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.
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.
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.
The need for welded structures of high-strength steels requires detailed studies on the factors influencing the behaviour of these steels during welding. The present work introduces results on the influence of the welding gap on the structure and some mechanical and technological properties of welded joints of high-strength steel S960QL, joined by submerged arc welding.
Purpose: The presented research aims to determine the microstructural changes in weldments of commercially pure titanium Grade 1 after welding by hollow cathode arc discharge in vacuum and related changes in the corrosion behaviour of the weldments. Design/methodology/approach: Macro and microstructure of weldments were studied using optical microscopy. Corrosion behaviour of untreated Grade 1 and heat-affected zone of weldments of Grade 1 was investigated using electrochemical testing, including open circuit potential measurements and potentiodynamic polarisation. As an aggressive environment, 1 M KBr water solution was used. Findings: Welding by hollow cathode arc discharge in vacuum leads to the formation of a coarse Widmanstätten structure in the heat-affected zone. This imperfect structure results in a passive layer with worsened protective properties, thus increasing the corrosion rate of weldments by up to two orders of magnitude compared to Grade 1 in as-received condition. The passive layer on the welded surfaces did not allow Grade 1 to acquire a stable corrosion potential during potenitodynamic polarization. Research limitations/implications: Titanium and its alloys are passivating metallic materials, and their corrosion resistance depends on the properties of a thin protective surface layer. Changes in the underlying metal microstructure can affect the passivation behaviour of titanium and the properties of this layer. Welding by hollow cathode arc discharge in vacuum alters the microstructure of heat-affected zone, thereby causing Widmanstätten microstructure to form. As the passive layer over that microstructure has worsened protective properties, we suggest additional heat treatment after welding to be applied. Future experimental research on this topic is needed. Originality/value: Welding by hollow cathode arc discharge in vacuum is a welding method allowing weldments to be done in a clean environment and even in space. In the specialised literature, information on the structure and corrosion resistance of weldments of commercially pure titanium Grade 1 welded by hollow cathode arc discharge in vacuum is missing. The present research fills in a tiny part of this gap in our knowledge.
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