Ion Pencea

Structural characterization and adhesion appraisal of TiN and TiCN coatings deposited by CAE-PVD technique on a new carbide composite cutting tool

A new composite matrix was developed for a cutting tool based on tungsten carbide ligated with cobalt (WC-Co) using sintering technique. The admixtures of niobium carbide, tantalum carbide, and titanium carbide with the WC-Co matrix aim to inhibit the grain growth of WC and to promote covalent bonding at the interface. The modified WC-Co tools were coated with titanium nitride and titanium carbonitride layers by CAE-PVD technique. To substantiate the performances of the new coating-substrate systems, we have performed X-ray diffraction, atomic force microscopy, and scratch test measurements to estimate: phase content, average crystallite size, average texture coefficient, residual stress level, coating thickness, average roughness, square mean root, fractal dimension, cohesive adhesion, and adhesive adhesion. The results enable the in-depth understanding of the coating growth mechanisms and provide an objective evaluation of the coatings adhesion to the new cutting tools matrix. The results provide evidence to support the potential of TiN and TiCN coatings to enhance the working performances of the composite WC-Co cutting tools and to differentiate their properties. TiCN coating is shown to be superior to TiN coating in terms of adhesion and thus represents a better alternative for coating the modified WC-Co composite matrix.

New Aspects Regarding the Structure of Spheroidal Cast Iron Carbon Inclusions Revealed by WAXD Investigations

The paper addresses mainly the atomic structure of the spheroidal carbon inclusions (CIs) from a magnesium treated cast iron. The qualitative phase analysis based on diffraction patterns shows that the CI by-products contain carbon, ferrite and iron oxides. Based on peak angular positions and their half-width at half-intensity, the distances between graphenes and the average height of the graphene stack were calculated. To comply with EN 13005 standard, the calculated results include the extended uncertainties U(95%). The Wide Angle X-ray Diffraction (WAXD) data proves clearly that the CI from the spheroidal cast iron do not have a polycrystalline graphite structure, but rather a turbostratic graphite-like structure with the d(002) surprisingly close to the graphite structure, e.g. to 3.34 Å. If this conclusion is accepted, a new approach of the nucleation and growth mechanisms of the CIs in spheroidal cast irons as turbostratic graphite-like structures should be explored, while the mechanisms based on crystallographic considerations should be revised.

Influence of high temperature exposure on the adhesion of a micro-composite refractory enamel to a Ni–18Cr–12W superalloy

Abstract A new micro-composite refractory enamel (MCRE) was designed to play a multifunctional protective role (thermal barrier coating, corrosive and erosive protection) for the hot working parts made of EI868 superalloy sheets i.e. burning chambers, fire tubes, volets, eclises, etc. The effect of the isothermal heating at elevates temperature (800 °C, 900 °C) were, for the first time, investigate for MCRE/EI868 couple. The adhesion strength has shown an enhancement of about 100% when the couple was heated at 800 °C or at 900 °C for 10 h compared with the unexposed one. SEM-EDS, OM, XRD, EDP-XRFS and SDAR-OES investigations support a chemical bonding mechanism between MCRE and EI868 substrate via a transient interface layer. Elemental EDS distributions show that the Cr selective oxidation is responsible for the formation of the transient layer. The XRD measurements can be correlated with the contribution of the spinellic transformation of the SiO2, Cr2O3, NiO to the adhesion enhancement. The most important result reported herein is the adhesion strength enhancement of the MCRE coatings to the EI868 supperalloy by isothermal treatment. Accordingly, the MCRE behaves as a self-healing coating. Noteworthy, the working lifetime of the MCRE-EI868 couple can be significantly enhanced if an optimum pre-treatment is applied before it comes into service.

Multiconvolutional approach for uncertainty estimation of the thermal diffusivity measured by flash method

The paper addresses the exactness of the results of the thermal diffusivity (a) of a Sn-Ag-Cu soldering alloy, mainly a new approach for measurement uncertainty (MU) estimation of the value assigned to the measurand. The method used for α measurement is the flash one implemented on an Anter Flash Line 3000. The weak point of this method is the exactness of the value assigned to the measurand due to the large uncertainty budget of the measurement process. Thus, uncertainty budget contains a great number of contributor factors to the MU assigned to the result as specimen factors (homogeneity, flatness etc), equipment factors (drift, calibration etc) operational factors (parameter settings, specimen coating etc). The authors purpose a multiconvolutional approach based on uniform probability distributions function (PDF) of the individual result. The fundamentals of the multiconvolutional approach are given in the paper together with the motivation for intentional use of this approach. This approach fulfills the requirements of the EN ISO/CEI 17025 and EN Guide 98-3 standards that underpin any effort for an accurate estimation of the MU. The paper brings a new view about MU estimation for α of Sn-Ag-Cu which could be extended for the interconnecting structures and not only.

Energy Dispersive Techniques Using X-Ray Fluorescence with Primary X-Rays for Human Hard Tissues Analysis

Among others, biomedical research is conducted for the systematic collection and analysis of data from which general conclusions can be drawn and which can increase the life quality of the patients. Given these issues, the aim of the research presented in this paper is to analyze the concentration of heavy elements from the human body, using complementary analysis methods, based on the energy dispersion spectrometry (EDS) technique.

New approach for measuring the surface tension of SnAgCu305 molten alloy

The aim of the research is to improve the exactness of the measurement of the surface tension of the molten SnAgCu soldering alloy at different temperatures. The method used for surface tension measurement of molten alloys is of pendant drop type. The weak point of this method is the exactness of the curvature radius measurement, but mostly the exactness of the first order derivative of the droplet profile function depending on the droplet height measured from its apex. The authors propose a modeling approach of the droplet profile by analytical function of the class C2. Based on the analytical profile function were calculated the curvature of the droplet and subsequently the surface tension. The paper will present the main data and results obtained during the first part of the researches regarding implementation the method for temperature in the range of soldering process. There were measured the surface tension of a SnAgCu 305 alloy obtained in a laboratory of UPB at temperature ranging from 225 to 265°C. The expanded measurement uncertainty of the results, with 95% degree of confidence, was estimated based on multi-convolutional approach of uniform probability density functions. The main result of the paper consists in finding of a simple way of simulating of the symetric shape profile with analytical function. Based on the first and second order derivatives of the simulated profile function were calculated the surface tension. An other important result consists in improving the quality of the test results based on measurement uncertainty estimation.

A Study on Trace Elements Concentration in Bone Particles by XRF Analysis

High concentrations of metals in the natural environment associated with industrial activity and increased migration of metals may cause an increase in the concentration of metals in living organisms, especially in the bone tissue, which reflects their total concentration in the body. Physiological basis for this assessment is based on the fact that the skeleton serves as a major reservoir for ingested heavy metals integrating them into bone matrix during calcification and where they remain until the bone is remodeled or resorbed. Investigations on the bone can be focused on three structural levels: mezostructural, micro, and nanostructural. In this study, we used X-ray fluorescence (XRF) to measure the residual amount of heavy elements in bone particles, obtained by a widely used method. The bones used to perform the experiments were collected from local hospitals, following certain surgical coxofemural prosthesis operations (according to agreed procedures on patient privacy and medical ethics).Studies carried out on samples taken from humans have shown that the variability in bone chemical composition is depending on subject living area, which is essential for understanding the contribution of these factors on bone mass and constitution. Comparing values obtained with concentrations of metals in bones reported by other authors allowed us to conclude that EDPXRF method can be used to assess tissue concentrations of natural elements and the results provide a basis for evaluating metal loading of the human body.