Emilia Wolowiec

Properties of Surface Layers Processed by a New, High-Temperature Vacuum Carburizing Technology with Prenitriding - PreNitLPC®

The variety of vacuum carburizing with prenitriding (PreNitLPC® technology) consists in metering ammonia in the stage of charge heating for carburizing to reduce grain growth in the surface layer of carburized steel. This paper presents the effect of nitrogen interaction on the reduction of austenite grain growth during vacuum carburizing and on the mechanical properties (fatigue strength, impact resistance) of the layer treated in this way in relation to conventional carburizing methods.

Mathematical Modelling the Low-Pressure Nitriding Process

This paper discusses the issues of modelling and smart computer support for low-pressure nitriding aimed at achieving more effectively the compatibility between the actual post-treatment properties of a material and the designed properties, which will contribute to improved repeatability of the processes. The principal objective of the experiment was to acquire better understanding of the cause and effect relationship of the low-pressure nitriding processes and to develop the methodology of designing functional and effective processes of low-pressure thermochemical treatment, using effective computational methods. The paper proposes a method of steel classification based on its chemical composition and a model used to forecast the properties of material after low-pressure nitriding, based on the artificial neural networks.

The Precipitation and Dissolution of Alloy Iron Carbides in Vacuum Carburization Processes for Automotive and Aircraft Applications - Part II

The article is dedicated to the experiments and tests on the phenomena of precipitation and dissolution of alloy iron carbides in vacuum carburization processes. Special attention has been paid to the possibility of using artificial neural networks to predict the speed of the processes examined. In the section below, we are presenting the precipitation phenomena taking place in vacuum carburization processes and the experiments that were conducted. Moreover, a qualitative and metallographic analysis of carbide phenomena was described together with the method of numerical modelling and predicting the processes with the use of artificial neural networks.

Airborne-particle abrasion parameters on the quality of titanium-ceramic bonds.

STATEMENT OF PROBLEM Airborne-particle abrasion of titanium is a clinically acceptable method of surface preparation. It is crucial to know the effectiveness of bond strength between the metal substructure and the veneering ceramics after this kind of surface treatment. PURPOSE The purpose of this study was to determine how the particle size of the abrasive material and pressure affected treated surfaces and the strength of titanium-ceramic bonds. MATERIAL AND METHODS Disks made of titanium (Tritan CpTi grade 1, Dentaurum, 99.5% Ti) were treated in an airborne-particle abrasion process with 50, 110, and 250 μm aluminum oxide (Al2O3) at pressures of 0.2, 0.4, and 0.6 MPa. To characterize the treated surfaces, the following values were measured: roughness, free surface energy, and the quantity of abrasive particles attached to the surface. Subsequently, the strength of the metal-ceramic bond was determined. Apart from the strength tests, fractures were observed to determine the character and fracture location in the course of the strength tests. The results of the experiment were analyzed with 2-way ANOVA and the Tukey HSD test (α=.05). RESULTS Both the pressure and the particle size of Al2O3 used in the airborne-particle abrasion affected the strength of the titanium-ceramic bond (P<.05). A statistically significant difference was found between the group subjected to airborne-particle abrasion under a pressure of 0.4 MPa with 110-μm Al2O3 particles and the other experimental groups (P<.05). CONCLUSION This study demonstrates that the highest bond strength between a ceramic and titanium substructure can be achieved after airborne-particle abrasion at an angle close to 45 degrees with 110-μm Al2O3 particles under 0.4 MPa of pressure.

Practical application of artificial neural networks in designing parameters of steel heat treatment processes

The article is dedicated to the possibilities of practical application of artificial neural networks in designing parameters of steel vacuum carburization processes and preparing for cooling in high-pressure gas. In the following sections, the nature of vacuum carburization technology, the course of research on the precipitation phenomena, the construction of an artificial neural network and the algorithm of searching process parameters have been presented.

