The aim of this study is to evaluate the effect of two nitriding heat treatments on high cycle fatigue of Ti64 (Grade 5) alloy. For this, axial fatigue tests have been performed on untreated and nitrided round bar specimens under constant amplitude load-controlled mode at a frequency of 20 Hz at room temperature and in laboratory air. After the testing, the fractured surfaces and microstructures were investigated by scanning electron microscopy, focused ion beam, transmission electron microscopy and scanning transmission electron microscopy. Cross-sectional studies show that two different layers were formed after the nitriding processes, namely, a top compound layer and a diffusion layer below it. Additionally, a very thin layer rich in aluminium was also detected. The fatigue results show that the nitriding treatments are detrimental to the fatigue life when compared to the untreated and extruded Ti64 alloy. The main conclusion is that the reduction of high cycle fatigue life is a result of the cracking of the nitrided layers.

This paper provides a comprehensive overview of the evolution of materials for aero engines, covering the past advances, current developments and future trends with a particular focus on sustainability due to increasing environmental impact of aero engines. Over the past 40 years, the development of materials for turbine parts has been impressive: their temperature capability has increased by 250 °C during that period. Today, we are almost at the maximum temperature for operation, but if the engines can manage a small increase, just 25 to 40 °C more than today, the engines would be more efficient and use up to a half to one per cent less fuel. In the past, aero engines primarily utilised materials like aluminium, titanium and steels. However, the consistent drive for improved efficiency and performance has shifted focus towards advanced materials such as superalloys, capable of sustaining prolonged operations at temperatures exceeding 800 °C. The present is characterised by the wider use of composite materials in fan and nacelle sections due to their superior strength-to-weight ratio and adaptability. Recent progress in additive manufacturing is also set to transform the production of complex engine components enabling more optimised and lighter designs. Looking into the future, the paper investigates the potential of emerging materials such as 2D materials, which can open for new possibilities in design and functionality. The paper concludes with a discussion on the challenges and opportunities associated with the development of materials for more sustainable aero engines and consequently society, also at a global scale as collaboration and innovation are the key to the green revolution.

Over the last 40 years, the Engineering Integrity Society has established a distinctive culture of bringing together practising engineers and researchers from industry and academia to share insights, understanding and expertise. Throughout this time we have organised workshops, seminars, exhibitions and conferences and Fatigue 2024 is our ninth international conference.Fatigue 2024 continues with the themes established in previous conferences to support the international fatigue and durability community. Participants at the conference will share knowledge and understanding of the challenges of using high performance materials for reliable, cost effective products. The papers presented will examine the interplay between the latest manufacturing processes, the properties of materials, and the integrity and performance of components operating in challenging conditions. The complex relationship between materials, process and manufacturing routes and the durability and reliability of the machines and devices forms the central theme of the conference.The EIS is a registered charity and one of our aims is to encourage young people to consider careers in the engineering professions. We are pleased that almost one third of the papers at Fatigue 2024 have been written and presented by early career engineers eligible for the Peter Watson Prize, which we award annually in memory of our Founding President.

Titanium is 40% lighter than steel and is very strong in relation to its low weight, which makes it veryinteresting for lightweight applications. However, the use of titanium in certain aircraft components islimited because titanium is a relatively soft metal that quickly deteriorates when mechanically stressed.In this research, a nitriding heat treatment has been developed for Ti64 (Grade 5) alloy with the aimto improve wear properties without negative effect on fatigue and strength. The mechanical propertieswere studied through hardness and wear tests performed at room temperature in laboratory air onuntreated and treated Ti64. Different measurements techniques were used to evaluate hardness onsurface as well as polished cross-sections due to uncertainties in hardness measurements of thinfilms. The wear properties were investigated with pin-on-disc tests. The microstructures and nitridedsurfaces were also investigated by optical microscopy, scanning electron microscopy (SEM) andsurface profilometry. The analysis has shown that the nitriding process has led to the formation of anuneven compound layer and a diffusion zone beneath it. The energy dispersive X-ray spectroscopy(EDS) mapping showed a high concentration of nitrogen in the compound layer and aluminium in thediffusion zone. The microhardness measurements and nanoindentation have revealed the formationof an approximately 2.5 μm thick diffusion zone. The wear tests results showed a large difference infriction behaviour between the nitrided specimens, which has been associated with the failure of thenitrided layer and the wear rate.

DevTMF (Development of Experimental Techniques and Predictive Tools to Characterise Thermo-Mechanical Behaviour and Damage Mechanisms) is focused on contributing to development of new materials and improving efficiency of aero engine components that will reduce fuel consumption and environmental impact. This is ultimately achieved by either introduction of novel engine design or development of new materials able to sustain complex loadings from take-off, cruise, descent and shut down. Specifically, Thermo-Mechanical Fatigue (TMF), which occurs at the rim of turbine discs, aero-foils and rear structures, requires assessment in terms of both crack initiation and crack propagation as the harsh thermal transients during take-off and descent may cause the formation of cracks.

A previous European project on TMF funded by the FP5, which ended in 2005, has been successful at evaluating and addressing issues related to strain-controlled TMF testing. This project led to the development of a code of practice for TMF studies, which has been implemented by testing houses and equipment manufacturers worldwide. Apart from work on strain-controlled TMF, DevTMF has been aiming to evaluate and develop TMF crack growth (CG) methods that are essential to demonstrate structural integrity and certification requirements of being tolerant of handling damage as well as to assess remnant lives in cracked turbine components.

