|
; Cu-Zn ([[brass]]): {{Anchor|Cu-Zn}}Copper-zinc. General purpose, used for joining steel and cast iron. Corrosion resistance usually inadequate for copper, silicon bronze, copper-nickel, and stainless steel. Reasonably ductile. High vapor pressure due to volatile zinc, unsuitable for furnace brazing. Copper-rich alloys prone to stress cracking by ammonia.
; Ag-Cu-Zn: Silver-copper-zinc. Lower melting point than Ag-Cu for same Ag content. Combines advantages of Ag-Cu and Cu-Zn. At above 40% Zn the ductility and strength drop, so only lower-zinc alloys of this type are used. At above 25% zinc less ductile copper-zinc and silver-zinc phases appear. Copper content above 60% yields reduced strength and melts above 900 °C. Silver content above 85% yields reduced strength, high liquidus and high cost. Copper-rich alloys prone to stress cracking by ammonia. Silver-rich brazes (above 67.5% Ag) are hallmarkable and used in jewellery; alloys with lower silver content are used for engineering purposes. Alloys with copper-zinc ratio of about 60:40 contain the same phases as brass and match its color; they are used for joining brass. Small amount of nickel improves strength and corrosion resistance and promotes wetting of carbides. Addition of manganese together with nickel increases fracture toughness. Addition of cadmium yields '''Ag-Cu-Zn-Cd''' alloys with improved fluidity and wetting and lower melting point; however cadmium is toxic. Addition of tin can play mostly the same role.
=== '''Carbides to steel joining by Ag-Cu-Zn-Cd filler alloy''' <ref>{{Cite journal |last=Habibi |first=Farzad |last2= |first2= |last3= |first3= |date=2023-11-01 |title=Microstructural evolution during low-temperature brazing of WC-Co cemented carbide to AISI 4140 steel using a silver-based filler alloy |url=https://www.sciencedirect.com/science/article/pii/S0263436823002548 |journal=International Journal of Refractory Metals and Hard Materials |volume=116 |pages=106354 |doi=10.1016/j.ijrmhm.2023.106354 |issn=0263-4368}}</ref> ===
The production of cemented carbide tools with complicated shapes and large sizes is a challenging task due to their brittle nature and high manufacturing costs. These are the reasons for dissimilarly joining the tougher steels to cemented carbides. A variety of processes are used to join tungsten carbide cermets to steels, including brazing, diffusion bonding, transient liquid phase bonding, and fusion welding processes. Moreover, active brazing is a method employed for joining metals to ceramic composites. Using fusion-welding procedures, the base metal can undergo dissolution resulting from intense thermal energy generated by the arc, which may then lead to often unfavorable complex reactions in the molten pool. Previous findings indicate that a variety of brittle η phases such as Fe<sub>3</sub>C, Fe<sub>3</sub>W<sub>3</sub>C, Co<sub>3</sub>W<sub>3</sub>C, etc. (M<sub>6</sub>C-type carbides) may be formed at the joint interface, thus reducing the joint toughness .The diffusion of decomposed tungsten and carbon from WC-based cermet into the molten pool can lead to the formation of these carbides. In addition, elevated temperatures during fusion welding processes can increase the grain size of the WC-Co component. Moreover, there is a high risk of crack propagation due to the potential phase transformation in the steel component accompanied by volume changes during the cooling of the joining process. Among the above-mentioned methods, brazing has demonstrated greater efficacy than fusion welding techniques for joining carbide/steel, due to the superior quality of the brazed joints and the reduced cost. The superiority of brazing in comparison with fusion-welding methods can be attributed to suppressed intense deformation and reduced residual stresses resulting from non-uniform heating in welding processes. The key issues in brazing WC-Co components to steel bodies are the relatively low joint strength because of the differences in their physical properties such as the great differences in coefficients of thermal expansion (CTE) and chemical properties such as wetting behavior. Additionally, the excessive diffusion can deteriorate the cermet structure and forms a Cobalt-Depleted Zone (CDZ). Achieving higher joint strength necessitates the proper selection of filler material, and optimal brazing process parameters, thus minimizing the residual stresses. The use of low-temperature brazing offers some advantages such as improved joint quality and reduced potential for thermal damage to the base metals as well as reducing the residual stresses around the joint area. Several types of silver-based alloys containing a melting point-depressant element, including those which comprise cadmium (Ag-Cd), zinc, and copper (Ag-Cu-Zn), as well as combinations of copper, zinc, tin, nickel, manganese, and cobalt (Ag-Cu-Zn-Sn, Ag-Cu-Zn-Ni-Mn, and Ag-Cu-Zn-Ni-Mn-Co) were used by various researchers to braze the WC-Co to steel. In addition, the temperature, time, heating, and cooling rates, initial filler thickness, the surface roughness of the base materials, and the pressure applied to the joint assembly affect the wettability, microstructural evolution, and mechanical properties of the joints. By optimization of the brazing process parameters, temperature gradients can be limited and the destructive diffusion processes suppressed, thus controlling the CDZ thickness. Diffusion of silver and cadmium in cemented carbide, as well as the formation of Co-Fe-Cu reaction product, were proposed as the bonding mechanisms. The effectiveness of brazing temperature in enlarging the cobalt-depleted zone appearing in WC-Co is comparatively higher than that of brazing time. It is also concluded that by increasing the brazing temperature and duration, the fraction of copper solid-solution dendrites distributed in the joint area decreases, however, the size increases.
