The Research Of Brazing Of Si₃N₄ Ceramic To 42CrMo Steel Using High-Temperature Active Filler Alloy

Ag-Cu-Ti-Pd active alloy is used to joint the Si₃N₄ ceramic to 42CrMo steelin this paper, which has shown that the microstructure and properties of the jointdepend on brazing parameters and the composition of filler alloys. Duringexperiments, 3-points bending test was used to get the properties of the joints;SEM,XRD and EMPA was used to observe the microstructure of the joints. Theoptimum brazing parameters was ascertained. When the brazing temperature was1193K, and the holding time was 40min, a joint with the maximum bendingstrength of 288.1MPa was obtained by active-brazing with the filler alloy ofAg54.2Cu35.8Ti5Pd5.By using the brazing parameters chosen in this research, Si₃N₄ ceramic wasjointed to 42CrMo heat-resistant steel using the active filler alloy Ag-Cu-Ti-Pd,and a strong joint could be obtained. Brazing joint was composed of three parts:the TiN reaction layer near the ceramic, eutectic of Ag rich phase and Cu richphase in the middle part of the joint in which there is CuTiPd phase, and Fe-Ticompound layer near the 42CrMo.As the holding time was longer, the interfacial active layer between brazingalloy and basic material was almost not changed, meanwhile, in the middle ofwelding seam, the phase of Ag[Cu] and Cu[Ag] was distributed more uniformly,and the amount and size of the CuPdTi phase tend to increase. As to the brazingalloy with a certain composition, under a certain brazing temperature, the 3-pointbending strength of the joint increased at first, and then got lower as the holdingtime was prolonged.The brazing temperature affected the microstructure of the joint in the similarway as the holding time. When using the brazing alloy with a certain compositionand keeping a same holding time, the 3-point bending strength of the jointincreased at first, and then decreased as the brazing temperature increased.It is showed that a good heat-resistant strength could be obtained as the Si₃N₄ceramic was jointed to 42CrMo. As the brazing temperature was 1193K, theholding time was 20 min, and the brazing alloy was Ag54.2Cu35.8Ti5Pd5, a 3-point bending strength of 228.1MPa was obtained at the temperature of 773K. With the same brazing parameters, a strength of 97.74MPa was obtained at 973K.A brazing joint with good oxidation resistant performance was obtained byusing Ag-Cu-Ti-Pd brazing alloy. The oxidation resistant performance wasimproved as the atom content of Pd increased.