V. Chitanov

Study of the Structural and Mechanical Properties of Nanocrystalline TiAlSiN Gradient Coatings

A study of the structural and mechanical properties of nanocrystalline TiAlSiN gradient coatings deposited by cathodic arc deposition techniques at 500 °C and post-annealed at 525 °C is presented. Analysis of the coatings, chemical composition and microstructure revealed that the coatings have a structure based on (Ti, Al)N nanocrystals with an average size of 10 nm embedded in an amorphous Si3N4 phase. The study of the mechanical properties showed that post-annealing causes improvement and increase of the coatings hardness. A maximum hardness of 48 GPa and elastic modulus of 560 GPa were measured. Also, excellent adhesion to the WC-Co substrate was observed in the post-annealed coatings.

Mechanical, Structural and Thermal Properties of Multilayered Gradient Nanocomposite Coatings

Multilayered, Gradient Tialsin-Based Nanocomposite Coatings Have Been Developed and Investigated with Respect to their Applicability in the Machining Industry. the Main Coating Layer Was Composed of 5-8 Nm Tin and Aln Nanograins. the Coating Possessed Hardness as High as 40 GPA, which Allows it to Be Classified as Superhard. during Heating up to 900oC in Air in Steps of 100oC for 6 H at each Temperature, the Coating Showed Good Stability up to 700oC. Thermal Treatment over this Temperature Caused a Decrease in the Hardness to Values Characteristic for Tialn Multilayered Coatings, while the Adhesion to the Substrate Remained Steady.

Increasing in the wear resistance of injection molds made of 1.2343 steel using Ti/TiN/TiCN/nc-TiCN:a-C/nc-TiC:a-C/a-C nanocomposite coating

Injection molds used in production of plastic components are subject of heavy abrasion wear. The increase of their wear resistance significantly reduces the production cost. In the current work are presented research results of the wear resistance of injection molds made of steel 1.2343, coated with Ti/TiN/TiCN/nc-TiCN: a-C/nc-TiC:a -C/a-C. The study of the wear rate was done using the volumetric method and the influence of the trace length was investigated. The coating thickness, nanohardness, elastic modulus and adhesion were also tested. The coating was applied on unhardened ground specimens, hardened ground specimens and hardened polished specimens.

Al-Free Nanolayered Metallization Systems for Sub-Micron HEMTs

Al-Free Nanolayered Metallizations Based on the Transition Metals Ti, Mo, Ni and Pd, with Varied Ti Content, Have Been Developed as an Alternative of the Al-Based Contacts for Sub-Micron Hemts. the Electrical, Morphological and Thermal Properties of the Metallization Schemes Have Been Studied with the Aim of Obtaining the Most Suitable Combination of Low Resistivity, a Smooth Surface and an Acute Edge. the Lowest Resistivity of 8.8x 10-6 Ω.cm2 Has Been Determined with the Ti/Mo/Ti/Au Contact, while the Lowest Surface Roughness of 6 Nm Has Been Measured for the Ti/Ni/Ti/Au Metallization. these Contact Schemes Have Shown much Better Edge Acuity in Comparison to the Al-Based Metallizations.

Search for a Suitable Ohmic Metallization Scheme to GaN/AlGaN Heterostructures for Sub-micron Devices

Ohmic properties, thermal stability and surface morphology of Al-based and non-aluminium metallizations are investigated in dependence on the annealing temperature and initial composition. Non-aluminium contacts show poor ohmic properties, while contact resistivity of 3.47x10-5 Ω.cm2 is achieved for Ti/Al/Ti/Au metallization with a former-Ti/Al ratio of (30 wt.% /70 wt.%). Thermal properties of the Al-based metallization are improved by application of Mo layer as a barrier under the upper Au film of the contact structure. These contacts show excellent thermal stability at operating temperatures as high as 400oC. The less Al amount in the contact composition and Mo barrier layer contribute to the smoother surface and better edge acuity.

Ti- and Cr-based hard coatings obtained at low temperatures by unbalanced magnetron sputtering

We prepared a set of Ti- and Cr-based ternary and quaternary hard coatings at low deposition temperatures (< 200 °C) by closed-field unbalanced magnetron sputtering in a gas mixture of Ar + N2. The morphological, structural and mechanical properties of the coatings were characterized by means of atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectrometry, a micro-scratch tester and a nanoindentation tester. The results of the analyses performed revealed that the surface of the deposited ternary Ti-Al-N coatings was rougher than that of the CrTiAlN coatings. The metallic elements in the coatings react with nitrogen to form CrN, TiN and AlN nitride phases, as no Cr2N phase was detected in the Cr-based coatings. The optimized quaternary coating demonstrated mechanical properties superior to those of the ternary ones in terms of hardness; adherence strength of 32 GPa and elastic modulus of 418 GPa were measured for the multicomponent coating of composition Cr0.68Ti0.19Al0.13N.

Dependence of the electrical and morphological properties on the Ti and Al content in Mo-based ohmic contacts for III–V nitrides

Four types of Mo-based ohmic contacts with a varied Al and Ti content are developed and investigated regarding the ohmic properties, surface morphology and edge acuity. It is found out that the Ti/Mo/Ti/Au metallization combines the lowest contact resistivity of 8.8×10-6 Ω.cm2 and low surface roughness of 3.8 nm. The presence of Al in the contact composition does not improve the electrical properties and the surface morphology. Its effect on these properties depends strongly on the Ti/Al ratio in the contact composition.

Mathematical Modelling the Power Supply-Load System for Electro-Discharge Polishing Process

The real electro-discharge polishing (EDP) system has been presented by an equivalent electrical scheme and described by a corresponded equation system. The Runge-Kutta-Merson method with automatically changed step is used for the numerical solution the equation system. The current through the resistor equivalent to the steam gas wrapper is defined with an I-V characteristic obtained by the method of multi-interval quadratic interpolation-approximation. A mathematical model of the power supply-load system has been realized in Basic and Matlab® languages. On the base of the developed modelling conditions limiting the current and voltage overload in the EDP system have been determined depending on the maximum polished area and the electrolyte temperature.