EP0758410A1

EP0758410A1 - Process for incorporating material into the surface of a solid body and altering it, in particular the surface of a material

Info

Publication number: EP0758410A1
Application number: EP95919345A
Authority: EP
Inventors: Eduard Igenbergs; Josef SPÖRER
Original assignee: Igenwert GmbH
Current assignee: Igenwert GmbH
Priority date: 1994-04-26
Filing date: 1995-04-26
Publication date: 1997-02-19
Also published as: JPH09512306A; WO1995029274A1

Abstract

A process is disclosed for incorporating material into the surface of a solid body by means of a short-duration pulse of a mass of high energy and density. Additional treatment can be carried out to further improve the characteristics of the surface layers thus created.

Description

METHOD FOR IMPACTING AND INFLUENCING A SOLID SURFACE, IN PARTICULAR A MATERIAL SURFACE

1. DESCRIPTION OF THE PROCEDURE

A briefly acting flow of a high-energy plasma is directed onto the surface layer to be influenced. With regard to chemical composition, temperature, density and speed, this plasma pulse must be such that the following processes take place:

The surface layer is melted. There is a brief high temperature in this melting or melted layer. When plasma hits this melted surface layer, a total pressure is briefly generated, which generates a shock wave that runs into this material. In the wake of this shock wave, components of the plasma pulse are transported into this boundary layer. At the same time, the gases forming the plasma are diffused into the boundary layer.

The duration of the action of the plasma pulse on the surface layer to be treated, as well as the energy supplied in the process, are set up in such a way that, on the one hand, the processes listed can take place, but on the other hand, short-term solidification can also take place.

With a suitable design and composition of the surface layer to be treated, rapid solidification can occur if the listed conditions are selected appropriately. This creates non-equilibrium phases and nanocrystalline structures.

The duration of action of such a pulse is determined by the desired layer density, which determines the duration of action and the total energy supplied, and by the desired final state after the treatment. This depends on the cooling rate, which decreases with increasing duration of action and energy supply. For a final state, a certain combination of composition and duration of action as well as temperature and density of the plasma pulse on the one hand and composition, configuration and physical-chemical initial state of the material on the other hand is required.

A certain, optimal configuration of the parameters mentioned is always part of the invention described here and inevitably results from the rules listed here.

A surge discharge of an electrical or electromagnetic energy In the storage device such as, for example, a capacitor bank, a high-energy, high-pressure plasma is generated in an electrothermal accelerator. The plasma pulse hits the surface of the material. As a result of the interaction between plasma and material, that is to say through the supply of energy, a layer close to the surface of about 25 μm thick and more is converted into the molten state, its chemical composition is changed by additions which are carried in the plasma pulse and by energy dissipation the cold base material immediately solidifies again. The influencing of the surface is dependent on the plasma pulse. The temperature is 10 ⁴ K, the short-term pressure 1 to 5 kbar, the density 0.1 kg / m ³ , the speed approx. 3.5 km / s and the exposure time 10 to 100 μs. The heat dissipation into the base material at room temperature takes place at about 10 ⁶ K / s, the power density at the active site is 10 ⁶ to 10 ⁷ W / cm ² at a plasma pulse duration of approx. 50 μs.

Such a rapid solidification results in non-equilibrium states. The surface layer modified in this way contains metastable phases, such as the ε phase or austenite (see figures from 1st additional application dated 3.3.94), and has a very fine-crystalline or fine-grained layer structure in the nanometer range. The alloying of carbon together with the rapid solidification results in a significant increase in microhardness in the surface layer.

2. SPECIAL FORMS OF PRESENTATION

Additives, in particular carbon, must be introduced in such a way that this carbon hits the surface to be treated in a state which is particularly suitable for this treatment. In this case, it proves to be advantageous to design the residence time of the additives in the plasma as far as possible so that the carbon, which is initially in powder form (graphite), is converted into a molecular and / or even atomic gas. The surface should be influenced as soon as possible after the heating and acceleration process. The composition and structure can be changed in a targeted manner by varying the energy supplied in the accelerator. As shown in Fig. 1 and Fig. 2, it results from a change in the energy supplied. In comparison to Fig. 1, the structure visible in Fig. 2 is created, which is a martensitic structure and only has about 50% of the hardness in Fig. 1.

