Titanium alloys are known for their good mechanical properties, low density, excellent corrosion resistance and low thermal conductivity. These properties define titanium and its alloys as highly suitable for medicine, automotive and aerospace industries. Unfortunately, the thermal cycle during welding of alpha-beta alloys (Ti-6Al-4V) can significantly change their strength, toughness and plasticity. The scope of present work is to investigate the possibility for producing Ti-6Al-4V welds by arc discharge in vacuum and to establish the influence of the welding parameters on dimensions and mechanical properties of the welds. The experiments presented here were carried out in an installation for hollow cathode arc treatment in vacuum. Cylindrical and elliptical tantalum cathodes were used. The welding was carried out without filler material and groove. Tensile test and hardness test of specific welds zones were used for mechanical properties determination. The results, presented in this work, describe the dimensions of the fusion zone and heat affected zone of welds, produced by hollow cathode arc welding using different welding parameters. The mechanical properties of the welds were determined.
Purpose: To present a technology for hardfacing of metal-cutting tools by arc welding in vacuum. Design/methodology/approach: The experiments were carried out using an installation for arc welding in vacuum. Objects of research were metal cutting tools (lathe knives), made of high-speed steel HS6-5-2 on a base metal of structural steel C45. The structure, hardness and wear resistance after hardfacing and after a triple tempering at 560°C have been determined. The heat resistance of the obtained instruments has been examined. Findings: The microstructural analysis showed that the structure of the built-up layer consisted of martensite, retained austenite and carbides. This was confirmed by the values of measured hardness after welding which were about 63-64 HRC. The triple tempering led to an increase in hardness by 3-4 HRC. It was found that the built-up layers (cutting edges of tools) retain their hardness (HRC=63-65) up to a temperature of 615-620°C, which shows that the heat resistance of the build-up layers was similar to that of the hardened and tempered tools of the same steel. The built-up work-pieces (excluding heat treated) and the reference knife showed the same cutting qualities at cutting speeds in the range of 55 to 120 m/min. It has been found that triple tempering after hardfacing led to increased wear resistance and consequently the durability of the tool also increased due to the higher hardness. Practical implications: The practical application is related to the production of metalcutting tools. Originality/value: The proposed technological method allows to produce defects free built-up layers. The cutting properties of the built-up in vacuum layers are comparable to or better than those of new tools made of steel HS 6-5-2.
The structure of Ti-6Al-4V alloy and Ti-6Al-4V weldments was examined. The welds were produced by hollow cathode arc discharge in vacuum using tantalum cathodes and different welding parameters. The corrosion behaviour of Ti-6Al-4V alloy and Ti-6Al-4V welds in solution containing Brwas evaluated quantitatively using potentiodynamic polarization tests. The corrosion behaviour of the base metal and welds was compared. Open circuit potential, pitting potential, corrosion current densities and corrosion rates were determined. The influence of the structure and its change during welding on corrosion behaviour is discussed in the present paper.
This paper presents research on vacuum quenching oils at different pressure conditions during the cooling stage of the heat treatment process. The aim of this work is to reveal the influence of the pressure, agitation (laminar or turbulent flow), and oil temperature on the cooling oil. Medium and low viscosity oils are investigated. The research is novel because it expands knowledge of quenching oil behavior at low and high pressure conditions (from 1 mbar to 2.5·103 mbars). The findings are presented as integral diagrams (time-temperature and cooling rate versus temperature curves) and tables of the local cooling ability valuations. It is found that the pressure in the chamber is the main factor that influences the cooling ability of the examined media. The trend of pressure influence can be generalised as: the greater the cooling oil ability, the stronger the pressure value influence. In addition to the above, the possibility of routine change of the pressure makes it a prospective factor to control the cooling oil ability.
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