Patent Publication Number: US-2022221015-A1

Title: Frictional Brake Element for a Friction Brake of a Motor Vehicle, Friction Brake, and Method for Producing a Frictional Brake Element

Description:
The invention relates to a friction brake element for a friction brake of a motor vehicle, in particular brake disk, having a main element made, in particular, of gray cast iron, having an antiwear layer applied to the main element and having an intermediate layer located between the antiwear layer and the main element. 
     The invention further relates to a friction brake for a motor vehicle, having at least one brake disk and at least one movable brake pad assigned to the brake disk and also a process for producing the above-described friction brake element. 
     PRIOR ART 
     Friction brakes for motor vehicles usually have, as friction brake elements, a brake disk and at least one brake pad having a brake lining, with the brake pad being pressed against the brake disk to achieve a braking effect. The brake disk is usually fixed to a wheel of the motor vehicle for rotation therewith and the brake pad is arranged so as to be movable but is fixed to the vehicle body. When the brake pad is pressed against the brake disk, abrasion occurs on the brake disk due to the frictional contact between brake pad and brake disk, leading to wear of the brake disk and to brake dust which gets into the environment. To reduce this wear, it is known that the friction brake element can be provided with an antiwear layer at least in the contact region with the brake pad. For example, application of antiwear layers based on hard metals or carbides to a main element of the friction brake element made of gray cast iron is known. Furthermore, provision of an intermediate layer between the antiwear layer and the main element so as to act, in particular, as bonding agent and anticorrosion layer between the antiwear layer and the main element is known. 
     DISCLOSURE OF THE INVENTION 
     The friction brake element according to the invention having the features of claim  1  has the advantage that adhesion of the antiwear layer to the intermediate layer and also the resistance to cracking and the corrosion resistance of the friction brake element are improved. According to the invention, the intermediate layer is for this purpose a metallic intermediate layer and is applied by laser buildup welding to the main element. 
     In particular, the metallic intermediate layer is a nickel-, cobalt- or iron-based alloy. Crack growth and corrosion in the layer system of the friction brake element are avoided because of the low porosity which can be achieved by means of laser buildup welding and the resulting high cracking resistance of this intermediate layer. In addition, the laser buildup welding ensures that good layer adhesion between the intermediate layer and the main element is achieved due to the substance-to-substance bonding and secondly between the antiwear layer and the intermediate layer due to a preferably high surface roughness of the intermediate layer applied by means of laser buildup welding and the high bonding force resulting therefrom. 
     The surface of the intermediate layer facing the antiwear layer has particularly preferably been thermally pretreated, giving even better adhesion of the antiwear layer to the intermediate layer. In particular, the surface of the intermediate layer is cleaned by the pretreatment, for example by means of laser beam treatment. 
     In a preferred further development of the invention, the metallic intermediate layer has an at least two-phase microstructure. The different phases result in an increase in the fracture toughness of the intermediate layer because crack propagation is inhibited at the transition from one phase into the adjacent phase by the different configurations of the phases. 
     The respective phase preferably makes up at least 5% by volume of the intermediate layer. This gives an advantageous microstructure which increases the fracture toughness. 
     Furthermore, the antiwear layer is preferably an antiwear layer applied by thermal spraying or laser buildup welding to the intermediate layer. The antiwear layer is thus also preferably applied to the intermediate layer by laser buildup welding, which results in a low-cost production process in the production of the layer system. 
     In a preferred further development of the invention, the antiwear layer is configured as ceramic coating or as iron-based alloy having embedded hard material particles consisting of carbides, oxides, nitrides or borides. The abovementioned additives reinforce the iron-based alloy and make it abrasion-resistant. The layer thickness of the intermediate layer is particularly preferably at least twice the average particle size of the hard material particles embedded in the antiwear layer. As a result, effective protection against corrosion is ensured by a closed, impervious intermediate layer even when a hard material particle is unintentionally incorporated in the intermediate layer during manufacture. 
     The friction brake of the invention having the features of claim  9  is characterized by the brake disk being configured as friction brake element according to the invention. This results in the advantages mentioned above. 
     The process of the invention having the features of claim  10  is characterized by the metallic intermediate layer being applied by laser buildup welding to the main element. This results in the advantages mentioned above. 
     Further advantages and preferred embodiments may be derived, in particular, from the claims and from the above description. 
     In particular, the main element is made of gray cast iron. Preference is given to the metallic intermediate layer being applied first to the main element and then the antiwear layer preferably being applied. The main element is preferably pretreated mechanically or thermally, in particular in order to satisfy the geometric requirements, before application of the intermediate layer. The intermediate layer is preferably also pretreated thermally, in particular cleaned, for example by means of laser beam treatment, in order to ensure good layer adhesion between the antiwear layer and the intermediate layer, before application of the antiwear layer. In particular, a nickel-, cobalt- or iron-based alloy is applied as intermediate layer to the main element. In this case, the intermediate layer is preferably produced in such a way that it has an at least two-phase microstructure in order to increase the fracture toughness. The intermediate layer is preferably produced in such a way that the respective phase makes up at least 5% by volume of the intermediate layer. The antiwear layer is preferably applied to the intermediate layer by laser buildup welding or thermal spraying, in particular as ceramic coating or as iron-based alloy and in particular with embedded hard material particles which preferably consist of carbides, oxides, nitrides or borides. 
    