This results in variations in the surface modification, such as the following variants already carried out: 1. unalloyed structural steel St37 with added carbon in the plasma pulse

2. Austenitic chromium-nickel steel X12CrNi18.8 with added carbon in the plasma pulse

3. Austenitic chrome-nickel steel X12CrNi18.8 with chrome-carbon addition in the plasma pulse

4. Alloying of materials that could not be alloyed in the standard processes used up to now, such as zirconium oxide

5. Alloy of tungsten carbide

The experiments were carried out identically for all variations with regard to the experimental procedure.

In the treatment according to the invention of the surface layer of austenitic steel and in particular of chromium-nickel steel, crystalline structures in the nanometer range are formed, within which chromium carbides and iron carbides are formed. In Fig. 3a a transmission electron microscope (TEM) picture of the untreated starting material is shown, in Fig. 3b a TEM picture of the treated edge layer as chromium-nickel steel. Even finer structures are found between the individual structures shown in this photograph and examined with an X-ray diffractometer. The result is shown in Fig. 4, from which references to chromium carbide and iron carbide can be found.

In the tests with St37, an edge layer of approx. 25 μm thickness was achieved, the microhardness in this layer increased to around 1200 HV ₀ .oι. These layer samples were then annealed at 570 K, 870 K and 1170 K in an oven in an air atmosphere for 30 minutes each. A drop in the layer microhardness to approx. 500 to 1000 HV _{0 01} could be observed from the heat treatment at 870 K. After annealing at 1170 K, the surface layer is no longer present, instead a thick scale layer appears around the entire material.

TEM investigations of the non-heat-treated layer show various structures, such as cell structures, stripe-like areas, carbide inclusions and areas without recognizable structures.

Similar results were found in the tests according to X12CrNi18.8 with added carbon. With an average layer thickness of 25 μm, the microhardness was increased to approximately 1600 HV _{0 0} . Here too, after the heat treatment at 870 K, lower microhardnesses of approx. 850 to 1500 HV ₀ .oι _{> result} gradually Annealing at 1170 K, the layer disappears and the workpiece becomes scaled.

In the experiments with plasma pulses, which in addition to the carbon also contained chromium in the plasma pulse, the heat treatment at 1170 K increased the microhardness to 750 HV ₀ r, and homogenized the layer. After the modification of the surface layer, soft and hard areas are present in the layer, so that hardnesses of 250 to 1700 HV _{0 0} ι resulted. After annealing at 870 K, the various layer areas were dissolved, but the hardness in the layer only ranged between 250 and 400 HV ₀ .Oι. Only when annealed at 1170 K did a homogeneous layer with increased hardness result , of around 750 HV ₀ . _υ ι •

During the investigations under the electron microscope, areas with cells and strips were often found, but also areas without structure. After the heat treatment at 870 K, no noticeable differences were found. Only after the heat treatment at 1170 K can the cell walls dissolve and the cells grow together.

The different behavior of the layer hardness during heat treatment can be explained by the fact that in the first two test series almost no or only little chromium was contained in the surface layer, which resulted in heat resistance of up to 870 K each. In the third series of tests, on the other hand, the addition of chromium to the plasma pulse contained carbide formers in the surface layer, which were responsible for increasing the hardness after annealing at the high temperatures.

In the process used in this work, two surface treatment forms (alloying and remelting) can be carried out in one work step to expand the known possibilities for surface layer modification.

The simultaneous alloying of the additives carried in the plasma flow takes place essentially by two processes:

• Diffusion of plasma components

• Material transport (in the target) of the shock waves induced by the plasma pulse

To estimate the extent to which the additional material carried in the plasma flow can be stored in the material during the melting phase of the surface layer, the conservation laws by Rankine-Hu goniot. With the shock wave speed for iron (Up = 6 km / s) and the physical law of the impact, the material speed Up in the target for the experimentally determined plasma speed of Up (ro _j e _kt ii) = Up | _ = 3.5 km / s, in experiments with an electrothermal accelerator system, the rate of expansion of the carbon carried in the plasma flow in the melting phase of the boundary layer is from about 500 μm / s to 1 m / s.

The plasma flow in this process lasts about 50 μs. It follows from this that additives which are co-accelerated by the plasma jet can be embedded in the entire melt layer, which is up to 30 μm deep, due to the tracking speed of the shock waves.

In contrast to the so-called shock hardening, the surface layer can be influenced in the molten state.

