Brazing of micrograin-filled quartz fiber reinforced silica composites and Invar using Ag-21Cu-4.5Ti alloy

Abstract

Brazing of quartz fiber reinforced silica composites (QFSC) to Invar alloy was carried out in a vacuum at 1173 K for 10 min using Ag-21Cu-4.5Ti metal filler. Experiments indicated that composites prefilled with CaCO 3 micrograins had good wettability. The CaCO 3 decomposed to CaO during brazing. After brazing, a joint of structure QFSC/3CaO·2SiO 2 +Ti 3 O 5 +Fe 2 Ti+NiTi+Ag(s,s)+ Cu(s,s)/Invar was established. The shear strength of the brazed joint reached 11.6 MPa at room temperature, which is about five times the shear strength of that obtained without surface filling. In the field of advanced composites, fiber braided composites are increasingly receiving attention because they are lightweight, and have excellent mechanical strength and high temperature resistance [1][2][3][4]. Quartz fiber reinforced silica composites (QFSCs) also have special electrical properties. Because they have poor machining properties, one focus of research into applications of these composites is on joining them with dissimilar materials. Recently, research into joining of fiber braided composites has focused mainly on brazing [5][6][7][8]. It has been suggested that fiber braided composites have low interlaminar contact strengths because their loose texture results in poor dynamic properties [9,10]; this could make it difficult to form perfect joints at the interfaces. Several techniques have been considered for reinforcement of composites, such as resin transfer molding and vacuum assisted resin transfer molding for different textile performs (2D or 3D textile architectures) [11]. Filler reinforcement using micrograins is an effective modification for reinforcing incompact structures [12,13]. We may infer that good joints could be achieved by reinforcing fiber braided composites with fillers. The aim of our investigation was to study the brazing of Invar alloy to QFSC through experiments examining the effects of micrograin fillers on the composite surface, using Ag-21Cu-4.5Ti as the braze filler metal. The microstructure and joining mechanism were also investigated.

The relation between residual stress, interfacial structure and the joint property in the SiO2f/SiO2-Nb joints

“…However, two crucial challenges: the poor wettability of SiO 2f /SiO 2 and the high residual stress in the joint exist in brazing SiO 2f /SiO 2 to metal, which seriously impairs the strength of the joints. In view of that, some researchers demonstrated that the wettability of SiO 2f /SiO 2 with active brazing alloy can be successfully improved by coated nickel 23 , CaCO 3 24 , or few-layer graphene 25 . Although the wettability of SiO 2f /SiO 2 with active brazing alloy is improved, a high-quality joint is difficult to obtain because of the negligence to the high residual stress.…”

Comparison between hybrid laser-MIG welding and MIG welding for the invar36 alloy

“…Grains coarsening in the heat affected zone and boundary migration were predicted by Jose [9] with fair accuracy by using a diffusive model. Zhao [10] brazed quartz fiber compound materials and invar36 alloy with Ag-Cu-Ti brazing filler metal. However, their process is relatively complex that keeping the compound materials with 1173 K temperature for 10 min.…”