EP0236247A1 - Metallic components of which at least one face presents at least one zone region resistant to wear - Google Patents

Abstract

These components consist of a controlled distribution of regions hardened by a localised melting effect and characterised in that the said regions, whatever their length and their shape, have a width and a depth of between 3 and 150 mu m and that the proportion of the regions per unit area is between 5 and 60% in the case of each mm<2> of a region. These components can be employed for the manufacture, in particular, of engine liners and pistons, of valve seats, of brake drums and discs, of cranked transmission pulleys, of dies, of gears, of journals, of drive shaft bearings, of ball bearings and of various electrical components for sliding contacts. <IMAGE>

Description

EXPOSURE OF THE PROBLEM

Those skilled in the art know that metal parts subjected to friction must have technological characteristics such as, in particular, resistance to wear and resistance to seizing at least on their "active" face, that is to say ie that which is in contact with the opposing part. Most often, these characteristics are only necessary in regions representing only a portion of said face, and in well localized areas of said regions.

These areas generally result from a surface hardening treatment of the parts obtained by different means.

PRIOR ART

For example, French patent 2,371,520 describes a process for treating a given exposed region of an aluminum article or one of its alloys in the presence or not of an alloying agent, with a laser beam or an electron beam of high energy (at least 10,000 watts / cm ² ) and of diameter between 250 and 1250 μm, so as to be able to heat the article in a first zone and to melt it in a second zone inside said first zone: a fine-grained structure is thus created at least in said zone, with the aim, inter alia, of improving the resistance to wear and eliminating or reducing the deformations resulting of treatment.

Claim 24 of this patent states that "said beam is moved along several separate and spaced paths so as to affect areas forming spaced regions on the exposed surface of said article".

Likewise, French patent 2,367,117 claims "a process for treating a metallic surface with a bearing surface of a component, characterized in that it consists in heat treating only bearing zones for modify their metallurgical properties and improve their resistance to wear ".

According to a particular example of this process, the treatment is applied to a casing of cast iron hardened by cementation and consists in directing on the latter a laser emitting a beam such that it forms a point with a diameter of 3000 μm.

Japanese patent application published under No. 59,212,572 also teaches a method for curing the inner surface of an internal combustion engine cylinder by means of a laser in which the area ratio of the untreated areas to treated areas is preferably between 10 and 70% and the dimension of the treated areas is several mm.

These documents therefore teach that zones suitable for friction can be obtained on parts by thermally treating their surface so as to locally obtain zones with a width exceeding 250 μm.

The Applicant, seeking to apply such lessons, has observed that it is certainly possible to obtain localized hardening in the treatment areas, but that this hardening is accompanied in the event of localized fusion, on the one hand, by a deformation of the part such that it required re-machining before use, on the other hand, sometimes cracking and the initiation of fatigue cracks due to the surface stresses developed by local overheating resulting from the treatment.

PURPOSE OF THE INVENTION

This is why, the applicants have sought to develop metal parts of which at least one face is treated by thermal melting effect so as to develop at least one region of zones resistant to wear and capable of friction but such that '' they contain very few surface stresses likely to develop cracks or other degradation during their use and also such that they can be used rough treatment, that is to say without rework, expensive and delicate operation on parts hardened and which by its thermal and mechanical effects, can modify the structure of the treated area and, consequently, its tribological characteristics.

STATEMENT OF THE INVENTION

According to the invention, metal parts of which at least one face has at least one wear-resistant region on the surface consisting of a controlled distribution of zones hardened by localized melting effect are characterized in that said zones, whatever their length and shape, have a width and a depth between 3 and 150 µm and that the surface fraction of the zones for each mm2 of a region is between 5 and 60%.

• - d'une part, une forme plus ou moins allongée, mais une largeur et une profondeur très faibles comparées aux pièces de l'art antérieur
• - d'autre part, une répartition fine desdites zones, puisque pour chaque mm² de surface appartenant à une région, elles représentent 5 à 60 Z de ladite surface, c'est-à-dire qu'elles sont espacées les unes des autres par une distance inférieure à 1 mm.