The current paper presents work on the identification and evaluation of a range of factors influencing accuracy, replicability, repeatability and comparability of data generated by three laboratories carrying out stress-controlled TMF CG tests. It addresses the crack length measurement methods, the temperature and heating methods, and the temperature measurement techniques. It also provides recommendations and guidance for the pre-cracking procedures and the use of various specimen geometries as well as the Digital Image Correlation (DIC) technique for monitoring cracks. The majority of the TMF CG tests has been carried out on a coarse grain polycrystalline nickel-base superalloy using two types of phase angles, namely Out-of-Phase (OP) and In-Phase (IP) TMF cycles with a triangular waveform.

The crack driving mechanisms in a coarse grained nickel-base superalloy RR1000 when subjected to in- and out of phase thermo mechanical fatigue are investigated. It is found that the difference in fatigue crack growth rate between these two load conditions is accounted for by the different mechanical conditions at the crack tip region, rather than oxidation effects. This is based on digital image correlation and finite element analyses of the mechanical strain field at the crack tip, which demonstrate that in phase leads to larger crack tip deformation and crack opening. Notably, it is demonstrated that in- and out of phase crack growth rates coincide when correlated to the crack tip opening displacement.

Smart Specialization (RIS3) is an innovative approach/strategy to bring together local authorities, academia, businesses and society to boost growth and jobs in Europe. It prioritizes domains, areas and economic activities where regions have a competitive advantage.

We introduce an innovation model to facilitate translation of ideas and knowledge into regional implementation. Instead of focusing on technology, the innovator / entrepreneur himself is in focus. The proposed model is based on the Buurtzorg model which originally focusses on supporting patients in health care, and which has an onion frame: the patient is surrounded by informal network (family, etc), next is the Buurtzorg support team, and final level is the formal network (society). The individuals need are steering the health care support, rather than adapting it to the social and economic constraints of the health care system. The team consists of specialists who decide how they organize the work, share responsibilities and make decisions. The team is self-managing and with entrepreneurial spirit.

We will argue in this paper that a support mechanism as innovation model may be applicable to regional capacity building, and the support acts as a clustering process. Clusters are often limited by geographical constraints, such as having a number of local actors in a certain field. Clustering may be based on other values than given by physical ones.

Our model approach is based on that there are innovators who have visionary ideas which are outside their traditional business. They could potentially be of great important for regional growth since they will create value chains, jobs etc, but given the non traditional innovation character they will not be realized unless there is a support mechanism. Similar to the Buurtzorg model, there is a team of specialists that will support the innovator and the innovator informal network. The specialist team has competencies related to smart specialization, regional growth etc (formal network).

When RIS3 is applied to broad areas like advanced materials or nanotechnology such a mediation becomes highly complex. Both these areas include an extremely broad range of areas, examples include anything from food (through modifying functional properties by physical and chemical changes), digital communication or connected systems (new materials’ approaches for faster processors or use of higher/faster band frequencies), to construction related materials (buildings, transport, etc). Very likely they do not have actors located geographically close to create a cluster.

For synergistic effects, activities in the RIS3 within advanced materials can be linked to other fields, as well as to implementation synergies. If the smart specialization of advanced materials can interact with efforts in building competence, smart industry, sustainable production, automation, digitalization etc, the advanced materials could then find a value chain in specific avenues instead of building ones in its own area. This is a viable route to hold together the fragmented and broad character of advanced materials field, where transferring/translation activities (competence, technical, etc) are a binding agent. Therefore, the specialist team is crucial for such transfer, and a core element in an innovation model.

In recent years, there has been an increasing interest towards the environmental impact of air travel. As a result, it is of vital importance to the European aviation industry to reduce the engine emissions. For this purpose, ACARE set new challenging targets aiming to reduce emissions, fuel consumption and raising temperature capabilities. This will ultimately be achieved by the introduction of novel engine design and new materials able to sustain complex loadings from take-off, cruise, descent and shut down. It is a prerequisite to understand the impact of such environments in current alloys.

Specifically, Thermo-Mechanical Fatigue (TMF), which occurs at the rim of turbine discs, aerofoils and rear structures need to be assessed. At these locations, the harsh thermal transients during take-off and descent may cause the formation of cracks.  A previous European project on TMF, which ended in 2005, has been successful at evaluating and addressing issues related to thermo-mechanical fatigue testing. This project led to the elaboration of a code of practice for TMF studies, which has been implemented by testing houses and equipment manufacturers worldwide. A European project has recently been awarded, under the umbrella of both `Horizon 2020' and Clean Sky 2, aiming to evaluate and model TMF crack initiation and growth.

TMF crack growth (CG) methods are essential to demonstrate that structural components meet the certification requirements of being tolerant at handling damages and the presence of melt anomalies. They are also needed to assess remnant lives in cracked turbine components such as vanes. However, crack growth in TMF loading cycles cannot be currently reliably measured experimentally nor predicted by existing CG models. Therefore, isothermal propagation data are used to conservatively handle TMF effects, which can lead to over-designed components and loss of engine efficiency. Our project aims to address those deficiencies.