Joining materials

Solid-State Welding. Sohd-state welding comprises a group of welding processes wherein a bond is made between two base materials upon the apphcation of pressure at a temperature below the soHdus of the base materials (Table 1). Interlayers are sometimes used. By joining materials in the sohd state, many of the difficulties of the fusion processes are avoided. 

A grass-like recreational surface system includes the top material directly available for use and observation, backing materials that serve to hold together or reinforce the system, fabric-backing finish, a shock-absorbing underpad system if any, and adhesives (qv) or other joining materials. The system is installed... 

When both components of a threaded joint are of weldable metal, the joint may be seal-welded as shown in Fig. 10-130. Seal welds may be used only to prevent leakage of threaded joints. They are not considered as contributing any strength to the joint. This type of joint is limited to new construction and is not suitable as a repair procedure, since pipe dope in the threads would interfere with welding. This method provides tight joints with a minimum of welding labor. When threaded joints used to join materials with widely dinerent coeffi-... 

Joining material used in joints Working temperatures, < F Maximum working pressure, Ibf/in ... 

The contact between the aluminium layers and the ceramic substrate requires a joining material which will wet both metal and ceramic, and solders such as the conventional Pb-Sn alloy have been used which are molten during the annealing process. The contact between the solder and the aluminium layer is frequently unsatisfactoty because of the intervention of the AI2O3 layer, and a practical solution appears to be to place drree layers of metal clrromium in contact widr the aluminium, copper in contact with the clrromium, and gold between the copper layer and the solder. 

Joining materials with different thermal expansion in a cryogenic structure which must stand repeated thermal cycles needs a careful attention to avoid stresses and breaking of the joint. In particular, the vacuum tightness at low temperature may be jeopardized. 

Seam - A line formed by joining material to form a single ply or layer. A splice or overlap. 

Why a section on bonding techniques The main reason is that, at this moment the bonding of materials is a live topic in both materials science and research. We want to combine ceramics with identical or different ceramics, but also with metals and plastic. Moreover ceramicists are also interested in joining materials from an artistic point of view. Certain developments in technology require not only identical, but mostly different materials to be linked. When an object or component is too big or too complex to make it entirely of ceramics, part of it is made of metals and consequently the metals and the ceramics have to be joined. Since ceramics are quite often brittle, is may be desirable to make the ceramic part of the object as little as possible and to manufacture the remaning part of metal. This section will make clear that materials can be joined in many different ways, depending on the combination of materials and the circumstances under which they must be joined. 

Some of the glassy silicate materials cited in Table 9.1 have been used as joining materials in laboratory studies but most are unsuitable for realistic applications. Thus the Na and K silicates are soluble in water and hence unsuitable... 

Many methods have been proposed to address this issue (see Chapter 9). Beside thermal and chemical resistances of the sealing materials other issues need to be considered as well. One such important issue is the mismatch of the thermal expansion coefficients between the membrane element and the sealing material or joining material. While similar material design and engineering problems exist in ceramic, metal and ceramic-metal joining developmental work in this area is much needed to scale up gas separation units ot membrane reactors for production. The efforts are primarily p ormed by the industry and some national laboratories. 

C.A. Lewinsohn, R.H. Jones, T. Nozawa, M. Kotani, Y. Katoh, A. Kohyama, and M. Singh, Silicon Carbide Based Joining Materials for Fusion Energy and Other High-temperature Structural Applications, Ceram. Eng. Sci. Proc., 22, 621-25 (2001). 

The thermal conduction in composite-to-Cu-clad-Mo joints is important for thermal management applications. For 1-D steady-state heat conduction, the joined materials form a series thermal circuit with an effective thermal resistance, Rcfr - S(Ax,/IC,), where Axi and K, are the thickness and... 

Figure 11(a) also compares the Reir values of the joints to the R u values of C-C and Cu-clad-Mo substrates of the same total thickness (5.1 x 10 m) as the joined materials the thermal resistance of the C-C block is about 40.8x 0 m. K/W and that of Cu-clad-Mo substrate decreases with increasing clad layer thickness. The decrease in the conductivity of our joints (Cu Mo Cu thickness ratio of 13% 74% 13%) relative to an un-joined Cu-clad-Mo substrate is compensated by 39%... 

For 1-D steady-state heat conduction, the joined materials form a series thermal circuit with an effective resistance, Reff = X(Ax,/K,), where Ax, and K, are the thickness and the thermal conductivity, respectively, of the i layer. Figure 8 shows the projected thermal resistance of ZS/Cu-clad-Mo joints made using the four brazes as a function of % clad layer thickness. This figure also shows the thermal resistance of the ZS composite and Cu-clad-Mo of the same total thickness (5.1 mm) as the joined assembly. For calculation Axzs= Axa,.Mo= 0.25x10 m, Axticusi1 = 100x1 o m, and K of Cu-clad-Mo with different Cu layer thicknesses is from ref . The conductivity of ZS (Kzs) is calculated from the Maxwell equation for spherical particles... 

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