Publications by authors named "Mihai Ovidiu Cojocaru"
The creation of strong adhesive layers of hydroxyapatite-based bioceramics (with or without bioinert metals, such as Ta, Ag, and Ti) on biocompatible metallic supports enhances the local biofunctionalization of surfaces. The processing of electroconductive materials using electrical impulse discharges is versatile, enabling precise coating of selected areas with perfectly adherent layers of varying thicknesses. This study aims to quantify the effects of varying the electrical power from the source generating the impulse discharge and the specific processing time per unit area of the cathode (made of titanium alloy) on the relative mass increase of the cathode.
View Article and Find Full Text PDFThe quantification of the single or combined variation of the process parameters specific to a thermochemical treatment is the key to a full factorial experiment and a first step in the development of computer-aided process engineering. Powdery solid media are frequently used in the practice of thermochemical treatments when the number of processed products is reduced, additional investments are not justified, or when there are no technological alternatives. The control of the process carried out in such powdery solid media involves both the control of the thermal and temporal parameters of the process on the layer growth kinetics and its phase composition, as well as the ratio of the powdery solid mixture mass percentage (active and neutral components, reaction activators, and components with the role of blocking the sintering tendency of the medium particles).
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- The paper examines both direct and indirect methods for synthesizing nickel aluminides using pack cementation, focusing on pure nickel and the IN 718 superalloy.
- The study highlights the formation of diffusion porosity due to the Kirkendall-Frenkel effect, noting that higher temperatures above aluminum's melting point lead to decreased porosity.
- It also reveals that altering the aluminum to nickel weight percentage ratio in the diffusion coating significantly enhances the performance of nickel-based superalloys like IN 718, particularly when using different aluminum and iron powder mixtures during the process.
The scholarly literature records information related to the performance increase of the cutting tools covered by the superficial layers formed "in situ" when applying thermochemical processing. In this context, information is frequently reported on the carbamide role in processes aiming carbon and nitrogen surface saturation. Sulfur, together with these elements adsorbed and diffused in the cutting tools superficial layers, undoubtedly ensures an increase of their operating sustainability.
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- - The paper examines how diluting ammonia with nitrogen affects the growth and composition of nitrided layers on two types of steel—Fe-ARMCO and 34CrAlMo5 nitralloy steel.
- - It employs experimental programming and mathematical modeling to analyze the impact of key parameters like nitriding temperature and ammonia dissociation on layer growth kinetics.
- - The study finds that both the dilution of ammonia and the degree of ammonia dissociation play crucial roles in determining the nitrogen potential of the gaseous mixture used in nitriding, which subsequently affects nitrogen concentration at the metal surface.