3. SELECTION OF SUBSTRATE MATERIALS AND ADDITIVES FOR THE SHORT-TERM PLASMA PROCESS

The main goals of the generation of new types of surface layers of any materials by means of short-term plasma treatment are:

1. Increase in corrosion and scale resistance

2. Increase in wear resistance

3. Generation of boundary layers for thermal insulation

4. Improve the sliding properties

The materials are summarized in the following groups:

1. Iron materials

1.1. Cast iron

1.2. steel

2. Copper materials

2.1. Lead copper

2.2. Copper alloys

3. High temperature materials

3.1. refractory metals

3.2. high-melting alloys 4. Light metals and light metal alloys

4.1. Light metals

4.2. Alloy alloys

5. Ceramics

6. Glasses

7. Sintered materials

The additives that are introduced into the accelerator during or after plasma formation are divided into two areas:

1. Additives that become the main component of the surface layer (addition of large amounts).

2. Additives that are mixed with the melted surface layer of the material (addition of small amounts).

4. MELTING ORDER OF ADDITIONAL MATERIAL

By treating the same surface layer several times, additional material is melted down. Because of the procedure according to the invention, the surface layer to be treated is melted with each plasma pulse treatment. The "depth" of this melting process can be varied via the parameters of the plasma pulse. In any case, a melting process occurs in which the material carried in the plasma pulse is partially melted into the surface layer. If there is sufficient material carried in the plasma pulse, material with the same plasma pulse that is not melted into the surface to be treated is additionally supplied. A coating can thus be carried out in which the coating produced is fused to the surface to be treated. In this case, the desired technical properties, such as hardness, corrosion resistance, etc., are also produced in the layer considered as coating, as in the modified layer.

A multiple treatment of the same area of the surface can be produced with this method, a combined surface treatment and coating with a desired coating thickness. A thickness of 200 μm has already been reached experimentally. Furthermore, the material carried in the plasma pulse can consist of the same material as the surface layer to be modified or of other materials. In addition, with multiple The composition of the material carried in the plasma pulse, as well as the parameters determining the plasma pulse, are changed from pulse to pulse, so that particularly structured surface coatings are produced.

It is also possible to harden the surface layer of non-ferrous metals, e.g. achieve Cu / B or Al / B in the system.

In addition, when using steels with a sufficiently high carbon content, a conversion behavior can be generated immediately below the edge layer that is no longer melted, in order to set the desired property changes in the material.

5. DESIGN OF THE INFLUENCED SURFACE LAYER

The surfaces to be influenced can be divided into

1. Outside surfaces

2. Inner surfaces

These can be symmetrical, such as a circle, cube, ball, cylinder, and strip-shaped surfaces as well as cutting, tips can be treated. Finally, any shape is conceivable.

The plasma generation, exposure to additional material, as well as the alignment and acceleration can take place electrothermally or electromagnetically as well as in any combination of these processes.

Arrangement for the treatment of cylindrical surfaces from the outside

As shown schematically in FIG. 5, a race is formed by two rings with the inner radius η and the outer radius r _a , which are arranged at a distance d from one another. A high-pressure ring adjoins the upper race and the electrode ring, which consists of only one part. This can be seen in Fig. 6. If necessary, the arrangement can be separated into two half rings which are put together before the treatment.

This is particularly necessary in the event that the surface to be treated cannot be inserted into the treatment ring, as could be the case, for example, with a crankshaft. Cylindrical interior spaces are treated by plasma pulses which are directed radially outwards, as shown in Fig.7. The cross section through which the plasma pulse flows could be kept as constant as possible in order to achieve a uniform treatment.

The linear arrangement as shown in Fig. 8 is intended for the treatment of "stripes". Just as with the cylindrical as well as punctiform (circular) arrangement, treatment areas can be connected to one another without interruption of the layer by sequential treatment.

The arrangement shown in Fig.8 can also deviate from the purely linear arrangement both in the direction of the x-axis and the z-axis (both at the same time), ie form a z-dimensional "serpentine line".

Influencing ring-shaped surface layers

Annular surface layers that lie in one plane or are also inclined (e.g. valve seats and / or contact surfaces on valves) can be treated with a single plasma pulse.

Fig. 9 shows an electrothermal arrangement for generating ring-shaped plasma pulses. The annular space between two concentric cylinders made of non-conductive material is closed on one side by one of the two electrodes. On the other side there is an annulus, which is formed by two coaxial cylinders made of electrically conductive material. These represent the second electrode. The plasma, with or without additives, is generated in the space between the non-conductive cylinder and then flows out through the annular space between the conductive cylinder and then strikes the surface to be influenced.

