Thanks for the detailed description. But could you know the range of real values – (0,1-10) atm as it is often mentioned in theoretical researches or (0,0001-0,001) atm as it is measured in experiments?

What kind of measurement have you in mind? A long time ago I did some measurements by myself , which were in good agreement with theoretical estimations based on Laplace pressure in keyhole, which corresponds to values 0,1-10 atm. I attach a paper where those experiments are described.

See above

Andrey, thank you so much for the document. But unfortunately , there are no announced experiments on measuring the pressure in the keyhole.

As for the measurements which I have in mind, they are described (for example) in the following articles:

1. Verigin А.М., Еrochin А.А., Shavyrin А.N., Reznichenko V.P. Fizika i chimiya obrabotki materialov, 1980, No. 2, pp 145-146 (in Russian)

2. Bondarev А.А., Voropai N.М. Fizika i chimiya obrabotki materialov, 1974, No. 2, pp 50-55 (in Russian).

I hope the Russian language is not a problem for science. References of other articles are welcome.

I should add the following:

The thesis that the pressure inside a keyhole is determined by the balance of static pressure of vapour and Laplace pressure, is erroneous because it excludes the influence of thermocapillary flow, which defines the hydrodynamics in welding

The balance of pressure in ideal fluid is defined by Bernoulli's equation as the ratio between static and dynamic pressure. The static pressure is created by vapor pressure, hydrostatic pressure and Laplace pressure. The dynamic pressure is created by thermocapillary flow of metal.

Published experimental data give us the possibility to estimate the real value of each part of Bernoulli equation. It has been done in my article published in J. Phys. D: Appl. Phys. 42 (2009) 175501 (7pp). It was shown that the Laplace pressure and the recoil pressure of vapour’s inside the keyhole can be disregarded.

Dear Amin,

this chart reflects the design pressure of saturated vapors of metal under conditions of thermodynamic equilibrium at temperature up to 2000 and has little to do with deep penetration welding, because the real conditions of welding are strongly nonequilibrium and correspond to temperatures of about 3000 K

So, the recoil pressure of vapors (not the saturated vapor pressure) is traditionally considered as the main and only factor of seam formation in deep penetration welding.

However, as outlined in my question, the measurement during EBW in vacuum does not confirm the presence of the required high pressure inside a keyhole. I know the measurements which were made in 70-80 years and were published in Russian:

1. Verigin А.М., Еrochin А.А., Shavyrin А.N., Reznichenko V.P. Fizika i chimiya obrabotki materialov, 1980, No. 2, pp 145-146 (in Russian)

2. Bondarev А.А., Voropai N.М. Fizika i chimiya obrabotki materialov, 1974, No. 2, pp 50-55 (in Russian).

Penetration of the protective gas into weld root defects in laser welding at atmospheric ambient pressure also indicates the formation of pores at low pressure and eliminates the decisive role of evaporation in the formation of the crater.

Dear colleagues! The dicussed problem is in center of another my question in RG - what experiments do you know which confirm the keyhole formation in laser welding by the action of recoil pressure of vapor?

You are welcome to discussion

I should add the following:

The thesis that the pressure inside a keyhole is determined by the balance of static pressure of vapour and Laplace pressure, is erroneous because it excludes the influence of thermocapillary flow, which defines the hydrodynamics in welding

The balance of pressure in ideal fluid is defined by Bernoulli's equation as the ratio between static and dynamic pressure. The static pressure is created by vapor pressure, hydrostatic pressure and Laplace pressure. The dynamic pressure is created by thermocapillary flow of metal.

Published experimental data give us the possibility to estimate the real value of each part of Bernoulli equation. It has been done in my article published in J. Phys. D: Appl. Phys. 42 (2009) 175501 (7pp).

It was shown that the Laplace pressure and the recoil pressure of vapour’s inside the keyhole can be disregarded.

See the fragment of article in attached file

Felix, thanks in advance. I will wait the opportunity to read your article with interest .

We have been working a bit with this topic based on the in-situ radiography of keyhole and followed with calculations of keyhole volume and thus the pressure. We will publish the paper by first author Mikko Vänskä during end of this year.

