Abstract:The paper presents the results of alloying titanium by oxygen in the process of chamber electroslag remelting. As

Abstract. This paper focuses on deoxidation of titanium alloys produced by aluminothermic reduction (ATR) and subsequent homogenizing and alloying by vacuum induction melting (VIM). The main goal of the performed research work is to outline the deoxidation limit during pressure electro slag remelting (PESR) of the described material. To obtain electrodes for deoxidation, a Ti-24Al-16V masteralloy was produced by ATR and afterwards melted in a 0.5 litre calcium-zirconate (lab scale) or 14 litres high purity calcia (pilot scale) crucibles with continuous addition of Ti-sponge after reaching liquid state in order to obtain a final Ti-6Al-4V alloy. During melting, in both cases evaporation of calcium was noticed. The cast ingots were analysed for oxygen using inert gas fusion method, matrix and alloying elements were analysed by XRF. Results show oxygen levels between 0.5 and 0.95 wt.-% for the ingots which were melted in calcium-zirconate crucibles and approx. 1 -1.2 wt.-% for the material produced by utilization of calcia crucibles. The subsequent deoxidation was carried out in lab and pilot scale electroslag remelting furnaces using a commercially pure calcium fluoride slag and metallic calcium as deoxidation agent. It could be shown, that deoxidation of the highly contaminated material is possible applying this method to a certain limit. Pilot scale trials showed a reduction of oxygen contents by 1500 -3500 ppm. Oxygen levels in lab scale trials showed weaker deoxidation effects. In order to describe the achieved deoxidation effects in a quantitative way, the analyzed oxygen contents of the obtained ingots are compared with calculated data resulting from a mathematical kinetic model. The modelled datasets are in good agreement with experimental oxygen values.

The hot isostatic pressing (HIP) technology is considered on the example of making of compacts made of VZh159 powder. It is shown that powders with fractional composition of –70 +25 µm, bulk density of 3.77 g/cm3 , fl uidity of 2.3 g/s, specifi c surface of 446 cm2 /g, and average Fischer particle size of 16 µm are prone to sorbed gases. Gases on the surface of the powder body as result of the HIP cycle can form non-metallic inclusions that reduce the properties of the compact. To effectively remove gases, vacuum heat treatment is used: degassing. It is established that the structure of HIP-compacts after two- or four-stage ageing has fi ner grain (point 9) compared to the cast alloy (point 7).The mechanical properties of the compacts obtained made of VZh159 power exceed the correspointing requirements of the standard process documentation for ultimate strength by 21...22 % and elongation by 36...45 %.

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The current work is devoted to the investigation of oxygen impact on the structure and properties of titanium. For this purpose, oxygen was introduced into titanium during chamber electro-slag remelting by three different methods: alloying by oxygen-rich residues from the Kroll process to final values between 0.053 wt.-% and 0.40 wt.-%, by reaction with the gas phase to 0.27 wt.-% and by introduction of TiO 2 nanoparticles to 0.73 wt.-%. The influence of oxygen on microstructure of titanium during crystallization, heat treatment and deformation is determined as well as the effect of oxygen on the hardness and the mechanical properties of the material in different structural states. Furthermore, control methods of the structure formation process by thermal effects are proposed. Results show that the chamber electroslag remelting allows obtaining a homogeneous structure of the ingot in the investigated range of oxygen content in titanium. The hardness does not vary by more than 10 percent in longitudinal or radial direction in any of the remelted ingots.