The Effects of Local Texture and Microstructure on Deformation Mechanism in IN 713C Alloy

The turbocharger is an essential part of a modern diesel engine. The turbine wheel is a key component in the turbocharger and it should be designed to sustain at high temperatures and high rotational speeds during the hostile operating conditions and strenuous duty cycles. Mainly the material used in the turbine wheel is Inconel 713C which is a precipitation hardenable, nickel- chromium base cast alloy. The turbocharger manufactures' requirements imposed on this cast alloy is high as it should includes high fatigue and creep resistance at high temperatures as well as resistance to corrosion in a media containing products of fuel combustion. However, the turbine wheel blades are thermally and mechanically loaded during the operation of the turbocharger that can lead to material failures. With the objective to design safe components and improve fuel consumption, it is necessary to understand the failure mechanisms of the employed materials under these complex loadings. Different failure modes reported in literature, but the two most prominent turbine wheel failure modes are Low Cycle Fatigue (LCF) and High Cycle Fatigue (HCF). In general, there is uncertainty in literature about the exact influence of individual microstructure parameters including porosity, inclusions, grain orientation and slip activity on fatigue life of IN 713C alloy. In a complex system such as cast IN 713C alloy, these parameters should be identified and quantified. This needs complete description of the microstructure and microtexture of the alloys prior and post mechanical testing using various microanalytical tools including HR-SEM, HR-EBSD, EDX, X-ray micro-tomography as it suggested in this proposed study.

Conventionally, the crack initiation and propagation during tension, creep and fatigue have always been correlated to some prominent microstructural features such as porosity, inclusions, voids, second phase particle, oxidation and surface conditions in most structure/property relationship studies. However, in a non-homogenous cast microstructure, the role of local zones/regions became very critical in materials performance and integrity. These local regions contain different grain/grain boundary distributions and local textures that create various microstructure/microtexture clusters that can promote/trigger crack initiation and provide fast crack propagation in some specific locations within the material. In this proposed study, along with defect distributions and surface condition of the alloy, other microstructure features including grain orientations, local/micro/macro/meso texture, strain distribution and grain boundary geometry/characteristics will be the focal points in understanding fracture mechanics, failure and deformation mechanisms. The aim of this study is to quantify and discriminate exact microstructural parameters that produced dissimilar crack characteristics in various zone/regions within a cast microstructure. Uniquely, here the parameters that caused crack formation at the surface will be quantified and compared with subsurface cracks and cracking in the bulk materials i.e., away from surface, edges and corners. Moreover, the crack formation in the absence of any microstructural defects will be characterised against the cracks formed in the vicinity of pores and inclusions. Identifying these microstructural parameters is fundamental in understanding the crack initiation and propagation correlation with microstructure and microtexture in cast alloys used at critical high temperature applications. Detailed investigation will be carried out in order to find exact interactions of the crack path, undulation and bifurcation with microtexture clusters that contain different strain/stress accumulations within the material. In this proposed study, in order to validate correlations between microstructure and crystallographic texture (local and global) with crack characteristic various micro-analytical tool will be employed.

As stated in the Pathways to Impacts section, this proposed research study aligns very well with two of the current EPSRC themes and a recent EPSRC call. The main beneficiaries of the project include industrial partner Cummins Turbo technologies, Swansea University and the wider community as described in the Pathway to Impact section. Moreover, it has direct impacts on environment, society and knowledge as described here.

Cummins Turbo Technologies will benefit from the outcomes of this research study to improve the microstructure, processing, mechanical properties and temperature capability of the material used in turbocharger components. This study will provide a better understanding of the deformation mechanisms and structure/property relationship in IN713C alloy that can guide Cummins towards enhanced product properties. From this fundamental scientific investigation, Cummins will gain better understanding of the material integrity and performance used in turbocharger and the methodology of improving the properties for such an alloy. A specific impact activity will be undertaken by the project to ensure the knowledge is transferred and embedded to the engine industry. This project will also lead to effective engagement and collaboration between Swansea University and Cummins. Furthermore, based on the originality and novelty, this project will attract further collaborators in automotive, aerospace and nuclear industries, especially in the field of deformation mechanism for the new designed alloys. This project also raises the UK profile and facilitates generation of additional international research funding for UK academics as this project will leads to better scientific understandings of materials integrity of the commercial alloys. This project will also help the industrial partner Cummins to engage actively with the research activity in Swansea University.

Swansea University will benefit from this study, as it will provide an opportunity for employing a Post Doctoral Research Associate (PDRA) to be trained in a directly related industrial project. There will be also an opportunity to allocate MSc and final-year BEng/MEng students to work directly with PDRA/PI on this projects. This will help in training new engineers for the materials engineering fields in a growing energy sectors.

This project is generic in nature and applicable to the majority of alloys used in critical aerospace and nuclear applications. This study provides a new approach to examine the materials stability and durability. This can applied to the newly designed intermetallic compounds and superalloys that are carefully manufactured to be free from any type of defects and considered to have superior microstructure and mechanical properties. This project will advance UK based fundamental science in deformation and failure mechanism research areas. This project will also help our existing expertise and knowledge in our college at Swansea University as well as the community through public engagement and awareness about the major issues in materials failures that can cause catastrophic failures. The outcomes of this project will be published and presented in national and international meetings, which helps in disseminating the findings to wider scientific and industrial communities.

Finally, this proposed project is directly related to the challenges facing the engine industry that have been focused on meeting emissions regulations. Improving turbocharger efficiency can reduce emissions and increase power and economy fuel consumption. Optimising the material integrity and performance of the turbocharger components can contribute greatly in achieving best functionality of the turbocharger used in many critical applications. This important related material aspects are directly relate to the energy and wealth management as well as emission legislation as it contributes greatly in controlling and reducing fuel consumption.