Volume 18 (2018): Edizione 2 (June 2018)

The present paper deals with the analysis of the course of oxidation of the cyclic Ti-46Al-7Nb-0.7Cr-0.1Si-0.2Ni alloy in a hot air atmosphere in the temperature range of 875-975°C. The constant rates of the oxidation were determined (separately for the first and second stages of oxidation) and the energy of oxidation activation of the tested alloy was established. It was discovered that the oxidation process of the Ti-46Al-7Nb-0,7Cr-0.1Si-0.2Ni alloy develops according to the parabolic correlation, and it is only possible to determine the apparent energy of oxidation activation.

The cavitation and cavitation erosion phenomenon have been shortly presented. The main four types of test rigs to investigate the cavitation erosion resistance have been shown. Each type of test design is described and an example of a design is shown. A special attention has been payed to the designs described in the International ASTM Standards: a vibratory design and a cavitating jet cell. There was shown that the design of a test device and the test conditions affect the resistance to cavitation erosion of a material.

The paper analyses the relationship between an increase of the inner diameter of tubes made of Manaurite XM cast steel and transformations occurring in their microstructure due to long-lasting operation in methane reformer. Examinations included metallographic analysis with light microscope (LM), scanning electron microscope (SEM) and microanalysis of the chemical composition of precipitates (EDX). It was indicated that there is a relationship between the microstructure degradation ratio, morphology of the precipitates and an increase of the inner diameter of the tubes.

The purpose of the present research was to determine the oxidation and hydrogenation behavior in the new Zr-2Mn alloy. The oxidation of alloy was performed at temperatures between 350°C and 900°C for 30 minutes. The hydrogen charging was made for 72 h at a current density 80 mA/cm². The charged samples were heat treated at 400°C for 4 h to obtain a uniform hydrogen profile content across the sample. The oxidation resulted in an appearance of non-uniform oxide layers of thickness increasing with temperature. The surface damage was observed at higher temperatures 700 and 900°C. After charging with hydrogen followed by annealing no hydrides were found. The observed effect is evidence that the oxide layers may form effective barriers against hydrogen diffusion even if they are partially degraded. The absence of hydrides or hydride cracking may be caused by an absence in Zr-Mn alloys of such phase precipitates, which may trap diffusive hydrogen and initiate the hydrides. The positive influence of manganese on the formation of the thick oxide layer and relative resistance to delayed hydride cracking may be attributed to its affinity of oxygen, the ability to form thick and compact oxide layers during oxidation, the formation of solid solution in zirconium and no precipitates enhancing nucleation of hydrides.

The present work investigates the ablative and thermal properties of phenol formaldehyde glass-fabrics laminates filled with mixtures of corundum Al₂O₃ and carbon C powders. The laminates specimens of dimensions 10x25x35 mm were treated with hot combustion gases having a temperature of more than 2800ºC. The carbonization of the thermosetting matrix was observed. Statistical methods for planning experiments were used, and the effect of components on the average rate of ablation, the maximum back side temperature of specimen and the average mass waste under intensive heat flow after 30 s of treatment with hot combustion gases was established. The best thermal protective properties were exhibited by the laminate containing 30% matrix, 25% fibre glass-fabric reinforcement, 9% corundum, and 36% carbon powder.

The results of conducted by the authors of the article numerical analyzes, indicate the importance of normal stresses, perpendicular to the adhesive joint, during the impact destruction of block adhesive samples. This kind of stresses are responsible for the occurrence of tearing or chipping in a joint. The very significant influence of adhesion in the impact-bonded adhesive joint was the reason for testing this parameter in joints made with adhesives with different Young’s modulus. It was assumed that adhesives differing in stiffness will have different adhesive properties, which should affect the impact strength of the adhesive joints. It was also assumed that the adhesion in the joint can be assessed by analyzing the surfaces of joint damage. Cylindrical butt joints connected with various adhesives were used to carry out the tests, in which they were loaded on tear-off. The nature of tested joints damage was usually cohesive or cohesive-adhesive. The assessment of the nature of joint damage allowed to determine whether they were the result of the loss of cohesion by the adhesive (cohesive damage) or the effect of poor adhesion between the hardened joint and adherends (adhesive damage). The assessment of the nature of the destruction was carried out by three methods: visual, using an optical microscope and using an electron microscope. As a result of the carried out observations, it was found that the visual method is the least useful and not very reliable, especially in the case of transparent or low-contrast in relation to the glued material joints. The use of electron microscope allows to obtain the most reliable results, however, the possible magnification is too large and the assessment of the entire weld fracture is difficult because it does not fit in the field of observation. Observations conducted using optical microscopy at a slight magnification (5-10 times), in most cases allow to determine the nature of the destruction to a satisfactory degree, with limitations such as in the visual method.

This article indicated at erosion as one of the causes of degradation of surfaces washed by fluids and conditions of its occurrence. Corrosive – erosive theory of metal surface degradation has been discussed linking it with an instance of destructive processes taking place in cylinder liner blocks of combustion engines. Physics and conditions influencing processes on liquid – washed operational surface phase boundary have been justified. Out of the contemporary hypotheses explaining the physics of cavitation erosion, the bubble theory has been considered. A mathematical model of erosion has been presented in the context of cavitation implosion energy determining crash interactions of liquid cumulative fluxes on the washed surface. Occurring plastic deformations have been graphically explained linking them with the occurrence of fatigue micro-cracks and later with erosive pits. Influence of initial steel hardness on intensity of cavitation erosion has been checked. Discussion of ways to increase metal surface resistance to cavitation erosion has been carried out.

The objective of this paper was study and analysis of damaging process of multi-ply structure applied in dentistry. The aim was to analyze and experimentally evaluate tolerance of macro-damage of first ply (FPF - first ply failure) of multi-ply composite. A studied structure of composite makes a carrying structure for dental applications e.g. adhesive bridges. Influence of reinforcement structure on the residual carrying capacity of the studied multi-ply materials has been demonstrated. It has been shown that the type of fiber and fiber ribbon architecture play a major role in strength of studied reinforcements. Structures included in the study differ by the moment of macro-damage occurrence, carrying capacity and residual stiffness.

In the paper, the issue of the cermet cutting tools wear resistance was addressed. The tool inserts made out of cermet composites were exposed to the ion implantation with ions of nitrogen N⁺ and with combination of nitrogen N⁺ and aluminum Al⁺ ions. In order to assess the impact of the ion implantation, the samples of stainless steel EZ6NCT25 were turned with the standard cutting tools and with the inserts after ion implantation. The results in general confirmed better wear resistance of the ion implanted inserts. In particular, they performed 20-40% smaller friction. After some time, when the destruction of the implanted surface layer took place, the friction coefficient rose up to the value typical for non-implanted inserts. For the implanted inserts, the wear index VB appeared to be lower, and even visual assessment revealed distinguishably smaller wear than in case of tools without ion implantation.