Dear colleagues! Оne of the best specialists in evaporation materialsV. V. Semak from Pennsylvania State University published just now in RG the new research - Atomistic misconception of current model for condensed matter evaporation and new formulation.

Below is a short quotation from this article:

" Evaporation is perceived by general community of scientists, engineers and educators as well studied and it is commonly believed that accurate physical model is mostly completed. However, those who attempt practical application of the existing models find that accuracy of predictions is unacceptably low for any real-world application. This indicates that current understanding of seemingly trivial evaporation phenomenon is inadequate."

Article Atomistic misconception of current model for condensed matte...

Dear colleagues! 332 specialists viewed this issue for 4,5 months. But nobody reported experimental data on measurements of recoil pressure of vapor in laser welding. Such data does not exist?

Dear Felix, I am just intrigued by the expectation of your posting. So I wish you success with presentation.

Felix, I have read your article. I liked the experiments and data obtained.

But as it is known there is a high thermodynamic nonequilibrium condition in the cavity during laser welding. But your opinion about the significant (up to 90 %) vapor recondensation of metals in this area means the recognition of condition close to thermodynamic equilibrium. How can this be reconciled?

As I see, the problem is that the vaporization hypothesis in welding conditions is not supported by experiments and even is in contradiction with many data. On this topic I am preparing to publish an article, which I hope to finish in a few months.

As for the accuracy of the applying evaporation theory for modeling in practical applications, here are a few reputable citations:

- “experimental data indicate that the vaporization rate under most welding conditions is five to ten times lower that the rate predicted by the Langmuir equation” - T. DebRoy, S. A. David Physical processes in fusion welding. Rev. Mod. Phys., 1995, Vol. 67, No 1.

- «The dominant and mostly researched theoretical model of evaporation… is based on the concept proposed more than hundred years ago by Hertz, Langmuir, and Knudsen (referred here as HLK model). This theoretical model is a straightforward physical model expressed in terms of relatively simpler mathematics; however, the HLK model in current interpretation is known to lack accuracy expected for practical applications. Because of this low accuracy the HLK model is used only for the educational purposes: it is taught as a concept to the students studying Thermodynamics, Heat Transfer and other related disciplines. In practice, researchers and application engineers use empirical relations (when such are available) that provide the evaporation rate, saturated vapor pressure, and other vapor parameters as function of temperature, pressure and other conditions that seldom include velocity and chemical composition of ambient gas.» V. V. Semak . Atomistic misconception of current model for condensed matter evaporation and new formulation. 2014. https://www.researchgate.net/profile/V_Semak https://www.researchgate.net/publication/262974273_Atomistic_misconception_of_current_model_for_condensed_matter_evaporation_and_new_formulation )

- “Comparison of the measured values of velocity, acceleration and pressure with those calculated from Anisimov’s theory show very poor agreement. The calculated values are in all cases far larger (by at least an order of magnitude).” - V. V. Semak, G. A. Knorovsky, D. O. MacCallum, D. R. Noble, M. Kanouff. Measurements and Calculation of Recoil Pressure Produced During CO2 Laser Interaction with Ice. International Conference on Lasers and Electron Optics, San Diego, CA (US), 9 Dec 1999

Article Atomistic misconception of current model for condensed matte...

There are some thoughts on a given topic in attached file

I suggest to get acquainted with the discussion of the topic here

https://www.researchgate.net/post/Why_does_the_depth_of_laser_weld_increases_in_a_vacuum

I am also very curious about the vapor pressure in the keyhole in the laser powder bed fusion process. Any recommended articles are very appreciated.

Dear Yuze, now my article on this topic is being prepared for publication. Until it came out, I can recommend the following my publications (see below). This topic seems simple, but numerous prejudices prevent it from being dealt with. It takes character and faith in yourself. In any case I am ready to help you if this topic interests you for real

Article Threshold conditions for thermocapillary transition to deep ...

Conference Paper Analysis of The Main Hydrodynamic Mechanisms in Laser Induce...

Conference Paper Verification of the melt displacement mechanism in deep pene...

Rinat Seidgazov Many thanks, Rinat. Looking forward to your publications.