Thus, the active faces of the invented parts have, on their surface, and in regions suitably chosen according to the use to be made of them, hardened zones meeting the following two characteristics:

• - on the one hand, a more or less elongated shape, but a very small width and depth compared to the parts of the prior art
• - on the other hand, a fine distribution of said zones, since for each mm ² of surface belonging to a region, they represent 5 to 60 Z of said surface, that is to say that they are spaced from each other by a distance less than 1 mm.

In addition to these characteristics, it has been found that it is advantageous when the zones intersect to limit the fraction of overlap surface of said zones for each mm ² of a region to 50% of 1 total surface of the zones.

Under these conditions, it is observed that in addition to the significant increase in the wear resistance caused by the presence of hard zones, the deformation stresses caused by the fusion-resolidification at the level of the zones were much lower than those observed on areas of greater width and depth or more widely covering the surface or even more frequently intersecting.

Likewise, it is noted that the differences in dimensions between the zones and the inter-zone spaces do not exceed 10 μm, which therefore avoids any re-machining of the parts before use. In other words, the treatment changes little the geometric profile of the treated part and only involves a slight change in the roughness.

In addition, the presence of spaces between the zones appreciably improves the ability of the parts to friction by creating on the surface and on a fine scale an alternation of hardened zones and soft spaces, a very effective arrangement generally in resistance to wear. by adhesion, fatigue or abrasion and also effective in friction since the soft inter-zone spaces constitute traps for lubricant, or even traps for wear debris.

However, in the range of width and depth of the areas claimed, it was noted that it was preferable to stick to the values between 10 and 100 μm to obtain the best results.

• - ni régularité de forme des zones : dans le cas d'une zone de forme quelconque, la notion de largeur citée plus haut peut être définie comme étant deux fois la dimension 1/2 qui conduit dans les techniques dites de squelletisation utilisées en analyse d'image à une disparition de la zone,
• - ni une disposition régulière des zones en surface.

The invention itself does not require:

• - nor regularity of shape of the zones: in the case of a zone of any shape, the concept of width quoted above can be defined as being twice the dimension 1/2 which leads in the techniques known as of skeletonization used in analysis of image of the area disappearing,
• - nor a regular arrangement of the surface areas.

The invention in fact involves in principle the statistical idea of reducing the width and depth of the zones and of separating them, the distribution on the scale of mm 2 and the shape of the zones having a second order effect with respect to with the width-depth effect and surface fraction.

However, for reasons of convenience of creating these zones on the surface of the parts, the invention also includes the zones regularly arranged on the surface of the parts in the form of periodic or quasi-periodic arrays of bands, the width and the depth of which are obviously between 3 and 150 pm.

Thus, the zones can be arranged in the form of continuous bands separated from each other by a distance of between 20 and 1000 μm, these bands having either any direction or representing at least one network of parallel bands. However, these zones can also be arranged in the form of discontinuous bands separated along their length and from each other by a distance of between 20 and 1000 μm; these bands having, as before, either any direction or representing at least one network of bands parallel.

The invention applies in particular to any alloy, in particular of aluminum, whose tribological properties are capable of being improved by a surface fusion treatment. It also applies to all parts where the zones consist of a base metal alloy melted with a filler element or a filler compound such that said alloy has better tribological properties than the base metal. This element can be, for example, iron or nickel, in particular, when the base metal is an aluminum alloy.

The zones corresponding to the characteristics of the invention can be obtained by any process making it possible to locally modify the nature or the structure of the surface of the part over a shallow depth and over a narrow width so as to give it by thermal effect and / or chemical better ability to friction.

Mention may in particular be made of the use of high energy radiation such as electron beams and laser radiation suitably focused so as to create by fusion zones of width and depth less than 150 μm.

Obtaining axial, circular or helical bands or any other shape can be easily achieved by controlling the relative movement of the part and the beam by means of a microprocessor.

For example, with a conventional argon laser beam with a power of 18 watts sufficiently focused to reach a power density greater than 1.10 ⁶ watts / cm ² , it has been possible to produce on the surface of parts made of aluminum-silicon alloy a square mesh network formed of strips of width 30 μm separated from each other by a distance of 100 μm and this by exposing the pieces to the action of the beam for less than 1.10 seconds and by moving the beam relative to the piece so as to make it describe a series of parallel paths in two perpendicular directions. But it is also possible to use energy sources capable of emitting a large number of beams which allows a more practical realization of the network.

