@phdthesis{Lemos2020, author = {Lemos, Georges}, title = {Development of Ni-based superalloy metal matrix composites, featuring high creep resistance}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-53985}, school = {BTU Cottbus - Senftenberg}, year = {2020}, abstract = {The increasing demand for competitive, whilst also environment-friendly airplane travel, compels the design of highly efficient engines in the aeronautical field. A potential for improvement of traditional polycrystalline Ni-based superalloys, aiming higher creep resistance, was investigated. The approach adopted the concept of metal matrix composites (MMCs) to incorporate a rigid discontinuous phase, in the form of particles, to a γ'-strengthened Ni-based superalloy. In order to make the concept feasible, different microstructures resulting from diverse manufacturing techniques were investigated. By using distinct mixing and sintering methods, powders of Inconel X-750 and TiC were combined to form composites containing 15 vol.\% of reinforcing particles. Powders were prepared with low and high energy milling processes, and formed by uniaxial pressure sintering and spark plasma sintering methods. Non-reinforced variants and composites had microstructures thoroughly examined at their initial state and after long isothermal aging treatments. Selected variants were further submitted to tensile and compression creep tests at temperatures between 700 and 800 °C, in the stress range of 200 to 500 MPa. A comprehensive analysis was conducted using techniques such as EBSD, XRD Rietveld refinement, EDS and TEM to evaluate the development of γ', η and TiC phases, determining the achievable microstructures with each fabrication method and establishing their evolution after aging treatments over times up to 1000 h. Likewise, creep properties were analyzed by obtaining parameters such as creep exponents, threshold stresses and activation energies. A creep life estimation was conducted with the use of a Monkman-Grant relationship and a Larson-Miller parametrization. Lastly, the potential for a reduction in creep strain rates in a working turbine blade, considering the density of investigated materials as a parameter, was evaluated. All produced composites presented power law creep, with dislocations surpassing γ' particles by climb. The variant produced by high energy ball milling and spark plasma sintering exhibited the highest creep rates, resulting from intense diffusion through grain boundaries. It also presented η phase after long isothermal aging, which affects negatively the creep resistance. Contrastingly, in the variant produced by low mixing combined with pressure sintering the lowest creep rates were observed. It was proposed that reinforcing TiC particles effectively acted as a load bearing phase, counterbalancing the adverse effects of the intergranular diffusion in the refined microstructure. Furthermore, a higher microstructural stability was observed in this variant, resulting from limited interaction between TiC particles and the matrix during fabrication.}, subject = {Superalloys; MMC; Creep resistance; TiC; Isothermal aging; Superlegierungen; MMC; Kriechbest{\"a}ndigkeit; TiC; Isotherme Alterung; Metallmatrix-Verbundwerkstoff; Titancarbid; Superlegierung; Kriechfestigkeit}, language = {en} }