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Characterization of reaction products of liquid Al and Mg3N2

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Aluminium matrix composites (AMCs) have gained a considerable interest in automotive and aerospace applications due to the light weight combined with higher stiffness, elastic modulus and strength, as well as better thermal stability and wear resistance compared with conventional alloys [1?€9], So far, in this group of materials most of the attention has been paid to Al2O3 [1?€3] and SiC [3?€5] reinforced composites. Some of them are now well developed and have been already commercially applied [4, 5]. However, constant efforts are being made to improve existing materials and to design new ones in order to meet the increasing demands for advanced structural and functional materials. Recently, an increasing attention has been paid to aluminium nitride as a reinforcing phase in AMCs. The addition of AlN, due to its good physicochemical, mechanical and thermal properties, allows to enhance the modulus, strength, hardness, wear resistance and high temperature performance of aluminium alloy matrix [6?€9]. The main advantage of the aluminium nitride over commonly applied in AMCs reinforcing phases is good bonding to aluminium matrix, higher wettability in aluminium, as well as stability of aluminium/ aluminium nitride interface [9?€12]. In conventional metal matrix composite production a reinforcing phase is usually prepared separately, prior to the composite fabrication and introduced into the matrix via powder metallurgy [3, 6?€9], spray deposition, casting techniques [1, 2, 5] etc. These, referred to as ex-situ techniques, have one major disadvantage, which is generally weak bonding between the reinforcements and the matrix. A possible solution to this problem are in-situ techniques, in which the reinforcement is produced directly in the metallic matrix, e.g. by chemical reactions betwe[...]

Characterisation of TCP phases in CMSX-4 single crystal superalloy subjected to high temperature annealing and creep deformation DOI:10.15199/28.2016.4.1


  A high temperature exposure of nickel-base single crystal superalloys leads to a formation of topologically close packed (TCP) phases, what can deteriorate their creep strength. Therefore, the aim of the present work was to investigate TCP phases precipitated in CMSX-4 superalloy after a two-step treatment consisting of annealing at temperature of 1100°C followed by a creep deformation at temperature of 900°C. The microstructure of CMSX-4 superalloy exposed to a high temperature was investigated by means of scanning and transmission electron microscopy as well as scanning-transmission electron microscopy in high angle annular dark field mode. The chemical composition in nanoareas was determined using the high spatial resolution and high count rate energy dispersive X-ray spectroscopy. A three-dimensional characterization of the microstructure of annealed and creep tested single crystal superalloy was carried out by means of electron tomography. Results of microstructural investigation have shown that after the application of two-step high temperature exposure the TCP precipitates present in CMSX-4 superalloy are P and μ phases. The most pronounced differences in the chemical composition of the investigated P and μ phase particles are concerned with W and Re content. It was determined that the P phase contains a higher amount of W, while the μ phase is mostly rich in Re. Key words: single crystal nickel-base superalloys, annealing, creep, TCP phases.1. INTRODUCTION Single crystal nickel-base superalloys are especially designed for gas turbine blade and vane applications. The microstructure of single crystal superalloys consists of two phases, namely the γ phase matrix and cuboidal γʹ phase precipitates. To increase the high temperature creep resistance of single crystal superalloys, high amounts of refractory elements such as Mo, W and Re are added. These elements provide a solid solution strengthening, but unfo[...]

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