Technologies / For Every Application

The combination of decades of experience and high-performance systems enables PVA Löt- und Werkstofftechnik GmbH to guarantee you future-proof and economic production across all key technology sectors.

  • Vacuum Brazing / Procedure

    The solder material used has a decisive impact on the technological properties of the joint. The filler metal can be applied as wire, foil, or paste, depending on the geometry of the parts to be brazed. Solders based on silver, which are particularly suitable for joining copper-parts, as well as nickel-based solders, suitable for brazing heavy-duty joints of stainless steels and super alloys, are widely used in vacuum brazing technology. However, active brazing alloys are also used increasingly for joining ceramic materials such as Al2O3 or Si3N4.

    The function of the hard and high-temperature filler metals described is based on their ability when in the molten state to dissolve elements of the materials to be joined, thus creating a strong metallurgical bond similar to a welded joint. In contrast to welding, however, the base materials do not melt because the melting ranges of the solder alloys are much lower than those of the base materials.
    The fact that the joining process is carried out in a vacuum atmosphere prevents any interaction between the solder and base materials with the surrounding atmosphere. This means that the use of highly-corrosive fluxes can be avoided on the one hand, while the vacuum atmosphere in the joining process means that the physical properties of the base materials are not influenced on the other.

    • Specifications

      Specifications

      Individual factors such as the pressing force and the holding time at working temperature can vary strongly from material to material and therefore require comprehensive metallurgic expertise when it comes to deriving the appropriate process parameters. Get in touch with us, and we can advise you in detail and identify the process that’s right for you in our Innovation Lab.

    • Vacuum Brazing Supported by Pressing Force

      Vacuum Brazing Supported by Pressing Force  / For Exceptional Stability

      The diffusion bonding system still offers the possibility of performing conventional vacuum brazing supported by pressing force. In this process, the pressing forces required are significantly lower than in diffusion bonding with the aim of minimizing component distortion as a consequence of the release of tension. Brazing supported by pressing force also enables vacuum brazing of large material joints, which could not be joined with sufficient reliability using conventional vacuum brazing. 

  • Vacuum Heat Treatment / Procedure

    Heat treatment under vacuum conditions offers numerous application possibilities. Various approaches have become established, depending on the composite material and the required properties of the adherend.

    In all of these heat-treatment processes, the vacuum atmosphere serves to avoid undesirable interactions between the workpiece and the environment. 

    • Quenching and Tempering

      Quenching and Tempering

      The quenching and tempering of steels is used to set specific strength and toughness properties. The quenching and tempering process consists of two process steps. In the first stage, the material to be treated is austenitized. For this purpose, temperatures of around 900 °C – 1000 °C are set in the vacuum furnace, depending on the material. This converts the entire steel structure into austenite. After a sufficient holding time, which is dependent on the part geometry, the steel is quenched. This takes place in PVA vacuum furnaces using a special rapid-cooling device, which allows cooled process gas such as nitrogen or argon to be blown into the batch directly. To increase the cooling effect, the rapid-cooling process can also be performed in the overpressure range of up to 1.4 bars. The resulting cooling rates that can be achieved are sufficient to bring about the required martensitic structure in air-hardening steels.

      In martensite, the carbon of the steel is present in forcibly dissolved form and ensures a strong lattice strain in the structure and therefore a high degree of material hardness. A material treated in this way is not suitable for technical applications due to its high brittleness. For this reason, the quenched workpiece is tempered in a second process stage. The aim of quenching is to improve the toughness properties compared to the hardened state. The tempering temperature and duration can be used to adjust the material properties, especially the strength, hardness, and toughness across wide ranges.

    • Recrystallization Annealing

      Recrystallization Annealing

      The purpose of recrystallization annealing is to transform a structure that has been straightened due to cold forming and therefore to restore the original material properties. Typical recrystallization temperatures are between 450 and 600 °C for unalloyed steels and between 600 and 800 °C for medium- to high-alloy steels. Recrystallization annealing is carried out chiefly after forming processes in order to relax and re-orient the heavily deformed structure of the workpiece. 

