Brazing Characteristics and Wettability of Laser Powder Bed Fusion Additive Manufactured GRCop-84 compared to CuCrZr and OFC, and Brazing to Titanium-Zirconium-Molybdenum Alloy Limiters

Laser Powder Bed Fusion (L-PBF) of Glenn Research Copper 84 (GRCop-84), a Cr2Nb (8 at. % Cr, 4 at. % Nb) precipitation hardened alloy, produces a fully dense, high conductivity alloy with a yield strength of 500 MPa and ultimate tensile strength (UTS) of 740 MPa with 20% elongation; superior to other competing copper alloys. Braze wetting characteristics of GRCop-84 with Ag-Cu-X, and Au-Cu brazes were similar to CuCrZr, but less than oxygen free copper. No difference in wetting was observed between infill and surface contour areas in L-PBF GRCop-84. Wet sanding to 240 grit (Ra=0.24 µm) was considered the optimal surface condition. Silver diffusing through GRCop-84 depleted Cr2Nb precipitates from the copper grain and deposited agglomerations of coarsened precipitates within silver-rich regions of intergranular diffusion once a density threshold was reached. Microstructure modification was minimized with 50Au-50Cu braze implying that silver caused precipitate coarsening and agglomeration, and not high temperature exposure. Coarsened precipitates were observed on the surface within braze pools implying a contribution to braze wetting. Palcusil-25, Ticusil, CuSil-ABA, and 50Au-50Cu brazes were suitable for brazing to unplated Titanium-Zirconium-Molybdenum (TZM), while sulfamate nickel plating to allows wetting with CuSil or other non-active brazes. Vacuum brazing techniques were developed to join a 1 mm thick layer of TZM to the front of additive manufactured GRCop-84 waveguides considering the brazing characteristics of both GRCop-84, TZM, and internal stress from the difference in coefficient in thermal expansion.采用激光粉末床熔融（Laser Powder Bed Fusion, L-PBF）工艺制备格伦研究中心铜84合金（Glenn Research Copper 84, GRCop-84）——一种成分为8原子%铬、4原子%铌的Cr₂Nb析出强化合金，可获得全致密、高导电的合金构件，其屈服强度达500 MPa，抗拉强度（ultimate tensile strength, UTS）为740 MPa，断后伸长率达20%，性能优于其他同类竞争铜合金。GRCop-84与Ag-Cu-X及Au-Cu钎料的润湿性与CuCrZr合金相近，但低于无氧铜。在L-PBF制备的GRCop-84中，填充区与表面轮廓区的润湿性无显著差异。将试样湿磨至240目（粗糙度Ra=0.24 µm）被认为是最优的表面处理工艺。当达到密度阈值后，银元素会在GRCop-84合金内部扩散，消耗铜晶粒中的Cr₂Nb析出相，并在晶间扩散的富银区域内形成粗化析出相的团聚体。采用50Au-50Cu钎料时，合金微观组织的变化被降至最低，这表明是银元素导致了析出相粗化与团聚，而非高温暴露。在钎料熔池内部的表面处可观察到粗化的析出相，这说明其对钎料润湿性存在贡献。Palcusil-25、Ticusil、CuSil-ABA及50Au-50Cu钎料均适用于与未镀覆的钛锆钼合金（Titanium-Zirconium-Molybdenum, TZM）进行钎焊；而采用氨基磺酸镍镀覆工艺，则可实现CuSil或其他非活性钎料的润湿。结合GRCop-84与TZM的钎焊特性，以及二者热膨胀系数差异带来的内应力问题，开发了真空钎焊工艺，用于将1 mm厚的TZM层与增材制造的GRCop-84波导正面进行连接。