; Cu-P: Copper-[[phosphorus]]. Widely used for copper and copper alloys. Does not require flux for copper. Can be also used with silver, tungsten, and molybdenum. Copper-rich alloys prone to stress cracking by ammonia.
; Ag-Cu-P: Like Cu-P, with improved flow. Better for larger gaps. More ductile, better electrical conductivity. Copper-rich alloys prone to stress cracking by ammonia.
; Al-Si: [[Aluminum]]-[[silicon]]. For brazing aluminum.
; Active alloys: Containing active metals, e.g., titanium or vanadium. Used for brazing non-metallic materials, e.g. [[graphite]] or [[ceramic]]s.
=== '''Active brazing''' <ref>{{Cite journal |last=Habibi |first=Farzad |last2=Samadi |first2=Ahad |date=2023-08-18 |title=Interfacial reactions in actively brazed Cu-Al 2 O 3 composites and copper using a newly developed Cu-Sn-Ag-Ti filler alloy |url=https://journals.sagepub.com/doi/full/10.1080/13621718.2023.2173878 |journal=Science and Technology of Welding and Joining |language=en |volume=28 |issue=6 |pages=444–454 |doi=10.1080/13621718.2023.2173878 |issn=1362-1718}}</ref> ===
: Among the different methods used to join dissimilar materials, active brazing is a flexible and single-step technique to join ceramic composites and metals, contrary to the moly-manganese coating process. For such materials, there would be a chemical potential gradient at the interface which the system tries to achieve a chemical equilibrium through predominant kinetics of chemical reactions. This procedure promotes joint strength by wetting the solid oxide surfaces and finally reacting with base materials to form one or more reaction layers that are responsible for the strong bonding. Active brazing is a method used to braze the ceramic parts to themselves or metallic parts. Using active filler alloys consisting a active metal in their chemical composition such as titanium, hafnium, etc., the ceramic ionic bonds can react with the metallic ions. Some filler alloys, including Ag-Cu, Ag-Cu-Ti, AgCu-In (or Sn)-Ti (or Zr), Cu-Sn-Ti, etc. have been successfully tested and used by various investigators experimentally to join the different metal/ceramic or ceramic/ceramic systems. In dissimilar brazing, the differences in physical properties between the components lead to residual stresses. For instance, lately, an active filler alloy Cu-20.5Sn-20Ag-3.5Ti was developed to braze the Cu-Al<sub>2</sub>O<sub>3</sub> composites (containing 25 and 50 volume pct. Al<sub>2</sub>O<sub>3</sub>) to copper. Two mechanisms were proposed for chemical bonding as a result of alumina reinforcements reduction by the active titanium, including the formation of Ti<sub>3</sub>(Cu,Al,Sn)<sub>3</sub>O layer beside the Ti<sub>2</sub>O in Cu/Cu-25%Al<sub>2</sub>O<sub>3</sub> joints; and the solidification of Ti<sub>3</sub>(Cu,Al,Sn)<sub>3</sub>O in the vicinity of TiO layer/Cu<sub>4</sub>Ti islands in the Cu/Cu-50%Al<sub>2</sub>O<sub>3</sub> joints. Some intermetallic compounds such as Cu<sub>3</sub>Ti<sub>2</sub> and Cu<sub>41</sub>Sn<sub>11</sub> are formed/coarsened with an extra increase in brazing temperature. An increase in brazing time improves the thickness of the TiO<sub>x</sub> layer with no sensible effect on Ti<sub>3</sub>(Cu,Al,Sn)<sub>3</sub>O width.
{| class="wikitable sortable"
|