    
     
       The invention will be illustrated in more detail below with the aid of the drawing. The figures show: 
         FIG. 1  an advantageous friction brake element in a simplified perspective depiction, 
         FIG. 2  a simplified depiction of a production process for the frictional brake element and 
         FIG. 3  a flow diagram to explain the production process. 
     
    
    
       FIG. 1  shows, in a simplified perspective depiction, a friction brake element  1  configured as a brake disk  2  for a friction brake, which is not shown in more detail here, of a motor vehicle. The friction brake element  1  has a circular main element  3  made of gray cast iron. A brake disk chamber which is optionally present on the brake disk  2  is not shown in  FIG. 1 . On each of its two faces, the main element  3  has an annular frictional contact surface  4  which is formed by an antiwear layer  5  of the friction brake element  1 . The antiwear layer  5  forms, in correct operation, a frictional contact partner for at least one brake pad or brake lining of the friction brake, which for carrying out a braking operation is pressed against the frictional contact surface  4  to achieve friction braking. The brake disk  2  is usually fixed to a wheel of the motor vehicle for rotation therewith, while the brake pad is fixed to the housing and can be moved only in the direction of the brake disk  2 . The relative movement of brake disk  2  and brake pad results, when the brake pad is pressed against the frictional contact surface  4 , in abrasion on the friction brake element  1 , leading to wear of the friction brake element  1  and to brake dust which enters into the surroundings of the motor vehicle. 
     The antiwear layer  5  reduces this wear and increases the abrasion resistance of the friction brake element  1 . In particular, the antiwear layer is configured as ceramic coating or as iron-based alloy which has embedded hard material particles consisting of carbides, oxides, nitrides or borides, in order to ensure the abovementioned advantages. 
     To ensure reliable adhesion of the antiwear layer  5  to the main element  3 , a metallic intermediate layer  6  is provided between the antiwear layer  5  and the main element  3 . The intermediate layer  6  is applied by laser buildup welding to the main element  3 . 
     In this respect,  FIG. 2  shows the process of laser buildup welding in a simplified sectional depiction. Here, an outer layer  7  of the main element  3  is heated by a laser beam  8  so that the outer layer  7  melts. At the same time, a supplementary material  9  for producing the metallic intermediate layer as nickel-, cobalt- or iron-based alloy is melted by the laser beam and subsequently mixed with the melted outer layer  7  so that, in particular, a welding bead  10  which forms the intermediate layer  6  is formed. 
     The antiwear layer  5  is, in particular, likewise applied by means of laser buildup welding to the intermediate layer  6  produced in this way. 
     The metallic intermediate layer  6  is preferably applied to the main element  3  in such a way that it has an at least two-phase microstructure. In particular, the phases each make up at least 5% by volume of the intermediate layer in order to ensure advantageous cracking resistance or fracture toughness of the intermediate layer. As a result of the presence of different phases, a crack which is being formed is stopped or inhibited at the transition from one phase into the adjacent phase, so that crack propagation through the intermediate layer  6  is advantageously prevented. 
       FIG. 3  shows an advantageous process for producing the friction brake element  1  with the aid of a flow diagram. In a first step S 1 , the main element  3  is provided. The main element is, as mentioned above, preferably made of gray cast iron. In a subsequent step S 2 , at least one face of the main element  3  is preworked or pretreated mechanically or thermally, in particular for roughening or geometric adaptation of the surface to which the metallic intermediate layer  6  is to be applied. The metallic intermediate layer  6  is subsequently applied in a step S 3  to the face of the main element  3  by laser buildup welding. In particular, the intermediate layer is a nickel-, cobalt- or iron-based alloy. The substance-to-substance bonding resulting from laser buildup welding ensures that advantageous layer adhesion of the intermediate layer  6  to the main element  3  is achieved. Subsequently, after the intermediate layer  6  has solidified or cooled sufficiently, the intermediate layer  6  is optionally pretreated thermally on its free surface in a step S 4 , for example by means of laser beam treatment. The antiwear layer  5  is subsequently applied to the intermediate layer  6  in a step S 5 , in particular by means of laser buildup welding or thermal spraying. As mentioned above, the antiwear layer  5  is, in particular, configured as iron-based alloy comprising carbides, oxides, nitrides or borides to increase the wear resistance, or as ceramic coating. 
     The finished friction brake element  1  is subsequently obtained in a step S 6 . The antiwear layer  5  is optionally after-treated mechanically or thermally, in particular ground, in order to ensure a desired surface roughness for interaction with the brake pad of the friction brake.