    • Diffusion Annealing

      Diffusion Annealing

      Diffusion annealing eliminates structure inhomogeneities or concentration differences in the workpiece. Since diffusion processes in solids are highly temperature-controlled, diffusion annealing is performed at very high temperatures (mostly between 1050 and 1250 °C) and frequently over long annealing durations (up to 50 hours). One example is diffusion annealing of nickel-based brazed joints at temperatures of around 1000 °C. During the annealing processes, the concentration of metalloids dissolved in the solder material shifts in the direction of the base material. This counters the formation of hard phases in the brazing joint and significantly increases the strength as well as the corrosion-resistance of the brazed joint. 

    • Bright Annealing

      Bright Annealing

      During bright annealing, the vacuum serves as a functional rather than a protective atmosphere. Bright annealing is used for lightly oxidized workpieces and is used to eliminate oxides. A typical application example is the bright annealing of copper. As a result, copper oxide can be reduced and removed without difficulty at temperatures as low as 900 °C in the high-vacuum. Likewise, bright annealing processes are used on steels in a high-vacuum.

    • Degassing Annealing

      Degassing Annealing

      During degassing annealing, the gases dissolved in the workpiece are released at high temperatures and exhausted by the vacuum pumps. This reduces the gas content in the workpiece, which is important for various high-temperature applications in an ultra-high vacuum atmosphere. A typical application example is the hydrogen degassing of steel.

    • Pure or Ultra-Pure Annealing

      Pure or Ultra-Pure Annealing

      Conversely, during pure or ultra-pure annealing, adhesive surface contamination such as very thin adhesions of carbon are removed at high temperatures with the help of a hydrogen atmosphere. In this case, use is made of the reducing effect of hydrogen, which reacts with the carbon to form volatile hydrocarbon compounds. Ultra-pure annealing processes are also carried out under a high-vacuum if the surface contamination consists of organic or volatile residues. The high-vacuum atmosphere then causes the contaminating components to vaporize.

    • Solution Annealing

      Solution Annealing

      Solution annealing is used primarily for austenitic stainless steel, where its main function is to dissolve precipitation phases (e.g. carbides) in mixed crystals. Rapid cooling can be used to prevent repeated separation of carbides. In addition, solution annealing can bring about the degradation of cold hardening, thereby generating a less strained structure. The standard temperature range for this heat treatment is from 900 °C to 1100 °C.

  • Diffusion Bonding / Procedure

    The pressure welding process involves the simultaneous application of pressing forces and high temperatures. The components to be joined are heated to the required temperature under high-vacuum. The pressing forces are then applied by the ram (uniaxially). This helps smooth the rough peaks of the material surfaces thus establishing close material contact between the mating surfaces. In contrast to many other welding processes, diffusion bonding does without a liquid phase and external materials.

    The join is formed by the transfer of material across the interfaces. Since the diffusion rates are strongly temperature-dependent, the joining process is performed at approx. 50% to 90% of the melting temperature of the materials to be joined.
    With holding times of sufficient duration, diffusion processes that coincide with grain growth cause residual pores in the joint to close, ideally resulting in the complete “healing” of the joint seam. The result is a monolithic component with no discernible joint (microscopic and macroscopic).

    • Specifications

      Specifications

      Individual factors such as the pressing force and the holding time at working temperature can vary strongly from material to material and therefore require comprehensive metallurgic expertise when it comes to deriving the appropriate process parameters. Get in touch with us, and we can advise you in detail and identify the process that’s right for you in our Innovation Lab.

  • Sintering / Procedure

    Sintering is a process that uses a powdery mixture to form stable and often extremely dense components. In the same way as diffusion bonding, processes involving the exchange of materials between the grains are triggered at high temperatures. At the same time, compaction of the mixture and the resulting material contact by means of a process gas are used. Compared with melt-based forming processes, this process does not normally generate a liquid phase, which in turn opens up a degree of freedom regarding the alloy composition or production strategy (forming etc.).

    The components are usually already in their rough-pressed or stabilized form (green body) when they are processed to create the final product. Since the green body only has to have a low degree of material cohesion, even injection molding techniques can be used for forming purposes (metal injection molding). In addition to the forming process itself, plant technology can be used to reduce porosities in the pre-sintered components or to carry out special recessing and forming processes (superplastic forming).

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PVA Löt- und
Werkstofftechnik GmbH

Im Westpark 17
35435 Wettenberg, Germany

Phone: +49 641 68690 750
Fax: +49 641 68690 810