Surface tension and excess volume of the liquid Ti-V system measured in electromagnetic levitation

Due to their light weight, high strength, increased ductility, large corrosion resistance, and biocompatibility, Ti-based alloys have raised significant interest in recent years. They are ideal candidates for operation under extreme conditions, such as high temperature or aggressive chemical environment. alpha + beta titanium alloys in particular are of high interest for aerospace applications as well as for medical applications, with vanadium being one of the most prominent beta stabilisers. The addition of vanadium can elevate the thermal as well as the corrosive stability of Ti-Al alloys, especially those of lower aluminum content. The fast-growing interest in these alloys requires precise knowledge of thermophysical properties of the liquid phase as input for process optimization, phase calculation and atomic modelling. Density and the molar volume are two of the most fundamental thermophysical properties. The rather high melting temperatures of titanium and vanadium of 1941K (1668°C) and 2183K (1910°C), respectively greatly complicate their measurement using conventional container-based methods. Due to the highly reactive nature of the liquid Ti-V system, a container-less measurement needs to be implemented in order to avoid any reactions of the investigated liquid with existing container walls. In this work the already established optical dilatometry method is used for the density and molar volume determination of the liquid Ti-V system in electromagnetic levitation [1]. So far, there is not yet any model or rule of thumb in order to predict the molar volume of any liquid alloy, its density, its excess volume, or even the sign of the latter. Titanium alloys generally show a strongly non-ideal behavior with regard to their mixing properties, depending on the alloying element [2]. However, it has been shown that liquid alloys consisting of elements with similar electronic configuration, which is the case for titanium and vanadium, seem to exhibit almost ideal behavior with respect to the molar volume [3]. It is therefore especially interesting to investigate, how Ti-V behaves with respect to the molar volume and density. The present work uses electromagnetic levitation in order to containerlessly measure density and thermal expansion of Ti-V as function of both, temperature and composition. Thereupon, the molar volume of the Ti-V system is discussed in relation to existing trends predicting the excess volume of metallic alloys. First data is presented

Density and excess volume of the liquid Ti–V system measured in electromagnetic levitation

The density of the liquid Ti–V system was systematically measured using the optical dilatometry method in electromagnetic levitation. Possible error sources have been discussed and minimized. A linear temperature dependency with negative slope of the density was found for all investigated alloys. Pure vanadium shows the highest density, pure titanium the lowest with every measured alloy ranging between these two extrema. The molar volume was utilized in order to interpret the compositional density dependency. No significant excess volume was evident. It was therefore shown that the Ti–V system acts like an ideal solution regarding density, molar volume and temperature coefficient. This result allows to reliably calculate the density for the complete Ti–V system at any given temperature

Density, molar volume and surface tension of liquid Ti-V-Al and its binary systems measured by electromagnetic levitation

Due to their light weight, high strength, increased ductility, large corrosion resistance, and bio-compatibility, Ti-based alloys have raised significant interest in recent years. They are ideal candidates for operation under extreme conditions, such as high temperature or aggressive chemical environment. Thus, Ti-Al alloys are used in a wide range of applications, from turbine blades to medical implants. The addition of vanadium can elevate the thermal as well as the corrosive stability of Ti-Al alloys, especially those of lower aluminum content. The fast-growing interest in these alloys requires precise knowledge of thermophysical properties of the liquid phase as input for process optimization, phase calculation and atomic modelling. However accurate systematic data on density, molar volume and surface tension for liquid Ti-V-Al ternary alloys and its binary sub-systems at high temperature are scarce. The high melting points and the high reactivity at elevated temperatures complicate the measurement of reliable data in the liquid state heavily. The present work uses electromagnetic levitation in order to containerlessly measure density, thermal expansion, and surface tension of Ti-V, Ti-Al as well as Ti-V-Al, as function of both, temperature and composition. First data are presented

Experimental study of density, molar volume and surface tension of the liquid Ti-V system measured in electromagnetic levitation