We thus created on a fine scale a set of treated areas of small dimensions (width <150 μm) separated from each other and formed a surface made of a hard material embedded in a softer matrix. The parts thus treated showed only a minor deformation of the surface profile, this avoiding rework; their application to an aluminum alloy motor liner did not lead to any degradation by release of stresses and their tribological behavior in contact with the piston / segment was better than that of the liners whose entire surface had been treated with beams creating areas of 3000 µm width.

The invention can be illustrated with the aid of the attached drawings which show, with regard to FIGS. 1, 2 and 3, different arrangements of zones produced according to the invention on a region of an active face of a part while FIG. 4 relates to a micrograph of a region portion of a part according to the invention and FIGS. 5, 6 and 7 to micrographic sections of parts according to the prior art (FIGS. 5 and 7) and according to the invention (fig. 6).

• . La figure 1 représente des zones (1) de forme et de largeur quelconques réparties de façon quelconque mais qui ont toutes une largeur comprise entre 10et 100 pm et une fraction surfacique pour chaque mm2 de surface comprise entre 5 et 60 %.
• . La figure 2 représente des zones disposées régulièrement suivant un réseau à mailles carrées constitué de bandes (2) d'une largeur de 40 pm espacées les unes des autres de 360 µm.
• . La figure 3 représente des zones ponctuelles (3) d'une dimension de 50 pm espacées les unes des autres de 100 µm.
• . La figure 4 est une microphotographie au grossissement 100 de zones réparties suivant des bandes de 40 um de large espacées les unes des autres de 200 um et s'entrecroisant à angle droit et qui sont obtenues sur des pièces en alliage d'aluminium du type A-S17U4G (Silicium 17% - cuivre 4% - magnésium < 1% - solde aluminium).

More precisely :

• . FIG. 1 represents zones (1) of any shape and width distributed in any manner but which all have a width comprised between 10 and 100 μm and a surface fraction for each mm 2 of surface comprised between 5 and 60%.
• . FIG. 2 represents zones regularly arranged according to a square mesh network made up of bands (2) with a width of 40 μm spaced from each other by 360 μm.
• . FIG. 3 represents point areas (3) with a dimension of 50 μm spaced from each other by 100 μm.
• . FIG. 4 is a photomicrograph at 100 magnification of zones distributed in bands of 40 μm in width spaced from each other by 200 μm and intersecting at right angles and which are obtained on aluminum alloy parts of type A -S17U4G (Silicon 17% - copper 4% - magnesium <1% - aluminum balance).

Figures 5, 6 and 7 will be commented on in the description of the example which follows.

APPLICATION EXAMPLE

Parts in A-S5U3 (that is to say containing by weight 5% of silicon, 3% of copper and the balance in aluminum and impurities) and in A-S17U4G (17% Si, 4% Cu, <1 % Mg) produced in the same way were divided into two batches numbered 1 and 2, both comprising the two types of alloy.

Lot 1 was subjected to a laser treatment to obtain areas according to the prior art and lot 2 to another laser treatment to obtain areas according to the invention.

The conditions for these treatments are as follows:

• Du point de vue relief :
  • . sur le lot 1 (fig. 5) qui représente, vue en coupe et au grossissement 25 une zone (4), on observe un relief macroscopique s'étendant sur toute la largeur de la zone et dont l'amplitude atteint 100 µm, ce qui oblige à réusiner la pièce.
  • . au contraire, sur le lot 2 (fig. 6) qui représente, vue en coupe, et au grossissement 1000 une zone (5), on n'observe aucun relief macroscopique. Seule la microrugosité est légèrement affectée mais elle ne nécessite aucun réusinage.

The following observations were made:

• From the relief point of view:
  • . on lot 1 (fig. 5) which represents, in section and at 25 magnification an area (4), there is a macroscopic relief extending over the entire width of the area and whose amplitude reaches 100 μm, which requires reworking the part.
  • . on the contrary, on lot 2 (fig. 6) which represents, in section view, and at 1000 magnification an area (5), no macroscopic relief is observed. Only the microroughness is slightly affected but it does not require any rework.

In these Figures 5 and 6, there is also a radical change in structure which allows precise location of the area and the measurement of its dimensions.