Investigating Fatigue Strength of Vacuum Carburized 17CrNi6-6 Steel Using a Resonance High Frequency Method

The bending fatigue strength of 17CrNi6-6 steel subjected to vacuum carburizing with high pressure gas hardening has been measured using a novel high-frequency technique. The test records the changes in resonance and consists of observing resonance frequency changes in a vibrating system with a single degree of freedom as a result of the forming of a fatigue crack. Moreover, a mechanism of fatigue nucleation and propagation in steel hardened by vacuum carburizing is presented.

Effect of Surface Treatment of Titanium Elements on the Bond Strength to Zirconium Dioxide

The aim of the study was to examine the effect of surface treatment of titanium elements on the bond strength to zirconium dioxide. Forty cylindrical titanium discs (Tritan CpTi 1) were divided into four groups (n=10) that were subject to: grinding (Group A), grinding and acid-etching with 5% HF (Group B), sandblasting with 60μm alumina particles (Group C) and sandblasting with 60μm alumina particles and acid-etching with 5% HF (Group D). Prepared materials were bonded to cylindrical discs made of zirconium dioxide (Ceramill Zi) by composite cement (Panavia F 2.0). The specimens were tested for the shear bond strength. The load was applied to the moment of the bond failure. Than the debonded specimens were vertically sectioned and the fractographic analysis of interfacial fractures under SEM as well as the analysis of chemical composition of the obtained fractures using radiographic spectrum were performed. The results were subject to the statistical analysis by using the analysis of variance. The highest values of bond strength were obtained for specimens whose surface was sandblasted and abraded. Fractographic investigation and the analysis of chemical composition of the cross-sections of the interfacial fractures revealed that the fracture occurred at the titanium-resin cement interface. Air abrasion treatment considerably improves the titanium and composite cement bonding and should be recommended for cementation of prosthodontic restorations constructed on titanium implants.

Complex XRD and XRF Characterization of TiN-TiCN-TiC Surface Coatings for Medical Applications

Article presents results of measurements of vital parameters of PVD coatings of potential application in medicine (joint replacements or medical tools). The phase identification, level of residual stresses and texture were determined for various coatings by X-ray diffraction method. Chemical composition of coatings was verified by means of XRF. A set of measurements reveled the existence of advantageous compressive stresses in coatings, the texture determination showed undesirable fiber texture in TiN coating and advantageous uniformity of TiCN ones. XRF analysis pointed out the necessity of careful preparation of samples during PVD process during which phenomena of inhomogeneity in chemical can be present as it is presented in the paper.

Simulation And Control Of Tool Steel Quenching Process.

Tool steels are widely used materials for making elements of metals, polymers, ceramics and composites. Inflated consumer expectations of contemporary civilization entail the manufacture of better and better tools, accompanied by reduced energy consumption. The application of simulators and controls of technological processes enables the design of optimum processes without the need for time consuming and costly experimental research. The present article is devoted to a tool for simulation and control of tool steel quenching in gases (helium, nitrogen, argon, hydrogen), both at negative as well as at high pressures. The simulator takes as its input the quenching parameters, the individual characteristics of the furnace and the material, dimensions and shape of the treated workpiece, yielding in effect a cooling curve and the forecast post-quench hardness. The monitoring program, which constitutes an integral part of the tool, works on-line with the industrial equipment, thus allowing continuous control of the quenching process with respect to the simulation in progress. In the subsequent sections the article presents the operation of the simulator and the monitor, the field of practical applications thereof, and describes a practical application working with an industrial furnace. Particular attention is drawn to the verification stage of the mathematical model and the results of experimental processes of tool steel quenching.

The Role of Carbides in Formation of Surface Layer on Steel X153CrMoV12 Due to Low-Pressure Nitriding (Vacuum Nitriding)

The mechanism of formation of surface layer on steel X153CrMoV12 in the process of vacuum nitriding (low-pressure nitriding) in a universal vacuum furnace in an atmosphere of dissociated ammonia at a pressure of 30 × 102 Pa (30 mbar) is studied by the methods of light microscopy and measurement of microhardness. The chemical composition of the nitrided layers is determined.