Systematical experimental data on density, molar volume and the surface tension, measured in electromagnetic levitation, has been summarized for the liquid Ti-V system. The optical dilatometry method as well as the oscillating drop technique have been employed to investigate the temperature- and compositional dependence. A linear decrease in density and surface tension with increasing temperature has been observed for all investigated compositions. Pure Vanadium shows hereby the highest density and surface tension while pure titanium shows the lowest density and surface tension respectively. Therefore, the density and surface tension decrease with increasing titanium content, however not linear. Since no excess quantities were available, simple models could be employed to cover the complete liquid Ti-V system. Experimental data as well as the corresponding linear fits are presented

Surface tension of liquid Ti, V and their binary alloys measured by electromagnetic levitation

The surface tension of the liquid Ti-V system is systematically measured using the oscillating drop technique during electromagnetic levitation. Temperature- and compositional dependence are both investigated. The entire compositional range is covered. A linear decrease with increasing temperature is found for the pure elements as well as for all investigated alloys. The surface tension generally increases with increasing V-content. The obtained data is in good agreement with the Butler model for the ideal solution. Additionally, the Butler model for the regular solution was evaluated in the context of the obtained surface tension data. In contrast to many other Ti-based alloys, the Butler model for the regular solution yields no additional benefit for Ti-V, since there is only a neglectable small deviation between the calculations for the ideal and regular solution. Segregation effects are modeled using the Butler equation for an ideal solution. The findings are discussed considering already existing trends for the mixing behavior of liquid Ti-alloys. The results strongly suggest, that the Ti-V system obeys in general the ideal solution law

SURFACE TENSION OF LIQUID TI, V AND THEIR BINARY ALLOYS MEASURED BY ELECTROMAGNETIC LEVITATION

Ti-based alloys are prime candidates for construction materials used for applications in extreme conditions and environments, due to the combination of light weight with high strength, high temperature stability, large corrosion resistance as well as their bio-compatibility. Alongside this rising industrial demand comes an increasing need for precise knowledge of the thermophysical properties of Ti-based alloys, as input for process optimization, phase calculation and atomic modelling. The Ti-Al-V system is currently the most relevant alloy system when it comes to industrial application. While, now, there are some data regarding the thermophysical properties of the Ti-Al [1] side of the system, reliable and systematic data for the Ti-V system are still sparse. One of the major reasons for this is the difficult processability of liquid Ti-V at elevated temperatures, due to the high chemical reactivity of the system. Electromagnetic levitation offers a container-less measurement method for density as well as surface tension without the risk of contamination of the sample by container walls. Density is hereby measured in a shadow graph technique where an expanded laser is directed onto the levitating sample. The molar volume is subsequently obtained from integration over the profile edge curve of the sample shadow captured by a camera on the other side of the sample. Surface tension is measured by means of the oscillating drop technique. Here a high-speed camera records the surface oscillations of the molten droplet and the frequency spectra are evaluated according to the sum formula of Cummings and Blackburn. The obtained density and surface tension data are analyzed by means of different thermodynamic models. In case of the density, it is found that Ti-V obeys the ideal solution model, so no excess volume needs to be considered [2]. The surface tension data can be evaluated using Butler’s thermodynamic model. Again, near perfect agreement is found only with the ideal solution model. Even while utilizing the levitation method, contact between the melt and the surrounding atmosphere cannot completely be prevented. Oxygen, plays a crucial role for metallic melts in most applications, since already small oxygen contents can greatly influence the thermophysical properties of liquid alloys [3]. Therefore, in a second step, the influence of oxygen on the before studied thermophysical properties of the Ti-V system will be reviewed

Thermoplastic forming of additively manufactured Zr-based bulk metallic glass: A processing route for surface finishing of complex structures

Additive manufacturing of bulk metallic glasses (BMGs) through laser powder bed fusion (LPBF) has drawngrowing interest in the last years, especially concerning industry-relevant alloys based on iron or zirconium.The process-inherent high cooling rates and localized melting pools allow to overcome geometrical restrictionsgiven for the production of BMGs by classical casting routes. Yet, the achievable surface qualities are still limited,making an adequate post-processing necessary. In this work, we report on applying thermoplastic forming onLPBF-formed parts for thefirst time to decrease surface roughness and imprintfinely structured surface patternswithout the need for complex abrasive machining. This BMG-specific post-processing approach allows tofunctionalize surface areas on highly complex LPBF-formed specimens, which could be of interest especiallyfor medical or jewelry applications