Defect and Diffusion Forum Vols. 326-328

Abstract: The development of aviation and outer space technologies necessitated working out new materials, resistant to increased temperatures, and satisfying specific requirements concerning high strength and low density. These requirements are met by metal composite materials produced by proper joining of the matrix (aluminium or magnesium alloys) and reinforcement components, mostly ceramic fibres, particles or whiskers. Such composite materials combine properties that traditional materials cannot yield. This contribution presents the method of composite foam production (SiC reinforcement, aluminium alloy matrix) by the mechanical method and testing of non-combustibility of these materials in accordance to the international FTP Code and the testing procedure PB-KTZ-01 (equivalent of ISO 1182).

Abstract: Metal-matrix composites for many years have been widely used as engineering material all over the world, also in Poland. It is due to good construction properties, small specific gravity, ease of product formation, also large size items, diversity of manufacturing methods, and great possibilities of changing their properties depending on the output products used [. The authors of this study deal with metal-matrix composites made by casting. One of the methods they use in their research includes the saturation of the reinforcement structure (short disordered fibres pressed like felt, forming a profile, called preform) with metal liquid matrix under pressure. Phenomena occurring in the production of a composite material are similar to those taking place during making casts from traditional materials (cast steel, cast iron, non-ferrous metal alloys). This article is an overview of a problem encountered while detecting and describing defects of metal-matrix composite materials produced by saturation. It focuses on phenomena that take place during casting solidificationespecially the influence of the matrix (with different temperatures of liquid metal) on the reinforcement during its saturation and crystallisation of silicon plates on it.

Abstract: The paper presents results of DSC and microstructural investigations of Mg-6Al-1Ca-1Sr-0.3Mn (ACJ611) and Mg-8Al-3Ca-1Sr-0.2Mn (ACJ831) magnesium alloy in as cast condition. The microstructure of this alloy consists of aluminum in magnesium solid solution and two types of eutectic: α-Mg+Al₂Ca and α-Mg+Al₃Mg₁₃Sr. The liquidus temperature of ACJ611 magnesium alloy is 613°C. The eutectic reactions L α-Mg+Al₂Ca and Lα-Mg+Al₃Mg₁₃Sr occurs at 510°C and 502°C temperatures, respectively. The increase of aluminum and calcium content increases the volume fraction of Al₂Ca phase, decreases the liquidus temperature and slightly increases the temperature of eutectic reactions.

Abstract: In this paper, a Finite Element Analysis is carried out in order to simulate the process of spreading and solidification of a micrometric molten droplet impinging onto a cold substrate. This process is a crucial key to have a good understanding of coatings obtained by means of thermal spraying. The effect of thermal contact resistance (TCR) on the droplet spreading and solidification was investigated using different values of TCR and different droplet sizes. The solidification time was found to be a linear function of the droplet diameter square. Viscous dissipation, wettability and surface tension effects are taken into account. The Level Set method was employed to explicitly track the free surface of molten droplets.

Abstract: To determine the possibility of carrying out the recycling process of metal-matrix composite castings with saturated reinforcement, only Dupre equation was used until now. Basing on this equation, one can determine superficial conditions in the system: liquid metal (matrix) solid reinforcement medium, favouring the process of autogenous outflow of liquid matrix from the porous reinforcement. It is however very difficult to determine the influence of the structure parameters of reinforcement preforms on examined process. Hence the need to preform analysis of process of liquid metal matrix outflow using Darcys law of flow. Application of this law allows replacing difficult to determine parameters of capillaries occurring in performs with one, quite simple to calculate parameter of permeability. It also makes possible defining the influence of temperature and time of recycling process on yield of matrix metal. To verify stated theses, study of permeability of selected reinforcement preforms and recycling of selected metal-matrix composites with saturated reinforcement was conducted. Furthermore, analysis of liquid metal matrix outflow process from studied preforms was performed, in aspect of application of Darcys law.

Abstract: Samples of a Ti6Al4V alloy were treated by thermochemical gas nitriding at 1120°C for 7 h. Gas nitriding provided formation of titanium nitride layer with a hardness over 1800 HV. The titanium nitride layer exhibited excellent wear resistance along with a lower coefficient of friction against alumina ball under dry sliding conditions when compared to the as-received state.

Abstract: Plasma Electrolytic Oxidation (PEO) is a powerful technique allowing hardening and corrosion protection of valve metals due to formation of an oxide layer on the metal surface. The addition of fluoride ions to the alkaline electrolyte for the PEO processing of aluminum and magnesium alloys produces significant changes in the structure and properties of the coating [1-, however the mechanism of these changes is not clear. A study of the influence of the fluoride concentration on the composition, structure and morphology of thin (to 20 µm) PEO layers was performed. The oxide layer thickness on aluminum is significantly smaller than that on magnesium. Fluorine is detected as an amorphous phase in the vicinity of the base metal.

Abstract: Mechanochemical activation (MCA) of electrode lignin was performed and the activated lignin was studied by IR-spectroscopy for different activation times. The activated lignin was tested for the ability of binding Cr₂O₇^2-, Cu²⁺, Ni²⁺ ions. It was established that structure deformation, which does not distort the stronger hydrogen bond lattice, but leads to the formation of highly developed surface with active functional groups, occurs in the course of MCA. Weaker inter-layer bonds are broken in the activation process and quickly recovered after the load release. The comparison of the sorption capacity of Cr₂O₇^2-, Cu²⁺, Ni²⁺ ions by the MCA treated vs. inactivated lignin for different activation times was performed.

Abstract: A superalloy is an alloy developed for elevated temperature service, where relatively severe mechanical stressing is encountered, and where high surface stability is frequently required. High temperature deformation of Ni-base superalloys is very important since the blades and discs of aero engine turbine, because need to work at elevated temperature for an expected long period. The nickel-base alloy Inconel 718 has being investigated because it is one of the most widely used superalloys. The objective of this work was to evaluate the creep behavior of the Inconel 718 focusing on the determination of the experimental parameters related to the primary and secondary creep states. Constant load creep tests were conducted with at 650, 675 and 700°C and the range of stress was from 625 to 814 MPa to according to ASTM E139 standard. The relation between primary creep time and steady-state creep rate, obeyed the equation for both atmospherics conditions at 650, 675 and 700°C. The microstructural characterization employing the technique of scanning electron microscopy has been a valuable tool for understanding the mechanisms of creep.

Abstract: Titanium and its alloys have been used a lot for its special and unique properties, and characteristics under different conditions [. When we want to use one of its alloys in aerospace industry, we have to assure that in these conditions the material will resist and keep its integrity [1,. We wanted to analyse a titanium based superalloy by modeling a routine and extracting information from it about the dependence between Gibbs free energy and the amount of weight from two components, titanium and aluminium, which is the second major element according to X-ray diffraction analysis. It was concluded that increasing Ti amount, or making the alloy richer on titanium, the system leads to a higher level of energy. The opposite behaviour happens with aluminium; increasing it, the energy of the system decreases which is great, once the equilibrium is obtained with lower levels of energy. Although the analysis had been done with a general database available in the software, its possible to predict how the material will be influenced under several situations in a quick and reliable method.