Fig. 10 shows an arrangement in which the same surface influence is achieved by a coaxial accelerator arrangement. Between two coaxial, conductive cylinders, which form the two electrodes, a coaxial cylinder made of an electrically non-conductive material is sometimes also attached. The material that forms the plasma with or without additives when the capacitor battery is discharged is introduced into the space not occupied by this insulator between the two coaxial electrodes. This is accelerated by electromagnetic forces towards the open end of the annular cavity between the two electrodes and applies to them there treating surface.

A ring-shaped influencing of a surface layer can also be achieved by partially covering the area which is treated in accordance with laid-open specification DE 42 26 229 A1 "method and device for impulse application to a solid surface, in particular a material surface".

The same procedure can also be used if the surface to be treated is conical. An oblique impact of the plasma pulse improves the surface quality, but generally reduces the depth of the affected layer.

Both arrangements according to FIGS. 9 and 10 can also be designed to be convergent or divergent in order to adapt to the angle of the surface to be treated. Furthermore, in both arrangements, coaxial cavities can be arranged within the inner electrode or within the inner combustion chamber wall, by means of which the valve tappets can be lifted, for example when treating the underside and valve plate of valves in automobile engines.

Process parameters shock hardening plasma pulse hardening

Duration [s] 1 Q-9. 10-8 10-6 - 10-5

Intensity [W / cm ² ] Q9 - 10 ¹⁰ 10 ⁶ - 10 ⁷

Temperature [K] approx. 10 ⁴ approx. 104

Pressure [kbar] approx. 1 1 - 5

Speed [km / s] 1 - 100 - 20

Direction perpendicular to the surface perpendicular to the surface with ~ ± 45 °

Table 1: Comparison of the process parameters for shock hardening and plasma pulse hardening

Corrosion, wear, heat, improvement in resistance, strength, insulation, sliding properties

Al, Ti, Cu, Zn, Sn, Cr, Mo and their ceramic Mo, Cu, Co, Ag,

Pb, Cr, Ta, Ni, Mo, combinations; Protective layers Au, In, Sn, Pb and

Fe, W, W, P and SiC, Al ₂ 0 ₃ , NiCr such as carbides, Bori¬ their combinations, their combinations and their combinations, silicides, nitrides; nen; nations; Oxides, silicates; Graphite;

TiB ₂ , ZrB ₂ , FeB, Ti, Zr, Hf, V, Nb, NiC, BN, HEX _. - PbO,

Fe ₂ B, CrC, Cr ₃ C ₂ , Ta, Cr, Mo, W- CaF ₂ , Fe ₂ B, MoS ₂ ,

Cr ₇ C ₃ , NbC, TaC, borides, carbides, MoSe ₂ , WS ₂ ,

WC, Al ₂ 0 ₃ , Ti0 ₂ , nitrides, oxides, WSe ₂ and their

Zr0 ₂ , MgO, CaO, silicides and their combinations

Si0 ₂ , Cr ₂ 0 ₃ and combinations of their combinations;

Au, Pt, Rh;

SiN, TiN, CrN;

ZrC, Hf0 ₂ , Y ₂ 0 ₃ ,

La ₂ 0 ₃ , La ₂ Hf ₂ 0 ₇ ,

CaZr0 ₃ , Be0 ₂ and their combinations (low 0 ₂ -

Permeability at high

Temperatures);

Table 2: Additives as the main component of the surface layer regardless of the material Material Corrosion Wear Wear Improvement Resistance Strength Insulation

Sliding properties

Cast iron Cu, Ni, Sn, Cr, C, Ni, Cr, W, Al ₂ 0 ₃ , Ti0 ₂ , Al, Si and Mo, Si and Si-Cr ₂ 0 ₃ , Zr0 ₂ , their combination compounds, MgO, CaO, nations; Mg and Mg-Si0 ₂ and their compounds; Combinations

Steel C, Si, Ni, Cr, C, Mn, Ni, Cr, Al ₂ 0 ₃ , Ti0 ₂ , Zn, AI (nitriding Si, B, NH ₃ , Mo, Cr ₂ 0 ₃ , Zr0 ₂ , suitability) , Cu, W, V, Nb, Ti MgO, CaO, Mo, S and by blinding Si0 and their combination of special combinations of nations; carbides

Conductive copper Be, Zn, B; Ag, Cd, Cr, Be; Incorporation of metal oxides such as Al ₂ 0 ₃ , Ti0 ₂ (dispersion hardening)