On the 2 batches, a Vickers hardness greater than 200 was measured in the zone and 80 between the zones.

Consequently, the parts according to the invention and which therefore have zones of small width and shallow depth have a rate of deformation of the surface profile such that it is no longer necessary to machine them.

Other parts of the same type were previously coated with an iron film by electrolysis in a quantity such that it allowed after fusion to produce on the surface an alloy with 15% iron.

These parts have also been divided into 2 lots which have undergone the same treatments as those described above, except for the layout of the treated areas.

Indeed, the surface of the parts of lot 1 was treated according to overlapping unidirectional parallel bands (lot lA) or not (lot 1B: distance between bands 2000 pm) while that of lot 2 was treated according to a network of bands parallels crossing at right angles and spaced from each other by 200 µm.

Micrographic examination of the surfaces showed that in some cases the treated areas of lots 1A and IB had cracks (6) (fig. 7) while those of lot 2 (fig. 6) were not.

In another series of tests, the iron was replaced by a galvanic deposition of nickel so as to produce an alloy on the surface after fusion. to 10 x nickel and the parts of the 2 lots were subjected to friction-wear measurements using the CAMERON-PLINT tribometer.

This tribometer consists of a segment in chromed cast iron which presses on the surface to be checked and which is driven in an alternating movement so as to approximate approximately the friction which occurs between the segments inserted in the piston and the jacket of an engine. internal combustion.

In this case, the support load was 100 N, the room temperature 100 ° C, the frequency of movement 12 Hz and the test time 30 min. The surface was previously lubricated with an oil of the Neutral 150 type.

The parts in lot 1 deteriorated rapidly (detachment of large debris> 1 µm from the treated surface). The same was true of the chromed cast iron segment.

As for the pieces in lot 2, they did not give rise to any visible deterioration or measurable weight loss.

The present invention finds its application in the manufacture of parts intended to be subjected to friction such as for example mechanical parts (engine liners and pistons, valve seats, brake drums and discs, toothed transmission pulleys, dies, gears , bearings, bearing surfaces of drive shafts, ball bearings, etc ...) and electrical contact parts where friction and passage of electric current are combined (connectors, sliding contact, electric motor collector, etc ... ).

It has been developed on aluminum alloys, but can also be applied to other metallic materials and alloys: steel, copper, zirconium, titanium, nickel. It has also been verified on a few examples: nickel, copper, titanium.

Claims (12)

1. Metal parts of which at least one face has at least one wear-resistant region on the surface consisting of a controlled distribution of the hardened zones by localized melting effect, characterized in that these zones, whatever their length and their shape, have a width and a depth of between 3 and 150 μm and that the surface fraction of the zones for each mm ² of a region is between 5 and 60 X. 2. Metal parts according to claim 1 characterized in that when the zones intersect, the surface fraction of overlap of said zones for each mm ² of a region is less than 50% of the total area of the zones. 3. Metal parts according to claim 1 characterized in that the zones have a width and a depth of between 10 and 100 µm. 4. Metal parts according to claim 1 characterized in that the zones are arranged in the form of continuous strips of any direction and separated from each other by a distance between 20 and 1000 µm. 5. Metal parts according to claim 4 characterized in that the zones are arranged in the form of at least one network of parallel strips. 6. Metal parts according to claim 1 characterized in that the zones are arranged in the form of discontinuous bands, in any direction, separated along their length and from each other by a distance between 20 and 1000 µm. 7. Metal parts according to claim 6 characterized in that the zones are arranged in the form of at least one network of parallel strips. 8. Metal parts according to claim 1 characterized in that they consist of an alloy whose tribologic properties ques are likely to be improved by a surface fusion treatment. 9. Metal parts according to claim 8 characterized in that they consist of an aluminum alloy. 10. Metal parts according to claim 1 characterized in that the zones consist of an alloy of the base metal with an element or a filler compound such that said alloy has better tribological properties than the base metal. 11. Metal parts according to claim 10 characterized in that the filler compound belongs to the family of iron, nickel. 12. A method of obtaining metal parts according to claim 1 characterized in that one applies a focused laser radiation so as to create by fusion areas of width and depth less than 150 µm.

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