EP0511131B1 - Method for preparation of reference samples for spectral analysis - Google Patents

Description

The invention relates to a method for preparing reference metal samples for spectrographic analysis.

The reference metal samples are generally prepared by conventional casting and peeling or by powder metallurgy (mdp) and compacting. They are generally in the form of cylinders, the machined cross section of which is subjected to analysis excitation (spark, X-rays, etc.).

The main quality of these samples is chemical homogeneity as perfect as possible over the whole of this circular surface. In addition, a large number of reference samples being taken from a given product, such as a bar, from the same cast billet, it is important that chemical homogeneity is also ensured between the different positions, in particular between the head and the foot of the initial bar.

These difficulties have hitherto been resolved in part by the effective use of the only central part of the peeled product obtained from a cast billet or by powder metallurgy; however, in the first case, elimination by machining of a large external part of the cast product leads to a significant mileage and a high price; in the second case, the implementation is delicate, complicated and costly (see Analytical Chemistry, vol.49, n ° 4, April 1977, p.679). In addition, in this case, the ignition of the spark is difficult because of the higher oxide content (typically between 2000 and more than 3000 "g / g of oxygen for the mdp against less than 200" g / g by spray-deposition and typically less than 100 ”g / g).

The method according to the invention therefore consists in developing a substantially cylindrical preform by spray-deposition, then in consolidating this blank in the form of a bar of appropriate diameter, and finally in cutting the reference samples. By spray-deposition is meant a process in which the metal is melted, atomized by a jet of neutral gas at high pressure in the form of fine liquid droplets which are then directed and agglomerated on a substrate so as to form a massive and coherent deposit containing a low closed porosity. This technique is also designated by the "Osprey" process. In the case of the invention, the deposit is essentially in the form of billets. The spray-deposition takes place under neutral or inert gas. The rate of wrinkling during consolidation must be sufficient to allow the closed porosity induced by the process to be eliminated. Consolidation can be obtained by any known means such as spinning, forging, rolling, hammering, etc.

• elle permet d'obtenir des préformes de grande dimension (par exemple ⌀ 200 x 500 mm) de grande homogénéité chimique en raison de l'absence de ségrégation majeure;
• la composition des alliages peut être facilement ajustée, en particulier les hautes teneurs en éléments d'alliages, en l'absence de la ségrégation majeure observée lors de la coulée classique;
• la pulvérisation-dépôt sous gaz neutre permet d'obtenir des alliages pratiquement exempts d'inclusions d'oxydes (ce qui est très difficile à éviter en mdp) même avec des éléments fortement oxydables tels que Ti Li, Na, etc...
• Comme déjà indiqué, elle permet d'obtenir moins de 200 »g/g et typiquement moins de 100 »g/g d'oxygène.

This method has the following advantages over the methods of the prior art:

• it makes it possible to obtain large preforms (for example ⌀ 200 x 500 mm) of high chemical homogeneity due to the absence of major segregation;
• the composition of the alloys can be easily adjusted, in particular the high contents of alloying elements, in the absence of the major segregation observed during conventional casting;
• spraying-deposition under neutral gas makes it possible to obtain alloys practically free of oxide inclusions (which is very difficult to avoid in mdp) even with highly oxidizable elements such as Ti Li, Na, etc.
• As already indicated, it makes it possible to obtain less than 200 »g / g and typically less than 100» g / g of oxygen.

The invention will be better understood with the aid of the following examples relating to Al-based alloys the chemical compositions of which (by weight%) are as follows:

These alloys were obtained in the form of billets ⌀ 180x600 mm by spray-deposition under the following conditions: Alloy (1) (2) Pouring temperature: 720 ° C 750 ° C Distance atomizer-deposit kept constant during the test 575mm 575mm Gas flow / metal flow (Nm³ / kg) 3.3 3.37 Nature of gas No. No. Stainless steel collector with rotational movement Yes Yes Oscillation of the atomizer with respect to the axis of rotation of the collector Yes Yes Reheating
Reheating by induction heating at 420-430 ° C, rise time 5 to 8 min Maintaining in ventilated oven (450 ° C) from 30 min to 1h20
Spinning
Spinning container temperature 340-350 ° C, Spinning speed 0.9 <v <4.5 m / min Spinning temperature 450 ° C Spinning ratio: 11

As an example, the coefficients of variation s / x comparisons of the 3 elements Fe, Cr, Pb, the contents of which were determined at different points in the same reference sample, with comparable Fe, Cr and Pb contents, obtained by the 3 methods indicated are respectively:

In this table, s represents the standard deviation and x the average value of the content of the element considered.

We can see the better chemical homogeneity of the products obtained according to the invention

For alloys (1) and (2), less than 60 g / g of oxygen was obtained.

Claims (5)

1. A method for the production of metal reference samples for spectrographic analysis, characterised in that:

   - an alloy having a given chemical composition is prepared by spray deposition in a neutral or inert gas, this alloy containing less than 200 ppm of oxygen.

   - the blank thus obtained is consolidated in the form of a bar of appropriate diameter.

   - reference samples are cut therefrom.
2. A method according to Claim 1, characterised in that the oxygen content is loss than 100 ppm.
3. A method according to one of Claims 1 or 2, characterised in that the consolidation is carried out by extrusion.
4. A method according to one of Claims 1 to 3, characterised in that the working rate is sufficient to eliminate residual closed porosity.
5. A method according to one of Claims 1 to 4, characterised in that the alloy is an Al-based alloy.