrystalline structure of stents and the type of deformation the structure of the stent undergoes inhomogeneous plastic deformation. This results in local differences in chemical and mechanical load. This research project focuses on the experimental investigation and additional simulation of deformation mechanisms of oligocrystalline stents. Further, the development of a quantitative model for the deformation under static and cyclic load will be established. The diameter of one strut of a stent is generally about 100 µm. Therefore, depending on the grain size, there are not more than five to ten grains within the cross section of a stent strut. Thus the microstructure of only very few or even just one grain can be responsible for the behavior of the entire stent structure. Oligocrystalline structures like stents can in fact neither be described as multi-crystalline materials like fatigue specimens nor can they be treated as single crystals. In crystalline samples a size effect of mechanical properties can be observed if the grain size approaches the dimension of the specimen itself. Therefore mechanical investigations (tension and bending fatigue) are carried out using oligocrystalline wires of commercially used stent materials. The analysis of the deformation behavior will give a more comprehensive understanding of the structure property relationship in such thin structures with focus on the deformation behavior of coronary stents. The present study will help to develop a model based on experimental data to reach a better prediction for the endurance of coronary stents.

Forschungsbereich: Biomedical Technology

Ansprechpartner: Priv.-Doz. Dr.-Ing. Sabine Weiß