Copper Al, Be, Sn, Ni Ag, Cd, Cr, Zr, Pb, Sn alloys and their Be, Mn, As, Si, combinations Al, Zn, Sn, Ni and their combinations; hoch¬ Zr0 ₂ , Al ₂ 0 ₃ ; Ti, Fe, Ni and Zr02, Al203; melting their Kombi¬ metals nations; for W and Mo: K, Si and Al compounds; hoch¬ Cr; C, Zr, Hf, Ti, Re MgO, Zr0 ₂ , melting and their Y ₂ 0 ₃ and alloy combinations; their combinations;

Light metals N, Cu, Al ₂ 0 ₃ , Al ₂ 0 ₃ , MgO; Al ₂ 0 ₃ ; AIN, B; Light metal Mg, Mn, Ti, Be, Cu, Si, Mn, Mg, alloys B and their Ni and combinations thereof;

Ceramics AI.Mg, Ti - metals for nitrides; Formation of cermets;

Glasses of carbides, oxides, carbides, oxides, borides, silicides, borides, silicides, nitrides, silicates; Nitrides, silicates;

Table 3: Additives that are mixed with the melted surface layer of the material.

Claims

Patent claims »

1. A method for applying and influencing a solid surface, in particular a material surface, characterized in that the application is carried out with a brief impulse of a mass of high energy and density, in which the energy stored in an energy store is conducted into an energy converter and there is transferred to an energy carrier to be accelerated in the direction of the solid surface in gas, liquid or solid form or a mixture of these substances in such a way that the impulse impinging on the surface of the solid body interacts with the surface layer of the solid body and changes in a thin surface layer Structure and / or in the structure and / or in the composition causes, and that after this influencing of the material surface, a heat treatment is carried out during which the treated material over a predefinable period of an elevated temper is set out.

2. The method according to claim 1, characterized in that the treated material during a period of one to five hours, in particular during a period of two to three hours, a temperature in the range of 400 ° K and 1500 ° K or between 400 ° K and 1500 ° K, in particular a temperature in the range of about 570 ° K and 1270 ° K or between 570 ° K and 1270 ° K, the plasma dynamic parameters of the plasma pulse and also the composition and amount of each in the respective temperature treatment Plasma pulse contained and carried by this substances can be specified.

3. The method according to claim 1 or 2, characterized in that austenitic steels, for example X12CrNi 18 8, are used as the materials to be influenced, and where to increase the hardness of the treated layer with a sufficiently large addition of chromium carbide in the Surface are created that ensure a high hardness up to a temperature of 1170 ° K.

4. The method according to any one of the preceding claims, characterized in that the desired properties such as hardness, corrosion resistance, thermal insulation and / or sliding properties by specifying and combinations of Plas¬ mapulparameters, composition of the plasma pulse as well as the additional materials and materials who achieved ¬ den (see table 2).

5. The method according to claim 4, characterized in that materials such as zirconium oxide or Wolf¬ ram carbide are alloyed in steel or non-ferrous materials such as copper surface layers with a hardness of approximately 800 HV _{001 are} generated by adding boron to the plasma pulse.

6. The method according to any one of the preceding claims, characterized in that, due to the extreme process conditions (see Table 1), non-equilibrium conditions are created on the surface of the material, which enable non-alloyable components to be alloyed in.

7. The method according to any one of the preceding claims, characterized in that a melting order is formed by combining the plasma pulse parameters and the composition of the plasma pulse and by the choice of additional materials becomes.

8. The method according to claim 6, characterized in that a surface treatment and coating is produced by a multiple treatment of the same area, with each treatment a melting and alloying and the parameters and the composition of the plasma pulse as well as the additives of plasma pulse Plasma pulse can be modified in order to achieve a structuring of the layer, wherein the material of the plasma pulse as well as the additives can also consist of erosion and / or ablation of the components of the generator of the plasma pulse.

9. The method according to any one of the preceding claims, characterized in that the plasma accelerators used to carry out the method are designed and / or equipped depending on the geometry of the predetermined material surface in order to ensure an effective treatment of the respective surface, with cylindrical surfaces from the outside with devices according to Figures 5 and 6, cylindrical surfaces are treated from the inside with an arrangement according to Figure 10, the plasma pulse generated electrothermally or plasma dynamically being deflected radially outwards and the new cross-section through which the plasma flows is kept as constant as possible.

10. The method according to any one of the preceding claims, characterized in that linear arrangements are treated with a device according to Figure 8, circular geometries with arrangements according to Figures 9 and 10 and also a treatment with combinations of the described arrangements is made possible.