Dynamically developing plant growing continuously sets challenges to the system for training specialists, who have to be able to develop competitive and sustainable agriculture. In the conditions of market economy and various forms of land management, for the development of plant growing are needed managers and executives, who will be able to apply successfully the scientific principles of research, analysis, support and management of cost-effective agricultural production units. The degree programme Plant Growing provides preparation of such specialists. Education in Crop Science and Production offers such kind of training by application of innovation moments such as practical semester and development of integrated project.
Author: Nikolova M.
Physical surface properties including surface roughness, topography, morphology, and wettability could influence the implant material behavior, bio-response, bacterial contamination and contact with other bio-active surfaces or fluids. This work investigates microand nanoscale roughness parameters and surface morphology of PVD deposited (Ti,Al,V)N/TiO2 coating using optical microscopy, white light interferometry (WLI), contact profilometer and scanning electron (SEM) microscopy. Results indicated that vacuum oxidized surface possessed medium roughness values, anisotropy in surface texture and irregular morphology. The vacuum oxidation of the nitride maintained the oxide with nano-crystal size and showed pores at the interface between the layers. The effect of prolonged exposure to Ringer-Braun solution droplet on the modified crystalline structure of the oxide was also explained.
Ti and its alloys are mostly used for implant production. Their biocompatibility depends on the formation of thin TiO2 layer on the surface. It can be improved by modification of oxide structure in tubular. For biomedical applications, the adhesion of the coating layers is essential. The aim of the present paper is to investigate the adhesion of TiO2 nanocoatings on titanium surface.
Commercially pure Ti (CP Ti) and Ti-6Al-4V alloy samples were grinded, etched and anodized. The anodization was done in 0.5 wt.% HF electrolyte with duration of 7 hours for the CP Ti samples and 6 hours for Ti-6Al-4V alloy samples. The adhesion was investigated by tape and scratch tests. The critical loads that generate the first failures during the scratch test are used for characterization of the adhesion of the TiO2 nano-tubular coating. The critical loads were measured by CSEM-Revetest macroscratch tester under progressive scratching mode. The samples were characterized by SEM and EDX analysis. The areas around the critical load were further observed by optical and scanning electron microscopy for detail inspection of failure mechanism.
It was established that the higher micro-roughness of the surface of CP Ti sample after anodization is responsible for the detachment only of small areas of the nano-tubular coating situated mainly on the top surface. The lower micro-roughness of the sample made of titanium alloy and the presence of large flat areas lead to detachment of large coating’s portions. The scratch test reveals that the TiO2 nano-tubular coating on the CP Ti fails at an early stage (Lc1 ~ 8 N; Lc2 ~ 26 N), while that on the Ti-6Al-4V sample undergoes cohesive failure and completely fails at higher load values (Lc1 ~ 13 N and Lc2 ~ 40 N respectively). As titanium alloy is ductile material with higher strength than the CP Ti, it provides better support for the coating and produces higher critical loads.
The present study aims to determine the optimum temperature regime for oxy-nitrocarburizing of AISI D2 steel in order to ensure high mechanical properties of both diffusion and compound zones. The examined samples are quenched and high temperature tempered in advance, thus having a hardness equivalent up to HRc 54-55 before saturation. The vacuum oxy-nitrocarburizing is held at temperatures of 500 ºС, 550 ºС and 590 ºС for 4 hours in a cycling gas flow rate. The proportion of NH3 and CO2 gases used is 90:10 volume fractions. The results of the examination are based on the analysis of X-ray diffraction patterns, cross-section microstructures and measurements of micro-hardness values on the surface and in depth of the diffusion zone. The core hardness of the substrate is also measured after the vacuum process for the purpose of establishing a possible hardness decrease after the oxy-nitrocarburizing process. Conclusions have been drawn in relation to the practice.